METHODS AND PROCESSES FOR MANUFACTURING ENDLESS ROD

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority of U.S. provisional patent application Ser. No. 63/709,346 filed Oct. 18, 2024, which is incorporated by reference into this application in its entirety.

TECHNICAL FIELD

The present disclosure is related to methods and processes for manufacturing endless rods.

BACKGROUND

Endless Rod Overview

Endless rods (“ER”) serve as critical components in progressing cavity pumps (“PCPs”) and reciprocating rod lift systems (“RRPs”), widely used in the oil and gas industry. These rods are continuously built without couplings to reduce the risk of failures commonly associated with standard rod couplings and sucker rod.

The rods are employed primarily for torque and axial load transmission, facilitating power transmission from the surface to the downhole pump. In their role, they are subjected to various operational conditions, such as high stress, temperatures ranging from 100 to 120 degrees Fahrenheit, and pressures varying between 500 to 3000 PSI. Moreover, they encounter corrosive environments, including production water containing chemical agents and corrosion-assisted like carbon dioxide (“CO₂”) and hydrogen sulfide (“H₂S”), along with occasional low pH or acidic fluids.

Endless rods experience performance limitations and common problems mainly due to their exposure to harsh operational conditions. The primary limitations include high fatigue stress from cyclic loading, corrosive environments, and surface defects from the manufacturing process. These can lead to fatigue, corrosion, and corrosion fatigue failures. Other contributing factors include wear, cross-sectional reduction, welding processes below specifications, and manufacturing defects like slivers, scabs, and longitudinal cracks, often arising from the hot rolling process. For the purposes of this specification, and the claims that follow, the term “surface defects” shall be defined as including, but not limited to, natural features, intrinsic features, natural discontinuities, scars, scabs, seams, slivers, and pits disposed on sections of rod.

The rods are typically manufactured using AISI 15XX, 41XX, and 43XX grades, but are not limited to just these specific grades. These steel grades are chosen for their enhanced characteristics offered by alloying elements like chromium (“Cr”), molybdenum (“Mo”), manganese (“Mn”), magnesium (“Mg”), among others. Certain stainless steel variants, possibly duplex types, are also used. The design methodology for endless rods seeks to achieve high fatigue resistance, improved corrosion resistance and overall, optimal mechanical properties.

The manufacturing process unfolds in multiple stages, beginning with the creation of raw materials at the steel mill. Here, billets are continuously cast, leading to the hot rolling of steel into coils. These coiled rods then move to the next stage where they are processed by Endless Rod (“ER”) manufacturers. This subsequent processing stage ensures product suitability by implementing a series of operations that include straightening and heat treatment. The heat treatment typically involves a quench and temper process, which is then followed by shot peening for product quality. In some cases, manufacturers do not shot peen the ER. It is noteworthy that shot peening is not only for product quality but has historically been considered a method to descale the rod while simultaneously adding a layer of compressive residual stresses that potentially improve fatigue life.

Although there isn't a single standard applicable specifically to endless rods, API 11B often serves as a reference point. Notably, this standard applies to conventional rods, which differ from endless rods though typically different, some conventional rods, such as alpha rod from Tenaris, can be quenched and tempered and, preferably, most conventional rods apply this method. Handling, transportation, and installation aspects differ due to the different lengths of conventional rods, which are typically 25 feet long in contrast to ER, which are very long rod strings. Other standards concerning metallurgical properties such as decarburization, grain size, and other mechanical properties of hot-rolled steel products are also considered.

The manufacturing quality process focuses on identifying and reducing defects and detrimental conditions on the rod surface. In some instances, the rod can be reworked to eliminate some of the defects. However, residual defects from the raw material or manufacturing process, such as slivers, scabs, and longitudinal cracks, can still persist, leading to potential failure points. These are crucial aspects to consider when investigating endless rod failure modes.

Endless rods often face performance limitations and common issues due to their enduring exposure to severe operational environments. Notably, these rods undergo high fatigue stress as a result of cyclic loading, wherein they endure repeated axial and torsional loads. This incessant cyclic loads can eventually lead to fatigue failure. Additionally, the rods may be subjected to harsh downhole conditions where they come into contact with highly corrosive fluids. This interaction can instigate corrosion-related failures, significantly impacting the rod's lifespan and performance. Additionally, surface defects originating from the manufacturing process can present serious challenges. These discontinuities can function as stress risers, exacerbating the fatigue stress and, in turn, precipitating premature failures. Therefore, the overall performance and lifespan of endless rods are subject to the cumulative effects of these harsh conditions and operational stresses.

Endless rods are susceptible to a variety of common failure modes, which primarily revolve around fatigue, corrosion, and a combination of the two, known as corrosion fatigue. Fatigue failure is a common occurrence, which results from repeated cyclic stresses endured during operations. Over time, these stress cycles can exceed the rod's endurance limit, leading to fatigue cracks and eventual failure. Corrosion failure, on the other hand, is particularly prevalent in harsh downhole environments where the rods are continuously exposed to corrosive fluids. This exposure can erode the rod's material, weakening its structural integrity and resulting in corrosion-induced failures. A challenging failure mode is corrosion fatigue, which amalgamates the destructive mechanisms of both fatigue and corrosion. In this scenario, the corrosion process not only deteriorates the rod's surface but also accelerates the initiation of fatigue cracks. This dual action compounds the rate of damage, often leading to a quicker and more devastating failure of the rod.

The design methodology of endless rods primarily focuses on achieving fatigue resistance via industrial software's, selection of suitable mechanical properties and selection of grade for corrosion resistance.

Hot Rolling Process

The hot rolling process, specifically within the context of producing coiled rods for use in Endless rod pumping applications, is a specialized sequence of stages. Endless Rod (ER) manufacturers have historically relied on hot-rolled coiled rods as their primary raw material, mainly due to the material's adaptability and cost-effectiveness. The fundamental product of the hot rolling process is a ‘green steel’ or hot-rolled steel that typically manifests a banded ferrite-perlite microstructure. This is particularly prevalent in the metallurgical series leveraged by ER manufacturers, such as the 15XX, 41XX, and 43XX AISI series. Furthermore, the process leads to the formation of a layer of oxides, known as mill scale, on the rod's outer surface. This layer is a byproduct of the hot rolling and cooling phases and is usually present when the coiled rod arrives as raw or ‘green’ steel at the Endless fabrication line. For the purposes of this specification, and the claims that follow, the term “outer surface” shall be defined to include, but is not limited to, to the outer surfaces of welds, and the weld beads thereof, joining sections of rod together.

However, the hot rolling process isn't devoid of challenges. Defects, subsequently mentioned in the following section, can appear on the rod's surface during the hot rolling stages. These features or defects can extend several millimeters in length and delve several hundred micrometers in depth. Certain surface features, depending on their nature and severity, may pose a detrimental risk to the rod's fatigue life and overall functionality.

The hot rolling process begins with casting materials, typically in the form of billets. These materials are pre-heated to temperatures ranging from 1500 to 1700 degrees Celsius. This pre-heating is a critical step because steel achieves optimal malleability at temperatures above its recrystallization threshold. In this state, the steel can be readily shaped and formed to meet specific requirements.

Once heated, the steel billets are passed through several pairs of rolls, which shape, flatten, and lengthen the steel while reducing the billets'cross-sectional area. This transformation undergoes four main stages: reheating furnace, roughing mill, finishing mill, and cooling zone. The reheating furnace is where the preheated steel billets are brought to the desired temperature for rolling. In the roughing mill, the heated billets are rolled to form the initial shape. The finishing mill imparts the final shape and specific dimensions to the steel. The cooling zone is where the hot-rolled steel cools down and solidifies, allowing the steel's microstructure to transform into the desirable banded ferrite-perlite. Finally, the coiler rolls the processed steel into coils for ease of transport and further processing, producing the so-called ‘coiled rod.’

Despite the challenges, hot rolling remains a favoured manufacturing process for ER manufacturers due to the inherent versatility and cost-effectiveness of hot-rolled coiled rods. The understanding and mitigation of defects that occur during this process are vital to maintaining the quality and functionality of the final product.

Defects of Hot Rolling Process

Hot-rolled material, particularly coiled rods, are frequently selected for low-carbon structural steel components and machine parts that will undergo extensive machining. The initial finish of the stock is less important in these cases given the later machining. Nonetheless, hot-rolled material like coiled rods can exhibit various surface defects that impact their structural integrity and application performance. The defects include but are not limited to slivers, mill scale, dents, scratches, seams, and pitting.

Slivers, small-elongated defects appearing on the surface, often result from metal being extruded from the interior during the rolling process. They can be caused by non-metallic inclusions or segregation in the original cast material, which are flattened and elongated under the pressure of the rolls.

Mill scale, a hard and brittle layer of iron oxides, is a by-product of hot rolling that forms on the steel's surface as it cools. While it can protect against some forms of corrosion, it can also cause issues such as reduced adhesion for coatings, and it may be undesirable in some finished products.

Dents, scratches or gouges, more obvious defects, are often induced mechanically during handling or processing. They not only mar the surface appearance but also create stress concentration sites, which may act as initiation sites for fatigue cracks under cyclic loading conditions.

Seams are longitudinal crevices that are often formed during the continuous casting stage of steel production. If not removed or reduced during the subsequent rolling stages, they remain on the finished product and can act as weak points where failure can initiate.

Pitting, a form of highly localized corrosion, can occur if the protective mill scale is broken or if the steel is exposed in a corrosive or oxidant environment. It leads to small pits on the surface that can act as stress concentration sites and decrease the material's fatigue resistance.

Some of these defects occur during the steel-making stages themselves, where issues in the melting, refining, or casting process can introduce impurities or segregation. Others arise during the subsequent hot-rolling and cooling stages due to mechanical stresses or oxidation. The rolling process itself can also introduce defects if the rolls are worn or if the rolling conditions are not ideal.

Understanding the causes and effects of these defects is vital to improve the quality of hot-rolled products. By optimizing the steelmaking and rolling processes, and by implementing proper handling and storage procedures, it is possible to reduce the occurrence of these defects and improve the overall quality of the finished product.

Natural Features and Their Impact on Fatigue Life

The integrity and performance of structural components such a sucker or continuous rods, are significantly influenced by the surface characteristics inherent to the material's processing history. While the disclosure above delves into defects introduced during the hot rolling process, this section shifts focus on the natural features of surfaces and their role in influencing fatigue life and corrosion fatigue phenomena. It's crucial to note that these natural features are not necessarily outside the manufacturers'specifications or industry standards. Instead, they represent inherent characteristics that, while falling within accepted manufacturing specifications, can still significantly impact the material's resistance to fatigue and corrosion fatigue.

Surface roughness is one of several potential indicators of the presence of natural features on the surface of a rod, playing a pivotal role in determining the fatigue strength of materials. While it serves as an effective marker for assessing these features, it's important to recognize that the presence of natural features can also indicate underlying metallurgical characteristics, such as decarburization. Decarburization, the loss of carbon from the surface layer, reduces the hardness and, consequently, the fatigue strength of the material. These conditions, coupled with the inherent roughness of hot-rolled surfaces, form a complex interplay that directly impacts the development and propagation of fatigue cracks. Furthermore, other techniques, ranging from macroscopic visual inspection to advanced visualization methods, can facilitate the identification of these natural features.

Rough surfaces introduce stress concentrations that significantly lower fatigue strength, a phenomenon that is further exacerbated in forged surfaces. These not only exhibit roughness but also decarburization, where the reduction in carbon content at the surface weakens the material at points where stress concentrations are likely to be highest. To quantify the impact of surface characteristics on fatigue life, the concept of a surface reduction factor is introduced in fatigue design methodologies. This factor accounts for the variations in fatigue life due to different surface finishes associated with processing history, encompassing both the physical roughness and the metallurgical implications of natural features. By acknowledging that these natural features are not necessarily outside the specifications set by manufacturers or industry standards, they play a relevant role in the integrity and performance of structural components.

The relationship between surface roughness and the associated presence of natural features is critical in assessing fatigue life. Material studies provide a more detailed understanding of how modified surfaces, with their specific roughness profiles, affect material fatigue strength.

Green Steel Condition

Once the hot-rolled coils are received for the internal ER manufacturing process in green condition (annealed condition), it is observed that the discontinuities are typically already present in the green condition (or raw material or from the hot rolling mills).

Shot Peening

Shot peening (SP) is the most commonly used and most extensively studied post-processing method to introduce compressive residual stresses and improve fatigue performance of components. In shot peening, hard spherical shots are air blasted against the surface of a component. Each impact point induces local plastic deformation on the surface.

It is, therefore, desirable to provide a process that overcomes the limitations and shortcomings of the prior art.

SUMMARY

An improved endless rod manufacturing process is presented that overcomes the problems and limitations of the prior art. In some embodiments, improved methods and processes for manufacturing endless rod can be provided that can include novel methods and techniques for reducing surface defects, decarburization, banding, and other metallurgical features that adversely affect the fatigue life of the rod and associated product performance.

Broadly stated, in some embodiments, a method can be provided for manufacturing an endless rod, comprising the steps of: drawing a rod through one or more dies to reduce its cross-sectional area; removing surface defects from at least a portion of an outer surface of rod sections of the rod; cutting out defects on the outer surface of the rod sections; welding the rod sections together to form the endless rod; heat treating the endless rod; peening the endless rod; polishing the endless rod; and applying corrosion resistance coating to the endless rod.

Broadly stated, in some embodiments, the method can comprise drawing the rod through the one or more dies at least one more time.

Broadly stated, in some embodiments, the method can comprise applying an intermediate thermal treatment to the rod prior to drawing the rod through the one or more dies.

Broadly stated, in some embodiments, the step of removing the surface defects can comprise milling or grinding the surface defects from the outer surface of the rod sections.

Broadly stated, in some embodiments, the step of removing the surface defects can comprise one or more of brushing, burnishing, and wire brushing the surface defects from the outer surface of the rod sections.

Broadly stated, in some embodiments, the step of removing the surface defects can comprise water-jetting the surface defects from the outer surface of the rod sections.

Broadly stated, in some embodiments, the step of removing the surface defects can comprise applying acid to the outer surface of the rod sections.

Broadly stated, in some embodiments, the step of removing the surface defects can comprise laser cleaning or plasma cleaning the outer surface of the rod sections.

Broadly stated, in some embodiments, the step of removing the surface defects can comprise removing about 0.005″ to 0.010″ of surface material from the outer surface of the rod sections.

Broadly stated, in some embodiments, the step of cutting out the defects can comprise cutting out the defects greater than 0.010″ deep from the outer surface of the rod sections.

Broadly stated, in some embodiments, the step of peening the endless rod can comprise one or more of shot-peening, machine hammer peening, and rotary flap peening.

Broadly stated, in some embodiments, the corrosion resistance coating can comprise a polymeric coating.

Broadly stated, in some embodiments, the polymeric coating can comprise one or more of high-density polyethylene and polyketone.

Broadly stated, in some embodiments, the corrosion resistance coating can comprise a metallic coating.

Broadly stated, in some embodiments, the corrosion resistance coating can comprise a composite of a polymeric coating and a metallic coating.

Broadly stated, in some embodiments, the step of heat treating can comprise one or more of normalizing, annealing, quenching, and tempering.

Broadly stated, in some embodiments, the method can further comprise the step of rolling the endless rod.

Broadly stated, in some embodiments, the step of rolling the endless rod can comprise one or more of hot rolling, cold rolling, and burnishing the endless rod.

Broadly stated, in some embodiments, the step of heat treating the endless rod can comprise applying heat to the endless rod to reach an austenitic phase.

Broadly stated, in some embodiments, an endless rod can be manufactured using any of the foregoing methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram depicting one embodiment of an endless rod manufacturing process line for material reception, straightening, cleaning, welding, and spooling.

FIG. 2 is a block diagram depicting one embodiment of an endless rod manufacturing process line for heat treatment, quenching, tempering, and surface residual stress optimization.

FIG. 3 is a block diagram depicting one embodiment of an endless rod manufacturing process line for non-destructive testing, welding, and final preparation.

FIG. 4 is a block diagram depicting one embodiment of an endless rod manufacturing process line for polymeric coating application thereto.

DETAILED DESCRIPTION OF EMBODIMENTS

In this description, references to “one embodiment”, “an embodiment”, or “embodiments” mean that the feature or features being referred to are included in at least one embodiment of the technology. Separate references to “one embodiment”, “an embodiment”, or “embodiments” in this description do not necessarily refer to the same embodiment and are also not mutually exclusive unless so stated and/or except as will be readily apparent to those skilled in the art from the description. For example, a feature, structure, act, etc. described in one embodiment can also be included in other embodiments but is not necessarily included. Thus, the present technology can include a variety of combinations and/or integrations of the embodiments described herein.

The presently disclosed subject matter is illustrated by specific but non-limiting examples throughout this description. The examples may include compilations of data that are representative of data gathered at various times during the course of development and experimentation related to the present invention(s). Each example is provided by way of explanation of the present disclosure and is not a limitation thereon. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to the teachings of the present disclosure without departing from the scope of the disclosure. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment.

All references to singular characteristics or limitations of the present disclosure shall include the corresponding plural characteristic(s) or limitation(s) and vice versa, unless otherwise specified or clearly implied to the contrary by the context in which the reference is made.

All combinations of method or process steps as used herein can be performed in any order, unless otherwise specified or clearly implied to the contrary by the context in which the referenced combination is made.

While the following terms used herein are believed to be well understood by one of ordinary skill in the art, definitions are set forth to facilitate explanation of the presently disclosed subject matter.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the presently disclosed subject matter belongs. Although any methods, devices, and materials similar or equivalent to those described herein can be used in the practice or testing of the presently disclosed subject matter, representative methods, devices, and materials are now described.

Following long-standing patent law convention, the terms “a”, “an”, and “the” refer to “one or more”when used in this application, including the claims.

Unless otherwise indicated, all numbers expressing quantities, properties, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and claims are approximations that can vary depending upon the desired properties sought to be obtained by the presently disclosed subject matter.

As used herein, the term “about”, when referring to a value or to an amount of mass, weight, time, volume, concentration or percentage is meant to encompass variations of in some embodiments +/−50%, in some embodiments +/−40%, in some embodiments +/−30%, in some embodiments +/−20%, in some embodiments +/−10%, in some embodiments +/−5%, in some embodiments +/−1%, in some embodiments +/−0.5%, and in some embodiments +/−0.1% from the specified amount, as such variations are appropriate to perform the disclosed method.

Alternatively, the terms “about” or “approximately” can mean within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e., the limitations of the measurement system. For example, “about” can mean within 3, or more than 3, standard deviations, per the practice in the art. Alternatively, “about” can mean a range of up to 20%, preferably up to 10%, more preferably up to 5%, and more preferably still up to 1% of a given value. Alternatively, particularly with respect to biological systems or processes, the term can mean within an order of magnitude, preferably within 5-fold, and more preferably within 2-fold, of a value. Unless otherwise indicated, all numbers expressing quantities, properties, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”. And so, the numerical parameters set forth in this specification and claims are approximations that can vary depending upon the desired properties sought to be obtained by the presently disclosed subject matter.

As used herein, ranges can be expressed as from “about” one particular value, and/or to “about” another particular value. It is also understood that there are a number of values disclosed herein, and that each value is also herein disclosed as “about” that particular value in addition to the value itself. For example, if the value “10” is disclosed, then “about 10” is also disclosed. It is also understood that each unit between two particular units are also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.

An improved endless rod manufacturing process is presented that includes a series of methods and techniques that address the issues and limitations described in the prior art. These methods and techniques can include, but are not limited to:

Materials Selection

The current and proposed process employs standard families of materials typically used in the industry, as well as by the Applicant. These materials can comprise of carbon steels alloyed with elements like chromium, molybdenum, manganese, magnesium, and nickel. These alloying elements are chosen for their ability to strike an optimal balance between mechanical properties, specifically in terms of stress resistance, hardness, and fracture toughness, making them suitable for various applications.

Surface Process

In the pursuit of engineering optimization of the endless products and associated properties, the optimization or modification of surface characteristics stands as a critical aspect of material performance. These alterations can be broadly categorized into physical or chemical methodologies, or a synergistic combination of both, each offering distinct advantages and applications.

Within the realm of physical methods, two main strategies prevail. One involves the permanent deformation or modification of the rod surface, essentially restructuring the surface to achieve desired surface quality and associated mechanical properties. The other involves the physical removal of an external layer from the surface, a process that may be essential for eliminating specific features or preparing the surface for subsequent treatments.

On the chemical front, methods often focus on targeted reactions to modify the surface selectively. A classic example within this category is the chemical removal of mill scale or pickling. Mill scale is a byproduct of the hot rolling process. These scales, often undesired in the final product, can be selectively etched away through controlled chemical reactions, leaving behind a refined surface ready for further processing or application.

The distinction between physical and chemical methods lies not just in their approach but also in the nature and quality of the results they deliver. Physical methods tend to be more mechanical in their operation, often involving force or abrasion, while chemical methods leverage the specificity and selectivity of chemical reactions. The choice between these approaches, or the decision to combine them, must be considered based on the requirements of the final product, the condition of the raw material (such as its arrival in a hot-rolled state), and the technical and economic constraints of the process.

The following description of the proposed methods, offering insights into their underlying principles, applications, and efficacy through a thoughtful understanding of these techniques.

Physical Methods

• • Drawing: Drawing is a metal forming process involving the plastic deformation of a rod by pulling it through a die or series of dies to reduce its cross-sectional area. This process can enhance surface finish, dimensional precision, and mechanical properties through strain hardening. In the context of endless rod manufacturing, drawing may be applied in one or multiple stages depending on the desired final geometry and reduction ratio. When substantial reductions in cross-section are required, the raw material may need to be subjected to interpass thermal treatments such as annealing or normalizing to restore formability between drawing steps. This method is particularly useful in eliminating or minimized surface discontinuities from hot rolling (e.g., seams or slivers) and is known to introduce a refined and smooth outer surface which increases fatigue life and wear resistance in PCP and RRP applications.
  • Shaving or draw peeling: Metal shaving or draw peeling refers to the mechanical removal of a thin layer of metal from the outer surface of a coiled rod. This can be important in removing natural features and some defects such as seams, slivers, mill scale, or other surface imperfections that might be present after hot rolling. The method ensures a smoother and more uniform surface that meets specific quality standards. The process can significantly enhance the steel surface finish by removing surface imperfections, creating a smooth and uniform surface.
  • Cold Rolling: This process often follows material cleaning and pickling hot rolling, enhancing the surface finish and mechanical properties of steel. Cold rolling, a type of plastic deformation process, produces a smoother surface and provides dimensional control over the part. It can also enhance steel's mechanical properties, including tensile strength and hardness.
  • Burnishing, deep rolling: These cold hardening processes employ guided tools with periodic or continuous contact with the workpiece. They can effectively reduce surface roughness, improve surface hardness, and impart beneficial residual compressive stresses to the component, and can also be used to remove surface defects.
  • Machine hammer peening (MHP): MHP is a relatively new surface modification process that uses guided tools for contact, which can be periodic or continuous. It can enhance the surface properties by imparting beneficial residual compressive stresses.
  • Warm Peening: Warm shot peening refers to the application of shot peening at elevated temperatures, typically between 150° C. and 300° C. This technique enhances the efficacy of the plastic deformation introduced by the peening media, thereby promoting deeper, more stable and consistent compressive residual stresses. The application of warm shot peening is particularly relevant to the Endless Rod manufacturing process since it can be synchronized with the thermal energy present in the heat treatment cycles such as quenching and tempering. Alternatively, external heating mechanisms can be integrated to maintain the rod within the optimal temperature window without exceeding the tempering temperature. Warm peening enhances surface hardening efficiency without compromising prior heat treatments and may significantly improve fatigue resistance in high-stress applications.
  • Rotary flap peening: Rotary flap peening employs a flap of balls trapped in a Kevlar matrix at its extremities. A pneumatic or electric grinding wheel can rotate the flap, which can be fixed on a shaft. The flap is applied to the peened or formed portion, and the end balls strike it to treat it. The process is controlled by the grinding wheel's rotational speed controller in conjunction with the flap's size.
  • Polishing and Grinding: These processes enhance the steel surface by eliminating rolling marks, scratches, and other imperfections, resulting in a smooth and shiny surface.
  • Heat Treatments: Some types of steel may undergo heat treatments such as normalizing, annealing, quenching, and tempering to improve their mechanical properties and surface finish.
  • High-Pressure Water Jets: This method cleans the steel surface by removing mill scale, rust, and other contaminants. The high water pressure can even eliminate surface imperfections or discontinuities.
  • Laser or Plasma Cleaning: Laser and plasma-based technologies can clean and modify the steel surface by removing mill scale, rust, and other impurities. They can also alter the surface texture for improved performance.
  • High-Temperature Plasma Technology: Similar to lasers, this method uses a high-temperature plasma jet to remove surface defects, thereby providing a superior finish to the steel surface.

Chemical Methods

• • Descaling: Descaling involves removing the layer of iron oxide (also known as mill scale) formed on the steel surface during hot rolling. Descaling methods include using steel brushes, high-pressure water jets, or acid chemical treatments (a process known as “pickling”).

The manufacturing process of a product can often be as critical as the material itself in determining its overall performance, especially in industries requiring high precision and reliability. In this context, the described process comprises an innovative approach to rod manufacturing, involving a distinct pre-manufacturing process to optimize the rod surface before being introduced to the main manufacturing line.

The Pre-Manufacturing Process

The uniqueness of the processes described herein can reside in the implementation of various during the pre-manufacturing stage. The rods are usually in an annealed state, which offers greater machinability or formability during these processes. These methods are not applied simultaneously, but rather selectively, depending on the specific requirements of the rod surface.

• • Surface Quality Enhancement. The pre-manufacturing process targets the enhancement of surface quality, aiming to remove partially or totally natural features, mill scales, and surface defects. This approach not only improves the rod's performance characteristics but also alleviates potential detrimental effects during the subsequent manufacturing stages. Methods such as draw peeling may further assist in straightening the rod and eliminating waviness along the reel, contributing to precise geometrical control.
  • Strategic Flexibility. The adoption of a potentially separate line or integration into existing processing lines illustrates flexibility in the manufacturing process. It aligns with the goal to deliver a tailored rod depending on the quality requirements and the final application of the continuous rods.
  • Main Manufacturing Process. Once the pre-processing is complete, the rods are integrated into the conventional manufacturing line, consisting of several stages, including receiving, uncoiling, straightening, welding, heat treatment, shot peening, non-destructive inspection, and finishing with protective coatings. The processes ensure the proper alignment of mechanical properties, such as tempering, quenching, and the introduction of a compressive residual stress layer.

Welding Process Improvements

The welding processes employed both in manufacturing settings and field applications are pivotal to the structural integrity and performance of continuous rods used in Progressive Cavity Pump (PCP) and Rod Pump (RP) systems. Welding, as a critical aspect of the rod fabrication and maintenance routine, involves complex interactions of thermal, mechanical, and metallurgical factors that significantly influence the final product's quality and operational efficiency.

In the realm of manufacturing, welding processes are designed to ensure robustness and adaptability across various production stages. These processes are not only about joining metal pieces but also about enhancing the intrinsic properties of the weld zone to withstand operational stresses and environmental factors. The manufacturing welds are subjected to rigorous post-weld heat treatments and finishing processes that aim to optimize the mechanical properties and surface conditions, thereby extending the fatigue life of the welds and ensuring consistency in performance.

Conversely, field welding presents unique challenges due to the variability in environmental conditions and the need for rapid, yet reliable, repair solutions that ensure minimal downtime and robust performance. The techniques employed in field welding must be versatile enough to address on-site repairs and adjustments, necessitating a understanding of the thermal dynamics and material behaviors under different conditions. This includes managing the heat-affected zones (HAZ) effectively to prevent detrimental changes in microstructure and ensuring that the welds are protected against environmental stressors that can precipitate wear and fatigue.

The continuous development and optimization of these welding processes represent a significant aspect of our inventive efforts. By advancing both the technical approaches in weld formation and the subsequent treatments applied to welded joints, we aim to significantly uplift the operational standards and longevity of continuous rods. The following sections detail specific improvements and innovations introduced in the welding processes used in manufacturing and field settings, illustrating our commitment to enhancing the durability and efficiency of welded constructions in industrial applications.

Manufacturing Welding

In a manufacturing context, welding is used to create strong joints between rod coils to ensure both the structural integrity and the performance consistency of endless rods. This process is particularly nuanced, involving a blend of mechanical, physical, and metallurgical transformations that enhance the overall characteristics of the welded joints. During manufacturing, the rods typically undergo welding in an annealed state in Line 1, allowing for easier manipulation and joining of materials. Post-weld, the rods are sent to Line 2 for tempering and quenching, processes that are critical for addressing the heat-affected zone (HAZ) induced by welding. These thermal treatments aim to mitigate or even eliminate the detrimental effects of the HAZ, although some metallurgical characteristics inherent to the welding process may persist.

The primary goal in manufacturing welding is to optimize the welded joint's microstructure. This includes managing the austenitic transformations—where the steel's crystalline structure changes at high temperatures, enhancing ductility and toughness. Controlled cooling then follows to ensure the desired microstructure is locked in, providing the necessary mechanical properties for operational demands.

Moreover, significant emphasis is placed on the surface finish and the introduction of beneficial compressive residual stresses during the final stages of the welding process. Techniques such as related and described within the section are employed to enhance the surface quality, removing imperfections that could act as stress concentrators. These surface optimizations not only improve the fatigue resistance of the welds but also contribute to their corrosion resistance, essential in harsh operational environments.

Field Welding

Field welding, often characterized by fire welding techniques, demands a degree of precision and adaptability under variable and sometimes harsh environmental conditions. In this setting, an oxy-acetylene torch is typically used to heat the rods to a temperature that exceeds the austenitic transformation point. This process phase facilitates the necessary microstructural changes for welding, enabling the material at the weld site to attain sufficient plasticity for forging. The welding process in the field involves aligning and preparing the rod ends, followed by applying heat to reach the austenitic phase. By subjecting the materials to mechanical forging after heating, they are consolidated into a weld that is solid-state. Controlled cooling, often using air, to refine the HAZ and ensure the newly formed microstructure is conducive to the weld's operational integrity.

The challenges of field welding include managing the directionalities of polishing and grinding on the weld surface. Longitudinal polishing, commonly practiced to align with the rod's stress lines, can introduce longitudinal residual stresses, which, while not inherently detrimental, must be carefully managed to prevent adverse effects in reciprocating applications like RRP or rotational applications like PCP. Transversal polishing or grinding, on the other hand, can inadvertently create stress concentrators that exacerbate fatigue wear unless properly managed with techniques that introduce beneficial residual stresses.

Improve Weld Quality With Surface Treatments and Compressive Residual Stresses

The enhancement of weld quality in both manufacturing and field settings is focused on optimizing the surface characteristics and introducing beneficial compressive residual stresses. These strategies are crucial for improving the longevity and performance of welds in continuous rods used in demanding applications.

Compressive residual stresses are inherently beneficial because they counteract the tensile stresses that typically lead to crack initiation and propagation under cyclic load conditions. In the context of welding, where thermal processes can inherently introduce various stress concentrations and potential weak points in the heat-affected zone (HAZ), the introduction of compressive stresses acts as a preventive measure. These stresses help maintain the integrity of the weld area, significantly reducing the likelihood of fatigue failure.

In typical welding processes, especially those involving high heat inputs like fire welding or induction coils, the rod material undergoes significant thermal cycles. These cycles can lead to the formation of tensile stresses due to the contraction of the weld metal and adjacent areas on cooling. If unmanaged, these stresses can exacerbate the formation of micro-cracks, particularly under operational loads that are cyclic in nature, such as in Progressive Cavity Pump (PCP) and Rod Pump (RP) applications. By applying controlled post-weld heat treatments and utilizing specific surface treatment techniques or surface modifications after welding, the surface of the weld can be conditioned to introduce compressive residual stresses. These stresses not only mitigate the adverse effects of the inherent tensile stresses but also enhance the overall fatigue resistance of the weld.

The proposed innovations in this patent aim to harness these synergistic effects fully. By improving both the surface condition and the internal stress state of the welds, the lifetime of the rods is significantly extended beyond current standards. This approach not only addresses the potential negative aspects introduced by conventional welding processes but also leverages advanced materials engineering techniques to ensure that the welds exhibit superior performance in both mechanical strength and fatigue resistance. Thus, the integration of these surface and stress modification and optimization techniques represents an advancement in welding technology, promising substantial improvements in the reliability and durability of continuous rods in industrial applications.

Welding Process Enhancements for Joining Rod Sections

One of the significant improvements in welding process involves the use of a dedicated rod section, known as an intermediary section, to join two rod strings. This section can be employed to weld rods of the same diameter (slip welds) or different diameters (taper welds). The intermediary section offers several benefits:

• • High Control of Surface Discontinuities: This section is engineered to be free from defects and possesses a high control over surface discontinuities. It can undergo the advanced processes described earlier in this document, such as deep burnishing, among others. These processes (previously discussed methods) ensure an improved fatigue life compared to the rod body itself.
  • Enhanced Flexibility in Welding Techniques: The use of an intermediary section allows for greater flexibility in welding techniques. This section can be shorter and more manageable, facilitating the use of innovative welding methods such as friction welding. This method involves creating relative movement between the intermediary section and the rod strings, leading to a solid-state weld. Instead of a single weld joining two rod strings, the process results in two welds with an optimized fatigue life section in between.
  • Improved Transition in Taper Welds: For taper welds, the transition from one diameter to another is smoother, reducing the mechanical stress concentrator associated with the diameter change. This smoother transition minimizes stress concentrations, effectively mitigating potential points of failure.
  • Stress Relief and Structural Benefits: The intermediary section acts as a stress relief zone, which is particularly beneficial when joining rod strings with different residual structural stresses. Residual structural stresses refer to the stresses that remain in the rod due to its deformation history, such as being wound in coils or the deformation during processing. These stresses can induce permanent deformation in a fraction of the rod's cross-section, leading to additional stresses when loads are applied in service. By using an intermediary section with optimized fatigue life and without residual structural stresses, this section absorbs and mitigates the differing residual stresses from the joined rod strings. This acts as a mechanical fuse, reducing or eliminating the negative effects of joining rods with different residual structural stresses.

The use of an optimized intermediary section for welding rod strings not only enhances the weld quality but also significantly improves the overall fatigue life and performance of the continuous rods. This innovation allows for more reliable and durable rod string constructions, capable of withstanding the demanding conditions of PCP and RP systems.

Corrosion and Chemical Properties Optimization

Banding, also known as segregation, is a microstructural phenomenon often observed in hot-rolled steels and be included in the processes described herein. It refers to the localized concentration of certain alloying elements or phases along the rolling direction, creating alternating bands of different compositions, which can severely impact both mechanical and corrosion properties. The presence of banding can make the material more susceptible to corrosion, as differences in chemical composition may create galvanic cells, acting as initiation sites for corrosive attacks. This concentration of banding originates from the segregation of solute elements during solidification, and it may be accentuated during hot rolling, where the deformation process can stretch and elongate the segregated areas. The phenomenon presents a significant challenge, as it has both intrinsic and unavoidable features associated with hot-rolled products.

Mitigating or eliminating banding can comprise a controlled thermal treatment known as homogenization, and can be included in the processes described herein. This treatment is performed at elevated temperatures close to the material's melting point, followed by a slow cooling process. The goal of homogenization is to promote diffusion, allowing the segregated elements to redistribute more uniformly throughout the material. This process can break down or mitigate the segregated bands, creating a more uniform microstructure that significantly mitigates the risk of localized corrosion, such as pitting. The exact temperature, time, and cooling rate for the homogenization process will depend on the specific alloy and the severity of the banding. Moreover, it is vital for manufacturers, such as LSI, to work closely with raw material suppliers to implement a rolling and cooling process that minimizes the risk of banding during the hot rolling stage. By carefully monitoring temperatures and deformation rates, the tendency for segregation to occur can be reduced, offering a substantial breakthrough in enhancing the fatigue life of the rods. Through this thoughtful and strategic approach, the processes described herein can transform the hot-rolled rods, targeting both the intrinsic features of the hot-rolled process and the extrinsic surface properties. The result is a product with a homogenized microstructure, effectively reducing or eliminating the detrimental effects of banding, thereby improving corrosion resistance and overall material integrity. This offers a substantial contribution to extending the life of the rods, reducing maintenance costs, and enhancing the overall efficiency of applications where these rods are utilized.

Beyond the microstructure, in some embodiments, the processes described herein can also target the surface of the rod, focusing on reducing or eliminating natural features that are inherent in hot-rolled products. By employing techniques modification techniques such as draw peeling, these features can be minimized or removed. The smooth and optimized surface minimizes the occurrence of crevice or micro crevice corrosion since the potential nucleation zones are significantly reduced. The minimized surface irregularities mean fewer locations where corrosive agents can take hold, lowering the susceptibility to both localized pitting corrosion and more generalized corrosion attacks.

The combination of homogenizing the microstructure and optimizing the surface presents a pioneering advance in corrosion resistance. It recognizes that both the bulk properties of the rod and its surface characteristics must be addressed to create a product with significantly enhanced corrosion resistance. This innovation is not merely an incremental improvement but a substantial leap forward in extending the life of the rods, reducing servicing costs, and enhancing the overall efficiency and sustainability of the applications where these rods are utilized in challenging applications. By targeting both the intrinsic features of the hot-rolled process and the extrinsic surface properties, the processes described herein can offer a holistic solution to a complex and long-standing challenge in the industry.

Beneficial Effects on Wear Resistance

Rod surface quality is crucial for wear resistance, especially in reciprocating or rotational movements within tubing. The introduction of an optimized, homogeneous surface on continuous rods leads to significant improvements in wear behavior and operational longevity. Initial Surface Condition and Its Impact:

Rod Material Features

Traditional rods in a hot-rolled condition exhibit a surface characterized by asperities and irregularities. During initial use, these irregularities create uneven contact patches between the rod and its counterpart tubing. This uneven contact not only accelerates the wear rate but also results in inconsistent measurements of wear, making it challenging to predict wear rates and replacement schedules accurately. Furthermore, these surface irregularities contribute to a phenomenon known as ‘wobbling,’ where the rod does not move smoothly through the tubing but rather jumps or vibrates due to inconsistent points of contact.

Optimization of Surface Properties

By implementing advanced surface optimization techniques such as peeling, shaving, or other forms of mechanical and chemical treatment discussed earlier, the rods are rendered with a much more even and round surface. This optimization results in a uniform contact patch between the rod and the tubing, which:

• • Enhances Predictive wear rate: With more consistent wear patterns, operators can more accurately predict the lifespan and maintenance needs of both rods and tubing, optimizing operational costs and downtime.
  • Reduction of Wobbling Effects: The enhanced roundness and smoothness of the rod minimize the wobbling effect, leading to more stable and efficient operation. Stability in the rod's movement reduces the mechanical shocks and vibrations transmitted through the system, further contributing to lower wear and tear.
  • Synergistic Effects on Corrosion-Wear Phenomena: A smoother, feature-reduced surface not only improves wear resistance but also mitigates corrosion initiation. Corrosion often exacerbates wear, particularly when corrosive fluids exploit the irregularities on the rod's surface to initiate pitting or crevice corrosion. By reducing these potential initiation sites through surface optimization, the rod's susceptibility to corrosion-wear interactions is significantly diminished, enhancing overall durability.

The implementation of a modified, homogeneous surface on continuous rods not only maximizes the fatigue life by reducing wear and stabilizing operational dynamics but also synergistically decreases the susceptibility to corrosion-related failures. This dual benefit underscores the importance of surface optimization in the design and manufacture of premium rods, making it a crucial aspect of our patented technology.

Reconditioning of Continuous Rods

The concept of reconditioning of continuous rods involves the modification and refurbishment of used rods to extend their service life by leveraging the surface optimization techniques discussed earlier in this document. This process offers a sustainable solution by enabling the reuse of rods that have been previously deployed in the field, thus minimizing waste and maximizing resource efficiency. Continuous rods in service are subjected to various forms of damage, primarily due to wear and corrosion. The following are the key mechanisms of damage that affect continuous rods:

• • Corrosion: Continuous rods often face corrosion due to factors such as H2S or CO2 in aqueous environments, low pH levels, and high salinity. The types of corrosion include pitting corrosion, which leads to small, deep pits on the rod surface; generalized corrosion, which affects the entire surface uniformly; and corrosion-wear, which is a combined effect of mechanical wear and corrosion. These types of corrosion result in significant material degradation over time.
  • Wear: Continuous rods also suffer from wear due to sliding contact in reciprocating rod pump (RRP) applications, rotary sliding contact in progressive cavity pump (PCP) applications, abrasive wear from hard particles or asperities, and erosive wear caused by high-velocity fluids carrying particles. Additionally, synergistic corrosion-wear interactions can exacerbate the mechanical wear process, leading to faster degradation of the rod surface.

The reconditioning process aims to refurbish used rods by addressing the aforementioned damage mechanisms and restoring the rods to a near-new condition. The steps involved in this process are as follows:

• • Inspection: The process begins with Non Destructive Inspection (NDT) conducted in the field or at the manufacturing plant to assess the depth and extent of surface damage. NDT techniques helps identify rods that are suitable for reconditioning based on the detected damage.
  • Surface Cleaning: Cleaning methods such as chemical descaling or high-pressure water jets are employed to remove corrosion products, mill scale, and other surface contaminants. This step is crucial for preparing the rod for further processing.
  • Straightening: Ensuring that the rod is perfectly straight, which is crucial for effective performance in both RRP and PCP applications.
  • Surface Modification: Utilizing methods such as peeling, shaving, deep burnishing, and others to remove damaged layers and improve surface quality. These techniques restore the surface to a condition that enhances fatigue resistance.
  • Welding: If necessary, damaged sections can be cut out and the remaining sections welded together using welding techniques. This step ensures that the reconditioned rod meets the required length and structural integrity.
  • Dimensional Adjustment: In cases where significant material removal is required, the rod's diameter may be reduced to the next nominal size. For example, a rod initially 1 inch in diameter may be reconditioned to ⅞ inch. Reconditioned rods treated as premium rods will have optimized fatigue resistance despite the reduced diameter, maintaining performance levels comparable to their original size.

The reconditioning process for continuous rods offers numerous benefits. It significantly extends the operational lifespan of the rods by restoring used materials. This reduces the need for purchasing new rods, thereby lowering operational costs. Additionally, it promotes the reuse of materials, minimizing environmental impact and resource wastage. Reconditioned rods with optimized surfaces exhibit improved fatigue resistance and reduced wear rates, leading to better overall performance. The even surface reduces contact stresses and wobbling effects, providing smoother and more efficient operation.

Synergistic Effect of Polymeric Coating on Optimized Rod Surface

The additional benefits of the described process reside in the combination of two crucial elements: an optimized or premium rod surface and a polymeric coating, typically comprised of High-Density Polyethylene (HDPE) or Polyketone (PK). This amalgamation offers a unique and advanced solution that significantly amplifies the rod's resistance to both corrosion and wear, far exceeding the sum of their individual benefits. The optimized rod surface is a product of premium quality engineering. It undergoes several refinement processes, as described, to create a surface with reduced defects, improved mechanical strength, and minimized potential zones of corrosion nucleation. Such optimization leads to increased surface life, thereby enhancing the overall quality of the rod.

The polymeric coating component provides a robust and resilient protective layer. This coating functions as a dual protective shield, guarding against corrosion, particularly in environments where the presence of water activates corrosive phenomena, and offering protection against wear, which is a natural consequence of rotary or reciprocating contact with wellbore elements or during regular service. This polymeric barrier thus adds to the durability and lifespan of the rod.

When combined, the optimized surface and the polymeric coating provide a greater enhancement of the rod's properties, more than the mere addition of their individual benefits. The synergy between the two results in a system that maximizes resistance to corrosion and wear, thereby reducing the need for regular maintenance and enhancing long-term performance. The effect of combining these two aspects leads to a more resilient and robust rod that can withstand environmental challenges with decreased degradation over time.

The process also considers application-specific design, factoring in the exposure to corrosive agents, water content, and wear mechanisms. This allows for the customization of the coating system, selecting the polymer type, thickness, and surface optimization techniques to achieve the desired performance attributes. Regular monitoring and quality assessments ensure that the coating's integrity is maintained, enabling early detection of any potential issues and assuring long-term performance. By tailoring the coating and surface optimization to specific needs, the processes described herein can provide an adaptable and finely tuned solution that can cater to various challenging applications and conditions.

Furthermore, the synergistic approach between the optimized surface and polymeric coating contributes to sustainability by reducing the frequency of services and repairs. This leads to more eco-friendly operations and a reduction in operational costs, achieving efficiency and cost-effectiveness without compromising on quality.

Advantages and Solutions to Problems

The innovation in the processes described herein is not confined to a singular step but permeates through a systematic approach that introduces supplementary quality improvement techniques into the traditional manufacturing process. By engaging in a meticulous pre-manufacturing optimization, the processes described herein can transcend conventional boundaries, enhancing fatigue resistance, and thereby potentially expanding the applications of the product.

Furthermore, the processes and methods described herein emphasize adaptability by allowing for different combinations of physical and metallurgical techniques, paving the way for customization according to specific industry demands. The novelty in both the pre-manufacturing stage and the coherent integration with the main manufacturing line can result in a future-oriented approach, promising increased operational efficiency, cost-effectiveness, and the potential to respond to evolving requirements in industries such as PCP and RP applications. It can set a new paradigm in manufacturing, where foresight, flexibility, and a commitment to quality guide the process from inception to completion.

Referring to FIG. 1, one embodiment of process line 100 for material reception, straightening, cleaning, welding, and spooling is shown. In some embodiments, raw material for making endless rod can be received at step 10. In some embodiments, the raw material can comprise metal rod in coiled form from steel suppliers. Depending on the source of the raw material, the coiled metal rod can arrive with temporary protective coatings such as lime-based deposits or organic films (e.g., light oils). In some embodiments, the microstructure of the material at this stage can vary, as it may have undergone a process anneal or other preliminary heat treatments, which can influence its machinability, heat treatability and subsequent transformation during endless rod fabrication.

In some embodiments, the coiled metal rod can be de-coiled at step 12 at a de-coiling station and gradually uncoiled. In some embodiments, the metal rod can be guided through a set of rolls that begin a straightening process to straighten the metal rod.

In some embodiments, at step 14, the uncoiled metal rod can pass through dedicated vertical and horizontal straightening rolls to remove the memory of bend (residual stress) and to align the rod axis. The essential principle at this step can involve applying adequate plastic deformation to the metal rod to rectify the curvature without causing over-bending or surface damage defects. In some embodiments, premium-grade rods may require significantly lower force for straightening due to improved incoming coil quality, yet controlled deformation settings can be maintained to ensure geometrical consistency.

In some embodiments, at step 16, oxide scale (mill scale) and/or any residual protective coatings can be removed from the metal rod. In some embodiments, this removal can comprise mechanical, pickling, or cleaning processes to prevent contamination during subsequent heat treatment of the metal rod, and to mitigate safety hazards such as coating combustion in induction furnaces.

In some embodiments, at step 18, individual straightened coils of metal rod can be joined end to end through forge welding (also referred to as fire welding). This process can comprise localized heating of ends of the metal rod to a temperature approaching the melting point of the rod, as a pressure-driven clamp system compels the ends of two metal rods to converge together in order to create a forged joint therebetween to form an extended length metal rod. In some embodiments, the welded joint zone can be subsequently machined and polished to remove and weld upset and to ensure that the welded joint zone meets dimensional specifications and requirements for a particular endless metal rod.

In some embodiments, at step 20, depending on product requirements for a particular endless rod, surface optimization steps (which can include one or more of draw peeling, polishing, and burnishing) can be applied to the metal rod at this stage of process 100 to further reduce surface irregularities or material surface features thereon.

In some embodiments, at step 22, the continuous metal rod, now be comprised of multiple coils of metal rod welded together, can wound onto large production reels. These spools can represent complete manufacturing runs and can further serve as the feedstock for heat treatment undertaken during line process 200, as discussed below.

Referring to FIG. 2, one embodiment of process line 200 for heat treatment, quenching, tempering, and surface residual stress optimization is shown. In some embodiments, the wound rod can be unwound from the large production reels prepared at step 22 on process line 100 and guided into the thermal treatment section of process line 200 by a set of pinch roller system that can hold the rod in the state of tension. This step can ensure proper alignment and tension control to the metal rod before it enters an induction heating system.

In some embodiments, at step 26, the metal rod can enter an induction heating line, wherein it can undergo austenitization at controlled temperatures, typically between 800 to 1000° C., depending on the microstructure and alloy type of the incoming metal rod.

In some embodiments, at step 28, rapid cooling can be applied to the heat treated metal rod through pressurized quench systems, wherein the temperature of the metal rod can be reduced to approximately 100 to 200° C., thus forming a hardened martensitic microstructure.

In some embodiments, at step 30, the metal rod can go under induction tempering to relieve stresses and to adjusts hardness thereof to produce a tempered martensitic microstructure with improved toughness. In some embodiments, multiple induction coils can be used for this step depending on required thermal exposure for the metal rod.

In some embodiments, at step 32, following the tempering of step 30, the metal rod can be cooled through a stage of air cooling wherein the metal rod can be cooled by radiation and convection, followed by water cooling to stabilize thermal conditions prior to surface treatment or shot peening. In some embodiments, optional cooling stages can retain the metal rod at elevated temperature levels (approximately 100 to 450° C.), so as to enable advanced surface processes such as warm shot peening.

In some embodiments, at step 34, surface residual stress optimization via shot peening can by applied to the metal rod. At this stage, in some embodiments, the metal rod can undergo a surface treatment by shot peening, which can remove partially or totally the residual oxide layer on the metal rod, and can introduce a compressive residual stress profile on the rod surface. In some embodiments, the metal rod can be processed in a warm state immediately after the line cooling at step 32, without water cooling, or following partial water cooling that can adjust the metal rod temperature to a specified intermediate range. Alternatively, shot peening can also be carried out at lower temperatures following full cooling, typically between 60 to 70° C. The ability to conduct shot peening at elevated or intermediate substrate temperatures (referred to as warm shot peening) can provide additional benefits in stabilizing residual stress fields, enhancing fatigue performance, and reducing susceptibility to corrosion, thereby broadening the scope and effectiveness of the surface optimization step.

In some embodiments, at step 36, final cooling and spooling of the metal rod can occur. In some embodiments, subsequent to surface optimization, the metal rod can undergo an additional water-cooling process to lower the surface temperature to ambient, or close to it, and can then be wound onto reels for storage or for transfer to process line 300, as described below.

Referring to FIG. 3, one embodiment of process line 300 for non-destructive testing (NDT), welding, and final preparation is shown. In some embodiments, at step 38, the metal rod can be unwound from the large production reels prepared at step 36 of process line 200 and then guided into process line 300 for the welding section and electromagnetic inspection (EMI). This step can ensure proper alignment and tension control of the metal rod before entering an induction heating system.

In some embodiments, at step 40, an optional welding step can take place. When defective segments in the metal rod are cut out, continuity of the endless metal rod can be restored by forge welding, followed by post-weld heat treatment at the same station to normalize properties in the weld zone.

In some embodiments, at step 42, an inspection and defect control step can take place. The metal rod can pass through a non-destructive testing (NDT) system, typically an electromagnetic inspection (EMI) system, to detect discontinuities or defects in the metal rod. Any defective sections that fall outside specifications can be either mechanically reworked or removed.

In some embodiments, at step 44, a protective coating can be applied to the metal rod. In some embodiments, for bare metal rod products, the metal rod can receive an atmospheric protection layer such as bituminous paint.

In some embodiments, at step 46, the metal rod can then be rewound onto reels, completing the endless rod product for delivery or for transfer to process line 400 if polymer coating for the metal rod is required.

At the end of process 300, after being spooled at step 46, a decision can be made at step 48 as to whether the endless rod is to be coated or not. If the endless rod is not to be coated, it can be placed on transport reel 50 for use by an end user of the endless metal rod. If the endless metal rod is to be coated for a particular application or specification, the endless metal rod can then proceed to process line 400 to have coating applied thereto.

Referring to FIG. 4, one embodiment of process line 400 for polymeric coating application is shown. In some embodiments, at step 52, the metal rod can be unwound from transport reel 50 prepared at step 46 in process line 300 and then guided into process line 400 for coating to be applied thereto.

In some embodiments, at step 54, metal rod destined for polymeric coating can be prepared by abrasive blasting or surface activation thereto to ensure adhesion of the polymeric coating.

In some embodiments, at step 56, controlled pre-heating can be applied to the metal rod to ensure that the metal rod reaches the required surface temperature for adhesive bonding of the polymeric coating.

In some embodiments, at step 58, an adhesive bonding layer can be applied to the metal rod to act as an interface or catalyst between the steel substrate of the metal rod and the polymeric coating.

In some embodiments, at step 60, a polymeric co-extrusion process can be applied to the metal rod. In some embodiments, the co-extrusion process can comprise the uniform application of a polymeric coating as a corrosion resistance coating, such as high-density polyethylene (HDPE) or Polyketone (PK), around the metal rod. In some embodiments, a continuous layer of the polymeric coating can be applied to the metal rod to meet the necessary barrier properties for the metal rod for corrosion resistance. In some embodiments, a metallic coating can be applied to the metal rod as a corrosion resistance coating as to provide corrosion resistance thereto. In some embodiments, the corrosion resistance coating can comprise a composite of a polymeric coating and a metallic coating. In some embodiments, the metallic coating can comprise a non-ferrous metal that is resistant to corrosion, as well known to those skilled in the art. In some embodiments, the metallic coating can comprise one or more of zinc, aluminum, aluminum oxides, titanium, magnesium, and any other non-ferrous metal, metal alloy, or metal composite having anti-corrosion properties as well known to those skilled in the art.

In some embodiments, at step 62, a post-coating heat treatment and cooling process can be applied to the metal rod. The coated metal rod can then be stabilized through controlled cooling of the polymeric coated metal rod, ensuring adhesion integrity and mechanical compatibility between the polymeric coating and the metal rod.

In some embodiments, at step 64, final spooling of the coated metal rod can take place, wherein the coated metal rod can be rewound onto transport reels 66, completing the production cycle of the coated metal rod.

In conclusion, the following encapsulates some of the key advantages and solutions of the processes described herein and the metal rod produced from these processes:

Enhanced Fatigue Life

By targeting the inherent issues related to surface defects and natural features through processes such as surface optimization, the improved process can significantly elevate the fatigue life of the rods. This, in turn, can diminish the likelihood of premature failure, especially in applications where exceptional endurance is requisite.

Improved Corrosion Resistance

The synergistic effect of premium surface treatments, banding or segregation, and decarburization, among other metallurgical features control and methodologies to minimize banding, can contribute to superior corrosion resistance. By implementing controlled thermal treatment and an optimized or premium surface combined with a polymeric coating, the processes described herein can ensure a robust defense against corrosion, which prolongs the rod's service life.

Wear Resistance

The specialized polymeric coating, including options like HDPE or PK, can serve as an essential barrier against wear. This surface protection is particularly significant in environments where sliding or rotary contacts are prevalent, ensuring the rod's sustained functionality.

Cost Savings

The reduced occurrence of defects and enhancement in overall rod quality can directly translate to significant cost savings. The processes and methods described herein can cut down on scrap rates, rejected parts, and warranty claims, all contributing to more efficient operations and a better bottom line.

Environmental Benefits

By embracing a design that minimizes waste and optimizes energy consumption, the processes and methods described herein can affirm a commitment to sustainable practices. The reduced need for replacements and repairs can contribute to a decrease in resource utilization, aligning with broader environmental goals.

Customization and Adaptability

Recognizing the diverse needs of various applications, the processes and methods described herein can provide for customization in coating systems and surface optimization techniques. This adaptability can ensure that the rods can be fine-tuned to meet specific demands and environmental conditions, promoting a versatile and responsive solution.

Comprehensive Approach

In some embodiments, the holistic approach to rod manufacturing can bring together modern technology, in-depth material science understanding, and innovative design. This integration of various facets creates a solution that is both progressive and effective in addressing the complexity of challenges faced in the manufacturing of endless rods.

In some embodiments, metallic coatings can be applied to the rod for cathodic protection of the rod, as well known to those skilled in the art. As metallic coatings do not have the wear resistance of polymeric coatings, as described, a coating can be applied to the rod that is a composite of both metallic and polymeric coatings to provide both the wear resistance of polymeric coatings and the cathodic protection provided by metallic coatings for the rod.

Overall, the processes described herein can revolutionize the endless rod manufacturing process by offering a coherent, adaptable, and highly efficient solution. By converging on critical areas such as fatigue life, corrosion and wear resistance, cost-effectiveness, and environmental sustainability, the processes described herein can pave the way for a new era in rod manufacturing, providing tangible benefits that transcend conventional approaches.

Although a few embodiments have been shown and described herein, it will be appreciated by those skilled in the art that various changes and modifications can be made to these embodiments without changing or departing from their scope, intent or functionality. The terms and expressions used in the preceding specification have been used herein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the invention is defined and limited only by the claims that follow.