Corrosion inhibitor intensifier and method of using the same

Description

FIELD OF THE INVENTION

The present invention relates to an aqueous acid composition containing a terpene and methods of using the composition to inhibit or reduce the corrosion of metals.

BACKGROUND OF THE INVENTION

Some well stimulation techniques, such as pickling, acid washing, matrix acidizing and acid fracturing, require the use of corrosion inhibitors to reduce the rate of acid attack on metal components and to protect wellbore tubular goods. In some instances, such as in stimulation processes requiring strong acids, high temperatures, long duration jobs and/or special alloys, the cost of corrosion inhibitors may be so high that it becomes a significant portion of total costs. In such scenarios, corrosion inhibitor intensifiers, also known as corrosion inhibitor aids and corrosion inhibitor boosters, are included in the formulation in order to reduce costs and ensure that the stimulation job can be performed cost effectively while complying with technical requirements.

Commercial corrosion inhibitors are usually reaction mixtures or blends that contain at least one component selected from nitrogenous compounds, such as amines, acetylenic alcohols, mutual solvents and/or alcohols, surfactants, heavy oil derivatives and inorganic and/or organic metal salts. Such combinations are often required in order to make the corrosion inhibitor more effective. In addition, such combinations assist in dispersing the hydrophobic components and providing uniform corrosion inhibition of metal components.

Corrosion inhibitor intensifiers typically are less expensive than corrosion inhibitors and exhibit a synergistic effect with at least one of the components of the corrosion inhibitor, such as the nitrogenous compounds and/or acetylenic alcohol, to reduce the reaction rate of the acid with the tubular goods. Corrosion inhibitors, such as copper or iodide salts, have been reported to further function as corrosion inhibitor intensifiers at low concentrations.

However, synergistic effects are typically only evident when the corrosion inhibitor intensifier is used at relatively high concentrations. Corrosion inhibitor intensifiers further are often incompatible with certain corrosion inhibitors. Thus, the ability to formulate compositions at their requisite concentration levels is often compromised.

The most common commercial inhibitor intensifiers are formic acid, acetic acid and derivatives thereof, aldehydes and salts, and/or derivatives of arsenic, mercury, iodine, copper, antimony, and bismuth. Weak organic acids, like formic acid, have limited application since their low pH makes them more difficult to handle. Further, such acids are only useful at high concentrations. For instance, a typical volume ratio of corrosion inhibitor to corrosion inhibitor intensifier may be as high as 1:10. Further, formic acid has limited applicability because it is only useful as an inhibitor intensifier in mineral acid, such as HCl systems.

The use of salts, such as salts of arsenic and mercury, as inhibitor intensifiers has further been unsuccessful in light of their toxicity. Further, salts are not typically cost effective since they must be used at high concentrations and coupled with a chelating agent in order to avoid precipitation upon transformation into liquids. Less toxic salts, such as salts of antimony and bismuth, are either insoluble in water or have such limited solubility that they require the use of special solvents and/or processes to transform them into liquid additives. Such salts, when used in conjunction with HF-containing acid systems in sandstone acidizing, must be used at such high concentrations that unacceptable levels of precipitation occur. For instance, potassium iodide, a common inhibitor intensifier, requires concentrations ranging from 10 to 100 pounds per 1000 gallons of treating acid. As the concentration demands of the intensifier increase, the salt reacts with by-products formed from the reaction of HF and sand or clay to produce potassium fluosilicate, a low solubility reaction product.

A need exists therefore for a corrosion inhibitor intensifier which may be used at low concentrations and which is compatible with conventional corrosion inhibitors used in well stimulation.

SUMMARY OF THE INVENTION

An acid composition, suitable for use in acidizing a subterranean formation or wellbore, contains, in addition to an aqueous organic acid solution and corrosion inhibitor, a corrosion inhibitor intensifier. The corrosion inhibitor intensifier contains a terpene. Such compositions substantially reduce the corrosive effects of the acidic solution on metals in contact with the acidic solution.

Suitable terpenes include hydrocarbons, alcohols, aldehydes and ketones which may be either monocyclic or bicyclic. Preferred terpenes include carotene, limonene, pinene, farnesene, camphor and menthol.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Corrosive effects of metal may be dramatically reduced by use of a composition containing a mineral or organic acid, a corrosion inhibitor and a corrosion inhibitor intensifier; the corrosion inhibitor intensifier containing at least one terpene.

In well stimulation, for example, corrosion may be reduced by introducing the composition of the invention into the well. In addition to being environmentally friendly, the terpene corrosion inhibitor intensifier greatly reduces the need for conventional corrosion inhibitors, compared to the use of the corrosion inhibition intensifiers of the prior art.

The combination of terpene corrosion inhibitor intensifier and conventional corrosion inhibitors exhibits synergistic effects on acid inhibition. The combination is therefore particularly efficacious in the protection of metals. When used in acidizing, the corrosive effect of the acid solution on metal in contact with the solution is greatly minimized. When used in-situ, acid soluble materials may react with the composition to decrease the corrosive effect of the acid solution.

Suitable terpenes include monoterpenes, sesquiterpenes, diterpenes, triterpenes and tetraterpenes. Further included as “terpenes” are those essential oils from which monoterpenes, sesquiterpenes, diterpenes, triterpenes and tetraterpenes are extracted, such as citrus oil, pine or pinus oil, hemp oil, needle oil, tea tree oil, etc. Derivatives of terpenes, such as turpentines (including blends of natural terpenes and synthetic terpenes, dipentines and/or allocimenes (building blocks of terpene resins) and pyrodenes (breakdown products of terpenes), may further be employed.

Preferred terpenes include hydrocarbons, alcohols, aldehydes and ketones. The terpenes for use in the invention include those which are acyclic, monocyclic and bicyclic. Monocyclic and bicyclic terpenes are preferred. The cyclic terpenes may include those having one or more benzenoid groups.

Preferred terpenes include carotene, d-limonene, pinene, farnesene, camphor, cymene and menthol. Biodegradable monoterpenes, such as d-limonene and alpha-pinene are especially preferred.

The acid employed in the composition is preferably a mineral acid or an organic acid and mixtures thereof. Preferred mineral acids include hydrochloric acid, hydrofluoric acid, nitric acid, phosphoric acid and sulfuric acid.

Preferred organic acids include formic acid, acetic acid, glycolic acid, citric acid and phosphonic acid. In addition, the organic acid may be a chelating agent including aminopolycarboxylic acids and sodium, potassium and ammonium salts thereof. N-hydroxyethyl-N,N′,N′-ethylenediaminetriacetic acid (HEDTA) and HEIDA (hydroxyethyliminodiacetic acid) are useful in the present process as free acids and their Na, K, NH₄⁺ salts (and Ca salts). Other aminopolycarboxylic acid members, including EDTA, NTA (nitrilotriacetic acid), DTPA (diethylenetriaminepentaacetic acid), and CDTA (cyclohexylenediaminetetraacetic acid). Mixtures of such acids may further be employed.

When the acid is a mineral acid, the concentration of acid in the composition is in the range of from about 1% to about 30% by weight of water in the composition, and more preferably from about 5% to about 28%.

When the acid is an organic acid, the concentration of acid in the composition is in the range of from about 1% to about 95% by weight of water in the composition, preferably from about 1% to about 15%.

The water utilized to form the composition may be any aqueous fluid which does not adversely react with other components of the composition. For example, the water may be fresh water, brackish water, brine as well as salt-containing water solutions such as sodium chloride, potassium chloride and ammonium chloride solutions.

The corrosion inhibition intensifier may be present in the composition of the invention is in an amount ranging from about 1 to about 10% by volume of the composition. More preferably, the intensifier is present in an amount in the range of from about 1.5 to about 5% by volume of the composition.

Suitable corrosion inhibitors are any of those conventionally used in the art. Such corrosion inhibitors reaction mixtures or blends containing at least one component selected from nitrogenous compounds, such as amines; acetylenic compounds, such as acetylenic alcohols; ketones, such as phenyl ketones; aldehydes, such as alpha, beta-unsaturated aldehydes including cinnamic aldehyde; phosphates; silicates; borates; zinc compounds; organic acids like aromatic carboxylic acids, like benzoic acid; phosphate esters; heterocyclic nitrogen and sulfur compounds, such as benzotriazole; and derivatives thereof. Such corrosion inhibitors include those set forth in U.S. Pat. No. 5,543,388, herein incorporated by reference.

The corrosion inhibitor may further include one or more solvents, surfactants, mutual solvents, antisludge, sequestering agents, friction reducers and gelling agents and other conventional additives as well as mixtures thereof.

Suitable solvents include alkyl alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol and butyl alcohol and alkylene glycols like ethylene glycol, propylene glycol.

One or more surfactants may also be utilized to facilitate the dispersion of the corrosion inhibitor and intensifier into the aqueous acid solution. Such surfactants include non-ionic surfactants, such as the 8 to 20 mole ethylene oxide adducts of octylphenol, nonylphenol and tridecylphenol. When used, the surfactant or surfactants preferably comprises less than about 20% by volume of the corrosion inhibitor.

The corrosion inhibitor is present in the composition in an amount in the range of from about 0.05% to about 5% by volume, more preferably from about 0.1% to about 3%. Typically, the volume ratio of corrosion inhibitor intensifier to corrosion inhibitor introduced into the well is from about 10:90 to about 90:10.

Since the composition dramatically reduces corrosion on metal, the composition can be used in a variety of industrial applications. The composition has particular applicability in well stimulation processes, such as, acidizing and fracture acidizing. Upon contact with the acid solution containing the corrosion inhibitor and terpene corrosion inhibitor intensifier, corrosion of metal surfaces is minimized. Such effects may be noted on all metallurgies, including carbon steel and special alloys. Further, the composition of the invention either does not react with by-products of the acid reaction or does not produce detrimental precipitates.

EXAMPLES

The following examples will illustrate the practice of the present invention in its preferred embodiments. Other embodiments within the scope of the claims herein will be apparent to one skilled in the art from consideration of the specification and practice of the invention as disclosed herein. It is intended that the specification, together with the example, be considered exemplary only, with the scope and spirit of the invention being indicated by the claims which follow.

In the Examples, the following abbreviations are employed:

CI-11 is a corrosion inhibitor containing alkylpyridinium quaternary, thiourea and oxyalkylated alkylphenols in isopropanol and water, commercially available from BJ Services Company.

CI-25 is a corrosion inhibitor containing a blend of quaternary salts, alcohols, formamide and ethoxylated nonylphenol, commercially available from BJ Services Company.

CI-14 and CI-30 are corrosion inhibitors, commercially available from BJ Services Company.

QA refers to a corrosion inhibitor of 100% active quaternary amine corrosion inhibitor, commercially available from Herga-Hib.

Antecor OG refers to a corrosion inhibitor composition containing a reaction of an alkyl quaternary amine and an acetylenic alcohol, commercially available from Poland.

GPT refers to gallons per thousand gallons acid.

The pitting scale used was as follows:

0	Zero (no staining or surface irregularities)
0-1	Slight staining of surface, but no surface irregularities
1	A trace amount of pitting on surface
Tr.	A trace, which is less than 1 but does exhibit a slight amount
	of surface irregularities (only the outer surface was affected)
2	A small amount of pitting on the surface
3	A medium amount of pitting on the surface
4	A large amount of pitting on the surface
5	Large holes or very deep pits anywhere on the test coupon

Examples 1-92

Corrosion inhibitor formulations were prepared containing a corrosion inhibitor, a terpene and an acid solution, as set forth in Table I. Metal coupons where then soaked in these acids formulations at various temperatures. Corrosion was measured for a number of hours as indicated in the tables. Based on the weight loss of metal coupon, the corrosion rate was calculated by the following formula:
Corrosion Rate=[Initial Metal Mass (gram)]−[Final metal mass (gram)]/[Metal area (square centimeter)]

The results are compiled in Table I.

TABLE I
							Test
Example	Corrosion	Inhibitor	Inhibitor,	Intensifier,	Acid Type,		Times,	Metal	Corrosion
No.	Inhibitor	Intensifier	GPT	GPT	Amount	Temp., ° F.	Hours	Type	Rate
Comp. Ex.	CI-11	None	4	0	15% HCl	180	16	N-80	0.0193
1
2	CI-11	Alpha Terpene	2	2	15% HCl	200	16	N-80	0.0335
Comp. Ex	CI-14	None	4	0	15% HCl	180	16	N-80	0.0195
3
4	CI-14	Alpha Terpene	2	2	15% HCl	180	16	N-80	0.0115
Comp. Ex.	CI-14	Antimony Salt	2	2	15% HCl	180	16	N-80	0.1572
5
6	CI-14	Alpha Terpene	2	2	15% HCl	200	16	N-80	0.0449
7	CI-14	D'Limonene	2	2	15% HCl	200	16	N-80	0.0344
Comp. Ex.	CI-14	None	4	0	28% HCl	180	16	N-80	0.1626
8
9	CI-14	Alpha Terpene	2	2	28% HCl	180	16	N-80	0.3877
Comp. Ex.	CI-25	None	4	0	15% HCl	180	16	N-80	0.0006
10
11	CI-25	Alpha Terpene	2	2	15% HCl	180	16	N-80	0.0007
Comp. Ex.	CI-25	Antimony Salt	2	2	15% HCl	180	16	N-80	0.0025
12
Comp. Ex.	CI-25	Alpha Terpene	2	2	15% HCl	200	16	N-80	0.0013
13
14	CI-25	D'Limonene	2	2	15% HCl	200	16	N-80	0.0017
Comp. Ex.	CI-25	Formic Acid	2	2	15% HCl	200	16	N-80	0.0064
15
Comp. Ex.	CI-25	EDTA + Copper +	2	2	15% HCl	200	16	N-80	0.0181
16		KI
Comp. Ex.	CI-25	None	4	0	28% HCl	180	16	N-80	0.0061
17
18	CI-25	Alpha Terpene	2	2	28% HCl	180	16	N-80	0.0029
Comp. Ex.	Poland	None	4	0	15% HCl	180	16	N-80	0.0004
19
20	Poland	Alpha Terpene	2	2	15% HCl	180	16	N-80	0.0014
Comp. Ex.	QA	None	4	0	15% HCl	180	16	N-80	0.0330
21
22	QA	Alpha Terpene	2	2	15% HCl	180	16	N-80	0.0167
23	Poland	Alpha Terpene	2	2	15% HCl	180	16	N-80	0.0011
24	CI-30	Alpha Terpene	2	2	15% HCl	180	16	N-80	0.0014
25	CI-30	Alpha Terpene	2	2	15% HCl	200	16	N-80	0.0109
Comp. Ex.	CI-25	None	4	0	28% HCl	180	16	Chrome 13	0.1264
26
27	CI-25	Alpha Terpene	2	2	28% HCl	180	16	Chrome 13	0.1358
Comp. Ex.	CI-14	None	4	0	28% HCl	180	16	Chrome 13	0.4116
28
29	CI-14	Alpha Terpene	2	2	28% HCl	180	16	Chrome 13	0.6945
Comp. Ex.	CI-11	None	4	0	15% HCl	180	16	CTU	0.0193
30
31	CI-11	Alpha Terpene	2	2	15% HCl	180	16	CTU	0.0099
32	CI-11	Alpha Terpene	2	2	15% HCl	200	16	CTU	0.0159
Comp. Ex	CI-14	None	4	0	15% HCl	180	16	CTU	0.0036
33
34	CI-14	Alpha Terpene	2	2	15% HCl	180	16	CTU	0.0036
Comp. Ex.	CI-14	Antimony Salt	2	2	15% HCl	180	16	CTU	0.0029
35
36	CI-14	Alpha Terpene	2	2	15% HCl	200	16	CTU	0.0022
37	CI-14	D'Limonene	2	2	15% HCl	200	16	CTU	0.0053
Comp. Ex.	CI-14	EDTA + Copper +	2	2	15% HCl	200	16	CTU	0.0046
38		KI
39	CI-14	Formic Acid	2	2	15% HCl	200	16	CTU	0.0036
Comp. Ex	CI-25	None	4	0	15% HCl	180	16	CTU	0.0026
40
41	CI-25	Alpha Terpene	2	2	15% HCl	180	16	CTU	0.0007
42	CI-25	Formic Acid	2	2	15% HCl	180	16	CTU	0.0002
43	CI-25	Alpha Terpene	2	2	15% HCl	200	16	CTU	0.0009
44	CI-25	D'Limonene	2	2	15% HCl	200	16	CTU	0.0038
45	CI-25	EDTA + Copper +	2	2	15% HCl	200	16	CTU	0.0106
		KI
46	CI-25	Formic Acid	2	2	15% HCl	200	16	CTU	0.0095
Comp. Ex.	CI-30	None	4	0	15% HCl	200	16	CTU	0.0038
47
48	CI-30	Alpha Terpene	2	2	15% HCl	200	16	CTU	0.0016
Comp. Ex.	Poland	None	4	0	15% HCl	180	16	CTU	0.0027
49
50	Poland	Alpha Terpene	2	2	15% HCl	180	16	CTU	0.0026
Comp. Ex.	Poland	None	4	0	15% HCl	180	16	CTU	0.0010
51
52	Poland	Alpha Terpene	2	2	15% HCl	180	16	CTU	0.0033
Comp. Ex.	QA	None	4	0	15% HCl	180	16	CTU	0.0473
53
54	QA	Alpha Terpene	2	2	15% HCl	180	16	CTU	0.0211
Comp. Ex.	CI-11	None	4	0	9:1.5	200	16	N-80	0.0299
55					HCl:HF
56	CI-11	Alpha Terpene	2	2	9:1.5	200	16	N-80	0.0262
					HCl:HF
57	CI-11	D'Limonene	2	2	9:1.5	200	16	N-80	0.0306
					HCl:HF
Comp. Ex.	CI-14	None	4	0	9:1.5	200	16	N-80	0.0032
58					HCl:HF
59	CI-14	Alpha Terpene	2	2	9:1.5	200	16	N-80	0.0726
					HCl:HF
60	CI-14	D'Limonene	2	2	9:1.5	200	16	N-80	0.0523
					HCl:HF
61	CI-14	D'Limonene	2	2	9:1	200	16	N-80	0.0020
					HCl:HF
Comp. Ex.	CI-25	None	4	0	9:1.5	200	16	N-80	0.0012
62					HCl:HF
63	CI-25	Alpha Terpene	2	2	9:1.5	200	16	N-80	0.0027
					HCl:HF
64	CI-25	D'Limonene	2	2	9:1.5	200	16	N-80	0.0207
					HCl:HF
65	CI-25	D'Limonene	2	2	9:1	180	16	N-80	0.0006
					HCl:HF
Comp. Ex.	CI-30	None	4	0	9:1.5	200	16	N-80	0.0023
66					HCl:HF
67	CI-30	Alpha Terpene	2	2	9:1.5	200	16	N-80	0.0019
					HCl:HF
68	CI-30	D'Limonene	2	2	9:1	200	16	N-80	0.0021
					HCl:HF
69	Poland	None	4	0	9:1.5	200	16	N-80	0.0110
					HCl:HF
70	Poland	Alpha Terpene	2	2	9:1.5	200	16	N-80	0.0232
					HCl:HF
71	Poland	None	4	0	9:1.5	200	16	N-80	0.0121
					HCl:HF
72	Poland	Alpha Terpene	2	2	9:1.5	200	16	N-80	0.0354
					HCl:HF
Comp. Ex.	QA	None	4	0	9:1.5	200	16	N-80	0.0365
73					HCl:HF
74	QA	Alpha Terpene	2	2	9:1.5	200	16	N-80	0.0156
					HCl:HF
Comp. Ex.	CI-11	None	4	0	9:1	200	16	CTU	0.0343
75					HCl:HF
76	CI-11	Alpha Terpene	2	2	9:1	200	16	CTU	0.0237
					HCl:HF
77	CI-11	D'Limonene	2	2	9:1	200	16	CTU	0.0288
					HCl:HF
Comp. Ex.	CI-14	None	4	0	9:1	200	16	CTU	0.0033
78					HCl:HF
79	CI-14	Alpha Terpene	2	2	9:1	200	16	CTU	0.0082
					HCl:HF
80	CI-14	D'Limonene	2	2	9:1	200	16	CTU	0.0033
					HCl:HF
81	CI-14	D'Limonene	2	2	9:1	180	16	CTU	0.0016
					HCl:HF
Comp. Ex.	CI-25	None	4	0	9:1	200	16	CTU	0.0036
82					HCl:HF
83	CI-25	Alpha Terpene	2	2	9:1	200	16	CTU	0.0040
					HCl:HF
84	CI-25	D'Limonene	2	2	9:1	200	16	CTU	0.0015
					HCl:HF
85	CI-25	D'Limonene	2	2	9:1	180	16	CTU	0.0007
					HCl:HF
Comp. Ex.	CI-30	None	4	0	9:1	200	16	CTU	0.0024
86					HCl:HF
87	CI-30	Alpha Terpene	2	2	9:1	200	16	CTU	0.0046
					HCl:HF
88	CI-30	D'Limonene	2	2	9:1	200	16	CTU	0.0014
					HCl:HF
Comp. Ex.	Poland	None	4	0	9:1	200	16	CTU	0.0038
89					HCl:HF
90	Poland	Alpha Terpene	2	2	9:1	200	16	CTU	0.0044
					HCl:HF
Comp. Ex.	QA	None	4	0	9:1	200	16	CTU	0.0378
91					HCl:HF
92	QA	Alpha Terpene	2	2	9:1	200	16	CTU	0.0320
					HCl:HF

These Examples illustrate that terpenes function as metal protection intensifiers for various types of acids and in conjunction with different types of commercial corrosion inhibitors. Further, the terpenes are illustrated to at least as good, if not better, than commercially available inhibitor intensifiers.

Examples 93-96

Corrosion inhibitor formulations were prepared containing Antecor OG as corrosion inhibitor, a terpene and an acid solution of 2% HF, 13% acetic acid and 9% formic acid. A QT-900 coil tubing metal coupon was soaked in the acid solutions at 329° F. (165° C.) at 3500 psi under agitation for 8 hours. The results are compiled in Table II.

TABLE II
			Corrosion
Example	Inhibitor,		Rate,	Pitting
No.	GPT	Intensifier @GPT	lbs/ft2	Number
93	20	Alpha Terpene @ 25	0.0109	Tr.
94	15	Alpha Terpene @ 25	0.0135	1
95	10	Alpha Terpene @ 25	0.0162	Tr.
96	20	None	0.0613	Tr.

Examples 97-102

Corrosion inhibitor formulations were prepared containing Poland as corrosion inhibitor, a terpene and an acid solution of 2% HF, 13% acetic acid and 9% formic acid. The formulations were then pumped over a QT-900 coil tubing metal coupon at 329° F. (165° C.) at 3500 psi under agitation for 8 hours. The results are compiled in Table III.

TABLE III
			Corrosion
Example	Inhibitor,		Rate,	Pitting
No.	GPT	Intensifier @ GPT	lbs/ft2	No.

97	20	None	0.0311	Tr.
98	40	None	0.0311	Tr.
99	60	None	0.0311	Tr.
100	20	25	0.0191	Tr.
101	40	25	0.0245	Tr.
102	60	25	0.0247	Tr.

Examples 103-108

Corrosion inhibitor formulations were prepared containing CI-corrosion inhibitor, alpha terpene and an acid solution of 2% HF, 13% acetic acid and 9% formic acid. The formulations were then pumped over a QT-900 coil tubing metal coupon at 329° F. (165° C.) at 3500 psi under agitation for 8 hours. The results are compiled in Table IV.

TABLE IV
		Inhibitor I		Inhibitor	Intensifier,	Corrosion
Example No.	Inhibitor I	Conc., GPT	Inhibitor II	II Conc., GPT	Conc.., GPT	Rate

103	Cl-11	60	Cl-25	15	25	0.0424
104	Cl-11	60	Cl-25	15	50	0.0410
105	Cl-11	35	Cl-25	20	50	0.0538
106	Cl-11	35	Cl-25	20	100	0.0528
107	Cl-11	60	Cl-25	25	25	0.0376
108	Cl-11	60	Cl-25	25	50	0.0295

These Examples demonstrate that corrosion rate decreases when the concentration of intensifier is increased.

Examples 109-116

Corrosion inhibitor formulations were prepared containing a mixture of corrosion inhibitors, alpha terpene and an acid solution of 2% HF, 13% acetic acid and 9% formic acid in a monoethanolamine (MEA) buffer. The formulations were then pumped over a Qt-900 coil tubing metal coupon at 329° F. (165° C.) at 3500 psi under agitation for 8 hours. The results are compiled in Table V.

TABLE V
			Inhibitor		Inhibitor
			I		II		Intensifier,
Example	MEA,	Inhibitor	Conc.,	Inhibitor	Conc.,		Conc.	Cor.	Pitting
No.	GPT	I	GPT	II	GPT	Intensifier	GPT	Rate	No.

109	20	Cl-25	40	Cl-11	20	None	0	0.0391	1
110	20	Cl-25	40	Cl-11	20	Alpha	25	0.0273	1
						Terpene
111	20	Cl-25	40	Cl-11	20	Alpha	50	0.0331	Tr.
						Terpene
112	20	Cl-25	50	Cl-11	30	Alpha	50	0.0249	Tr.
						Terpene
113	13	Cl-25	42	Cl-11	15	None	0	0.0395	1
114	13	Cl-25	42	Cl-11	15	Alpha	30	0.0320	1
						Terpene
115	10	Cl-30	45	Cl-11	20	None	0	0.0662	1
116	10	Cl-30	45	Cl-11	20	Alpha	25	0.0610	Tr.
						Terpene

Comparative Example No. 109 and Example Nos. 110-112 demonstrate that the addition of alpha terpene reduces the corrosion rate at low or trace pitting. Further, Example No. 112 illustrates that an increase in the concentration of corrosion inhibitor has an effect on decreasing the corrosion rate. Comparative Example No. 113 and Example No. 114 demonstrates that the addition of alpha terpene reduces corrosion rate. Comparative Example 115 and Example 116 demonstrates that the addition of alpha terpene reduces corrosion rate and eliminates pitting.

From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the true spirit and scope of the novel concepts of the invention.