API TITLE*VT=2 90 moo 0732290 0095595 9 R1 CORROSION OF OIL- AND GAS-WELl EQUIPMENT BOOK ~ OF THE VOCATIONAL TRAINING SERIES SECOND EDITION, OCTOBER 1990 ft»f%(Q)[))l\J<C1l'D<O>N [))IE[!»Ali\!.1l'MIEN1l' AM~~~CAN PET~OL~UM ~N§f~1U1~ API TITLE*VT-2 90 mi 0732290 0095596 0 mD Issued by AMERICAN PETROLEUM INSTITUTE Production Department FOR INFORMATION CONCERNING TECHNICAL CONTENT OF THIS PUBLICATION CONTACT THE API PRODUCTION DEPARTMENT, 2535 ONE MAIN PLACE, DALLAS, TX 75202-3904- (214) 748-3841. SEE BACK COVER FOR INFORMATION CONCERNING HOW TO OBTAIN ADDITIONAL COPIES OF THIS PUBLICATION. Users of this publication should become familiar with its scope and content. This publication is intended to supplement rather than replace individual judgment.
OFFICIAL PUBLICATION REG. PATENT OFFICE Copyright © 1990 American Petroleum Institute API TITLE*VT-2 90. iii POLICY API PUBLICATIONS NECESSARILY ADDRESS PROBLEMS OF A GENERAL NATURE. WITH RESPECT TO PARTICULAR CIRCUM- STANCES, LOCAL, STATE AND FEDERAL LAWS AND REGULA- TIONS SHOULD BE REVIEWED.
API IS NOT UNDERTAKING TO MEET DUTIES OF EMPLOYERS, MANUFACTURERS OR SUPPLIERS TO WARN AND PROPERLY TRAIN AND EQUIP THEIR EMPLOYEES, AND OTHERS EXPOSED, CONCERNING HEALTH AND SAFETY RISKS AND PRECAUTIONS, NOR UNDERTAKING THEIR OBLIGATIONS UNDER LOCAL, STATE, OR FEDERAL LAWS. NOTHING CONTAINED IN ANY API PUBLICATION IS TO BE CON- STRUED AS GRANTING ANY RIGHT, BY IMPLICATION OR OTHERWISE, FOR THE MANUFACTURE, SALE, OR USE OF ANY METHOD, APPARATUS, OR PRODUCT COVERED BY LETTERS PATENT. NEITHER SHOULD ANYTHING CONTAINED IN THE PUBLICATION BE CONSTRUED AS INSURING ANYONE AGAINST LIABILITY FOR INFRINGEMENT OF LETTERS PATENT. GENERALLY, API PUBLICATIONS ARE REVIEWED AND RE- VISED, REAFFIRMED, OR WITHDRAWN AT LEAST EVERY FIVE YEARS.
SOMETIMES A ONE-TIME EXTENSION OF UP TO TWO YEARS WILL BE ADDED TO THIS REVIEW CYCLE. THIS PUBLI- CATION WILL NO LONGER BE IN EFFECT FIVE YEARS AFTER ITS PUBLICATION DATE AS AN OPERATIVE API PUBLICATION OR, WHERE AN EXTENSION HAS BEEN GRANTED, UPON REPUBLICATION. STATUS OF THE PUBLICATION CAN BE ASCERTAINED FROM THE API AUTHORING DEPARTMENT (TEL. A CATALOG OF API PUBLICATIONS AND MATE- RIALS IS PUBLISHED ANNUALLY AND UPDATED QUARTERLY BY API, 1220 L ST.
API TITLE*VT-2 90 II 0732290 0095598 4 II iv IMPORTANT INFORMATION CONCERNING USE OF ASBESTOS OR ALTERNATIVE MATERIALS Asbestos is specified or referenced for certain components of the equip- ment described in some API standards. It has been of great usefulness in minimizing fire hazards associated with petroleum processing. It has also been a universal sealing material, compatible with most petroleum fluid services. Certain serious adverse health effects are associated with asbestos, among them the serious and often fatal diseases of lung cancer, asbestosis, and mesothelioma (a cancer of the chest and abdominal linings).
The degree of exposure to asbestos varies with the product and the work practices involved. Consult the most recent edition of the U. Department of Labor, Occupa- tional Safety and Health Administration (OSHA) Health Standard for Asbestos, 29 Code of Fedw,.al Regulations Section 1910:1001; the U. Environmental Protection Agency's National Emission Standard for Hazardous Air Pollutants concerning Asbestos, 40 Code of Fedeml Regula- tions Sections 61.156; and the final rule by the U.
En- vironmental Protection Agency (EPA), concerning phased banning of asbestos products, 40 CFR Part 763, published at 54 Fedeml Register 29460-29513 (July 12, 1989). There are currently in use and under development a number of substitute materials to replace asbestos in certain applications. Manufacturers and users are encouraged to develop and use effective substitute materials which can meet the specifications for, and operating requirements of, the equipment to which they would apply. SAFETY AND HEALTH INFORMATION WITH RESPECT TO PARTICULAR PRODUCTS OR MATERIALS CAN BE OBTAINED FROM THE EMPLOYER, THE MANUFACTURER OR SUPPLIER OF THAT PRODUCT OR MATERIAL, OR THE MATERIAL SAFETY DATA SHEET.
API TITLE*VT-2 90. v FOREWORD The practical value of corrosion countermeasures, no matter how per- fect they may be in the theoretical or laboratory sense, depends upon cer- tain knowledge and attitudes on the part of foremen, pumpers, well tenders, and individuals with related responsibilities. This book is directed at field operating personnel, in the hope that steady use will enhance the knowledge and attitudes mentioned, specifically: Appreciation of the enormous cost of oilfield corrosion. Ability to recognize early indications of corrosion.
Awareness of the importance of early reporting. Desire to take effective part in the solution. The book is not intended to produce technical experts. Therefore, it makes full use of the simplest possible terms and descriptions.
The control measures it describes are only typical, and should not be automatically accepted as the best solution for any specific problem. The circumstances of corrosion vary widely, and technical advice should always be sought when causes are obscure, or cost or severity is high. This second edition was prepared by an Ad Hoc Task Group with guid- ance and review by the API Production Department Executive Committee on Training and Development. It updates and supersedes the 1958 first edition.
The first edition was developed in cooperation with the National Association of Corrosion Engineers (N ACE), which later issued a separate publication: NACE TPC Publication No.5, Corrosion Cont'rol in Petroleum Production. Personnel needing a more thorough understanding of corro- sion technology may obtain that and other technical publications from: NACE, Box 218340, Houston, TX 77218. API TITLE*VT-2 90 II 0732290 0095600 9 II vii TABLE OF CONTENTS Policy. v CHAPTER 1: GENERAL ASPECTS OF CORROSION.
1 Types of Corrosion. 1 Economics of Corrosion Problem. 2 Importance of Field Personnel in Corrosion-control Programs. 2 CHAPTER 2: SWEET CORROSION.
4 DESCRIPTION OF DAMAGE. 4 Chemistry of Reaction. 4 Gas-condensate Wells. 5 Sweet Oil Wells.
7 METHODS OF EVALUATING THE PROBLEM. 9 Corrosion Test Coupons. 17 Design and Operating Techniques. 22 CHAPTER 3: SOUR CORROSION.
23 DESCRIPTION OF DAMAGE. 23 Chemistry of Reaction. 23 Oil-well Tubing. 24 Annular-space Corrosion.
28 METHODS OF EVALUATING THE PROBLEM. 29 Analysis of Produced Fluids and Gas. 29 Equipment failure Records. 32 Design and Operating Techniques.
32 Non-metallic Materials. 34 Economics of Corrosion Control. 36 CHAPTER 4: OXYGEN CORROSION. 37 DESCRIPTION OF DAMAGE.
37 Chemistry of Oxygen Corrosion. 38 API TITLE*VT-2 90 II 0732290 0095601 0 II viii Surface Equipment. 39 Water-flood Injection Equipment. 41 METHODS OF EVALUATING THE PROBLEM.
43 Design and Operating Techniques. 43 Treatment with Corrosion Inhibitors. 44 The Use of Resistant Alloys. 45 Selection, Application, and Inspection of Protective Coatings.
45 CHAPTER 5: ELECTROCHEMICAL CORROSION. 51 DESCRIPTION OF DAMAGE. 51 Chemistry of Reaction. 57 Soil Corrosion of Pipe and Surface Equipment.
59 METHODS OF EVALUATING THE PROBLEM. 60 Recognizing Electrochemical Corrosion. 60 Current and Potential Measurements. 66 ECONOMICS OF CATHODIC PROTECTION.
71 PART 1: GLOSSARY OF TERMS. 76 PART 3: OIL WELL PUMPS. 77 PART 4: SURVEY METHODS USED IN CATHODIC- PROTECTION STUDIES. 82 Qualitative Field Test for Iron Sulfide on Steel Equipment.
82 Simplified Procedure for the Field Determination of Hydrogen Sulfide in Water. 83 Field Method for Determination of Iron (Ferrous) in Sweet Oilfield Waters. 85 API TITLE*VT-2 90. 1 CHAPTER 1 GENERAL ASPECTS OF CORROSION The useful life of oilfield equipment is often shortened as a result of corrosion.
In the last several years great strides have been made in corro- sion detection and remedies as applied to the oilfield. This book has been written to put this information in a form easy to use. In simplified technical terms, corrosion has been defined as the destruc- tion of a metal by either chemical or electrochemical reaction with its en- vironment. Some general statements concerning corrosion rates can be briefly made.
Carbon steel will usually corrode faster than corrosion resistant al- loys used in the oilfield. There are notable exceptions, such as the failure of strong alloy steels in H 2 S systems. The major corrodents encountered in the oilfield are carbon dioxide, hydrogen sulfide, organic acids, hydrochloric acid, and oxygen dissolved in water. Films or scales at the interface between metal and c01·rodent influ- ence corrosion rates.
These films include corrosion products, mill scale, and corrosion inhibitors. Environmental factors - such as chemical composition of water, temperature, and velocity - affect the rate of corrosion. In some cases, so- called natural inhibitors present in produced fluids greatly reduce corro- sion rates. Impressed voltages and stray electrical currents are often a source of serious corrosion damage.
Velocity of the flowing media plays an important role in erosion/ corrosion. It exhibits mechanical wear effects at high velocities, particu- larly when the media contains solids in suspension. Types of Corrosion For practical considerations, corrosion in oil and gas well production can be classified into four main types, each of which will be discussed in a following chapter. C02 corrosion is also referred to, and will be referenced in this book, as Sweet Corrosion.
It occurs as a result of the presence of carbon dioxide. This type of corrosion occurs in both gas-condensate and oil production as well as in produced water handling systems. H2 S corrosion is also referred to, and will be referenced in this book as, Sour Con·osion. It is designated as corrosion in oil and gas wells pro- API TITLE*VT-2 90 II 0732290 0095603 4 II 2 CoRROSION OF OIL- AND GAS-WELL EQUIPMENT ducing even trace quantities of hydrogen sulfide.
These wells may also contain oxygen, carbon dioxide, or sulfate reducing bacteria. Oxygen coTrosion occurs wherever equipment is exposed to atmos- pheric oxygen. It occurs most frequently in offshore installations, brine handling and injection systems, and in shallow producing wells where air is allowed to enter the annular space. The presence of even trace amounts of oxygen in produced fluids containing C02 increases the corrosion rate by several orders of magnitude.
Electrochemical corrosion is designated as that occurring when cor- rosion currents can be readily measured or when corrosion can be miti- gated by the application of current, such as in soil corrosion. Economics of Corrosion Problem The annual cost of corrosion and corrosion protection in the United States alone is estimated at approximately eight billion dollars per year. This figure was only for direct costs and no attempt was made to estimate indirect costs due to lost production, safety, and environmental factors. Furthermore, this figure did not take into consideration specific corrosion costs in oil and gas well production.
Refinery and pipeline problems were the only aspects of the oil industry considered. It has been demonstrated many times that where a costly corrosion problem is properly defined, mitigation procedures can usually be initiated with resultant savings to the industry. It should be cautioned that the establishment of a good, scientifically sound, corrosion-control program requires the expenditure of considerable effort by the corrosion expert and the field operating personnel. We would all like to have a simple magical device which would miracu- lously cure all the troubles caused by corrosion, as well as every other phase of our lives.
There is usually not a short-cut "cure all" treatment to prevent all corrosion problems. Importance of Field Personnel in Corrosion-control Programs Certain of the principles of corrosion and corrosion-control procedures have been worked out in corrosion research and engineering laboratories. However, it must be realized that the final success in the battle against corrosion rests on the shoulders of field operating personnel. Their respon- sibilities in this program can be briefly outlined.
Recognition of the corrosion problem: Field personnel are in the best position to recognize the onset of corrosion. They know when pulling cost and equipment maintenance costs begin to climb. They further have the opportunity to observe the condition of tubing, christmas trees, casing, pumps, etc., during routine maintenance and inspection. API TITLE*VT-2 90 II 0732290 0095604 6 II 1.
GENERAL AsPECTS OF CORROSION 3 2. Record keeping: Many times the real costs of corrosion are not apparent without ~p-to-date and accurate records kept specifically for corrosion-control purposes.