A Working Party Report on Corrosion Resistant Alloys for Oil and Gas Production

General Requirements and Test Methods for H2S Service (EFC 17)

Liane Smith

• Publisher: CRC Press
• Year: 2022
• eBook ISBN: 9781000640625
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

This book addresses the selection and qualification of corrosion resistant alloys for use in oil and gas field production facilities that handle raw and partly processed reservoir fluids at, and below, reservoir temperatures.

1 Terminology and Definitions

DOI: 10.1201/9781003311058-1

All terminology in this document is advisory terms such as: shall, should; require, requirement; etc., are not to be taken as mandatory when there are sound technical reasons for acting otherwise.

The document uses established oilfield terminology Some key generic terms are explained in Section 1.1 below. Conventional definitions of other terms and abbreviations follow in Section 1.2.

1.1 Generic and Oilfield Terms

Oilfield and Oilfield Facilities

‘Oilfield’ and ‘oilfield facilities’ should be taken to include oil, condensate and gas producing facilities.

Carbon Steels

‘Carbon steels’ is used as a generic term to designate the full range of carbon, carbon-manganese and low alloy steels, used in the construction of conventional oilfield equipment.

Corrosion Resistant Alloys (CRAs)

CRAs are alloys that are intended to be resistant to general and localised corrosion in oilfield environments that are corrosive to carbon steels, as defined above.

Sweet Service / Sour Service

Conventionally these terms are used to distinguish between service in H₂S free (sweet) and H₂S containing (sour) fluids; the distinction is commonly made in accordance with the criteria of NACE MR0175. Because there is no satisfactory standard definition of these terms as they apply to the use of CRAs, the terms are not used in this document. Instead the term H₂S service is used to identify environments that contain measurable amounts of H₂S. H₂S is conventionally measured in gas streams. Measurement down to 0.5 ppm by volume is routinely available in accordance with ASTM D 4810.

Environmental Cracking, Sulphide Stress Cracking, Stress Corrosion Cracking

This document proposes test methods for assessing the resistance of CRAs to environmental cracking in H₂S service. Cracking may be caused by sulphide stress cracking (SSC) or stress corrosion cracking (SCC) which occur by different mechanisms as described in Appendix 1. As the objective of the tests is to identify conditions that cause cracking, irrespective of the mechanism, the tests are referred to throughout as SSC/SCC tests unless the immediate context requires that the cracking mechanisms be differentiated.

Titanium Alloys

The term titanium alloys includes the commercially pure grades.

Test Methods and Specimens

The terminology of ISO 7539-1 has been followed in describing SSC/SCC test methods and test specimens.

Yield Strength, Proof Strength, Elongation under Load

These terms cause confusion because they are defined and used differently in Europe, the USA, ISO and oilfield specifications. In this document, yield strength and yield stress have been used, according to the ASTM and oilfield conventions, to indicate the stress (factored for design purposes) at which significant plastic yielding occurs in a tensile test. This usage is an imprecise convenience as the strength cannot be quantified without specifying the extent and method of measurement of the plastic deformation. In the proposed SSC/SCC test procedures the recommended test stresses are defined rigorously according to ISO convention.

In this context it should be noted that for some commonly used CRAs, API standards specify measurement of yield at 0.5% extension under load (EUL). Examples are Grade L80 13Cr casing and tubing in API 5CT and the CRA line pipe grades in API 5LC. By contrast, the ISO draft specification for CRA casing and tubing (ISO/WD 13680-1) uses the 0.2% proof stress to define ‘yield’.

Although the difference between these two definitions of proof stress is typically insignificant in carbon steels and 13Cr, the difference may be significant for alloys that have a high strain hardening rate. This includes many stainless steels and nickel base alloys to which this document applies.

1.2 Definitions and Abbreviations

...

CRA	Corrosion resistant alloy, see also Section 1.1 above.
Constant load, constant total strain	ISO 7539 terms for methods of loading SCC specimens. C-rings and 4 point bent beams are conventionally loaded in constant total strain.
Compliance	Elastic stiffness.
εair	Strain to failure in air in SSRT.
εn	Normalised strain to failure = εs/εair in SSRT.
	Strain to failure in solution in SSRT.

Table of contents

• Cover Page
• Half-Title Page
• Title Page
• Copyright Page
• Table of Contents
• Series Introduction
• Preface to the First Edition
• Preface to the Second Edition
• 1. Terminology and Definitions
• 2. Standards Referred to in this Document
• 3. Introduction
• 4. Scope
• 5. Objective
• 6. Overview of Requirements for Selection and Qualification of CRAs for Oil and Gasfield Use
• 7. General Principles and Limitations of Proposed SSC/SCC Tests
• 8. SSC/SCC Test Procedures
• Appendix 1: Mechanisms of Environmental Cracking
• Appendix 2: The Source, Nature and Analysis of Produced Water in Oil and Gas sroduction
• Appendix 3: Titanium Alloys-Limitations of Use
• Appendix 4: Reference Environments for Comparative (or Ranking) SSC/SCC Testing that is not Application Specific
• Appendix 5: Normalisation of Slow Strain Rate Test Ductility Measurements
• Appendix 6: Autoclave testing of CRAs
• Appendix 7: Stressing of Bent Beam Specimens and C-Rings
• Supplementary Appendix S1: Test Methods for the Evaluation of the Corrosion Performance of Steels and Non-Ferrous Alloys in the System: Water-Hydrogen Sulphide- Elemental Sulphur