ISO 15156-1:2020 establishes the general framework for selecting and qualifying metallic materials against cracking in H2S-containing oil and gas production environments. It connects the documented service environment with the material requirements in ISO 15156-2 and ISO 15156-3. For duplex stainless steel, super duplex stainless steel and nickel alloy pipes and tubes, Part 1 provides the selection principles; the applicable alloy requirements and environmental limits must be checked in Part 3.
This guide covers the fourth edition, published in November 2020. It is an original technical overview of the supplied standard, rather than a substitute for the complete document or a project-specific material assessment.
What Is ISO 15156-1:2020?
ISO 15156-1 addresses metallic materials used in oil and gas production equipment and natural-gas sweetening plants exposed to H2S. Its purpose is to define a consistent basis for evaluating the environment, selecting suitable materials, qualifying materials when needed, and recording the selection method.
The ISO 15156 series is associated with NACE MR0175/ISO 15156. The introduction to the 2020 document explains their shared technical development. When ordering materials, identify the specified publication, part and edition instead of using “NACE compliant” as a complete purchasing requirement.
Standard at a Glance
| Item | ISO 15156-1:2020 |
|---|---|
| Edition | Fourth edition, November 2020 |
| Subject | General principles for selection of cracking-resistant materials |
| Primary environment | H2S-containing oil and gas production and natural-gas sweetening service |
| Material-specific requirements | Use Part 2 or Part 3, as appropriate |
| Selection and qualification | Existing lists and tables, documented field experience, or laboratory testing |
| Main deliverable | Documented service conditions and the basis for material selection or qualification |
ISO 15156 Part 1 vs Part 2 vs Part 3
| Part | Function | Relevance to Pipe and Tube Procurement |
|---|---|---|
| ISO 15156-1 | General selection principles, service assessment, qualification and reporting | Defines the common basis for specifying sour service requirements |
| ISO 15156-2 | Cracking-resistant carbon and low-alloy steels and the use of cast irons | Provides applicable material provisions for these material families |
| ISO 15156-3 | Cracking-resistant corrosion-resistant alloys and other alloys | Provides applicable requirements for stainless, duplex and nickel alloy products |
Part 1 alone does not establish a universal hardness limit, chloride limit or H2S pressure limit for every alloy. Those decisions require the applicable material provisions and the documented service conditions.
Scope and Equipment Applications
Clause 1 and Table 1 address equipment such as wells and wellheads, flowlines and gathering systems, field processing facilities, water injection equipment, natural-gas treatment plants and certain transportation pipelines. The table also includes exclusions, so equipment type alone does not establish applicability.
The standard supplements the relevant design codes and material specifications. Its scope does not automatically extend to refining or downstream processing. It addresses equipment designed by load controlled methods; strain-based designs can require separately agreed testing and acceptance criteria.
Cracking Mechanisms Covered
- Sulfide stress cracking (SSC).
- Stress corrosion cracking (SCC).
- Hydrogen-induced cracking (HIC) and stepwise cracking (SWC).
- Stress-oriented hydrogen-induced cracking (SOHIC).
- Soft-zone cracking (SZC).
- Galvanically induced hydrogen stress cracking (HSC).
These mechanisms differ. Evidence supporting resistance to one mechanism does not automatically demonstrate resistance to every mechanism relevant to the application.
Service Conditions to Define Before Material Selection
Clause 6 requires the equipment user to evaluate and document both intended exposure and relevant unintended exposure resulting from failure of containment or protection. The assessment should identify the factors that influence H2S-related cracking:
| Factor | Information to Establish |
|---|---|
| H2S exposure | Partial pressure, or the relevant aqueous concentration or chemical activity; distinguish gas-containing and gas-free systems |
| Water chemistry | In situ pH, dissolved chlorides and other halides |
| Other species | Elemental sulfur and other oxidants |
| Temperature | The relevant operating and exposure conditions |
| Loading and interaction | Mechanical stress and galvanic effects |
| Wet exposure | Time in contact with a liquid water phase |
For gas-containing systems, Part 1 discusses the use of H2S partial pressure and refers to Part 2 Annex C for further evaluation guidance, including fugacity. It does not supply a universal conversion from partial-pressure limits to fugacity or aqueous chemical activity limits.
Three Routes for Material Selection and Qualification
1. Selection from Existing Lists and Tables
Clause 7 directs users to Part 2 Annex A for applicable carbon and low-alloy steels and Part 3 Annex A for applicable corrosion-resistant and other alloys. Listed materials must satisfy the stated metallurgical, environmental and mechanical conditions. Additional testing is generally unnecessary for this route, although the equipment user may require specific testing where the consequences of failure justify it.
2. Qualification by Documented Field Experience
Clause 8.2 permits qualification using recorded field experience with adequately described materials and service conditions. The documented duration must be at least two years. The proposed service must not be more severe than the conditions supported by that experience.
3. Qualification by Laboratory Testing
Clause 8.3 requires a defined material, representative samples, appropriate test methods, justified environments and mechanical conditions, and the acceptance criteria in the applicable part. Application-specific testing must represent conditions at least as severe for the relevant failure mechanism as the documented field exposure. Laboratory testing approximates field service; its results require an explicit application basis.
What This Means for Duplex and Nickel Alloy Pipes and Tubes
For sour service procurement, combine the pipe or tube product specification with the relevant ISO 15156 requirements. An ASTM specification defines the purchased product; ISO 15156 addresses cracking resistance in a defined H2S environment. Neither a grade name nor compliance with an ASTM product specification establishes sour service suitability by itself.
For duplex stainless steel and nickel alloys, check the applicable Part 3 provisions against the supplied product form and metallurgical condition. Clause 8.1 identifies properties relevant to qualification, including chemical composition, manufacturing method, product form, strength, hardness, cold work, heat treatment and microstructure. Do not treat a PREN value or a general corrosion test as complete evidence of ISO 15156 conformity.
Purchasing and Documentation Checklist
The following is a practical procurement checklist derived from Clauses 5, 6, 8 and 9; it is not a replacement for the contractual requirements.
- Specify the material grade, product form, dimensions and applicable product standard.
- State the required ISO 15156 part and edition.
- Supply the assessed sour service environment and relevant exposure limits.
- Identify the delivery condition, manufacturing and metallurgical requirements.
- Record whether selection uses listed materials, field experience or laboratory qualification.
- Agree any additional testing and required reports before manufacture.
- Document the service evaluation and the supporting selection or qualification evidence.
Clause 9 requires the service-condition assessment together with evidence for the selected route. A laboratory qualification report includes the material, specimen sampling and preparation, test-condition justification and results. The equipment user is responsible for ensuring that the required documentation is prepared.
Frequently Asked Questions
Does ISO 15156-1 approve duplex stainless steel for all sour service?
No. Part 1 establishes the selection process. A duplex product must meet the applicable Part 3 material provisions and the limits relevant to the documented environment and supplied condition.
Is ISO 15156-1 a pipe manufacturing specification?
No. It addresses material selection and qualification for H2S-related cracking. Pipe and tube dimensions, manufacturing requirements and product acceptance still require the applicable product specification and contract.
Does Part 1 define one maximum hardness for all materials?
No. Material-specific hardness requirements must be checked in the applicable Part 2 or Part 3 provisions. A single hardness value cannot be applied to every alloy family.
Is laboratory testing mandatory for every order?
No. Clause 7 generally allows selection from existing lists and tables without further laboratory testing when all stated conditions are met. Project requirements or the consequences of failure may justify additional testing.
What is the relationship between NACE MR0175 and ISO 15156?
The introduction to ISO 15156-1:2020 describes the development of the technically identical ISO 15156 and NACE MR0175/ISO 15156 documents first published together in 2003. Procurement documents should identify the exact publication and edition required.
Can a change in operating conditions affect an existing material selection?
Yes. Clause 6.2 includes reassessment of existing materials when actual or intended service conditions change. The original qualification basis must be compared with the changed exposure.
Related Standards and Engineering Resources
- ASTM A790 duplex stainless steel pipe
- ASTM A789 duplex stainless steel tube
- ASTM B444 nickel alloy pipe and tube
- ASTM B829 general requirements for seamless nickel alloy pipe and tube
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