NACE MR0175 vs ISO 15156: Sour Service

NACE MR0175 and ISO 15156 are effectively the same standard. NACE MR0175/ISO 15156 is a jointly published document that defines material requirements for equipment used in oil and gas production environments containing hydrogen sulfide (H2S); commonly referred to as “sour service.” The dual designation reflects the merger of the original NACE MR0175 with the ISO framework, creating a single international standard.

Comparison Table

Feature	NACE MR0175 (original)	ISO 15156 / NACE MR0175 (current)
Status	Superseded (absorbed into ISO 15156)	Active (jointly published)
Issuing bodies	NACE International (now AMPP)	ISO + NACE (AMPP)
Scope	Metallic materials in sour oil and gas	Metallic and non-metallic materials in sour oil and gas
Parts	Single document	Part 1: General, Part 2: Carbon/low-alloy steel, Part 3: CRAs and alloys
H2S threshold	Defined (partial pressure limits)	Same methodology; refined regional limits
Sour environment definition	pH2S > 0.3 kPa (0.05 psia)	Same threshold with detailed qualification methods
Carbon steel requirements	Max hardness 22 HRC (248 HV10)	Same: 22 HRC / 248 HV10 max
CRA requirements	Material-specific limits	Detailed environmental limits per alloy family
Weld hardness	Max 22 HRC in HAZ and weld metal	Same; additional provisions for specific welding processes
SSC/SCC testing	NACE TM0177 (tensile), TM0284 (HIC)	Same tests referenced
Qualification method	Prescriptive (lookup tables)	Prescriptive + performance-based (Annex B)

When Sour Service Standards Apply

Sour service materials are required when the process fluid contains H2S at a partial pressure exceeding 0.3 kPa (0.05 psia) in the gas phase. This applies to:

• Upstream production equipment (wellheads, flowlines, separators)
• Gas processing plants handling sour gas
• Refinery units processing sour crude or sour gas streams
• Pipeline systems transporting sour hydrocarbons
• Any piping system where H2S may be present in the process fluid

Specifications: Parts of ISO 15156

Part	Scope	Key Requirements
Part 1	General principles and definitions	Defines sour environment, qualification methods, responsibilities
Part 2	Carbon and low-alloy steels	Max hardness 22 HRC / 248 HV10; PWHT required; restricted chemistry
Part 3	CRAs, nickel alloys, and other materials	Environmental limits (temp, pH2S, Cl-) per alloy family; SSC/SCC testing requirements

Pro Tip

ISO 15156 Part 3 provides two qualification routes for CRAs: (1) Prescriptive: select materials from the approved tables within specified environmental limits, or (2) Performance-based (Annex B); qualify materials by laboratory testing under simulated service conditions. The performance-based route allows materials outside the prescriptive tables but requires project-specific SSC/SCC testing per NACE TM0177 or EFC-17. Always confirm which route the project specification permits.

Common Material Restrictions

Material	NACE/ISO 15156 Requirement
ASTM A105 (CS forgings)	Max 22 HRC; PWHT mandatory for weldments
ASTM A106 Gr. B (CS pipe)	Max 22 HRC; normalized or normalized + tempered
ASTM A182 F316 (SS)	Anneal; subject to Cl-/temp limits per Part 3
ASTM A182 F51 (Duplex)	Solution anneal; PREN > 40 for severe sour
ASTM A216 WCB (CS casting)	Max 22 HRC; additional NDT per project spec
Nickel alloy (Alloy 625, C-276)	Per Part 3 environmental tables

All sour service materials require full traceability. Mill test certificates must confirm hardness testing (base metal, weld, HAZ), chemistry compliance, and heat treatment condition. NDT requirements are typically more stringent for sour service piping.

Read the full guide to piping engineering