What Is Sour Service Pipe?

Sour service pipe is any pipe designed to safely handle fluids containing hydrogen sulfide (H2S) above defined threshold levels. The primary standard governing sour service material requirements is NACE MR0175/ISO 15156, which specifies the acceptable materials, hardness limits, heat treatments, and environmental conditions that determine whether a service is classified as “sour.”

H2S causes specific forms of cracking in steel that do not occur in sweet (H2S-free) service. Without proper material selection and processing, these cracking mechanisms can cause sudden, catastrophic failure.

Property	Sour Service Requirement
Governing standard	NACE MR0175 / ISO 15156
H2S threshold	> 0.05 psi partial pressure in gas, or per region annex
Hardness limit (CS)	22 HRC (248 HV10 / 237 HBW)
Heat treatment	Normalized, normalized + tempered, or Q+T
Weld hardness	22 HRC max (including HAZ)
PWHT	Required for carbon steel welds (per code)
Testing	HIC and SSC testing per NACE TM0284 and TM0177

H2S Cracking Mechanisms

Mechanism	Abbreviation	Description	Affected Materials
Sulfide Stress Cracking	SSC	Hydrogen embrittlement under tensile stress	High-hardness steels, bolting, weld HAZ
Hydrogen-Induced Cracking	HIC	Internal cracking from hydrogen blistering	Dirty steel with high S, P, inclusions
Stress-Oriented HIC	SOHIC	HIC cracks linked by through-thickness stress	Carbon steel in high-stress zones
Chloride Stress Corrosion Cracking	Cl-SCC	Cracking in austenitic SS from Cl- + H2S	304, 316 stainless steel

Material Requirements for Carbon Steel

Parameter	NACE MR0175 Requirement
Carbon content	0.23% max (recommended for HIC resistance)
Sulfur content	0.003% max (for HIC-tested pipe)
Phosphorus content	0.015% max (recommended)
CE (IIW)	0.43 max
Pcm	0.25 max
Heat treatment	Normalized, N+T, or Q+T (no as-rolled)
Hardness	22 HRC max (base metal, weld, HAZ)
HIC testing	Per NACE TM0284 (CLR, CTR, CSR limits)
SSC testing	Per NACE TM0177 (Method A or D)

Acceptable HIC Test Limits

Parameter	Acceptance Criteria
CLR (Crack Length Ratio)	15% max
CTR (Crack Thickness Ratio)	5% max
CSR (Crack Sensitivity Ratio)	2% max

These limits are tested per NACE TM0284 using NACE Solution A (5% NaCl + 0.5% acetic acid, saturated with H2S) at room temperature for 96 hours.

Sour Service Pipe Grades

Specification	Grade	Sour Service Notes
API 5L PSL2	B to X65	With Annex H (sour service)
ASTM A106	Gr. B	Hardness-controlled, N or N+T
ASTM A333	Gr. 6	Low-temp sour (hardness-controlled)
ASTM A312	TP316L	Cl-SCC resistant with controlled Ni
Duplex SS	2205, 2507	Per ISO 15156-3, with limitations
Alloy 625	UNS N06625	Excellent sour resistance

Pro Tip

Hardness is the single most critical parameter for sour service carbon steel. A weld HAZ that exceeds 248 HV10 (22 HRC) is susceptible to SSC, even if the base metal chemistry is acceptable. PWHT after welding is the standard method to reduce HAZ hardness. For pipeline girth welds where PWHT is impractical, use low-hydrogen welding consumables with controlled heat input and verify hardness on production welds per the project specification.

Applications

• Sour gas production and gathering pipelines (upstream)
• Sour crude oil pipelines
• Gas sweetening plant piping (amine units)
• Sulfur recovery unit piping
• High-H2S wellhead and manifold piping
• Subsea flowlines in sour fields

For CRA-lined or clad alternatives in severe sour conditions, see the clad vs lined pipe comparison.

Read the full guide to pipe types