NACE MR0175, also published as ISO 15156, is the industry standard governing metallic material selection for equipment used in H2S-containing (sour) oil and gas environments. It sets limits on materials, hardness and heat treatment to resist sulfide stress cracking (SSC) and other environmental cracking.

Which drill pipe grade is used for sour service?

Sour service typically uses controlled-hardness grades kept at or below about 22 HRC in the critical areas, such as the sour variant of grade E and dedicated sour drill pipe grades. Higher-strength grades like S-135 are generally more susceptible to sulfide stress cracking and are used only where qualified for the specific environment.

What is sulfide stress cracking?

Sulfide stress cracking (SSC) is a form of hydrogen embrittlement in which atomic hydrogen from H2S corrosion enters high-hardness steel under tensile stress and causes sudden, brittle cracking. Susceptibility rises with hardness, tensile stress, H2S partial pressure and lower temperature and pH.

Sour Service Tubulars: NACE MR0175 and Drilling in H2S

Updated July 23, 2026 · By Drillstrings Technical Team

Sour service tubulars are drill string and downhole components selected to survive drilling in hydrogen sulfide (H2S) environments without cracking. The governing standard is NACE MR0175 / ISO 15156, which limits materials, hardness and heat treatment so that steel resists sulfide stress cracking (SSC) and related hydrogen-induced failures. In a sour well, getting the metallurgy right is a safety-critical decision, not just a performance one.

Why H2S changes everything

H2S in the formation reacts with steel and moisture to generate atomic hydrogen. That hydrogen diffuses into the steel lattice and, under tensile stress, embrittles hard microstructures — causing brittle cracks with little warning. The main damage mechanisms are:

Sulfide stress cracking (SSC) — Brittle cracking of high-hardness steel under tensile stress in the presence of H2S; the dominant concern for drill pipe.
Hydrogen-induced cracking (HIC) and stress-oriented HIC (SOHIC) — Internal blistering and cracking, more relevant to line pipe and vessels.

Susceptibility increases with hardness, tensile stress, H2S partial pressure, and lower temperature and pH — which is why standards focus on capping hardness and controlling stress.

What NACE MR0175 / ISO 15156 requires

NACE MR0175, dual-numbered as ISO 15156, defines acceptable materials and processing for sour service. For drilling tubulars its principles are:

Hardness limits — Critical regions are held at or below roughly 22 HRC for carbon and low-alloy steels, since low hardness resists SSC.
Controlled heat treatment and microstructure — Quenched-and-tempered structures with limited hardness gradients, avoiding hard spots at welds, upsets and connections.
Environment-based qualification — Material acceptability is tied to the actual service environment (H2S partial pressure, pH, chlorides, temperature), not a blanket rating.
Chemistry and process control — Restrictions on composition, cold work and manufacturing that raise hardness or crack susceptibility.

Selecting sour-service drill pipe grades

There is a direct tension between strength and SSC resistance: higher-strength grades are generally harder and more susceptible.

Sour E-75 (SS grades) — Controlled-hardness variants of the baseline grade are the common sour-service workhorse, kept within hardness limits.
Dedicated sour drill pipe grades — Purpose-built grades qualified for defined sour environments where more strength is needed than sour E allows.
Higher grades (G-105, S-135) — More susceptible to SSC; used in sour service only where specifically qualified for the environment and often reserved for milder or higher-temperature sour conditions.

Because acceptability depends on H2S partial pressure, temperature and pH, grade selection must be made against the specific well, ideally with a corrosion or materials engineer. See our drill pipe grades and tubular selection guides for the strength side of the trade-off.

Beyond the tube: the whole string

Sour-service discipline applies to every wetted component, not just the tube body:

Connections and tool joints — Held to the same hardness limits; hard bands and hardfacing must be qualified for sour use.
Drill collars and BHA components — Sour-qualified materials and controlled hardness, with attention to high-stress thread roots.
Pressure control and handling tools — Elastomers, trims and metallic parts rated for H2S.
Workstring tubing for sour completion and intervention follows the same MR0175 basis.

Operating and inspection practice

Material selection is necessary but not sufficient — operating practice and inspection close the loop:

Control the environment — Maintain high mud pH, use H2S scavengers and corrosion inhibitors to lower H2S activity at the steel surface.
Limit tensile stress — Corrosion fatigue is severe in sour service, so keep drill pipe in tension, control doglegs, and manage rotating hours per our fatigue-prevention guide.
Inspect to standard — DS-1 inspection with MPI and blacklight targets crack initiation sites; see our DS-1 inspection-class guide, and monitor hardness on repaired or hardbanded areas.

Renting qualified sour-service tubulars

Sour wells demand documented, correctly-qualified materials, and the certification travels with the pipe. Renting from a supplier that stocks and certifies sour-service inventory means you run tubulars qualified to NACE MR0175 for your environment without owning a specialized string for occasional sour intervals. Drillstrings.com supplies sour-qualified drill pipe, drill collars, BHA components and pressure control equipment with material and hardness documentation through our quality program. Share your H2S partial pressure, temperature and pH with our team via contact and we will match tubulars to your sour drilling environment.