NACE MR0175 (officially titled ISO 15156) is an international standard that provides requirements and recommendations for selecting and qualifying metallic materials for equipment used in oil and gas production in environments containing Hydrogen Sulfide ( H2S ).
In the industry, these environments are known as "Sour Service."
Upstream or Downstream? Not Sure if You Need MR0175 or MR0103? Contact Us for the Correct Technical Specification.
Preventing Brittle Failure
The primary purpose of the standard is to prevent Sulfide Stress Cracking (SSC) and other forms of Hydrogen-Induced Cracking (HIC).
When H2S is present in the presence of water, it releases hydrogen atoms that penetrate the steel. If the steel is too hard or under high stress, it will crack and fail suddenly-often without any warning or prior thinning of the metal.
Setting Hardness Limits
The most famous rule in NACE MR0175 is the Hardness Limit.
For carbon and low-alloy steels, the hardness is generally restricted to a maximum of 22 HRC (Rockwell C).
The standard establishes that steel softer than this limit is much less likely to become brittle and crack in sour environments.
Material Selection & Heat Treatment
The standard specifies which materials are suitable for sour service and how they must be treated. For example:
Heat Treatment: It often mandates Quenched & Tempered (Q+T) or Normalized processes to ensure a uniform grain structure.
Chemistry: It requires low levels of impurities like Sulfur (S) and Phosphorus (P).
Cold Work: It limits how much the steel can be cold-formed, as cold work increases hardness and internal stress.
Defining "Sour" Environments
NACE MR0175 provides the formula to calculate the Partial Pressure of H2S. It determines at what point a well becomes "Sour" enough to require these special materials (typically when the H2S partial pressure exceeds 0.05 psi).
Scope of Equipment
The standard applies to almost all metallic equipment in the production stream, including:
OCTG: Casing and tubing.
Pipelines: Line pipes.
Wellheads: Valves, manifolds, and Christmas trees.
Refinery/Processing: Pressure vessels and heat exchangers.
GNEE NACE MR0175 API OCTG Process Line
GNEE NACE MR0175 API OCTG Pipe Test Equipments
GNEE NACE MR0175 API 5CT OCTG Pipe certificate
FAQ
Q1: Is NACE MR0175 the same as ISO 15156?
A: Yes, they are essentially the same. Since 2003, NACE and ISO have harmonized these standards. The official title is ANSI/NACE MR0175/ISO 15156.
Part 1: General principles for selection of cracking-resistant materials.
Part 2: Requirements for carbon and low-alloy steels.
Part 3: Requirements for corrosion-resistant alloys (CRAs).
GNEE Value: We provide Material Test Certificates (MTC) that explicitly reference both NACE MR0175 and ISO 15156, ensuring your project passes international compliance audits without any friction.
Q2: My project is for a refinery; should I use NACE MR0175 or NACE MR0103?
A: This is a common and critical distinction.
NACE MR0175 is for Upstream (Oil and gas production, drilling, and gathering). It assumes the presence of elemental sulfur and higher pressures.
NACE MR0103 is for Downstream (Refineries and petrochemical processing). It assumes a different chemical environment (lower pH, different amine treatments).
Our Value: If you are building a refinery, MR0103 is usually the correct standard. We can help you review your project specs to ensure you aren't "over-specifying" or "under-specifying," saving you both time and money.
Q3: Does NACE MR0175 compliance guarantee that the pipe will never corrode?
A: No. NACE MR0175 is specifically designed to prevent Stress Cracking (Brittle Failure), which is sudden and catastrophic. It does not necessarily prevent "weight-loss corrosion" (general rusting or thinning).
Our Value: If your environment is also highly corrosive (high CO2 or Oxygen), NACE compliance is just the first step. We can suggest additional solutions like Corrosion Inhibitors or upgrading to 13Cr/Stainless alloys to ensure your pipeline doesn't just "not crack," but also doesn't "thin out" over time.
