ISO 15156-2 Note 1: Understanding Discontinuities in H₂S Partial Pressure Measurements

This webpage discusses a question regarding a sentence in Note 1 of Figure 1 in ISO 15156-2, which states that discontinuities below 0.3 kPa (0.05 psi) and above 1 MPa (150 psi) partial pressure H₂S reflect uncertainty regarding the measurement of H₂S partial pressure and steel performance outside those limits.

Using Carbon and Low-alloy Steels in Sour Service Above 1 MPa Partial Pressure of H₂S

The question asks what to do if carbon and low-alloy steels are used in sour service above 1 MPa partial pressure of H₂S, and whether a special laboratory test for SSC is required and which solution to use.

NACE MR0175/ISO 15156-2, Fig. 1: Defining Environments with Respect to SSC of Carbon and Low-Alloy Steels

The response clarifies that NACE MR0175/ISO 15156-2, Fig. 1 is a schematic definition of environments with respect to SSC of carbon and low-alloy steels. Qualification for use of a material not listed in Annex A for use in one or more of the Regions of Fig. 1 is always dependent on reported field experience or laboratory testing.

SSC Resistance of Carbon and Low Alloy Steels in H₂S-Containing Environments

There is little documented evidence that describes the SSC resistance of carbon and low alloy steels in H₂S-containing environments outside the H₂S limits of Fig. 1. The user must decide whether the listing of a steel in Annex A serves as an adequate guide for its behavior in severe H₂S-containing environments.