FAQ's

Water handling facilities and the exceptions in NACE MR0175 / ISO 15156

ISO 15156 Table 1 provides a non-exhaustive list of equipment to which this part of ISO 15156 is applicable, including permitted exclusions. Among the exclusions are :

  1. “Water-handling facilities operating at a total absolute pressure below 0,45 MPa (65 psi)” .
    Q1. What are the fundamentals of such exclusions in this standard?
    Q2. Can they be ALWAYS excluded independently of the H2S amount, HCN, pH, material strength, etc.?
    Question comes because HIC damage could be present regardless of the pressure. Also SSC might be expected in the Welds/HAZ in not PWHT CS at H2S >670ppm and 65 psi (sour service).
    There is a perceived danger with this interpretation, as the current tendency to minimize H2S flaring and to comply with the environmental regulations is to by-pass the H2S scrubbers moving the waste water from a non-sour service in the original design (<50 ppm H2S) to sour service ranges (up to 1000 ppm H2S). Because the standard doesn’t establish any boundary, it looks acceptable to do so.
  2.  “Water injection and water disposal equipment” .
    Q3. Usually the water injection works at a very high pressure (i.e. 90 bars in our facilities and original design 50 ppm H2S). Such case is already considered sour service (PpH2S>0.3 kPa). What are the fundamentals to permit exclusions under this standard then?

ANSWER:
ISO 15156 Table 1 provides a non-exhaustive list of equipment to which this part of ISO 15156 is applicable, including permitted exclusions. Among the exclusions are “Water-handling facilities operating at a total absolute pressure below 0,45 MPa (65 psi)”.
Question 1: What are the fundaments of such exclusions in this standard?
Answer 1: The exclusions are historical and based on successful applications over many decades.
Question 2: Can they be ALWAYS excluded independently of the H2S amount, HCN, pH, material strength, etc.?
Answer 2: Table 1 of NACE MR0175/ISO 15156 does not impose any limits on the equipment with permitted exclusions unless otherwise noted at the bottom of Table 1.
Question 3: Usually the water injection works at a very high pressure (i.e. 90 bars in our facilities and original design 50 ppm H2S). Such case is already considered sour service (pPH2S>0.3 kPa). What are the fundamentals to permit exclusions under this standard then?
Answer 3: The User has the responsibility to ensure that materials selected are suitable for the intended service (see Warning paragraph under Part 1: General principles for selection of cracking-resistant materials). You have the responsibility to determine whether your application is safe under intended service conditions; you may wish to employ a consultant to assist you in your evaluation.

Reference: Maintenance Panel inquiry 2016-18 (NACE MR0175-2 Table 1)

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