Title: Understanding Water Handling Exclusions in ISO 15156

Introduction

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).””

The Fundamentals of Exclusions

The exclusions are historical and based on successful applications over many decades. 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. The user has the responsibility to ensure that materials selected are suitable for the intended service (see the Warning paragraph under Part 1: General principles for selection of cracking-resistant materials).

Safety Considerations

You have the responsibility to determine whether your application is safe under intended service conditions, and you may wish to employ a consultant to assist you in your evaluation. The question arises whether exclusions can always be excluded independently of H₂S amount, HCN, pH, material strength, etc. This is because HIC damage could be present regardless of the pressure, and SSC might be expected in the welds/HAZ in non-PWHT CS at H₂S > 670 ppm and 65 psi in sour service.

Perceived Danger

There is a perceived danger with this interpretation because of the tendency to minimize H₂S flaring and to comply with environmental regulations, which is to bypass the H₂S scrubbers by moving the waste water from a non-sour service in the original design to sour service ranges (up to 1000 ppm H₂S). Because the standard does not establish any boundary, it looks acceptable to do so.

Water Injection and Disposal Equipment

Water injection and water disposal equipment are also excluded in Table 1. Usually, water injection works at a very high pressure (e.g., 90 bars in our facilities and original design 50 ppm H₂S). Such cases are already considered sour service (pPH₂S > 0.3 kPa). What are the fundamentals to permit exclusions under this standard then?

Conclusion

In conclusion, understanding the fundamentals of water handling exclusions in ISO 15156 is crucial for ensuring the safety and suitability of materials for intended service conditions. Employing a consultant may be necessary to evaluate the safety of your application.