ISO 15156 (=NACE MR0175) and NACE MR0103
1. A part of job specification
All materials for components exposed to wet hydrogen sulphide in concentrations
exceeding 100 mg/kg (100 ppm) or exceeding the limits prescribed by ISO 15156 or NACE MR0103 (as applicable) shall conform to the reduced hardness requirements of ISO 15156 or NACE MR0103 as follows:
a. ISO 15156 is applicable to oil and gas production facilities and natural gas sweetening plants. (NACE MR0175 is equivalent to ISO 15156).
b. NACE MR0103 is applicable to other applications (e.g., oil refineries, LNG plants and chemical plants).
c. The previous requirements (a) and (b) equally apply to all external bolting on the casing and seal glands even if ISO 15156 or NACE MR0103 (as applicable) restricts the requirement to enclosed bolting.
2. Interpretation by NACE MR0103 and ISO 15156 (=NACE MR0175)
The hardness limitations specified in NACE MR0103 and ISO 15156 vary depending on the specific materials and conditions. Here are the general hardness limitations provided by these standards:
NACE MR0103:
For metallic materials, the maximum hardness limit in NACE MR0103 is typically specified as 22 HRC (Rockwell C hardness). However, different materials and specific requirements may have different hardness limits.
ISO 15156:
ISO 15156 provides hardness limits for different material groups based on their susceptibility to sulfide stress cracking (SSC). The specific hardness limits vary based on the material's alloy composition, heat treatment, and other factors. ISO 15156 divides materials into several categories (e.g., Group 1, Group 2, etc.), and each group may have different hardness limits.
It's important to note that the hardness limits in NACE MR0103 and ISO 15156 are subject to the specific requirements and conditions outlined in each standard. Therefore, it's necessary to refer to the respective standards for the precise hardness limitations applicable to a particular material and service condition.
3. Inspection Check Point
Materials in the following process services shall be verified by matching heat numbers
of components to the mill test reports:
a. Where Hydrogen Induced Cracking (HIC) resistant material or maximum hardness
levels are specified.
b. Where materials for Wet Hydrogen Sulphide (H2S) services are specified.
c. Where materials with minimum silicon (Si) content critical to corrosion resistance
are specified.
d. Where low temperature enhanced mechanical properties are specified
(e.g., impact tested material) or drop weight tear tests for pipelines.
NOTES:
1. Items (a) and (b) above apply to sour services
2. Item (c) above is applicable when carbon steel is used in high temperature
(>250 °C) (482 °F) high Sulphur services
3. Low temperature applications are limited as defined in section (2.2) from the
scope of this SPEP