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NACE MR0175/ISO 15156-2 provides guidelines for materials used in environments containing hydrogen sulfide (H2S) in oil and gas production, which are often referred to as sour service conditions. Post Weld Heat Treatment (PWHT) is an important consideration in these environments due to its impact on reducing residual stresses and improving toughness, especially in carbon steels.
NACE MR0175/ISO 15156-2 specifies conditions under which PWHT may or may not be required for carbon steels:
General Requirements:
Exemption Conditions:
If PWHT is exempted, there are several metallurgical changes and potential risks to be considered:
Residual Stresses:
Hardness and Brittleness:
Microstructural Changes:
Hydrogen Embrittlement:
Exempting PWHT for carbon steels as per NACE MR0175/ISO 15156-2 is possible under specific conditions, primarily if the weld hardness can be controlled to below 250 HB and residual stresses are managed. However, it is important to note that:
Therefore, exemption from PWHT should be approached with caution and should strictly adhere to the conditions set forth in NACE MR0175/ISO 15156-2 to ensure the integrity and safety of the welded components in sour service environments.
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