The previous edition’s pressure classes were refined. The 21st Edition clarifies requirements for and PR 3 (Extreme High-Reliability) . This includes mandatory verification testing for pressures exceeding 20,000 psi (HPHT designs).
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Performance Specification Levels (PSL) 1 through 4 now have stricter chemistry controls and impact testing for carbon and low-alloy steels. Notably, the 21st Edition expands requirements for (Annex H), aligning closer with NACE MR0175/ISO 15156. The previous edition’s pressure classes were refined
The is the current global standard for "Specification for Wellhead and Tree Equipment," establishing rigorous requirements for the design, manufacturing, and testing of oil and gas wellhead components. Accessing the Document api specification 6a 21st edition pdf link