This standard specifies requirements and gives recommendations for the design, qualification, and production of closed die forgings for use in API service components in the petroleum and natural gas industries when referenced by an applicable equipment standard or otherwise specified as a requirement for compliance. Applicability This standard is applicable to equipment used in the oil and natural gas industries where service conditions warrant the use of closed die forgings. Examples include pressure-containing or load-bearing components. Forging Specification Levels (FSLs) This standard establishes requirements for four FSLs. These FSL designations define different levels of forged product technical, quality, and qualification requirements.