The number 553 does not appear in the current API manual of standards (up to my last update in 2025). It is not listed as an active RP, Standard, or Specification.
– Process Measurement Instrumentation This is a well-known API Recommended Practice. If you meant 551, that PDF is available for purchase from the API’s publisher (IHS Markit / Global Engineering). api 553 pdf
Offers extensive recommendations for Emergency Block Valves (EBVs) and on/off valves used in Safety Instrumented Systems (SIS). The number 553 does not appear in the