The American Petroleum Institute's (API) publication 521, "Guide for Pressure Relieving and Depressuring Systems," is a widely adopted standard in the oil and gas industry. This guide provides detailed information on designing, operating, and maintaining pressure relieving and depressuring systems for various process facilities. If you're looking for a free PDF version of API 521, you've come to the right place!
You can buy the authoritative copy through the API Publications Store . api 521 free pdf
Many universities with ABET-accredited chemical/mechanical engineering programs subscribe to the API Standards Collection . Check your university library’s database. Similarly, if you work for an EPC firm or refinery, your corporate library already has a licensed copy. Ask your manager for the internal shared drive. api 521 free pdf