PD 5500 "Specification for unfired, fusion welded pressure vessels" is a standard that provides rules for the design, fabrication, and inspection of pressure vessels. It was formerly known as BS 5500 but was withdrawn from the list of British Standards because it was not harmonized with the Europeran Pressure Equipment Directive (97/23/EC) and was replaced in the United Kingdom by EN 13445. It is currently published as a "Published Document" (PD) by the British Standards Institution.