ASME
ASME PCC-1
Guidelines for Pressure Boundary Bolted Flange Joint Assembly
How to actually assemble a flanged joint: cleanliness, alignment, lubrication, the tightening pattern and the target bolt load. Most flange leaks are assembly failures rather than gasket failures, and this is the document that addresses them.
This is an explanation, not the standard. PipingInspector is not affiliated with ASME and reproduces no part of the document. Always work to the current edition of the standard itself and to your project specification.