API RP 7HU1 (R2020) PDF
This recommended practice (RP) sets forth procedural recommendations as well as an engineering solution to the mismatching of the most common hammer unions used in oilfield applications. The mismatching of hammer union components is a worldwide issue in the industry and can cause serious incidents. Complete and proper make-up of hammer union components is required to attain the rated working pressure of the equipment. The procedural recommendations described in this RP should be implemented to reduce further incidents.
The engineering solution applies to the manufacture of new hammer union components and should not be applied in the modification of existing hammer union components due to unknown factors caused by field wear.
