46 CFR §56.97-5

1. (a)All nonstandard piping system components such as welded valves and fittings, nonstandard fittings, manifolds, seacocks, and other appurtenances must be hydrostatically tested to twice the rated pressure stamped thereon, except that no component should be tested at a pressure causing stresses in excess of 90 percent of its yield strength.
2. (b)Items for which an accepted standard appears in table 2 to § 56.60-1 need not be tested as described in paragraph (a) of this section, but need only meet the test required in the applicable standard.