46 CFR 61.15-5: -5 Steam piping.

(a) Main steam piping must be subjected to a hydrostatic test equal to 1.25 times the maximum allowable working pressure at the same periods prescribed for boilers in § 61.05-10. The hydrostatic test must be applied from the boiler drum to the throttle valve. If the covering of the piping is not removed, the test pressure must be maintained on the piping for a period of ten minutes. If any evidence of moisture or leakage is detected, the covering must be removed, and the piping thoroughly examined.

(b) All steam piping subject to pressure from the main boiler should be subjected to a hydrostatic test at a pressure of 1.25 times the maximum allowable working pressure of the boiler after every five years of service except as otherwise provided for in paragraph (a) of this section. Unless the covering of the piping is removed, the test pressure must be maintained on the piping for ten minutes. If any evidence of moisture or leakage is detected, the covering should be removed, and the piping thoroughly examined. No piping with a nominal size of 3 inches or less need be hydrostatically tested.

(c) The setting of safety and relief valves installed in piping systems must be checked by the marine inspector at each inspection for certification for vessels whose Certificates of Inspection are renewed each year. For other vessels, the setting must be checked twice within any 5-year period, and no more than 3 years may elapse between any check and its immediate predecessor.