The hydraulic test I found from ASME, based again on permissable stresses in annealed copper at elevated temperature.

To quote: UG-99: "The hydrostatic test pressure shall be at least 1.3 times the Maximum allowable working pressure multiplied by the lowest ratio of the stress value St for the test temperature for the design temperature." - In the case of a boiler for Max. 100psi (Max limit as required by ASME for Copper boilers) the ratio of St/Sd = 6700/3142 = 2.132: So the test pressure (Hydraulic at 70degrees F.: designed for 100psi = 338degrees F.) shall be 1.3 x 100 x 2.132 = 277psi.

My information source is a design document written by Kozo Hiraoka published in 2006, so I may be out-of-date by now?

The logic I expressed is based on sound engineering principles, of stress calculations and compensation for copper at elevated temperature, but if there is a Service test for in-service annual tests (as the UK test at 1.5 times the NWP) then that is accepted for that certification. But for new boilers there is usually a design hydraulic test - at least done by the designer or agent to prove the strength of the design is good for the simulated stress for 8 x NWP and factored for the material strength at the temperature of the NWP.

My recommendation to Wazrus was that if he had a boiler deform due to pressure, then that pressure should have been at least 8 times the NWP. So there was something wrong with the original design.

If you think being able to withstand 8 times the NWP is excessive for your boiler, then you misunderstand the purpose of the Regulations, in my opinion. It is the regulating authorities' decision that this is the level of safety required to prevent injury to people. So I have re-rated some of my boilers that were "inadequate" when I applied the ASME principles to the designs of those boilers. But I am just an engineer (following Kozo Hiraoki's explanation paper on ASME Boiler and Pressure vessel code and general engineering calculations for stress), with my opinion expressed on this site, so please check with your local test authority if you need your calculations or testing to be confirmed/ratified.

My prime interest is the safe operation of steam boilers by safe design.

Happy ( and safe!) steaming!

K2