US State Boiler Code

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True, but careful testing is always necessary, to ensure the validity of the test, if nothing else. And careful testing doesn't normally fail things that are good, so in any failure, while I would concentrate on the cause by studying the failed item, I would check test procedures were performed properly. In my 24 years working in a manufacturing Quality dept. (Production testing, and early design and pre-production confirmation testing), it was very rare that the procedure was at fault, perhaps better than 99% success rate of test procedures, and 99% the failed item was the cause. Of course, the Hobby Club may not be so precise, nor the guy-in-the-garage, but most things will not fail on "production level" NDT when they are good. Hydraulic testing of boilers built with a design FOS of 6 or more almost cannot fail at routine NDT at half that pressure. If they do, I seriously worry that the manufacture has a fault. But when handed a boiler that is potentially scrap after failing I check the material thicknesses and design (spacing/size of stays, etc.). Usually inherently bad design or thin materials are the cause. In my experience.
Guys who make things that are really "un-designed" usually over-rate their well made thin-walled boilers. - I did before I understood ALL the calculations. A boiler my Dad told me should be OK for at least 45psi NWP - failed a test pressure of 160psi... Stupid me trying it to see what it would take! So I de-rated it to 20psi NWP after repair and testing... And later calculations told me that's what I should have expected... Thin tube error.
Design it properly and it should be OK.
Don't use "any old copper" that is "to hand"... - use proper thick walled stuff you have bought. I have a lot of scrap, only usable for household plumbing!
Problem: "Everyone" stocks household plumbing copper pipe. Almost no-one stocks thick copper - except the model suppliers who are expensive... I used to buy from scrap yards, but, as the name suggests, they have all been scrapped now, and "Re-cycling Depots" exist that do not sell copper materials at scrap prices!
I have just added stays to 2 boilers with thin ends that were failed after the boiler tester said the bulged ends were a reject according to his standard. Fair cop. Calculations proved the un-stayed thin-ends were worse than useless. Re-designed to ASME, and repaired and GOOD! - The system works.
Enjoy and stay safe.
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