Anyone know what ASME code to "as welded" vessels is concerned?
I am building a small 3 drum water tube marine boiler (27sqft heating surface 200 psi mawp) to power a boat.
As I am a pipewelder by trade, I will be using ASME approved material and butt joints for said project. As this boiler is being used for marine use in a private vessel it is exempt from local (Canada) codes as well as Coast Guard.
If I need to stress relieve my boiler, could someone let me know.
Material will be 6", 2"and 3" sch 80 A106 gr B for steam, mud drums, and down commers. SA 515-60 5/16" plate for top of mud drums, SA 182 1000 pound 1/2" forged couplings, and pipe caps on steam drum made of equivelent material.
Thanks
Skip
Hello Skip,
"As welded" means prior to any PWHT.
I am not sure how anyone is going to be able to answer your question regarding PWHT with any certainty. The ASME Codes of construction require PWHT unless there is a specific exemption given in the chart appropriate for the materials welded (in your case P-1).
The codes I'm familiar with are all a bit different in defining those exemptions (I, VIII, B31.1 & B31.3).
Even though you say the construction is exempt from local and Coast Guard Codes, there must be a specified code of construction. Without that information, giving advice on PWHT is just a guess.
Chalres Hall
Skip, Charles; my read on ASME Codes, though none specific are mentioned would be these materials would NOT required PWHT due to their thicknesses. If in doubt, preheat the materials to 200 degrees Fahrenheit and that would exempt from PWHT to most of the ASME Codes.
Thanks for your input fellas.
Skip
Hi Skip
I hope that the said boiler has been designed by someone that knows how to do this. If so, the design code used by the designed will tell you exactly if you need to PWHT or not.
If however you are just building this boiler by "rule of thumb", I would be a little uneasy about comming for a ride on your boat! We have to remember the reason why boiler codes were originally introduced. It was to solve the problem of the many deaths caused by inadequate boilers exploding. The explosion of even a small boiler will almost certainly result in the end of your boat, and all on board!
Regards
Niekie Jooste
Absolutely concur 1000% Niekie.
I assume that the tube attachment method is not by mechnical means.
If you have to weld the tubes to drum, & the tube holes forms a ligament in which the drum strength calculation is based on the effiency of those ligament, than you must at least to perform PWHT to these drums (since the tube attachment weld does not allowed to be a single fillet weld form outside only, and I would guess you can't weld these attachment welds form internal of the drum). All of circumferential butt-welded joints of the water tubes, does not require PWHT. All of the circumferential butt-welded joints of the down comer also no need to PWHT. As for the attachment weld of the down comer to the steam drum/mud drum, if there is a nozzle attached to the drum, then the down comer connecting to these nozzle welding end apply to above circumferential butt-welded joints. On the contray, if the down comer is to be welded directly to the drums, then these welds shall be at least designed as a partial penetration plus external fillet weld, then you have to think about to PWHT the whole boiler proper in a furnace.
Kind regards
Please refer to ASME Section I, Table PW-39 (for material P-No.1 Group No.1,2,3), study the notes (1),(2), & (3), then you will have a clear picture of which kind of a weld is exempted from PWHT.
Kind regards
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