B31.8 Age old Fillet Weld Question

[NDTHAND1992]

I have a client that called me last evening with questions about B31.8 and the use of Fillet welds to 36"X1" X52 material. They are wanting to weld a saddle type support in three places along the bottom of the pipe ( Ad Hoc Vessel ) using a circumferential weld down the sides and a longitudinal weld across the tops of the saddle. 31.8 is not my regular construction code but I do know that they only allow fillet welds in certain situations. Any tips would be great as my schedule does not allow myself to research it myself. My first and quickest answer was yes to the circ. welds and no to the long. welds. Any help would be great

Thanks

 

[LittleInch]

I've had a search for this (fillet weld) on 31.8 and can't find too much. section 825.5 allows for not needing to stress relieve it if the weld is less than 10mm for "supporting members or other non pressure attachments" However unless the pipe needed to be stress relieved, which at 1" thick it doesn't, this doesn't apply anyway.

Other than that I can't find a reference which says you can't weld longitudinally, but I do recall some discussion on that, but still can't find anywhere in the code where it says that.

I would be more concerned about the use of the saddle support and noting that 31.8 is a pipeline code and not a pressure vessel code. Yes people do it, but you really shouldn't and it would be interesting to know what design factor they were using. 36" 1" thick X52 sounds like quite a big pressure to me and if you weld on a support then presumably bolt it to something the stress and stress concentration at the "support" could be enormous. Is there any reason he can't just clamp this thing and not weld it?


My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[BigInch]

NO! It is not permitted to weld a support directly onto B31.8 pipe, if the pipe is designed to operate at a stress level over 50% of SMYS, fillet weld or other.
See B31.8 Clarification 15.8 (at the back of the 2010 Edition)

you must get smarter than the software you're using.

 

[LittleInch]

Need to look at the right thing, but BI is correct.

This has been included in the 2010 and 2012 version in section 834.5 which a) states that where hoop stress is less than 50% you can weld supports or anchors. Above 50% (b) there should be a full encirclement, with the anchor welded to that.

In your case I hope that the design factor is quite low and hence 834.5 a) will apply , but you will need to check the design....


My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[zdas04]

When you look at the inclusions/exclusions of the BPVC, anything with a pressure-containing longitudinal weld with an ID greater than 6-inches and pressure over 15 psig is a pressure vessel and must be built to the BPVC. I make a lot of "pipeline accessories" out of components manufactured to a published standard and that stuff is excluded from the BPVC (except in the rare case where the regulators have gotten involved and specified by fiat that a certain class of kit like a pig launcher must be built to BPVC). The first time I bend a sheet and do a longitudinal weld I've changed the game from "just pipe" to "pressure vessel" and have to start thinking about nameplates and pressure safety devices.

David Simpson, PE
MuleShoe Engineering

In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. —Galileo Galilei, Italian Physicist

 

[NDTHAND1992]

Thank guys for the insight into this , I am checking with there design group and see what the intended design was originally. Unlike a vessel , nothing is stamped when it shows up on location. Once again thanks.