Does B31.3 permit tube socket welds? 1

[trottiey]

Does B31.3 permit socket welds on thin-walled tube? Paragraph 311.2.5 says socket dimensions shall conform to B16.11 or SP-119, which only include pipe dimensions. So does that exclude any socket welds on 3/8" OD X .065" wall tubes? Does it exclude Swagelok TSW fittings, or is that fair use of 304.7.2(a)?

I'm more of a vessel guy new to piping codes, so please excuse my primitive question.

 

[moltenmetal]

I have seen no specific exclusion against tube socket welds in B31.3, nor would I take the reference you've given as a reason not to use them.

When there are exclusions of particular kinds of joints in a particular fluid service, or if "safeguarding" of the joints is required, they're pretty clear in the code about this.

 

[Duwe6]

Small sockets, like the "Cajon" series can be welded under B31.3 without anything 'special'. Just make sure that the WPS specified will run thin enough to be reasonable for the weld.

Yes, I know that fillet [socket] weld size is a nonessential variable. But using an SMAW or FCAW procedure for 3/16" thru 8-inch material is laughable. Pick a Tig/GTAW procedure with a 1/16" low-limit for groove welds. It works well.

There are/were a LOT of socket-welded tubes in Pressurized Water Nuclear Reactor systems. Ultra-high reliability and vibration resistant.

 

[trottiey]

The only Cajon fittings I'm aware of are threaded pipe fittings. Swagelok owns Cajon, and I was referring to Swagelok socket fitting (TSW) in my original post.

Got the WPS covered, thanks, but that's not what I'm asking about.

I know that we have lots of socket welds in nuclear, but that follows section III piping rules. I'm asking under B31.3.

 

[Duwe6]

Again, like moltenmetal said, B31.3 does not forbid it, thus it is acceptable if it is "according to sound engineering judgement". Which it is.

Was working from memory, thought Cajon was Swagelock's welded fitting line. Also, the Nuke reference was to show that if Sect III finds this acceptable, it is more than OK for B31.3 refinery & process piping. The desingn, enginering and weld quality standards are *much* more stringent for nuke Code.

 

[trottiey]

Sorry, but I have to disagree with the "much more stringent for nuke code" bit, especially in this context: Section III allows socket welds, but Section VIII does not.

There's other examples, the biggest one being that Section III Class 1 allowables are higher than Section VIII Div. 1. That means a Section III vessel could have thinner walls than a Section VIII vessel at the same design pressure.

According to Reedy's commentary, the ASME committee believes that all of their codes are equally safe. It's just different combination of safeguards. Thicker paperwork in Section III, versus thicker metal in Section VIII. The regulators like paper better because that's all they see, but technicians often take the opposite view.