Slip-on Flange to pipe engagement code requirement 1

[tomecki]

I'm looking for a code requirement for how much pipe engagement is necessary on a slip-on flange. I know the industry practice is to leave 1/8" -1/4" from the face of the flange to the internal fillet weld, but I need something authoritative in a code or standard to point to. Unfortunately B31.1 does not specify this. I found a reference in BPVC Sect VIII, Fig 2-4 which shows what I'm looking for, but I'm not sure I can argue that it applies to B31.1 piping.

 

[MJCronin]

ASME B31.1 shows required slip on flange placement and welding ... As I recall, B31.3 does also

MJCronin
Sr. Process Engineer

 

[Cobra17]

B31.3 = Figure 328.5.2B
B31.1 = Figure 127.4.4-2

 

[tomecki]

Figure 127.4.4-2 in B31.1 does NOT show the setback. It only gives the size of the fillet weld.

 

[LittleInch]

Why do you need this?

Anyone with half a brain knows that.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Cobra17]

the actual set back, my bad. It's not shown anywhere I know of except if you look in VIII-1, appendix 2, which isn't for B16.5 flanges, but they do show a 'max', which, I believe, is where the 1/8" to 1/4" comes from. You don't want to weld right up to the face of the flange because you might damage it and the gasket won't seal correctly.

so exactly what you said in your first post. but B31.3 does say to go to VIII-1 if there is something not covered in B31.3

 

[LittleInch]

Now 127.4.4-2 does show a set back, but doesn't specify it. It could be inferred from other drawings in this set that this is min of 1/16" or 2mm.

You do have to zoom in a bit alright....

Still don't understand why you need to find a code reference for something which is normally specified in a welding procedure or piping construction specification.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Gator]

I've seen this specified as being equivalent to the pipe wall thickness.

 

[JStephen]

A couple of related questions:
-Does the weld size have to be increased based on the gap between pipe and flange?
-Does corrosion allowance need to be factored in on the internal weld size?
I would think both of these items (as well as your question) would be addressed by the applicable code(s) so that there was no ambiguity. (What's the point of specifying a fillet weld size if the gap behind it is not limited in any way, after all?)
However, when I have submitted inquiries on these items (Request for interpretation for Section VIII Div. 1), the response was that these were non-code issues, engineering judgment/whatever, and basically wouldn't be clarified in any way.
So use your own judgment and go with it.

 

[Cobra17]

I knew one of the B31 codes had it... B31.5 shows it

 

[Cobra17]

- Does the weld size have to be increased based on the gap between pipe and flange?

No, because a B16.5 slip on flange gives the ID of the flange with tolerance. And lets assume you are using the correct flange size for the pipe​

-Does corrosion allowance need to be factored in on the internal weld size?

Yes, all codes talk about 'in the corroded state'​

 

[IFRs]

API 650 figure 5.10 calls for the setback to be the thickness of the pipe plus 1/4" max.