MODIFICATION OF ELBOWS 3

[Tman1]

HY ALL

I HAVE A QUERY CONCERNING TRIMMING/MODIFYING OF ELBOWS:-

AS WE ALL KNOW AS A STANDARD WE NORMALLY GET ELBOWS MANUFACTURED IN 90 OR 40 IN DEGREES,
PRIOR TO CUTTING THEM TO ANY ANGLE SUCH AS 30/25.1 ETC WHAT ONE SHOULD HAVE?
IS AN ITEM MANUFACTURER(ELBOW) APPROVAL IN WRITING ALLOWED OR CALCULATIONS NEED TO BE
OBTAIN AS WELL AS PER ASME B 31.3 PAR 304.7.2 FOR UNLISTED MATERIALS.

CAN SOMEONE CLARIFY FOR ME.

BEST REGARDS

 

[pennpiper]

jte,
You wrote
- "If one were to take an elbow with a bit of a straight section on each end intended to make connections to SW fittings easier and cut it in the middle, the resulting part would not be symmetric."

I read the original post as referring to only the trimming of Butt Welded 90 and 45 degree elbows.

You are now introducing Socket Weld fittings into the mix. This has me confused, can you enlighten us?


prognosis: Lead or Lag

 

[XL83NL]

Clearly, the B31.3 committee wanted us to 'believe' something else by means of Int. 18-06, i.e. qualification by 304.7.2 (which is what I referred to in my 1st post from 13 Nov 13).
Qualifying to 304.7.2 to do may I think best be done on the basis of 304.7.2 (a).
Nonetheless Im not saying all this makes any sense.

 

[moltenmetal]

While jte is correct that the geometry of a butt welding elbow is allowed to "vary", the thickness in EVERY part of the elbow is controlled to a minimum unless I'm mistaken. When the part is trimmed, a new weld preparation is required, no different than when you cut a piece of pipe. While jte is correct that the formed part of the elbow may have greater ovality than the pipe itself, I'm having a hard time seeing how any resulting butt weld joint that is prepared such that it could have a hope of passing a radiographic inspection would modify the real MAWP of the assembly. Note that the pipe itself has substantial OD and wall thickness and ovality tolerances which must be considered during fit-up.

I'd personally rather see trimmed elbows used when required than cold bent pipe, since the bend radii you can achieve cold without internal guiding and without excessive ovality and thinning in the finished product are fairly large. Done properly, both are safe methods in my opinion- but I've seen a lot of pipe bent without consideration of wall thinning.

 

[jte]

pennpiper - You probably know better than I about elbows. It was my understanding that some elbows are provided with a bit of a straight section. This allows them to be either butt welded or fully (minus the gap, naturally) inserted into a female socket welding fitting.

It seems that you are arguing that (non-manufacturer) cut elbows be accepted into B31 piping assemblies without any further justification besides that they were cut from a B16.9 product. Or am I missing something?

jt

 

[GenB]

Nice thread:
The
"Dunno where this is coming from, but trimming back a butt-welding elbow is not modifying a listed component to my mind any more than cutting a piece of pipe to length would be."
No, Its not just cutting a pc of pipe. elbows: a modified pipe which get thin along probably 50% of it.
For my understanding (I also red the Code Case some one posted. Listed component means ANSI Std. By trimming an elbow you are violating the Mfr's certification.
But the Code does not prohibit the trimming. Once the Fabricator/Mfr trims an elbow It shall Certify that the Elbow kept its
properties. I believe the original elbow Mfr/fabricator may be relieved of responsibilities but that can only be seen if the elbow fails and prompts an investigation to find the guilty.

 

[DSB123]

Whoops I directed my question to the wrong poster - appologies Tman1.

roteqpmt,
please answer my question as I am intrigued by your response.
"Can you direct me to where in the Code it says that by trimming the ends of an elbow modifies the Stress Intensification and the Flexibility factors because I have never heard that one before?? You seem to be suggesting that a 45 deg elbow and a 90 deg elbow have different SIF's and flexibility factors (since they have different angles) but Appendix D does not agree with what you are suggesting. Please enlighten us as to where your deduction comes from? "

 

[XL83NL]

B31.3:2012 para 328.4.2(b)(6) may provide more nuance to this discussion, and where Int. 18-60 kicks in.

 

[moltenmetal]

jte: the butt welding elbows < 2" I can look at in my stockroom don't have sufficient straight land on them to safely insert the fitting the required distance into socket welding fittings. If you look at the geometry of the resulting joint and welds, the stress intensification is pretty obvious. So-called "long tangent" elbows are available (which have the extra straight land length), but in CCTF's catalog they start only at 1.5", which is of little use to us for socket welding. We prohibit the practice of inserting a BW fitting directly into a SW flange or fitting for that reason- we require a pup piece in that case.

 

[rodofgod]

Hi All!

I fail to see the reason for any arguing or further debate over this matter, roteqpmt's reply seems to have answered the OP's question quite well! Any further debate over the matter seems to require ASME's input and approval. It's quite simply, you're not allowed to alter the angle of an elbow without incurring penalties as per 304.7.2.

 

[GenB]

Well said... Good bye...

 

[DSB123]

rodofgod,
I was trying to establish where the "Changing the geometry of a listed component modify its stress intensification and flexibility factors" response came from as I am intrigued and wanted to know the basis of the response.

 

[rodofgod]

To be honest, does it matter? I doubt it does!

However,

ASME has clearly stated that modification of pre fabricated listed elbows exit angles are a no no!

Simple!

If you need to know the background, contact ASME.