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MODIFICATION OF ELBOWS
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(Petroleum)
(OP)
13 Nov 13 02:27HY 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
(Petroleum)
(OP)
13 Nov 13 02:51JUST TO ADD ON THAT CAN A SUPPLIER OF THE MATERIAL SEND AN APPROVED REPORT ON THE MANUFACTURES BEHALF?
QUESION IS REGARDING MODIFICATION OF 90 AND 45 DEGREES ELBOWS.
REGARDS
(Mechanical)
13 Nov 13 07:19Well Tman1,
To answer your question "PRIOR TO CUTTING THEM TO ANGLE SUCH AS 30/25.1 ETC WHAT ONE SHOULD HAVE? (By the way use of capitals is considered as shouting)
If you want to cut a bend to arrive at a bend angle of say 47 Degrees then to answer your question you need a 90 Degree elbow since a 45 degree elbow would not work.
If you want to cut a bend to arrive at a bend angle of say 30/25.1 Degrees then to answer your question you need a 45 Degree elbow.
You do not need calculations. An elbow can be cut/trimmed to suit site requirements provided you still have sufficient distance between the butt welds.
(Mechanical)
13 Nov 13 15:05I vaguely remember of reading an older post here at eng-tips.com that cutting an elbow is modifying a listed component, which then requires calcs per 304.7.2, as it is non-standard anymore?
(Industrial)
13 Nov 13 15:53There may have been an old post, XL83NL, but I agree with DSB123 in that cutting off slices [shortening them] is fully acceptable without any special instructions or calculations. Engineerng-wise, it is the same as shortening a length of pipe.
Cutting them at odd angles, or splitting them is another story. You need 'permission' from the Eng-of-record, may need concurrence of the Inspector, may need NDT. And the engineer may have some calc's to do.
(Petroleum)
(OP)
14 Nov 13 05:17Hy alltwo more questions1) which items are regarded as unlisted components to name a few if possible?(2) if trimming of elbows is not a concern do we still need an approval from themanufacture to trim?note:- the elbow has been certified as a 90 degrees trimming it to 60 degrees takes away the manufacuresresponsibility because the item will be considered as been tempered.
(Mechanical)
14 Nov 13 07:14Tman1,
You say "....the item will be considered as been tempered". You did not mention in your first post that you were heat treating the component!!!! All bets are off if you are tempering the component!!!!!
(Chemical)
14 Nov 13 07:36Dunno 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.
Now if you make a mitre of more than a few degrees in your butt weld, whether that be between two pieces of pipe or a pipe and any other component, now you need to do some analysis rather than just jumping to it.
(Mechanical)
15 Nov 13 02:20It was just my memory (playing tricks?), to me it doesn't sound very probable that cutting back an elbow requires 304.7.2-calcs.
(Mechanical)
15 Nov 13 05:11DBS123,
I think the OP meant 'tampering', not 'tempering'...are the bets back?
(Mechanical)
15 Nov 13 07:24gr2vessels,
I knew he meant tampering but just wanted to show how incorrect spelling etc can lead to misunderstandings!!! So yes my original comments still stand. I cannot understand why the original question was being raised in the first place. If it was not allowed or you needed to perform additional calcs/analysis or get the manufacturer to approve the trimming then all I can say is that there must be millions of elbows out there which contravene this.
(Mechanical)
15 Nov 13 09:01Correct, common sense.
(Mechanical)
16 Nov 13 19:45If you need "odd size" elbows, instead of trimming existing elbows why would you want to purchase a hydraulic tube bender with appropriate set of dies and make these elbows yourself out of piping or tubing.
(Mechanical)
17 Nov 13 11:52Haha, DBS123, how right you are! Sorry chicopee, it's your reply...
(Mechanical)
26 Nov 13 10:47One caution I can think of: markings. Typically the markings for a wrought part are very close to one end. If this item is to be Code-compliant, it must retain it's markings, correct? Be sure you trim the correct end.As far as calculations go, well...I'm not familiar enough with 31.3 without digging into it. I can't comment, but it would make sense to me that you'd do a seperate calculation for the wrought material vs. the pipe it was being welded to (if that is the case).
--------------------------------
Fitter, happier, more productive
2
roteqpmt(Mechanical)
9 Mar 14 08:25Tman1,The answer to this is on ASME B31.3 interpretation 18-06Changing the geometry of a listed component modify its stress intensification and flexibility factors.
(Mechanical)
10 Mar 14 08:27Tman1,
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?
(Mechanical)
10 Mar 14 18:29 XL83NL - Perhaps you recall my second reply in- Perhaps you recall my second reply in http://www.eng-tips.com/viewthread.cfm?qid=270560 If you have a non-B16.9 product [which you've created by field cutting an elbow], how do you justify its use in a B31 system without calcs?jt
(Mechanical)
10 Mar 14 19:21jte,Are you in the design office or in the pipe fabrication shop?What calcs would you do?What do you expect the calcs to tell you?How many times have you done calcs for a trimmed elbows?What did you do after you did the calcs?
prognosis: Lead or Lag
(Mechanical)
10 Mar 14 19:49Penn-
I'd say I'm neither in the design office nor the pipe fab shop. My main focus is on providing direct engineering support for operating facilities. You and I have both been around for a while (though I took a bit of a sabbatical from eng-tips), as anybody poking at our profiles can see. We both probably have a fairly practical perspective on life based on our past experience and our client base. Even though we both have submitted to the "management lobotomy" to some extent.
What calcs would I do? I'd perhaps run a -579 calc. Maybe an FEA if I felt so inclined.
What would I expect the calc's to tell me? I'd expect them to tell me the required thickness. Which, I'll point out, is not provided by B16.9 - at least not last time I checked.
How many times have I run such numbers? Not many.
What did I do after performing the calc's? I checked the required thickness vs the provided thickness.
Keep in mind that the geometry of an elbow in between weld points is allowed to vary from fabricator to fabricator. Only the mating weld bevels are strictly controlled. If one were to take an elbow with a bit of a straight section on each end intened to make connections to SW fittings easier and cut it in the middle, the resulting part would not be symmetric. I'm not saying that this would cause an issue - but the potential exists that in some circumstance it could.
Is this something I lose sleep over? No. I have many other horror stories to worry about without bothering to lose sleep over cut elbows. If it is a burning issue for others... Write some PVP papers, lobby the code committees to make changes, or join the committees and implement the change yourself.
jt
(Mechanical)
10 Mar 14 21:44jte,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
(Mechanical)
11 Mar 14 03:15Clearly, 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.
(Chemical)
11 Mar 14 10:35While 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.
(Mechanical)
11 Mar 14 20:44pennpiper - 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
(Mechanical)
11 Mar 14 21:43Nice 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.
(Mechanical)
12 Mar 14 08:17Whoops 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? "
(Mechanical)
12 Mar 14 10:12B31.3:2012 para 328.4.2(b)(6) may provide more nuance to this discussion, and where Int. 18-60 kicks in.
(Chemical)
12 Mar 14 12:02jte: 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.
(Materials)
13 Mar 14 01:11Hi 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.
(Mechanical)
18 Mar 14 02:37Well said... Good bye...
(Mechanical)
18 Mar 14 08:44rodofgod,
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.
(Materials)
19 Mar 14 21:12To 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.
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