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

 

[Tman1]

JUST 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

 

[DSB123]

Well 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.

 

[XL83NL]

I 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?

 

[Duwe6]

There 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.

 

[Tman1]

Hy all

two more questions:-(1) 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 the
manufacture to trim?
note:- the elbow has been certified as a 90 degrees trimming it to 60 degrees takes away the manufacures
responsibility because the item will be considered as been tempered.

 

[DSB123]

Tman1,
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!!!!!

 

[moltenmetal]

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.

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.

 

[XL83NL]

It was just my memory (playing tricks?), to me it doesn't sound very probable that cutting back an elbow requires 304.7.2-calcs.

 

[gr2vessels]

DBS123,
I think the OP meant 'tampering', not 'tempering'...are the bets back?

 

[DSB123]

gr2vessels,
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.

 

[gr2vessels]

Correct, common sense.

 

[chicopee]

If 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.

 

[gr2vessels]

Haha, DBS123, how right you are! Sorry chicopee, it's your reply...

 

[BigTank]

One 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

 

[roteqpmt]

Tman1,

The answer to this is on ASME B31.3 interpretation 18-06

http://cstools.asme.org/csconnect/FileUpload.cfm?View=yes&ID=17941

Changing the geometry of a listed component modify its stress intensification and flexibility factors.

 

[DSB123]

Tman1,
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?

 

[jte]

XL83NL - 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

 

[pennpiper]

jte,
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

 

[jte]

Penn-

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