Tube to Tube sheet welding

[leedrong]

Dear All ~!

I have one question for the tube to tube sheet welding of heat exchanger.
We did 2 layer strength welding on tube end which have high-integrity weld figure as specification and dye penetrant test.
This welding figure was selected without RT by client's design engineer.
But Client requested us to do RT additionally after completion of welding .
How can we judge the film which should be repaired or accepted when we find some defect such as polosity and LF at root area ?.
We have no experience RT and repair on Integrity welding of tube end ( 1st layer ).
Anyone have a good idea how we treat the additional RT and judge and repair?

 

[metengr]

Radiographic testing (RT) of fillet weld (tube-to-tubesheet) joints is extremely difficult, any may not even be practical. I would consult with an NDT Level III RT examiner to verify if RT could even be performed in your application.

 

[pve5]

Leedrong (Mechanical)

Radiography of tube to tube sheet joint is not practical and I have never seen this requirement even for heat exchangers with very high pressure and temperature on tube side. Radiography of tube to tube sheet weld is only recommended where the tubes are butt welded at shell side face of tube sheets . For very critical service, apart from DP check of each pass of tube to tubesheet strength weld , leak test with helium is done.

 

[leedrong]

Thanks ~!!!

NDE Vender have special source and fixture to take RT.
Taing RT is no problem , Problem is guide line ( or applicable code )to judge accept or reject for the defect.

 

[metengr]

If this is the case, you are on your own. Go back to your client's design engineer and ask them for acceptance/rejection criteria.

 

[rmw]

While I don't necessarily disagree with metengr's advice, I shudder at the prospect of what might come from it. You are plowing new ground here, and they don't know either, so I fear any criteria that they might impose on you. It could be impossible to meet, if not even ridiculous.

When Hx tubing is eddy current tested, the eddy current probe if first passed down a check piece of tubing with known and well defined defects in it so as to get a look at how these known indications will show up on the screen. It establishes a known baseline. That is what you lack here.

With that in mind I suggest the following.

Test your welded tubesheet with other well known and accepted testing methods. At a minimum, dye penetrant and air or even better, hydrogen leakage methods. Others on the forum might want to suggest additional methods.

Surely if the statistical bell curve is right, there will be some small number of detectable defects that can be determined by those methods. If any are found, then shoot those, and see what the film looks like. Fix those defects test again, and if the defect is gone, then shoot it (them) again, and compare the film to the previous result.

Short of that, the only other thing you can do is prepare a mock-up tubesheet with some known defects and shoot those to establish your baseline. I don't know how to accomplish this, as, while it is hard to prevent a small percentage of defects, I don't know how you make a defined defect this way. It is different from drilling a hole or simulating wall loss in an eddy current check piece.

Maybe these thoughts will give you a place to start with your unusual requirement.

rmw

 

[MJCronin]

leedrong.....

My experience with this type of HX construction has been that these weld are considered to be "seal welds" only and that the tubes are retained within the tubesheet by rolling.

Is this true with your heat exchanger ?

If so, you may want to consider a destructive tube "pull-out test with a mock-up section of tubesheet and several rolled and welded tubes...I believe that there may be an ASTM standard test already developed for this testing.

My opinion only

-MJC

 

[GenB]

I have seen a lot of filet welds RT be performed (at my NDT vendor's shop),
mostly fillet-root welds for nuclear components, so I NDT on fillets of tube to tubesheets are not impossible.
I would ask an ndt expert as a level III for advise,
if the customer wants it and it can be done, you have to make a good weld that will pass the test.
I hope you get paid for the good work. most of this weld will be probably domne with machine or a good hand welder using tig, very difficult but not impossible.
genb

 

[robsalv]

I can see how you'd RT a socket fillet weld for LOF and socket gap... but how the hell do you RT the seal/strength weld of the tubes to a tube sheet? Where do you put source and the film???

We recently had a very critical heat exchanger built. To ensure tube to tubesheet integrity we went through the following process:
* Helium tested from the shell side after doing the mechanical expansion rolling,
* Rerolled any passing tubes, then...
* Seal welded the tubes to tubesheet.
* Dye penned the welds.
* Repair welded any unnacceptable defects then re-dye penned to confirm.
* Then we helium tested the lot again.
* And went around the merry go round again if any problems were found.

Not once did we consider RT.

I'd be interested to hear more on how one would do this.

Cheers

Rob

 

[vesselguy]

Same here. How do you RT a fillet weld or even a butt weld on a 25mm Dia. tube? Where do you put the film? Don't tell me you have to RT all the tube joints? I think your Client's Engineer is a newbie to all this and just don't really know what he/she is talking about.

The methods robsalv listed above is much more the norm. Please let us know what was your final resolution to your problem.

 

[leedrong]

vesselguy~!
RT is requested by client for the butt weld shape tube end welding with tube sheet for Lethal servise .
Normally 10% of tubes on each tubesheet be taken RT .
Helium leak test and dye check also is madatory.
We know that high integrity fillet weld applied for the
case RT is not mandatory.
A shoot with a film for each selected tube hole.
The D4 type film which have a center hole, attached on film support plate with rod shape compensate block .
Compensate block inserted to tube hole and then the
film be closely located between tubesheet and film support plate.
Ir192 be located end of compensator through the bore of it.
It is little bit difficult for me to describe the RT Jig exactly without Photograph.
Please ask big NDE company near your office for the detail.

Taking RT is no problem.
Problem is guide line ( or applicable code )to judge accept or reject for the defect.

 

[robsalv]

Leedrong

We must all be thinking about something else.

My apologies, I don't understand what the "butt weld shape tube end welding with tube sheet" is?

A tube is pushed through a hole in the tubesheet and usually remains a little bit proud of the tubesheet. It is then typically joined to the tubesheet by mechanical rolling/expanding. The OD of the tube is welded to the tubesheet for seal welding or if the tubesheet hole has a bevel, then this is considered a strength weld.

This weld is not RT-able.

The scenario I'm considering is similar to the picture on:

http://www.spectool.com/hydes.htm

???


Thanks,

Rob

 

[robsalv]

Check out this paper on the typical designs of seal welding / strength welding of tube to tubesheets. Some of the figures are missing, but figure four is what I'm talking about.

http://www.wahchanglabs.com/pdf/2k1ConfProc/2001011.pdf

Cheers

Rob

 

[leedrong]

robslv~!
It is strength welding ( 2 layer ).
For the item which RT is requested from contract stage , the tube sheet side bevel is 2.2 mm depth with 5mm radius
and tube end is 1 mm lower than tube sheet surface.
We finished RT without any problems.

For the item designed High Integrity welding , 3mm proud
from tube sheet surface with bevel 2.2mm depth ,5 mm radius.
It was designed without RT,but Client requested us to do RT additionally after completion of welding .