steam drum repairs 3

[gibsi1]

A couple of recent tube leaks have turned into a larger headache. The leaking tubes were plugged, only to show they were still leaking in between the steam drum and tube. They could not be re-rolled due to the plugs, so it was decided to seal-weld around the tube. When pressuring up with air, before doing a hydro, the leaks had become worse. It seams as though their is a problem with the steam drum itself. I'm looking for information/guidance regarding repairs to the steam drum itself... code/approach/feasibility/etc.

 

[chicopee]

Do a dye penetrant test of the ligament between the leaking tubes inside and outside the drum to see if there are surface cracks in the shell-first.

 

[gibsi1]

It seems as though 1/3 of the tubes have been seal welded, and the leaks seem to spread. I think I have them convinced to seal weld all of the tubes. The most recent question was whether or not to slightly trim the tube flare in order to get a better weld. Can anyone shed some light on this?

Thanks!
Ike

 

[GenB]

Look at the Code about the minimum/maximum tube extending above the tubesheet, you can trim only if you are within specifications. you may be limited to the minimum as the tubesheet thickness and not be able to trim anything.
ER

 

[deanc]

This is why I consider seal welding "a" leaky tube a last resort. Suggest you reroll(re expand) the tubes that are leaking before you seal weld any more. It is good practice to reroll all seal welded tubes in anycase. If you continue to weld you will chase leaks,maybe until you have them all welded anyway.

Not being negative-just been down this road before.

 

[deanc]

Sorry-your question. I would hope you have a qualified firm doing the welding. If so refer to ASME SecI PWT-11. For your location there may need to be a R-1 form and perhaps this may be considered an alteration if you trim the tubes to the example in Fig. PWT-11. It is understandable that it is hard to weld around the flare,undercut and poor tie in.

Talk to your boiler inspector or the people who issue your operation cert.

 

[chicopee]

Seal welding the tubes is not strength welding them thefore leave tube extension within steam drum intact since such extension is a minimum requirement set by boiler code.

About rerolling the remaining tubes. Perhaps there was a low water condition not serious enough to damage the drum and tubes but enough to have loosened them when they were flared into the drum during installation.

 

[metengr]

The seal weld repair to this drum falls under the NBIC. A Form R-1 will be required. Some clarification;
1. This is a repair not an alteration (refer to the 2001 NBIC, 2003 Addendum, RD 2040 a) and Figure RD 2040 d) for seal welding tubes.

2. Starting in Section I, tubes can be expanded into a component as long as they are under 6" diameter. Reference is then made to PWT- 11.1. When you read PWT-11.1, there are 4 permissible methods to install rolled tubes;

a. expanded and flared
b. expanded and beaded
c.expanded, flared, seal welded, re-expanded
d. expanded, seal welded, re-expanded

The issue for tube stick out is before flaring not after. Seal weld deposits are limited to 3/8".


Seal welding is a last resort. However, I have to respectfully disagree with deanc. You MUST complete seal welding - otherwise you are wasting time and $$$$ by trying to re-roll tubes. Re-rolling is not effective once you commit to seal welding the tubes.

 

[deanc]

Thats what I get when I do not explain myself.

Yes,metengr gibsi1 may be past the point of no return and it would be wise to "seal weld" all the tubes.

Here is the problem-old boiler,problems with obtaining a good weld because of the flare. Been there-the tubes may be very close,the flare may be large,the tubes may be thin,and the joint is probably full of unweldable "stuff". The welder is unable to obtain a good joint,leak proof,with the flare. Therefore you remove some of it. Does it still fall within UW-11,maybe-maybe not. If you need to remove enough of the flare for a good weld it may become an alteration(always need to ask the jurisdiction,yes?)

As stated,once you are already here,may as weld complete the job in a satisfactory manner. Think I would of rerolled after the first seal weld-no matter now.

What to do when a job goes south? Well just my opinion.