Boiler Repair Assistance

[integrated93]

June 21, 2013

Dear All,

I was called by the owner of a candy factory to repair their 150 Bhp Ray Boiler manufactured in 1999 with a maximum design pressure of 150 psig. Their boiler operates at a maximum of 100 psi and uses bunker fuel. It is a three pass boiler which had some leaking tubes at the rear section of the end of the first pass. The boiler is constructed wherein all its ends are expanded/rolled at the tube sheets with flared ends.

The boiler's appurtenances such as main steam valve was blinded including removal/blinding of main steam valve and isolation of safety controls. After which a hydrostatic test at 225 psig was conducted. i was able to identify certain leaking tubes at the rear section of the end of the 1st pass. I had rolled and expanded the tube ends numbering 27 pcs. and conducted another hydrostatic test at 225 psig with no more leaks. I gave instructions that the boiler could be operated normally.

In less than two days of operation, the boiler leaked. We again subjected same to hydrostatic testing and identified the leaking tubes. Later, we inspected water column and found no water blowing off. We decided to open all manholes/covers and flushed scale/sludge out.

After seeing the water clear, we closed all and subjected the boiler to another hydrotest at 225 psig and rerolled the 27 +2 or a total of 29 tubes. With no more laaks we had boiler operated.

Initially after operation of 4 hours, no leaks but after boiler was stopped it leaked again. I was informed that the same tubes expanded leaked.

Would like to know or get feedback why after a successful hydrotest of 1.5 times the maximum operating pressure, boiler leaked. and what other things should i take into consideration in repairing this boiler.

I was also thinking of descaling the boiler and subject same to hydrotest or replace all leaking tubes? Thank you.

 

[metengr]

The problem with re-rolling existing leaking boiler tubes on small industrial boilers is that once the tubes leak and debris can make its way into the tube roll joint, you may not be able to simply re-seal the leaking tube. This can be problematic and may require replacement of the original tubes using dutchman and re-rolling the new tube ends into the lower drum.

How much did you expand the existing tube? Did you measure the percent wall reduction after rolling? Did you have a tube rolling procedure?

 

[chicopee]

So we are talking about a fire tube boiler. Descaling the boiler tubes is a good idea if there is scale build up on the water side of the tubes as I have inspected boiler having too much scale and the tube would leak out. Another check may be that the boiler is over fired so check the burner heat input/ output to make sure that it is within the intended specification that produces the steaming rate. I am assuming that you know the calculations required to determined the burner heat output based on the heating surface of the boiler.

 

[chicopee]

One more thing, you may need to seal weld the tube ends of those leaking tubes short of replacing damaged tubes with new tubes. With this type of boilers, it may not be cost effective depending on the conditions of the leaking tubes and on the number of good tubes that have to be removed, one of the procedures is to cut out the bad tube ends and weld new tube ends. Also re rolling may have enlarged the tube holes of the rear tube sheet so ferrules may be needed over tube ends of new tubes and that will require careful installation of the ferrules prior to rolling and expanding the tube ends..

 

[Compositepro]

There are boiler leak sealers. I have no experience with them but it does seem to be a better idea than re-rolling the seams.

http://www.oatey.com/doc/boilerliq.pdf

 

[metengr]

I would NOT recommend seal welding the leaking tubes to the tubesheet because you will disturb adjacent tube roll joints and have a real mess on your hands. Also, seal welding existing leaking roll joints provides no guarantee of leak free tubes in the future.

 

[chicopee]

I have seen many fire tube boilers whereby rolled tube ends were seal welded with no problem. I suspect the welder's experience has a lot to do with reliability of such work.

 

[metengr]

Perhaps. But, if you seal weld leaking tubes, all of the tubes on the tubesheet may require welding because the heat from welding may disturb existing rolled tubes. I have seen it first hand.

 

[Duwe6]

"But, if you seal weld leaking tubes, all of the tubes on the tubesheet may require welding because the heat from welding may disturb existing rolled tubes. I have seen it first hand"

and I've seen the opposite -- it worked fine -- too. Without a detailed exam, everybody [including me] is guessing.

He needs to hire an EXPERIENCED small-boiler repair company to evaluate his boiler prior to comming up with ANY repair recommendations. The tubes could need to be replaced and seal-welding will only stop the leaks for a month or less. Or the tubes could be OK and the previous roll was shallow, and rerolling is the cure. Or the tubes have been rerolled twice before and there is nothing left to roll and ALL the tubes need replaced. And an experienced boilermaker superintendant experienced in small boilers can diagnose the problem quickly, once he/she looks at the boiler. Hire some experience, it will be cheaper than learning the requisite lessons yourself, using trial & error.

Good judgement comes from Experience. Experience comes from Bad Judgement.

 

[GenB]

Integrated. Can you tell us about a ray boiler 150hp? I can find any data on it' without is not possible to identify a problem. tubes that are weak and cannot hold anymore can be repaired by the experts but these experts are hard to find. The procedure require annealing the end tubes after rolling and then final rolling. Also If you have an R stamp you can weld the tubes as an alteration. the adjacent tubes will be okay. Post specs and some design detailed.genblr