VFT tube leak

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wsmcycle
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VFT tube leak

Post by wsmcycle » Mon Dec 16, 2019 3:57 pm

While preparing for our Fort Smith, AR annual Christmas parade Saturday I discovered a leak in the VFT boiler. I am not sure where the leak is but is seems to be one or more of the tubes. I will include a few pix. The boiler was built in 2005 by Everette Engineering . It has 84.1 sq ft heating area It is not a relic. I am concerned to know whether it rusted through or just developed a leak in the swedged/rolled edge of a tube. Does that happen? I am going to wire brush the area today to better locate the leak. If the tubes are not rusted through why is it leaking and can it be repaired further tightening the swedge (in place)?
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Lopez Mike
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Re: VFT tube leak

Post by Lopez Mike » Mon Dec 16, 2019 4:11 pm

I would be very surprised if the tubes were rusted through although there certainly is a lot of corrosion. What sort of fuel are you burning?

I would see about at least wire brushing the bottom tube sheet (is that what we are looking at?) and cleaning the inside of the tubes as well so that you see better where it's leaking. Even some gentle sand blasting wouldn't be out of order. Running a roller in there to seal things isn't a major task other than getting to it if it's the bottom sheet.

In my locomotive boiler I have rolled in the tubes and then done a sealing TiG sealing weld. Not that hard to grind away the weld if you need to replace a tube and insurance against weeping.

I have plugged a failed tube with tapered wooden plugs at each end and a through rod with washers and nuts. Worked very well.
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Re: VFT tube leak

Post by RNoe » Mon Dec 16, 2019 4:26 pm

Rolled fire tubes like your boiler has can begin leaking after thermal shock from normal usage. Or from accumulated scale inside.
It is normal to need to clean and re-roll a fire tube on occasion.
Your photo looks like a weeping leak, probably not sufficient to cut the tube sheet like a large leak could do.
That might require tube removal and sheet repairs.

I would perform a careful internal washing and removal of scale, then clean the suspect external tube sheet area and tubes on your boiler.
Next, hydrostatically pressure test the boiler to exactly locate the leaking tubes(s). Mark them with white chalk to make sure you don't "lose" the locations.
Then gently re-roll, and re-test until the leak stops. Not a big deal.
Light re-rolling is best. Don't over-roll the tubes causing the sheet holes to become distorted.

Often a small leak will self-seal after the boiler reaches operating temperature and pressure. I see that every year on scale steam locomotive boilers during their annual hydro and steam tests. Even the Washington State boiler inspectors accept this fact.

Everett Engineering (Washington State, USA) boilers are good ones. Many years ago I worked nights in their machine shop swaging 5-1/8" OD boiler superheater flues for a locomotive boiler re-tubing we were doing. Everett Engineering was a capable business, and probably still is.

Let us know how your tube sealing goes.
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Re: VFT tube leak

Post by Mike Rometer » Mon Dec 16, 2019 5:46 pm

RNoe wrote:
Mon Dec 16, 2019 4:26 pm

Edit : -

Often a small leak will self-seal after the boiler reaches operating temperature and pressure. I see that every year on scale steam locomotive boilers during their annual hydro and steam tests. Even the Washington State boiler inspectors accept this fact.
Is this really the case, or is the leak so slight that the water evaporates quicker than it escapes, once up to temp? How often is a re-test done after a couple of heat cycles, to see it it has genuinely sealed? ;)
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Re: VFT tube leak

Post by wsmcycle » Mon Dec 16, 2019 6:51 pm

I have wire wheeled and the damage looks only skin deep. The boiler had 100 psi in it when I discovered the leak. That was for a few whistle blasts. I am going to put 10 psi in to find the culprit tube or tubes. Is it possible to rent a tube roller? These tubes are 1.050 ID. Would that be a 1 inch tube expander?
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Re: VFT tube leak

Post by wsmcycle » Mon Dec 16, 2019 11:11 pm

It looks like I have at least two tubes leaking at the rolled flange. I read elsewhere on the forum that "radiator fix" products can stop such leaks. I don't have a tubing expander. If I did, I would try swedging. can I rent one somewhere?
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Re: VFT tube leak

Post by Lopez Mike » Tue Dec 17, 2019 12:48 am

Someone on here may have a tube roller. I have used a tapered mandrel driven in to seal up a weeper but not on this large of a flue.

A tube roller isn't an impossible project at all. The three rollers are not tapered. Only the mandrel. The rollers are available from a bearing supplier or from the junk box of an auto shop. I've used the rollers from failed automotive rear wheel bearings on a bit larger rolling tools. With the number of flues done in a hobbyists shop per year, you could probably get by without surface hardening the mandrel. Look carefully at a professionally built roller for tips. And make up a test sheet and flue for practice. This isn't rocket science.

I would invest in a decent flue cleaning brush. I see considerable buildup of what looks like combustion products. You might notice a fair increase in steaming performance.

There has been a lot of back and forth about welding flues whether after rolling them in or without rolling them in at all. I do both. That is, if the tubes and sheets are of the same material. When removing an old flue, a hand grinder removes the sealing weld easily. The weld isn't intended to take structural loads but only to seal. No penetration to speak of. I've not had a tube with a sealing weld start to weep. And with the sealing weld you can get away with big thermal shocks. I'm a major offender.
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Re: VFT tube leak

Post by RNoe » Tue Dec 17, 2019 2:58 am

Mike Rometer wrote:
Mon Dec 16, 2019 5:46 pm
RNoe wrote:
Mon Dec 16, 2019 4:26 pm
Often a small leak will self-seal after the boiler reaches operating temperature and pressure. I see that every year on scale steam locomotive boilers during their annual hydro and steam tests. Even the Washington State boiler inspectors accept this fact.
Is this really the case, or is the leak so slight that the water evaporates quicker than it escapes, once up to temp? How often is a re-test done after a couple of heat cycles, to see it it has genuinely sealed? ;)
After operating a boiler, any leaks tend to leave visible traces. So post-steaming visual inspections can reveal a lot.

My normal procedure is to do a hydro test to find leaks, then re-roll the weeping flues. Then perform a hot water hydrostatic pressure test to make sure any detected weeps have sealed when hot.

Re-tests should be performed any time a leak is suspected. Or annually, even if all seems OK. (That's also a good time for the annual washout.)
Or after any work has been performed on the pressure vessel.
A little attention goes a long way toward safer steaming.
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Re: VFT tube leak

Post by wsmcycle » Tue Dec 17, 2019 1:46 pm

RNoe
what does your roller look like? Please send a pic. I guess you can use it inside the fire box is it pneumatic?
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Re: VFT tube leak

Post by wsmcycle » Tue Dec 17, 2019 2:10 pm

Mike
Is the only force radial in the repair process? Is the flange only to prevent axial movement of the tube? What creates the flange in the building process? It seems like this roller device mounted in a hammer drill might make a good effect. If the process is simply rotary, what makes the tapered tool move into the tube.
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