bad hole!

[sadielou]

I have a 9"thick s.s. tube sheet that we drilled a 5/8" hole through in the wrong location. This is for a high pressure vessel. I need to fill the hole with weld and be able to pass x ray. We are currently trying to develop a proses with our sub arc to save this tube sheet from going to scrap. It's 10 grand for the material alone not to mention the 300 hrs. of machining I have in it already any suggestions.

[MicroZone]

Yes - measure twice and cut one.

Honestly, weld it with 308 wire and GTAW process, using either material and filler or just filler. The filler itself is stronger than the material. What pressure? You don't give specifics so that's about all one can suggest. What thickness? You say 9" thick but then say TUBE SHEET. Is it sheet material or is it 9 inches thick?

What is your location as well? The requirements for pressure differ from US to Canada to Europe to who knows where.

More info. needed...

[76GMC1500]

Cut it bigger, throw a hand-hole plug in it, and call it an inspection port.

[WHughes]

Maybe use a counter sink drill bit to taper the hole and ensure 100% penetration?

Bill

[Engloid]

Both good ideas, but with a tubesheet, I kinda doubt that you can make it some sort of inspection port. Most likely, the hole is going to be in the way of another hole with a different center.

You could drill it out to about an inch on top and bottom, then set up a purge rig that fills the hole with argon from the bottom and weld it from the top with tungsten sticking out about 4.5" and the cup at or near the surface. What that does is it protects the entire length of tungsten, and the puddle.

I'm sure it can be done for less than $10k that it would take to replace the piece. If nothing else...you buy and I'll fly.

[MicroZone]

Engloid - what is tubesheet?

[olddad]

Drill it to about 1 1/2" and use a flexhead pencil tig torch. I've never done it over 3" deep but don't know why the 6 extra inches wouldn't pass x-ray. Inch and a half is plenty to see around the torch to see what you're doing and feed filler. Slow process but a whole lot more sensible than scrapping something you've got at least 25G tied up in already.

[Engloid]

Originally Posted by MicroZone

Engloid - what is tubesheet?

Imagine this piece of 9" thick plate, with 1/2" holes all over it. Now think of having two of them about 10 feet apart, and tubes linking the holes together. Where the tubes come out the outer sides of the tubesheets, they will often "roll" them (expand) to get a tight seal, or use a tube welder to seal them off.

Sometimes, the span of tube length may need support inbetween, so they use other sheets that have larger holes in them and the tube slides easily through. This keeps them supported and equally spaced apart.

This similar deisgn is used in many boiler and evaporators.

[MicroZone]

Okay - gotcha. It had been a long time since hearing that term and it didn't register. Thanks for the illustration.

[76GMC1500]

My post was kind of a joke.

If you want to know what a tube sheet is, Micro, it's the perforated plate at the ends of a heat exchanger where the tubes pass through. They are usually pretty thick because all of the holes subsantially weaken the plate. They can be flat like in a shell and tube heat exchanger, they can be curved like on the bottom of a steam drum for a boiler. They've got some pictures of tube sheets and heat exchangers here: http://www.amerindustrial.com/heat.htm

As for the repair, simply welding in a small hole on such a thick piece of metal would worry me, especially something exposed to such high pressures and temperature cycles. There would certainly have to be preheat and PWHT. Any residual stresses from welding could cause a failure. Even under normal operating conditions, boilers and heat exchangers often have supprisingly little safety factor built in to their construction.

[aczeller]

Originally Posted by 76GMC1500

As for the repair, simply welding in a small hole on such a thick piece of metal would worry me, especially something exposed to such high pressures and temperature cycles. ... Even under normal operating conditions, boilers and heat exchangers often have supprisingly little safety factor built in to their construction.

if they are made with such low engineering safety factors, then what kind of pressures and heat cycles are we talking here? not many things have a greater safety factor than about 1.5 in manufacturing any more (that i have been exposed to anyway), and i have never seen any plate that needed to be 9" thick. i don't doubt you, but i woudl tend to think that there would be a enormous amount of holes in that plate to weaken it that much.

Later,
Andy

[tanky321]

Originally Posted by aczeller

if they are made with such low engineering safety factors, then what kind of pressures and heat cycles are we talking here? not many things have a greater safety factor than about 1.5 in manufacturing any more (that i have been exposed to anyway), and i have never seen any plate that needed to be 9" thick. i don't doubt you, but i woudl tend to think that there would be a enormous amount of holes in that plate to weaken it that much.

Later,
Andy

Check out the link in the post above yours, there's allot of holes in that bad boy.

[MoonRise]

Andy,

The appropriate safety factor for a design depends a lot on how many unknowns there are and also the amount of analysis that can be done to narrow down the needed safety factor. As well as inspections, before and during and after the device is made and in use. And also code required safety factors or minimum size requirements, that could give you effective net safety factors that are pretty big. Like OSHA regs about fixed ladders and a minimum rung diameter of 3/4 inch solid steel (or equiv in a suitable hollow shape). That gets you a safety factor of almost 5 for a Type I-A static load of 300 lbs. Building codes for structural steel public structures usually call for safety factors of 5 or 10. etc, etc, etc

For highly engineered, critical applications, with tons of inspections and certifications, safety factors may go down in the 1.1 range. Think NASA and spacecraft or aircraft.

The monster truck Bigfoot IIRC was breaking things when the SF was 5 or 10, so the designer was going to bump the SF up to 20. Because the drivers were going airborne so much and his analysis tools or conditions or loads or whatever couldn't narrow things down, he's into 'unknown' territory and hence is going to boost the SF to compensate.

As to the OP and his hole in the wrong place, pre and post heat the thick plate and maybe a big-big-big diameter electrode onto a backing plate. Basically cast the hole closed with the arc melting the electrode and some of the workpiece at the same time, then remove backing plate and clean up and touch-up the other side?

[hotrodder]

like other posts here i could come up with several methods to fill the hole but,...

given the procedures in place for the welding of pressure vessels i would have thought a specific procedure would be required for this repair

if there isn't, then would the repair actually be allowed? i would have thought a procedure would have to be qualified first?

maybe i'm very wrong (wouldn't be the first or last time) but i can't see (for example) 'use GTAW with 308 filler' cutting it, especially as we don't know the alloy of the tube sheet

[tresi]

I too would think that a proceedure would have to be in place and followed. Perhaps the accepted proceedures allow no defects or repairs. If no proceedures exist couldn't the hole be machined for a stepped plug, the plug shrink fit to the hole and then welded on both sides. I don't know what pressures you're talking about nor am I any kind of engineer that could say for sure it would be OK. Given the money your company could be out of pocket they should run some ideas past an engineer.

[welderman1]

If the alloy is known than welding it with proper pre and post heat should work. I would contact the steel manufacturer.

[hotrodder]

i don't see physically fixing it as the problem. this is a pressure vessel and welds are subject to specific procedures. the weld procedure has to be qualified as well as the actual weldors.

the point of my post was, will filling a 5/8x9" hole fall within the procedures in place for the tube to tube sheet welds? i don't know much, and even less about this but i doubt the procedures used to manufacture the vessel will cover this repair

[OldSparks]

You could check into 'Electroslag Welding'.....http://vertaslag.com/electroslag.html...... We used a similar system to weld 1-5/8" thick tank verts. In that case you fit for a 1-5/8" gap and attach two watercooled shoes, one inside and one outside, and the weld is made by wire feed through an insulated guide tube which melts as the weld rises. This was for 8 foot high butt welds and they turned out excellent. Basically your round hole is the same as a square gap with the shoes on so you may get lucky. It's possible they have the engineering and procedures to fix your problem.

[Sober_Pollock]

In the mills, Ive seen large holes through thick slabs filled in using a process called "Electroslag" welding.

Here is the first link I found doing a google search on it.

http://www.twi.co.uk/j32k/protected/.../ksokg001.html

[Supe]

In regards to the original question, I don't see this being done with sub arc in any way. Start shopping around to have this sort of thing outsourced.

[Sober_Pollock]

I wasn't suggesting Submerged-Arc, I was suggesting Electro-Slag.

[denrep]

Originally Posted by Sober_Pollock

In the mills, Ive seen large holes through thick slabs filled in using a process called "Electroslag" welding.

Ah Ha... I thought I've found "knotholes" in plate!

[Sober_Pollock]

Many, Many years ago, I watched them deliberately "Blow" three inch holes through slabs. Then fill them back in with Electroslag process.

It was all part of some sort of inspection process I doubt anyone does today.

It was pretty spectacular to watch them "Blow" a hole through an eighteen or twenty inch thick slab in mere seconds!

Watched from a good distance of course.

[Supe]

Originally Posted by Sober_Pollock

I wasn't suggesting Submerged-Arc, I was suggesting Electro-Slag.

Well aware of that. The original poster was wondering if it was possible through the adaptation of their sub arc equipment.