Header Crack Repair Question???

[bird]

HEY GUYS ME AGAIN . REPAIRED MY D.S. STOCK HEADER WITH A MIG WELD AND A SUPPORT GUSSET BETWEEN #3 AND 5. I KNOW SHOULD HAVE TIGGED IT WITH STAINLESS ROD, HAD A BUDDY WITH A MIG WELD IT FREE OF CHARGE JUST TO SEE HOW IT WILL HOLD UP. HES CONVINCED I WILL WORK JUST AS WELL AS THE TIG. WHATS SPECIFICALLY IS THE DIFFERENCE BETWEEN THE TWO WELDS? ANYONE ELSE HAVE IT MIGGED? HOW LONG BEFORE I HAVE TO WELD IT AGAIN?

 

[blackplague]

It depends on how it was mig welded

If it was mig welded with ER70s-6 wire and 75ar\25co2 and a gusset was used it might last a little while but it will probably crack or tear in the weld again. The reason the factory mig welds the header is time and money. Tig welding is much more labor intensive process than mig by far. The problem with using er70s-6 {mild steel wire} is that it doesn't expand in relation to the stainless. Stainless expands at a much greater rate than mild steel.

 

[bird]

thanks guys. ill give em a shot...

 

[turbocamino]

I mig welded two of them. One over five years ago without the bridge support between cyls 3 and 5, and it is still fine. The other I did about three years ago with the support. Also is still fine. However, after welding each one, I heated them cherry red all around the area that was welded and then let them cool slowly. This did not distort the flange in any way. Both are run with no gaskets, and no leaks. I suppose if they get hot enough to glow red under hard running conditions, that this heat treatment wouldn't be needed. If they don't get that hot, I would do the heat treatment deal. Rember that when a weld cools down, the metal contracts and creates stress on the weld. When you heat the whole area around the weld untill it gets red and let it cool slowly and evenly, it will relieve the stress. Anything that has a pre-stressed weld that is expanding and contracting thru heat cycles will crack. Hope this helps, Jeff.

 

[Tim Cucci]

The process is not the problem. They can be tig welded or mig welded. You have to use the correct filler material and use an inside purge. 309 stainless is a bi-metal welding material and works great on the headers. I prefer to use tig because you can control your starts and stops and thus control warpage to a minimum when making repairs. Making repairs are considerably different than a factory productin weld. The factory welds seem to be almost just an overlay. Grinding and preping the factory weld and cracks is somthing else to before welding. There is a lot more to making the repairs than just welding over the cracks and factor welds. Tig works well because you can purge the inside of the header and prevent internal defects which occurs when welding SS.
Just my opinion.
Thanks
Tim

15 Nuclear Plant Welding Certifications. From 1/4" SS tubing to Plastic.

 

[et10sec]

header repair

tim cucci, repaired my d.s. header, it worked fine, my other headers are in the mail to get repaired & ported by tim, cant beat the price for a certified welder, thanks again tim. ed z

 

[OneLethal87GN]

What is the charge for something like this. I'm sure my DS header is cracked, as usual, but my PS is also cracked. I think this came from the time my bigger turbo was installed and the support bracket for the header broke. How much for both headers repaired, and how much extra to port them out? Thanks.

 

[Nashty]

Originally posted by Tim Cucci
The process is not the problem. They can be tig welded or mig welded. You have to use the correct filler material and use an inside purge. 309 stainless is a bi-metal welding material and works great on the headers. I prefer to use tig because you can control your starts and stops and thus control warpage to a minimum when making repairs. Making repairs are considerably different than a factory productin weld. The factory welds seem to be almost just an overlay. Grinding and preping the factory weld and cracks is somthing else to before welding. There is a lot more to making the repairs than just welding over the cracks and factor welds. Tig works well because you can purge the inside of the header and prevent internal defects which occurs when welding SS.
Just my opinion.
Thanks
Tim

15 Nuclear Plant Welding Certifications. From 1/4" SS tubing to Plastic.

Tim - Why does TIG inherently create an inside purge? Is there enough fouling of the pool on the back side? If so, then you're over penetrating. Most cracks I've ever seen are pretty thin and wouldn't require back gassing. TIG and MIG shouldn't matter but most people think TIG is somehow superior. The main advantage of TIG, as I'm sure you are aware, is actually puddle control and ability to much more finely control the action at the interface. In the end, the advantage lies with the very source of the problem which is fatigue and the best method to abate that. TIG welding makes it much easier to get a nice large toe radius which is mandatory in increasing the endurance limit. Controling starts and stops? I can do that with a MIG torch just fine. I have mine set up for some post purge if that's what your worried about. The factory welds are usually adequately penetrated. Whenever making a repair, you should remove all the bad weld. A gusset would always be a good idea to distribute and abut the stresses generated under operation. Ever heard of scab plates?

The entire area surpasses any annealing affects you do to it but that should be important if you are not going to use gaskets. You should anneal it so it will sit flat on the head. Tempering it will lessen (but not eliminate) the welding stresses in the HAZ. Scab plates aren't evil.

Anybody can weld pipe, putting together equipment is REAL welding ! (Just a friendly jab) I've worked with nuclear welders and inspectors from Clinton, IL and Cordova, IA at my previous jobs when they got laid off and came to work for us.

BTW, I've talked to several OSU weld engineers who think they know it all about welding. Give me a break. I understand the electrical and mechanical theories and have been involved heavily in welding steel (65mm to .8mm plate) for a few years.

I will admit that my expetise in the material end of it isn't what it should be. 99% of all my welding has been with Lincoln L-50 wire.

 

[UNGN]

The factory welds may be MIG, but the pipes aren't cracked when they are assembled. Crack repair welding is different from assembly welding. The entire crack really needs to be mechanically removed and the resulting area filled with weld to ensure complete penetration and a clean weld. If any portion of the crack remains hidden under the weld, it WILL propogate back into the new weld over time.

Tim's repair methods sound pretty good to me.

 

[Blown&Injected]

The back purge is always a god idea with SS. Just close off the ends of the pipes with some metal duct tape and use another Ar bottle to fill the inside of the headers with the gas.

I believe that the TIG would be better because one has much greater control over the heat going into the metal.

I recall somebosy talking about drilling a hole at both ends of the crack to eliminate the re-formation of the crack after welding - sounds like a good idea.

It also sounds like the conversation in this thread is covering two different things. 1) welding around the area where the pipes meet the flange - MIG in this area seems like it would not as critical because the welder could favor the thicker flange area. Also since MIG is faster, there is less chance of warping the flange.
AND
2) fixing a crack in the header tube. This is where the TIG process would be better due to the thinner metal.

Also, the OP asked about the difference between MIG and TIG. Basically the MIG uses a fixed heat and wire (filler metal) range by setting the volts and wire speed on the machine and then going for it. Ya pull the trigger on the torch and the arc starts, the shieling gas flows, and the filler wire feeds all through the end of the torch. With TIG, the arc and gas comes from the torch and the filler metal is in the form of a rod held in the welders other hand an added as needed. The arc is controlled by a a foot device kinda like the gas peddel in a car - push down for more power.

 

[Nashty]

The cracks form because of thermal cycling has worked the material past it's endurance limit. Like bending a coat hanger back and forth over and over. Drilling a hole at the end of the crack decreases the stress concentration factor (K). Increasing the toe radius of the weld does the exact same thing. That's why TIG is preferred over MIG. No other advantage - PERIOD. If you melt and the metal at the crack formation point, you don't need to drill the hole.

MIG is a constant voltage process, amperage varies with wire stickout. TIG is a variable by means of the foot pedal. Back purging sounds like a good idea then from what has been mentioned.

 

[Tim Cucci]

A back purge or internal pipe purge is an independent gas source such as argon or nitrogen used to keep all O2 and air impurities away from the puddle and arc. This is the same thing that happens with your shield gas in any kind of arc welding. This is a specific use when Tig welding open cracks or full penetration welds on Stainless Steel. To repair a crack correctly you must have full penetration to the back side of your base metal. If you don't use a back purge you WILL have defective welds when making full penetration Tig welds on Stainless Steel tube and piping or thin metals for that matter. You have to shield the back side of the weld.
As for drilling a crack at the ends. Sometimes while welding a crack on certain irons and metals the crack will actually try to run while you are welding it. In some cases this is prevented by drilling each end of the crack. Not a bad idea and doesn't really hurt anything.

OH Yea,
Nashty , You can train a monkey to weld pipe. No problem if he is just welding in a shop but you put that monkey in a bowl of spaghetti and tell him to weld that noodle in the center and your gonna have to get a real welder. It is not really what your welding as much as it is the enviroment that you are welding in. Ask your Local Union Boilermakers, Iron Workers, Ship Builders, and Pipefitters. Now those are real welders.
Welding engineers are engineers and very few are real welders. Put them in that bowl of spaghetti and see what happens.

I didn't say that Mig was not ok to weld these headers I just said that I prefer Tig and that was my opinion. I think the weld prep, full penetration and internal purge is most important. I am by no means a metalurgist or engineer. I just have my opinions based on welding pipe.

Oh yea, Thanks Ed

 

[325DR]

Drilling a hole at the end of the crack sounds like a good idea before getting repaired.

How big of a hole are we talking? Just a tiny drill bit enough to do the job? Or something a little bigger? I am going to have some repairs done by a friend and will do this before I give them to him.

Thanks welders!