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Old 21-02-2016, 11:16   #1
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Welding a pipe in the exhaust system

Doing a repair in the exhaust on my old but working W58. There is a 2" D 8" L steel pipe running from the heat exchanger to the mixing elbow and the pipe has rusted through. The elbow and exchanger are in pretty good condition. I was able to get the pipe out of the Al mixing elbow but the end threaded into the Al heat exchanger body and has so far resisted all efforts at non destructive removal.

I have a spare elbow from a parts engine that I can use but have not been able to remove the pipe from this elbow. So my idea is to cut both pipes and join the pipe from the spare elbow to the pipe from the heat exchanger. But how to do it.

Confession, I am very ignorant of the finer points of welding but have heard rumors that welded joints can be more brittle or weaker than the surrounding metal. My concern is this pipe is hard bolted to the manifold which is attached to the block. So the engine vibrations will transmit directly to the pipe and elbow. Is it a concern that over time the vibration will weaken the welded joint and cause break?

Would one type of welding be better than another MIG, TIG, brazing?
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Old 21-02-2016, 12:15   #2
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Re: Welding a pipe in the exhaust system

posting pictures would help. Rusted steel does not weld very well, too many impurities. From your description it sounds like this is a line with dry exuste exiting the heat exchanger prior to the mixing elbow is that correct? In order to properly weld it you will need acess to get all the way around with a grinder and tig torch. Also NEVER weld to a engine unless there is no other option, you run the risk of puttign current though bearing and all sorts of bad things. So it will have to be removed from the engine one way or the other. Aluminum can take plenty of heat and you may be better off using heat and trying to remove the fitting. If you heat it up let it cool some then put a penetrating spray on it, repeat several times in a well ventialted area. Alternately you could try pickling the entire thing in a mild acid solution, clean with fresh water and then try the heating method.
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Old 21-02-2016, 12:26   #3
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Re: Welding a pipe in the exhaust system

Absolutely use heat, you will need an oxygen acetylene torch and keep moving it around. Eventually that pipe will break loose
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Old 21-02-2016, 16:04   #4
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Re: Welding a pipe in the exhaust system

Welding steel pipe, if it's not too rusted is easy enough. Even with a stick welder. Should get near enough to 90% strength.

I've welded a few galvanized exhaust risers. Seem to get 5-10 years out of them. The welds don't seem to be the weak spot. They always go where the hot salt water gets injected.





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Old 21-02-2016, 17:22   #5
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Re: Welding a pipe in the exhaust system

The remains of the old pipe nipple are junk and not worth trying to weld to. If it rusted out in one spot you really think the rest of it is in great shape?Take it out and put in a new one.

Are you trying to do this in situ? That might limit what you can do because of space, etc.

I agree that heat is a good option to start with. If you can put some serious heat on the female side of the fitting it should expand and break the corrosion between the threads.

If nothing else works, cut the nipple off almost flush leaving just the threaded part inside the heat ex. Carefully make some little cuts to the inside of the remains to the nipple.You can do this with a Sawzall but you can also do it with ahacksaw blade in one of the little hack saw holder gizmos and be much less apt to cut too deeply. Don’t cut down to the female thread but come very close.

The more cuts the better. Now get behind a piece of the old nipple with a cold chisel and a hammer and drive it to the inside.It works, might take a little time and you have to learn the fine points but it is a pretty safe way to get it loose.Often don’t even need to break it into pieces as a few hammer taps will shrink the old nipple enough that it will be loose in the threads and you can spin it out.
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Old 21-02-2016, 19:00   #6
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Re: Welding a pipe in the exhaust system

Quote:
Originally Posted by motion30 View Post
Absolutely use heat, you will need an oxygen acetylene torch and keep moving it around. Eventually that pipe will break loose
One would think enough heat would work but not always. I had a SS bolt frozen into an aluminum hatch frame. I heated the bolt to bright glowing red 4-5 times and still had to drill it out.

I do believe that the bond between ferrous and Al parts that have pickled in salt water a few years to be one of the strongest in the universe; right up there with the strong force that bonds subatomic particles.
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Old 21-02-2016, 19:07   #7
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Re: Welding a pipe in the exhaust system

Quote:
Originally Posted by Cruisingscotts View Post
posting pictures would help. Rusted steel does not weld very well, too many impurities. From your description it sounds like this is a line with dry exuste exiting the heat exchanger prior to the mixing elbow is that correct? In order to properly weld it you will need acess to get all the way around with a grinder and tig torch. Also NEVER weld to a engine unless there is no other option, you run the risk of puttign current though bearing and all sorts of bad things. So it will have to be removed from the engine one way or the other. Aluminum can take plenty of heat and you may be better off using heat and trying to remove the fitting. If you heat it up let it cool some then put a penetrating spray on it, repeat several times in a well ventialted area. Alternately you could try pickling the entire thing in a mild acid solution, clean with fresh water and then try the heating method.
I could post a picture but the essential issue is connecting two pieces of steel pipe. Don't think a picture of two pieces of pipe will contribute much.

Yes this is the dry exhaust pipe between the block and the water injection elbow. All that heat and salt water for 30 years has welded these pieces together quite firmly.

Regarding removal, I know all the tricks: heat then soak with PB Blaster, heat then soak with Kroil, tap, soak, let it sit, soak, heat, tap, curse, soak some more. The only way this is coming out is the method Um Saudade suggests; cut the pipe off flush, cut channels out of the pipe inside the hole and piece it out.
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Old 21-02-2016, 19:11   #8
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Re: Welding a pipe in the exhaust system

Quote:
Originally Posted by Snowpetrel View Post
Welding steel pipe, if it's not too rusted is easy enough. Even with a stick welder. Should get near enough to 90% strength.

I've welded a few galvanized exhaust risers. Seem to get 5-10 years out of them. The welds don't seem to be the weak spot. They always go where the hot salt water gets injected.
Thanks. This is what I'm looking for. In my engine it isn't the riser that's the problem but the dry exhaust pipe between the block and the riser. My riser is aluminum and in pretty good condition as is most of the pipe. It was just the very tip where it entered the Al riser that rusted away.

So the engine vibration didn't break the welds you did at the riser?

If I could get 5-10 years out of this it would good enough.
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Old 21-02-2016, 20:25   #9
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Re: Welding a pipe in the exhaust system

Working on a exhaust for generator right now. I'm worried about the weight of it breaking/ cracking the exhaust manifold


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Old 21-02-2016, 20:28   #10
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Re: Welding a pipe in the exhaust system

Hit send before picsClick image for larger version

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I need to support somehow, real worried what will happen over time with vibration. Not real happy with the set up


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Old 21-02-2016, 21:44   #11
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Re: Welding a pipe in the exhaust system

Quote:
Originally Posted by skipmac View Post
Thanks. This is what I'm looking for. In my engine it isn't the riser that's the problem but the dry exhaust pipe between the block and the riser. My riser is aluminum and in pretty good condition as is most of the pipe. It was just the very tip where it entered the Al riser that rusted away.

So the engine vibration didn't break the welds you did at the riser?

If I could get 5-10 years out of this it would good enough.
If you must weld..........

For strength and addressing the rust factor use a sched 80 socket weld coupling. Will be plenty strong and easy to fit. If you don't have access to one a regular steel NPT coupling will work just use a lathe and bore out.
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Old 21-02-2016, 22:58   #12
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Re: Welding a pipe in the exhaust system

Quote:
Originally Posted by brantleychuck View Post
Hit send before picsAttachment 119376Attachment 119377
I need to support somehow, real worried what will happen over time with vibration. Not real happy with the set up


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I have had an identical situation on my Universal M 40B except my pipe isn't fused to the block, it is rigidly connected though and is subject to all of the vibration. I've had it welded twice. The second time I asked the guy to built me a new one and he just re-welded the ugliest hugest sleeve over it. His recommendation was to, the next time it cracks, build a new pipe and put a piece of flexible SS motorcycle exhaust pipe between it and the block to absorb the engine vibration. Something like this:

JEGS Performance Products 30770, JEGS Universal Flex Couplers | JEGS Performance Products
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Old 22-02-2016, 08:32   #13
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Re: Welding a pipe in the exhaust system

I have all the welders and the machine shop and know pretty much how to use it. I would remove the stub and replace with new.It sounds like you are not a welder, don’t have machine tools and want to pay to have someone cobble it up.

If you ding up the female thread a little it will still seal just fine. Cut a little less thread on the pipe end when you replace it so you engage on a bigger diameter on the male threads.

It is out in less than an hour tops, including setup and cleanup. Meanwhile you are still trying to find someone you can pay good money to do what is at best a temporary fix.

Neither TIG or MIG are very rust friendly, neither like less than perfectly clean and oxidation free metal. Stick works better on rusty stuff, particularly E6010.I would weld with a machined coupler or sleeve and probably use oxyacetylene and braze it with silicone bronze.Unless this is straight off an exhaust manifold with no cooling jacket it will take the heat just fine.

On using heat: You always try to heat the part with the largest diameter as you want the clearance between the parts to increase, thus breaking the bond.Heating the smaller diameter part ( such as the bolt inside a bracket) can result in a worse mechanical bond than you started with, especially with dissimilar metals.Does not happen all the time and once and a while it works just fine, but you don’t know before hand how those odds will play out.

Magic solvents don’t do much to pipe thread. There is no space for it to run in and do its thing.
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Old 22-02-2016, 09:21   #14
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Re: Welding a pipe in the exhaust system

I had the dry exhaust section go on my old engine years ago. The yard fabricated a whole new one from scratch from welded steel. It was square, not round like the original, but it lasted fine for 10 plus years and was still fine when that engine was replaced for other reasons.

I was a sales rep (not a welder) for a while for a repair welding company 40+ years ago. Your repair is possible but would be considered a specialist welding job to be done by an experienced welder. From what I recall the cleanliness & preparation of the weld is key (V angle, etc) and you will need to do it all on a bench "downhand" so you can get above the job all round the pipe. If it still connected to the aluminium heat exchanger, be aware that aluminium will soak the heat away from the job very efficiently, so preheating that part will help the weld penetration into the steel. You can get specialist low amperage arc welding rods - or at least you could do when I used to sell them - which are designed for this sort of work. If using arc rods you will need several passes and be sure to clean out all the slag - no inclusions in the weld. What we used to call "low hydrogen" rods can be self peeling. I have little knowledge of TIG or MIG welding so cant help with that.

Still tend to think you'd be better off getting the old pipe out if you can, though.... Can you weld something to the pipe to help you turn it?

If heating, it is definitely the aluminium you need to heat up, not the steel pipe.
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Old 22-02-2016, 09:23   #15
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Re: Welding a pipe in the exhaust system

OK. Time to get serious.

Photos and further details.

The first photo is the heat exchanger which also passes the engine exhaust. 90 degree exhaust elbows come off the block and bolt to the bottom of the heat exchanger. An internal passage sends the exhaust out the pipe on the end to the mixer elbow where the raw water is injected and passes out the exhaust hose.

In the photo the original elbow where I was able to remove the rusted pipe is on top, the spare which I cut off leaving some pipe is on the bottom.

So I see a couple of options.

1. Attach the spare elbow with pipe to the pipe coming out of the exchanger. This is the easiest and cheapest but is it "good enough"? In this situation, for me good enough would be a reliable fix that will give me min 4-5 years service. The pipe on the elbow is very solid with very little loss of material to rust or corrosion as is the pipe out of the exchanger for the first several inches.

2. Get the pipe out of the exchanger and go with all new pipe. This would be doable but will require cutting the pipe off flush and cutting it out of the female hole in the exchanger in pieces.

BUT!!

There's another issue. The engine is mounted with a V-drive and facing backwards in the boat. This means the front of the block (aft in the boat) is higher than the rear of the block (fore in the boat). The exhaust pipe comes out of the block front side and has a slight rise (see the drawing). This means that any residual water in the elbow runs down to the block and can wreck havoc. A friend with a sistership just had to replace his engine because the elbow corroded out and water drain back into the manifold and severely rusted the head and exhaust valve in the first cylinder.

So while I'm doing all this I would also like to somehow make angle the pipe down so the water runs the right way. But I can't angle it down too much due to clearance issues.

Now I'm thinking a new pipe with a bend in it? What about welding the two together using an angled sleeve?

Definitely not trying to cheap out but don't want to get too insane with a 30 year old engine. I do have access to a machine shop but not MIG or TIG.

Thanks all !!
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