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Old 22-02-2016, 09:33   #16
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Re: Welding a pipe in the exhaust system

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Originally Posted by um saudade View Post
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 22-02-2016, 14:09   #17
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Re: Welding a pipe in the exhaust system

Why is the pipe so long? Can it be shortened much to reduce any bending loadings on everything. Provided both pipes are in good condition and a decent wall thickness, which they should be be to take a thread I see nothing wrong with getting a good welder to cut and angle the pipe down slightly then with a proper bevel weld it up with a stick machine.

The whole lot would best to be taken off so the welds can be done with good access and downhand.

I do like the idea of cutting out the threads. This looks like the only way to reuse that old riser with the rusted out stubb, if the other pipes have lost much metal that would be the best way to go.

I take it all these components are dry except the mixer. If so what caused the rust in the first place? An external leak, or was it internal rust?

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Old 22-02-2016, 14:33   #18
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Re: Welding a pipe in the exhaust system

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Originally Posted by Snowpetrel View Post
Why is the pipe so long? Can it be shortened much to reduce any bending loadings on everything.

The length is there for the exhaust to clear the block and have a clear run down to the water lift muffler. So can't really be shortened more than a fraction of an inch without causing problems.

Provided both pipes are in good condition and a decent wall thickness, which they should be be to take a thread I see nothing wrong with getting a good welder to cut and angle the pipe down slightly then with a proper bevel weld it up with a stick machine.

The pipe going into the exchanger is good up to the last inch or so. That can be cut off. The pipe in the spare elbow is even better.


The whole lot would best to be taken off so the welds can be done with good access and downhand.

Photo was taken sitting on the counter in the kitchen. Whole lot is now down at the welder/machine shop.

I do like the idea of cutting out the threads. This looks like the only way to reuse that old riser with the rusted out stubb, if the other pipes have lost much metal that would be the best way to go.

I take it all these components are dry except the mixer. If so what caused the rust in the first place? An external leak, or was it internal rust?

Correct, all dry until you reach the elbow. Rust was caused by water running back down the pipe from the mixing elbow (see the hand drawn diagram). As far as I can tell no damage to the valve or head but it did in the cast iron elbow (not in the pictures) that connects the exhaust port on the block to the bottom of the heat exchanger.
Went to the head guy at the shop and showed him all the pieces. Have dealt with him for several years and he's pretty good.

After looking at them he recommended leaving well enough alone and welding the spare elbow with the pipe stub to the pipe stub on the exchanger. He will reinforce the weld and add a couple of small plates along the side, like sister ribs. If that fails then the next step is to fabricate a whole new assembly.
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Old 22-02-2016, 16:04   #19
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Re: Welding a pipe in the exhaust system

If heating the pipe could be dangerous you can get a freezing solution in a pressure pack. Spray the inside of the fitting this works.
You should try and get a flexible joint as close to the engine as possible this will reduce the chance of cracking.
You can get a stainless steel flexible exhaust joint to do the job which will last.
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Old 22-02-2016, 20:56   #20
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Re: Welding a pipe in the exhaust system

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Originally Posted by skipmac View Post
Went to the head guy at the shop and showed him all the pieces. Have dealt with him for several years and he's pretty good.

After looking at them he recommended leaving well enough alone and welding the spare elbow with the pipe stub to the pipe stub on the exchanger. He will reinforce the weld and add a couple of small plates along the side, like sister ribs. If that fails then the next step is to fabricate a whole new assembly.
Sounds like a simple strong solution, and with water being kept out, it should last for a long time.

I usually lag the riser with fibreglass lagging tape, but the stuff does seem to stink and smoke for a while, and any salt water getting on it causes serious rust, but without it the damn things get real hot, can't stand those water jacketed ones. Had one fail and hydraulic an engine once, so I'm pretty wary these days of anything over fancy.

What did you have before, out of curiosity, or was it just left bare?
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Old 22-02-2016, 21:03   #21
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Re: Welding a pipe in the exhaust system

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Originally Posted by Snowpetrel View Post
Sounds like a simple strong solution, and with water being kept out, it should last for a long time.

I usually lag the riser with fibreglass lagging tape, but the stuff does seem to stink and smoke for a while, and any salt water getting on it causes serious rust, but without it the damn things get real hot, can't stand those water jacketed ones. Had one fail and hydraulic an engine once, so I'm pretty wary these days of anything over fancy.

What did you have before, out of curiosity, or was it just left bare?
Worst case scenario, the weld breaks after XX hours use on the engine and I just come up with a better solution so I figure why not give it a go.

Before I took it apart the pipe was wrapped with something that was probably 30 years old, greasy and smelly; probably was fiberglass. To replace it (once everything is all back together and working) I bought Titanium Exhaust Wrap
https://www.designengineering.com/ca...-lr-technology

Since it's still in the package can't tell you how well it works but gets good reviews.
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Old 22-02-2016, 21:27   #22
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Re: Welding a pipe in the exhaust system

That Titanium wrap stuff looks good. Careful with that old lagging, thirty year old lagging might make it asbestos..


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Old 22-02-2016, 21:28   #23
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Re: Welding a pipe in the exhaust system

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Worst case scenario, the weld breaks after XX hours use on the engine and I just come up with a better solution so I figure why not give it a go.
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Old 23-02-2016, 09:53   #24
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Re: Welding a pipe in the exhaust system

um saudade had the best input. Would it make sense to remove the heat exchanger so you could work on it on the bench. If you need to cut the threads it would probably be easier and less chance of getting the threads in the exchanger. That is a fine line when peeling out a pipe that way.
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Old 26-02-2016, 09:08   #25
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Re: Welding a pipe in the exhaust system

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Originally Posted by Cruisingscotts View Post
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.
+1 on the socket weld coupling (assuming you can't remove the nipple). Granted, it would be best to replace the nipple altogether, but I agree you might nevere get it out without destroying the mixing elbow. Order the coupling from McMaster-Carr.
McMaster-Carr
Also, if you can get the ends of the two nipples nice and clean (and assuming they're Schedule 80 pipe), you won't have to actually weld the coupling. Silver braze it with high-content silver (Silvaloy A56T, for example). I built a new exhaust for my A4 last summer, using 316 SS, but did a dry run brazing the raw water injection with steel pipe (photo). You silver braze that socket weld coupling, it'll last for years.
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