Encapsulate stainless muffler?

[nimrod1230]

As per title. My stainless muffler which looks in as new condition has developed 4 or 5 holes maybe 1.5mm dia. Only 1 by a weld, the others beside internal webs. Various opinions from classic weld pinhole problems to resonance pulse damage. The muffler has bracing tubes across the main body sections to prevent deflection and had heavy rubber sheet glued to all flat sections. I have had the holes welded but would it be belt and braces to encapsulate the entire muffler with grp? As it fits inside an engine bearer it is difficult to keep an eye on any problems and is extremely difficult and time consuming to remove. A new unit is £2k and not presently in stock. What are your collective thoughts?

 

[DownWest]

Our resident expert will be by soon but it sounds like corrosion from welding altering the metal, either from inside with the webs, or outside from welding up the box.
Replace with a Vetus plastic one?
I took out a Volvo SS muffler/lifter box, that had corrosion and replaced it with a fabricated GRP one. Main reason was it didn't have enough capacity and water was getting back to the engine. The corrosion was serious, but not visible 'till I got it out.
To add: covering it with GRP would work, doubt that it would stick to the SS well, but even if the ss rotted low down, as long as the input & output pipes remained sealed up in place, any seepage of water would be minimal.

 

[PCUK]

If you're going to sheath it, use epoxy and bi-axial cloth. That will make a permanent job. What size are the inlet and outlets on the muffler as we have a spare Halyard Marine GRP muffler with 3 inch in and out!

 

[Graham376]

I found the problem with encasing in grp is the inlet and outlet exhaust pipes wouldn't fit if a larger diameter and the different coefficients soon allowed the two materials to part a little and leak around the unencapsulated pipe stubs. Fabricator should be able to make a new stainless one for far less than £2k. Replaced ours with a grp one.

 

[vyv_cox]

Difficult to advise on the metal problem without knowing the composition of the sheet and the filler metal. I would hope at least 316L with the same filler, better for the application would be 309 or 347. Did the pits appear randomly, anywhere else on the muffler body or only associated with welds? In either case it seems likely that more will follow.

I know of at least one water tank that suffered severe weld corrosion that has been repaired successfully with epoxy and biaxial cloth, only on the welds, not the whole tank. With good preparation by abrasives the adhesion should be good.

It's the thermal cycling that will make the difference compared with your problem. Not sure how well the adhesion would survive.

 

[nimrod1230]

Thanks for your thoughts. I think I’m on my own on this one. Difficult to re engineer a new muffler position due to space though not impossible. Not too confident on sheathing being anything other than a temporary fix. May have to bite the bullet and spend whatever on a new one.

 

[William_H]

If you want to sheath the muffler. You really need to view the repair as building a new muffler using the old as a male mold (which is left in place). ie make the GRP really thick and as said bring it down to cover the inlet and outlet pipes. I imagine min 4mm thick all over. I think you could use polyester resin as even epoxy will lose it's adhesion to the ss with heat cycles but the outside should remain solid if thick enough. Use glass cloth cut on diagonal or CSMat. olewill