Wet Exhaust Repair

Good Afternoon,
I'm helping a friend repair the wet exhaust duct work on a Grand Alaskan powered by Cat 3208s. There is a long section of fiberglass exhaust duct work that appears to have been laid up in place. With the exception of the joint where the duct joins the mixing elbow, all the bends and joints including those to the muffler appear to have been glassed in place. The duct is also faired into the aft bulkhead. The 8" duct work has been built up with fiberglass material (I'm assuming for strength). This original installation is leaking in several places and must now be repaired.

We are thinking of using commercially available 8" fiberglass exhaust tubing and elbows and reconstructing it as close as possible to the original configuration. This includes fairing the new ductwork into the bulkhead, building up the ductwork and making all connections permanent with fiberglass material.

Because of a confined workspace and need to control fumes (and the added strength), we would like to use a 2 part epoxy for our resin on all the fabrication. Does anyone see any problem with this application in a wet exhaust system? Any other input is appreciated.

Thanks in advance for any help.
Eric

 

I've watched this thread for a day hoping someone more familiar with epoxy than I would respond, I avoid a epoxy for reasons I won't go into, but do a lot of work on marine exhaust systems with polyester.
When purchasing polyester for exhaust systems I specify a high temperature, fire retardant resin. I'm not familiar with an epoxy resin with those properties but I'm confident one exists, most epoxy's don't do well with heat.
When you purchase your 8 inch tubing be sure to specify at a minimum fire retardant.
Some polyesters are made fire retardant by the addition of chlorine hydroxide, others are formulated to not support combustion without fillers and I prefer those. I understand the need to control fumes, overcome that and you can do a fine job with polyester.
Are you able to determine what caused the failure? high temperature, wrong product, or workmanship

 

Commuter Boats,
Thanks so much for the info and suggestions. It could be a materials or workmanship issue as there are several places where raw water is bleeding through the duct. Only one side presently shows these symptoms. It is leaving prominent rust colored stains which makes me wonder if metal tubing was used and is now disintegrating inside the fiberglass covered duct.

I’ve had good luck with epoxy resins on several other jobs but never tried a repair that will be exposed to heat. The repair is down stream from the mixing elbow so in theory the heat should not rise above a level where you can place your hand on the duct. I don’t know much about the heat resistant properties of epoxy but will check into the availability of resins designed for this purpose. I’m also comfortable with polyester resins so I won’t hesitate to use it if epoxy is just not suitable in this application.

Thanks again and I would welcome any other input or suggestions.

Thanks again,
Eric

 

The most common need for repairs that I see on wet exhaust systems is the result of interruptions in the water supply, when a water pump fails the exhaust temperature climbs much quicker than the engine temperature does. There are other reasons for interruptions in the waters supply and a alarm on the exhaust system will be a much faster indicator then the engine temperature alarm( a cooling water flow alarm would be faster).

Eric S
"The repair is down stream from the mixing elbow so in theory the heat should not rise above a level where you can place your hand on the duct."

The thermal distortion limit of most epoxies is near 200°.

 

Thanks again, your advice and comments are well taken. I have actually been considering exhaust temp/warning indicators for my boat.

I'll do some additional research and if not 100% comfortable with epoxy resin in this application, I'll go with polyester and just ventilate the heck out of the work space.
Thanks again for your help!
Eric

 

There are many very heat resistant epoxies (better say hardeners) on the market, they all have one disadvantage: they must be tempered to 180°C or even 230°C in three independent curing steps. A proven one is "Martens plus EP advanced" . Adding PORAVER® makes it even a bit more heat resistant but is not absolutely neccessary. So, if you have a good oven and install EGT gauges, youll have no problem.
Here is a test giving you some ideas how much these resins (incl. standard Epoxy) can stand:
http://lightweight-structures.com/images/stories/projects/hightemp.pdf

Regards
Richard