Exhaust Riser Pipe Question

Reed · Post by **Reed** » May 14th, '05, 07:12

The Mary Alice is currently disabled in Southport, NC by a rusted out exhaust riser pipe after an amazing four day ride North on the Gulf Stream from the Little Bahama Bank. After going through pages of the Board archives on exhaust I've gleaned some excellent ideas on replacing my exhaust riser pipe, but I need some fine tuning from the CD brain trust. Should I be using black iron elbows and nipples for this job, or 316 stainless steel elbows and nipples? The engine, a BetaMarine 722, is only four years old, and I want this replacement to last longer than four years. Any and all suggestions would be appreciated. I'm only grateful that the riser didn't break off 100 miles off the coast on the run north.

Thanks, Reed CD31 #51 Mary Alice

Parfait's Provider · Post by **Parfait's Provider** » May 14th, '05, 09:16

Reed,

Parfait had a black iron riser with the Perkins. I can't say that it lasted all that long, it didn't see that much service. I don't recall ever seeing a stainless riser, but that could simply be a lack of experience with these things. It would seem to me that heft is important, especially between the engine and the water injection.

Oswego John · Post by **Oswego John** » May 14th, '05, 10:30

Hi Reed,

Whenever I deal with anything that concerns water, If possible, I try to use galvanized pipe and fittings. Black pipe would do the job but IMHO, I think that galvanized piping is better.

Fittings and precut and threaded nipples of varying lengths are readily available in popular diameters in most hardware and home supply depots. Don't forget to plate the threads.

Speaking of plating threads, I'd like to segue into a sidebar that will probably have little, if any, effect on the good people reading this. (Big yawn)

People don't realize that when you cut and thread a nipple using galvanized pipe, doing so eliminates the galvanizing protecting the threaded area. The raw steel threads can be protected by painting them with pipe dope or teflon. Precut nipples that you purchase are generally hot dipped, but not always. Also, pipe dope helps prevent leaks.

Good luck,
O J

Kurt · Post by **Kurt** » May 14th, '05, 15:50

Hi Reed,
Galvanized iron pipe should not be used for an exhaust system. I forget the exact reason why except to say that very hot galvanized pipe emits some type of toxic fume. There's a danger involved with it's use.
Instead, I suggest you use the standard cast aluminum elbow that is sold with the Beta 722. I have a Beta 482 installed in my CD27 and was able to use the standard (very long lasting) aluminum elbow in conjunction with a Centek side inlet water lift muffler. It was a tight fit, but worked out very well.
Kurt

Phil Shedd · Post by **Phil Shedd** » May 14th, '05, 19:19

Reed

Some time in the past the riser on Gamblin' CD 31was replaced by P/O.
The replacement was done in Stanless steel pipe and elbows. It works well and I hope it does so for a long time . Even now I am still cleaning up the carbon exhaust that was on everthing after the orginal pipe broke.

Hope this helps

Phil
Five days from launch

Reed · Post by **Reed** » May 15th, '05, 06:10

Thanks for all the feedback. Just to clarify: the raw water mixing elbow at the top of the riser is in excellent shape. The 10 inch pipe nipple it was sitting on top of had cracked at the bottom where it screwed into the elbow. The pipe threads had created a weak point, corrosion further weakened the joint and the weight of the whole assembly combined with the heat and vibration made this failure inevitable. It appears that using iron fittings for this job requires mandatory replacement every 3 years. Stainless steel pipe and fittings is the only way to go. Some kind of support bracket for the riser would also be a good idea. A failure of this assemby could be catastrophic under certain conditions.

Again, Thanks, Reed CD31 #51 Mary Alice

jambalaya · Post by **jambalaya** » May 15th, '05, 07:24

This was an exellent topic to offer to the Board. I don't know that I have previously seen a discussion of this, but since the failure potential is catastrophic, it is important. I have a new Beta 482 with high rise exhaust riser and am unsure of what the composition is. It does seem light weight like aluminum, but it may just be mild steel. Anyway, I didn't know the MTBF was so short. Sounds like it might be good to keep a spare on hand.
Will
Jambalaya

Warren Stringer · Post by **Warren Stringer** » May 15th, '05, 22:53

Another thing about exhaust risers:

On Eendracht, we had about a 6-8 inch galvanized riser leading to the mixing elbow. It was supported only at the bottom, at the exhaust manifold, and we twice had catastrophic failure shortly after running the engine at high (NOT maximum) RPM. It seems that the engine vibration set up a counter oscillation in the riser and elbow which fractured the riser within ten minutes. Beware - unless you look at your engine through its full RPM range you might not be aware of this happening. (And, as it turned out, we could not reach full RPM at the dock, only underway.) Our solution, after the second failure, was to bolt heavy steel braces to the engine, bend the ends upright and triple hose clamp them to the riser, then surround the whole riser with insulation. Since then we have had no more problem. Our engine is a Yanmar 3JH3E.

Warren
s/v Eendracht
CD 36 # 54, 1981

Bob Miller · Post by **Bob Miller** » May 16th, '05, 18:36

I am in the dairy business here in NY and we have a lot of stainless steel, so I fabricated a new riser assembly out of 304 grade stainless steel...316 is better as it has a higher molybdenum content and is easier to weld, but it costs a lot more. 7 years and counting and the pipe is still like new...even with the salt water. Hope this helps.

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