sailingdeacon
Member III
Probably a dumb question but i cant fine a for sure answer. If I construct an exhaust elbow riser out of black iron and bronze pipe, are they compatible?
Mix black iron pipe and bronze pipe?
sailorman37
Member II
The iron is less noble than bronze, -0.7 v compared to about - 0.25. If the iron is stout enough (meaning you can afford the corrosion), you'll probably be OK. Water boxes of cast iron were used to protect copper tubing. Take a look at the International Nickel attachment. Note their comment on painting. Also, the data is based on flowing seawater.
Brad
Brad
sailorman37
Member II
sorry the pdf cut off the second page. The second entry down on the left is steel and cast iron
sailorman37
Member II
If your joint is away from the seawater and dry, probably even less of an issue.
I would use neither attached to the manifold in an exhaust system, but galvanized instead. Do note the galvanized will give off nasty (toxic) fumes when first heated, so make sure you are well ventilated when you first run it. The one place I would use bronze is for the exit fitting through the hull.
looking for same ideas...
In the process of replacing an OEM exhaust mixing elbow on a yanmar genset. This is the 3rd replacement and the dealer admits that they only last about 5 years. I'm fed up with the $270 crap they sell so I am building one I hope I wont have to deal with again. The existing junk is a thin steel nipple into the cast iron mixing elbow. The nipple sheared completely off while the engine was running.
I'm making the new one with 1.5" NPT pipe fittings.
Considered bronze and I cant find any data to suggest its not good for this. Groco tells me their silicone bronze melts at 1800F so I think it will be fine for the dry nipple connection at the manifold. Never checked the temp there but I don't think its even close to that.
Stainless steel has a problem with pitting in an exhaust system and I have seen it with a previous thin SS setup on a genset. I will have no welds which is where the first problems seem to start. The Beta Engine guys I chatted with at the show said they use SS and never have any issues.
My idea so far is to go with 316 SS pipe fittings. 316 is not quite as strong as 302/304 but has better corrosion resistance. Since it's a single cylinder engine
I want a strong part that can handle the vibration. I found schedule 80 316ss nipples along with Hi pressure 316ss elbows. The elbows are rated for 3000psi steam. (not a typo). They have a 1/2" wall thickness and the schedule 80 pipe is about 1/4" wall thickness. I also sourced a 316ss hose barb for the 1.5" exhaust hose connection.
The thick-walled elbow may be overkill but will be good to drill and tap in a SS fitting for the water injection on the downside. The stuff isn't cheap but still less $$ than the OEM crap.
I may be wrong but I don't think dissimilar metals is a concern in the dry part of the exhaust (manifold to pipe nipple). None of it is immersed in liquid and any moisture is quickly dried by hot exhaust. None of my previous problems have been galvanic corrosion but rather hot saltwater/exhaust gas corrosion.
I replaced the aluminum elbow on my 62hp Perkins diesel only because it was corroding at the hose barb end where the wet exhaust was in contact. The dry upstream section was fine after 15 years.
I notice that lab testing of corrosion resistance on materials always seems to include hot saltwater spray.
OEM stuff for small diesels always seems to be cast iron and galvanized/black iron but the high-end big diesels now are touting SS exhaust systems. (I think all the premium car makers also use SS for exhaust)
happy for any input/experiences/opinions from all of you ....
In the process of replacing an OEM exhaust mixing elbow on a yanmar genset. This is the 3rd replacement and the dealer admits that they only last about 5 years. I'm fed up with the $270 crap they sell so I am building one I hope I wont have to deal with again. The existing junk is a thin steel nipple into the cast iron mixing elbow. The nipple sheared completely off while the engine was running.
I'm making the new one with 1.5" NPT pipe fittings.
Considered bronze and I cant find any data to suggest its not good for this. Groco tells me their silicone bronze melts at 1800F so I think it will be fine for the dry nipple connection at the manifold. Never checked the temp there but I don't think its even close to that.
Stainless steel has a problem with pitting in an exhaust system and I have seen it with a previous thin SS setup on a genset. I will have no welds which is where the first problems seem to start. The Beta Engine guys I chatted with at the show said they use SS and never have any issues.
My idea so far is to go with 316 SS pipe fittings. 316 is not quite as strong as 302/304 but has better corrosion resistance. Since it's a single cylinder engine
I want a strong part that can handle the vibration. I found schedule 80 316ss nipples along with Hi pressure 316ss elbows. The elbows are rated for 3000psi steam. (not a typo). They have a 1/2" wall thickness and the schedule 80 pipe is about 1/4" wall thickness. I also sourced a 316ss hose barb for the 1.5" exhaust hose connection.
The thick-walled elbow may be overkill but will be good to drill and tap in a SS fitting for the water injection on the downside. The stuff isn't cheap but still less $$ than the OEM crap.
I may be wrong but I don't think dissimilar metals is a concern in the dry part of the exhaust (manifold to pipe nipple). None of it is immersed in liquid and any moisture is quickly dried by hot exhaust. None of my previous problems have been galvanic corrosion but rather hot saltwater/exhaust gas corrosion.
I replaced the aluminum elbow on my 62hp Perkins diesel only because it was corroding at the hose barb end where the wet exhaust was in contact. The dry upstream section was fine after 15 years.
I notice that lab testing of corrosion resistance on materials always seems to include hot saltwater spray.
OEM stuff for small diesels always seems to be cast iron and galvanized/black iron but the high-end big diesels now are touting SS exhaust systems. (I think all the premium car makers also use SS for exhaust)
happy for any input/experiences/opinions from all of you ....
sailingdeacon
Member III
See photo of my riser. Despite every attempt I could not get the nipple unscrewed from exhaust adapter - nor the pipes. So bucks for another one. The mixer is the Onan discussed earlier. If the straight Y-pipe discussed earlier is cast I may go that way to save dollars, but I suspect it is stainless and I am just not comfortable with that since it will be at least partially wet. Before cleaning the pipes, there was a lot of scalling/rust on the black pipe especially at the threads, causing me to worry about the inside portions and a pipe break. I have a new ONan and trying to decide to keep the entire riser as shown as a backup. The Onan will unscrew I think. The pipes and Onan was replaced 500 ours earlier with holes in the pipe and riser.
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