Genset elbow longevity - how long should they last?

[Simi 60]

As the title says...

We had what I assume was the original cast aluminium elbow on ours and at around 2000 hours says the hour metre, it got a gradually worsening hole which I Mcguyvered together for another season with aluminium plate over hole and epoxy glue bandage.

Last time out we had it addressed, a new ebow welded into the stub and 456 hours later we have a bloody hole in it.

What's the story here?
Shouldn't have crapped out this fast surely?

Today's fix is a screw, as the weeks go on it'll get worse and require more creative "fixes".

 

[rslifkin]

It'll depend on the material and design. Some seem to last forever, others not so much. And number of years exposed to salt water can be as much of a factor as hours.

I'd expect good stainless or thick cast iron to last longer than aluminum. A design that drains fully at shutdown will help as well.

 

[Simi 60]

It'll depend on the material and design. Some seem to last forever, others not so much. And number of years exposed to salt water can be as much of a factor as hours.

I'd expect good stainless or thick cast iron to last longer than aluminum. A design that drains fully at shutdown will help as well.

It's a copy of the previous
Machined billet now vs cast then
Just over a year now vs 10+ years then
And both drain fully on shutdown, hole is on the top side.

 

[O C Diver]

I don't really see generator exhaust elbows as any different than primary engine exhaust elbows. A stainless steel one made out of 316 stainless should out live your generator.

The wrong alloy of aluminum won't survive whether it remains full of water or drains completely. BTW, aluminum is becoming far more common as an anode. Maybe your exhaust elbow became the sacrificial element on your generator. How's the anode in your heat exchanger?

Ted

 

[Pete Meisinger]

Aluminum exhaust elbow? Never heard of such a thing.

pete

 

[Simi 60]

. How's the anode in your heat exchanger?

Ted

First thing I checked.
About 60% of new.

 

[jungpeter]

Aluminum exhaust elbow? Never heard of such a thing.

pete

Ditto. Aluminum in the presence of hot saltwater in an exhaust system-NOT! Seems like one of the poorer choices I've heard of.

OC Diver, would you please share the manufacturer of your generator?

Regards,

Pete

 

[jungpeter]

Hi OC Diver. Aluminum being used as a generator exhaust elbow may be the poorest choice I've ever encountered. Strongly suggest you replace with stainless steel or ferrous alloy at your first opportunity.

And regarding your question of longevity in exhaust elbows, my rule of thumb (assuming a proper choice of design and material has been made in the first place) is ten years. I routinely remove, clean and inspect mine every five years (generators AND mains), and plan for replacement after ten, irregardless of engine hours. This may be fairly conservative, but failure of an exhaust elbow can be insidious and internal, and can have a poor outcome.

Regards,

Pete

 

[jungpeter]

I don't really see generator exhaust elbows as any different than primary engine exhaust elbows. A stainless steel one made out of 316 stainless should out live your generator.

"should". One of the worst words in the dictionary, whose meaning ought to be erased from the public mind. For every exhaust elbow that has "...outlived your generator", there are thousands in the trasheap that have failed. 316 stainless or other ought to be routinely cleaned and inspected, and an integral part of a routine replacement plan. To assume 316 stainless elbows "should" live in perpetuity in any water cooled marine engine exhaust is (in my opinion) a path to grief.

Regards,

Pete

 

[O C Diver]

Ditto. Aluminum in the presence of hot saltwater in an exhaust system-NOT! Seems like one of the poorer choices I've heard of.

OC Diver, would you please share the manufacturer of your generator?

Regards,

Pete

I'm not the OP with the problem, but my generator in this boat is an Onan / Cummins with a Kubota engine.

Ted

 

[jungpeter]

I'm not the OP with the problem, but my generator in this boat is an Onan / Cummins with a Kubota engine.

Ted

Hi Ted. Thanks, I understand you're not the original poster. I've responded directly to his original post as well.

Regards,

Pete

 

[O C Diver]

First thing I checked.
About 60% of new.

Is your heat exchanger electrically isolated from the engine? It might be worth a continuity test between the exhaust elbow, the heat exchanger, and the raw water pump.


Ted

 

[Simi 60]

Ditto. Aluminum in the presence of hot saltwater in an exhaust system-NOT! Seems like one of the poorer choices I've heard of.

OC Diver, would you please share the manufacturer of your generator?

Regards,

Pete

Reading through posts on cruisers forum it seems that smaller Westerbeke, Volvo, Nanni, yanmar, Perkins use aluminium for exhaust elbows

And, like previously mentioned. Near 2000 hours on previous cast aluminium elbow.

Ours is a Kubota based Diecon engineering build

 

[Simi 60]

Is your heat exchanger electrically isolated from the engine? It might be worth a continuity test between the exhaust elbow, the heat exchanger, and the raw water pump.


Ted

Water pump should be - it's 240v, mounted off engine and connected by hose.

Heat exchanger has rubber mat between it and engine but is held on with S/S hose clamps which "may" allow continuity

 

[kchace]

This past fall I pulled the 31 year old aluminum exhaust elbow off my Westerbeke 12.5 thinking it must be on borrowed time but it is in excellent shape! I had already bought the replacement so I put it on, also aluminum. Must be the alloy. Guess it will outlast me….

Ken

 

[Simi 60]

This past fall I pulled the 31 year old aluminum exhaust elbow off my Westerbeke 12.5 thinking it must be on borrowed time but it is in excellent shape! I had already bought the replacement so I put it on, also aluminum. Must be the alloy. Guess it will outlast me….

Ken

How many hours?

 

[BruceK]

Aluminium/Aluminum(spelt and pronounced differently in OZ and USA) can vary in composition, we used a harder version called Duralium as the skid plate under rally cars, way better than ordinary aluminum plate.

 

[kchace]

how many hours?

5300

 

[sunchaser]

Our WB Al elbows show no sign of wear after 8 years which is our change out interval. When we bought the boat new I was skeptical, no more.

 

[diver dave]

Non copper containing alloys of Al should be used. So, 6000 series is a bad choice.
They are expensive, but a portable XRF is a great investigative tool.

For cast alloys, this is a good reference if you want to avoid corrosion https://www.sciencedirect.com/topics/materials-science/cast-aluminum-alloy

 

[diver dave]

Aluminium/Aluminum(spelt and pronounced differently in OZ and USA) can vary in composition, we used a harder version called Duralium as the skid plate under rally cars, way better than ordinary aluminum plate.

Duralium contains Cu; good choice for strength, poor for corrosion....
similar to 2000 series....

 

[rslifkin]

Alloy will make a difference for sure. And if it's a thick, heavy casting, it may also be working on the "even if it corrodes, it'll take a long time to reach the point of failure" method of design.

 

[Bernman]

Using the Aviation Failure philosophy (my expertise) you can "Fly to Failure" or perform "Periodic Inspection".
I would say with the old 1 installed you need to inspection every 100 hrs. Obviously needs to be removed or accessed and looked at for material lost from the inside.
Remove find corroded/wear spot, remove bad material, take a straight edge across bad area and use a piece wire of known thickness to measure material lost. For example if elbow is 0.125" thick & material loss is 0.625" that's 50% loss.
How comfortable are you with the remaining material is the next question, 50% is a lot.
Put a tag on the unit with inspected date, remaining material AND NEXT DUE DATE. My opinion 20% is good time to Repair or Replace.
Aluminum corrosion can spread quickly, daaa. Material needs to match application.
New unit knowing you got 2k hrs> Personally with same material, start with Inspection at 500 to 750 hrs and reduce interval based on % loss.

Not to be critical but be cautious of statements such as no wear showing. This application requires an internal inspection for material loss.

 

[arcadia]

1 st Onan lasted 16 years 13.5 kw. Second Onan lasted two years 7.5 kw We were told by Cummins mechanic
This model was a lemon. 0 help from Cummins. Did get some help and a sorry from broker and Beneteau.

 

[Circumnavigator]

On Fintry, one of the two original cast iron elbows on the two Northern Lights generators failed after about 2200 hours. The replacement is stainless. The other went about the same and then we swapped the generator for a 12kW when we added the gyro stabilizer.


Jim

 

[Southern Boater]

I certainly agree with a previous post about internal hidden corrosion.
While doing a routine strip down and inspection/replace on the new to me boat, it was advised to remove and check/replace the SS exhaust elbow on the 2006, 950 hour, Cummins/Onan 7KW, as this was a “known” failure point. Other cruising forums had also identified this elbow failure location.
Sure enough, right at the junction point where the smaller raw water pipe injects to the larger sleeved exhaust gas pipe, it was 2/3’s corroded/pitted away.
The elbow needed to be cut apart to view this, as it was internal, so I was taking a guess initially, and at $1000 AUD, not cheap either, but still cheaper than having to rebuild the Kubota because of sea water ingress.