Got the generator running

[dLj]

With all due respect, the question of if or where a sacrificial anode is has nothing to do with this specific problem, even if there is "splashing". This is in a dry location within this HX. Dry locations are not protected by sacrificial anodes. Just a FYI.

dj

 

[All U Get]

I cleaned up the Hx flange and will try some J-B Weld, hopefully to get us back north and then look at getting a new one. I took the mixing elbow ashore to clean out the carbon, less than a tablespoon. If you look over my coffee cup you can see where the elbow is divide. The raw water flows to about that pin before mixing with the exhaust. Both Hx and elbow were new in 2013, the elbow looks nearly new.

 

[dLj]

Can you take a photo of the flange connection end of the elbow also please? Like the one you took on the opposite end from the flange showing the inside. Can you perhaps put a flashlight into the elbow from the opposite end from the flange to illuminate the internal surface?

dj

 

[All U Get]

Hope these are good for you.

 

[DArcy]

What material are the heat exchanger and the mixing elbow? It really looks like galvanic corrosion. I can't see how it would not be wet with sea water most of the time since the water injection is right above the flange. Maybe an appropriate anode is required.
When assembling, try to isolate the two parts electrically as much as possible. It will be challenging since they are bolted together. Maybe some tefgel on the screws would help.

 

[SycloneDriver]

I thought I saw a long slot of galvanic corrosion in the very first picture, but it might be a shadow. If that's the case then an anode, aka zinc, probably wouldn't help.

If it's leaking at the flange, just have the flanges resurfaced and call it a day.

You can use a file to easily find high and low spots on flanges. Even new parts need checked, especially if they are hard to reach or prone to leak.

 

[dLj]

Apologies I still have some questions - see photos below. Does it look like that flange is welded onto the heat exchanger? And can you please measure the two diameters?

 

[dLj]

It looks from here that both the HX and the elbow are a cast aluminum. Can you confirm if they are both aluminum? I do not see indications of galvanic corrosion. It is looking like an under-deposit corrosion mechanism. I would like to know the diameters of the holes both coming out of the HX and the hole going into the elbow. It's also looking like that flange might be welded onto the HX, but it is hard to tell from the photos. That would be a bit unexpected, but hey, I don't know how they made that HX.

dj

 

[JamesG161]

Can you confirm if they are both aluminum?

Magnet on the exchanger will confirm cast steel or not.
The riser appears to be stainless steel.
Jim...

PS: The amount of Carbon in the riser should not be an issue. Looks very clean considering hours on genset.

 

[dLj]

Magnet on the exchanger will confirm cast steel or not.
The riser appears to be stainless steel.
Jim...

PS: The amount of Carbon in the riser should not be an issue. Looks very clean considering hours on genset.

I guess they could have made it from cast stainless steel. But that seems unlikely to me. You say riser - you are referring to the elbow?

dj

 

[JamesG161]

You say riser - you are referring to the elbow?

That is what is called on my Volvo Penta by Perkins.

The mixing elbow that exhaust is quenched in.
Jim...

 

[All U Get]

Apologies I still have some questions - see photos below. Does it look like that flange is welded onto the heat exchanger? And can you please measure the two diameters?
View attachment 174100

View attachment 174101View attachment 174102

Yes, 40 mm on the Hx flange and 42 mm on the exhaust elbow. Hx was non-ferric per my magnetic test, my engineer friend said aluminum would create havoc with the cast iron block. The elbow may be stainless which might be the reason for galvanic reaction. Could the Hx be magnesium? I resurfaced the Hx flange with J-B Weld temporally unless it works.

 

[dLj]

Yes, 40 mm on the Hx flange and 42 mm on the exhaust elbow. Hx was non-ferric per my magnetic test, my engineer friend said aluminum would create havoc with the cast iron block. The elbow may be stainless which might be the reason for galvanic reaction. Could the Hx be magnesium? I resurfaced the Hx flange with J-B Weld temporally unless it works.

There is no problem with the HX being aluminum and the engine block being cast iron. The HX could be a.magnesium casting, but I doubt it. I don't see any driving engineering rationale for doing that.

It is possible for the exhaust elbow to be made from cast stainless steel. But that would still not usually make for a problem with dissimilar metals galvanic corrosion. Stainless steels tend to be more passive in that setup. In any case it would be good to positively identify what each component is made from.

I'm going to take a look at the two different diameters but I am on my cell phone so can't at the moment.

You are heading home to New Hampshire at the moment, correct? Your JB weld should get you home. But you sure need to know the root cause when performing permanent fix.

dj

 

[JamesG161]

My guess is Sulfurous Acid corrosion from the hot exhaust gas. Not Galvanic corrosion.

Galvanic corrosion requires that flange to stay flooded with water.
Jim...

PS: Our Zinc discussion was on the HX internals, not the Exhaust gas quench.
PSS: No Zinc needed if the genset engine is "electrically connected" to your prop/shaft zinc.

 

[DArcy]

Galvanic corrosion requires that flange to stay flooded with water.

Galvanic corrosion does NOT require the dissimilar metals to be flooded. I have done a bunch of salt fog testing which exposed galvanic corrosion problems by just wetting the surface intermittently.

 

[JamesG161]

just wetting the surface intermittently.

Galvanic requires a conductive path through water. The design of that quench system, has no liquid water where the apparent corrosion is seen, unless it is flooded [perhaps intermittently in heavy seas and muffler slosh back].
Jim...

 

[dLj]

Magnet on the exchanger will confirm cast steel or not.
The riser appears to be stainless steel.
Jim...

PS: The amount of Carbon in the riser should not be an issue. Looks very clean considering hours on genset.

The amount of deposit on the riser does look normal and should not be a problem. But the amount of deposit on the HX does not look as normal to me. Here's one of the original images prior to cleaning with the arrow that @All U Get put in to indicate where the leak was.

This image to me is rather confusing. You can see the 8 holes from the mixing elbow imprinted onto this flange, but none of those holes line up with holes on the flange itself. In this image, it appears that the gasket is still on the flange. It's a square gasket, smaller than the HX flange with four holes closer together than the holes on the HX. Here's the image with the surface cleaned off:

Looking closely into the holes, they don't even look like bolts were in there. How were these two parts held together? It's just not all making sense to me. It looks like mismatched flanges and however they bolted them together may simply have not given the correct sealing pressure.

I think at this point, all I can do is wish @All U Get good luck in getting home. Do let us know what you find out in the end. From my arm chair position, I can't reliably give an answer to this problem. I'd have to see the whole setup.

dj

 

[DArcy]

Thanks for bringing this up @dLj I was really confused about the round peg in a square hole appearance of this setup. It looks like someone grabbed whatever water injection pipe they could find and strapped it on regardless of the fit.

 

[All U Get]

Just a little update on the mixer elbow connection, after filling the Hx flange flat from adding J-B Weld where the corrosion took place, I had two stainless bars fabricated so I could secure the round mixer elbow to the square Hx flange. I applied some perma-tex to both sides of the gasket then managed to get it together. I also added Tef-gel to the bolts to try and isolate some of the galling which may have been a factor before. This also offered me the option of using bigger bolts instead of the little ones tapped into to the flange in 2013, you can see those in my earlier posts.



No leaks during my testing.

 

[JamesG161]

I applied some perma-tex to both sides of the gasket then managed to get it together.

I used perma-tex on my riser too [I didn't have the thin gasket replacement]. Works like a charm in the high temp service.

Hopefully it will still release someday.
Jim..