Cavitation in head of power engines

[Weldinspect]

Dear friends, a client has found a cavitation problem in his exhaust systems of large 18 piston power engines, it´s happening in all heads and at the same place. Any ideas of why this is happening? please see attached pictures.

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[TugboatEng]

Cavitation in the coolant passage around the exhaust port? That's caused by insufficient head pressure on the cooling system.

Or, are you seeing corrosion of the exhaust port? That might be a result light loading and high sulfur content in fuel.

 

[Weldinspect]

here is another picture and waiting for more info from our expert, thanks TugboatEng

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[Tmoose]

Hi weldinspect,

Is the area surrounded in red in the attached image what you consider "cavitation?"

 

[TugboatEng]

Are any of the engines sharing exhaust stacks?

 

[catserveng]

Cavitation erosion mainly impacts cylinder liners, but can also show up in water cooled manifolds and turbo housings, in cylinder heads, and other areas in an engine of relatively high surface temperatures and low coolant flow rates. Here is a nice summary from Cummins,

https://www.cumminsfiltration.com/s...oduct_lit/asia_pacific_brochures/3300963A.pdf

The pitting in your picture looks more like a corrosive attack, I'm assuming this is an exhaust port based on the color of the deposits, correct? Although I have seen corrosive pitting and erosion on large turbocharged engines in high ambient humidity environments in the inlet valve pockets as well.

Could be the result of high sulpher and/or vanadium if this engine is using HFO or a heavy marine diesel oil, could be due to extended run times at lower loads, a shared exhaust system as mentioned above, or several other factors. Had one a few years ago that had a pin hole leak in the liner wall that only allowed coolant to leak when the engine was at a higher temp and load, the indication was a low cylinder temp, and when we pulled the head, both exhaust valve pockets had similar erosion, pulled another head and its exhaust pockets didn't show the erosion, so we looked harder, finally found the problem.

If this is affecting all cylinders as you said, likely fuel or air system related, could be a possible leak if engine equipped with a charge air cooler.

Hope that helps, MikeL.

 

[enginesrus]

So what are we looking for?
First off uneven valve seating, second looks like some carbon flaked off and from sitting a bit of rust showed up.
And could be some combustion gases blowing trough on to that area that is rusted and maybe a bit eroded, and is that a burned area on the seat at 4 oclock? That is one of those we need to see it in person deals.

 

[Weldinspect]

-Not shure about the exhaust sharing, this is a clients plant I will search
-Yes exhaust port
-The burn at 4 o´clock, I have to ask

Thanks everyone, I will ask my client for more answers

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[gruntguru]

It looks like the second exhaust valve for this cylinder is also at 4 o'clock in the photo which means the seat area indicated is the hottest part of the combustion chamber. Blue discoloration of the seat in this location may be normal for this engine - have you checked? Is the valve rotating? (helps distribute heat around the circumference of the seat) Does the valve itself display similar heat concentration?

je suis charlie

 

[Artisi]

A closer camera view would help.
It looks like corrosion erosion.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[Weldinspect]

Blue discoloration ... have you checked? No, we will include it in our next
Is the valve rotating? Will have to check with the owner
Does the valve itself display similar heat concentration? Will have to check thanks

Better pictures... you bet we wil ask the owner to get them Thank you

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[enginesrus]

So it looks like it has 2 exhaust valves per cylinder? How is the other port?
What brand of engine, number, rpm's, turbo or not? What is the fuel being used? And how many hours running when this showed up?
What is the engine used for? Marine, electric generation, etc.

 

[Weldinspect]

@enginesrus
Yes, 2 exhausts per cilinder
Only one port has the problem
Brand: Wartsila 46
RPMs, not sure
Yes they have turbos
HFO is the fuel
More than 100,000 hours
Engines used for power generation (Electricity)

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[catserveng]

So a Wartsila 18V46? 500 RPM at 50 Hz, 514 RPM at 60 Hz are the most common ratings as I remember.

"HFO" covers a broad range of fuels, so getting some more specific info on the fuel may be helpful.

I guess a good next question is what did Wartsila say? Have you or the owner contacted them for their opinion? In my dealings with them in the past I always found them very professional and helpful.

We had a similar issue on the Mak VM43 generator set engines that was related to a combination of fuel contaminants (Vanadium and Sodium) and low load factors, and was more noticeable on the exhaust valve pocket away from the manifold.

You state 100,000 hours on the engine, how many hours on the heads?

You may have better luck at the Wartsila user forum here,

http://wartsilausersgroup.com/forum/

MikeL.

 

[enginesrus]

Still looks like an uneven seat (photo's only do so much) and hot localized turbulent gas erosion. If it was strictly fuel chemistry related all the ports should show some sort of distress. I agree contact Wartzila, and please keep us updated on what they have to say.

 

[Weldinspect]

Yes, 60 Hz
It´s a clients engines and right now I don´t have more info but will search
The heads are the same age
Wartsila has not being contacted yet, maybe because of budget matters
I udnderstand fuel is very contaminated, very user around here is complaining about it
Will keep you posted guys thank you

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