thread407-509102 Reference this th

[Emenent1999]

thread407-509102
Reference this thread, now we have faced 8th big end bearing failure.
Can anyone provide details how Cavitation can be verified if there is any. As the other two pumps has same parameter but failure is being observed only in one

Also comment on the Babbitt of the bearings. Previous or old se bearings have ASTM Babbitt Grade 2 while new bearings which are failing have Babbitt Grade 3

Grade 2 Babbitt has high toughness due to low copper and high tin
Grade 3 Babbitt has high hardness due to relatively high copper and low tin

 

[3DDave]

Cavitation should not cause bearing failures. Usually it just destroys the surfaces inside the pump.

I would repair this pump, again, and swap it to one of the other positions.

If this pump fails in the different position, then start swapping parts between pumps** and see if the failure moves with them.

If the other pump that is moved to where this one is now fails, then it's a system design problem that will require a lot more information.

** This assumes they have interchangeable parts, like the crankshaft if it is a crank driven piston pump, or valves. The other posting never did give enough detail to identify the particular construction of the pump, like a maker and part number.

 

[1503-44]

I think I would change the bearings to Grade 2 before I'd go about swapping parts or locations with other units.

Provide some details about pump type, operating conditions and piping configuration and maybe we could try to actually help you. It could be a misalignment caused by thermal stress, but how could we tell you that with no info.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[3DDave]

I would too, if it weren't that the OP wrote the previously failed bearings were Grade 2.

 

[Emenent1999]

The Cavitation in reference is in the lubrication oil which is being provided to big end bearings of the crankshaft. It is a recip pump

The oil is fed from the lube oil pump to the small end.gudegeoj pin has a hole which aligns with the hole in connecting rod through which oil is supplied to big end bearings. It is quite opposite to normal recip machines.

Big end bearings are being damaged

 

[Emenent1999]

Attached is the picture of lube oil path

 

[Emenent1999]

The pump is a quintuplex pump having crankshaft with 6 main bearings (sleeve type) and 5 main bearings (sleeve type) lubricated by a lube oil pump.

 

[Emenent1999]

Please also comment if ESD can develop on the crankshaft which can deteriorate the Babbitt layer. The RPM of the shaft are 75 normal and Max are 117

 

[1503-44]

3DDave, it's Grade 3 thats failing, so I guess we agree.

Here's your posted image. Much easier than making us all download a copy. See the little camera icon? Try it.

Switch back to Grade 2.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[3DDave]

It is made difficult when pictures of the broken part are shown and no pictures of any of the other parts that could be doing the breaking. "Attached is the picture of lube oil path" was exciting until I saw it was another picture of the broken part and not a diagram from the pump, the oil galleries, any pressure regulator, or any other things that are supposed to deliver the oil to that bearing.

The other post listed the following, but made no comment on checking to see if the lubrication oil pump could develop the correct pressure.

•Connecting Rod Distortion.
•Cross Head Liner and cross head clearance.
•Cross head liner and housing clearance.
•Casing level checks.
•Thrust line run out.
•Crankshaft end run out.
•Crankshaft web deflection.
•Big end bore face straightness.
•Cross-head bore concavity and ovality checks.
•Cross-head straightness.
•Connecting rod deflection.
•Pump main bearing bore alignment.
•Main & Big end bearing clearance and ovality.
•Lubrication system port checks for blockage

 

[1503-44]

Given that its happening on only one pump and 2 out of 3 bearings are fine,
I think it's probably
Bearing material 95% probability, or
Other: 5% probability

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[Artisi]

Have you considered cavitation within the crankshaft journal / bearing interface?

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.)

 

[Emenent1999]

Sorry for the broken part picture. Now attached is the picture of oil passage.
The lube oil pump is gear type and is making enough pressure, we always check the lube oil path and flow before assembling the pump.

 

[Emenent1999]

Can you comment on ESD. Can ESD be developed in crankshaft having 75 to 117 RPM. And how can we check ESD without using proximity probes

 

[3DDave]

To have electrostatic discharge one must first have an electrostatic buildup. Where would the electrostatic charge be coming from?

To show the previous linked image:

 

[Emenent1999]

When 1st bearing got damaged. The white metal was seen to flow and melted. And this first damage consisted of Grade 2 Babbitt. The crankshaft got damaged also sowe have to replace the crankshaft with new one.

Afterwards when new bearings were used the OEM provided us with Grade 3 Babbitt and the failure mode shifted from melting to fatigue and chipping off the Babbitt white metal.

Till now we can't figure out the exact cause. And the difference of Babbitt was noticed yesterday. The failures are happening since 2021.

 

[Emenent1999]

Also coming to ESD. As in Steam Turbines, ESD can develop due to blades coming in contact with droplets of moisture etc. can electrostatic build up be developed with oil as in crankcase 1/3 portion is filled with oil, and their might be relative motion of crankshaft with oil

 

[Emenent1999]

1st damage

 

[Emenent1999]

2nd damage

 

[Emenent1999]

You can clearly see the difference of damage mechanism