Cavitation Erosion Particle Size

[TugboatEng]

I have a high pressure piston type pump that is experiencing supply line cavitation erosion. Has anyone experienced wear or damage to a pump from erosion of the supply piping? I found this article which describes large amounts of particles in the 8-20 micron region which are much larger than the upstream 1 micron rated filter the manufacturer brags about.

https://caltechconf.library.caltech.edu/58/1/hattori.pdf

 

[Chumpes]

hello
you dont need abrasion with solid particles to activate erosion. erosion can occur even with full liquid or full gas systems.
maybe the pressure at inlet is so low that bubbles forms and promote cavitation. cavitation increases the average fluid velocity and promote impact-related damage.
regards

 

[TugboatEng]

I need to clarify, i have cavitation that is causing erosion. This must create particles. I am interested in whether any one else has experienced damage later in the system due to the presence of wear particles in the fluid.

 

[EdStainless]

If the particle count is low and velocities are fairly low then it is probably not much of an issue.
Is it actually cavitation tearing material off or is it knocking loose surface debris?

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P.E. Metallurgy, consulting work welcomed

 

[TugboatEng]

We are getting holes in pipe between the final filter and pump inlet.

 

[EdStainless]

What is the pipe material?
Is this associated with any fittings or joints?
What is the fluid and the max velocity?

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P.E. Metallurgy, consulting work welcomed

 

[TugboatEng]

It's carbon steel tubing, roughly 1" OD and maybe 1/32-1/16 wall, bent to shape. Think of automotive tubing. The erosion is occuring in a bend near the inlet to the pump. In response to the problem the manufacturer has added a section of PTFE/stainless braided hose to the section of tubing. This is supplying diesel fuel at 10 bar and ambient temperature to a 4 piston pump boosting it to 2200 bar.

 

[TugboatEng]

A follow-up question. What is the most cavitation resistant metallic material available in tube, that is bendable, and that is weldable or brazeable?

 

[btrueblood]

Is there any way to increase the feed pressure to the inlet of the pump (kinda surprising that you could get cavitation at 10 bar static pressure, but dunno the velocities that elbow is seeing). Could also be likely that there is a leaking check valve on the piston pump? Alternatively, look at locating the elbow farther away from the pump, and/or making the elbow radius larger, and/or adding a resonant damper on the suction line.

 

[3DDave]

I would expect that harder materials erode more slowly.

I think a cure is using a far larger filter element to prevent the formation of localized vacuum formation where the fluid exits or by easing the transition out of the filter to remove areas of high shear in the flow. It's possible the configuration has made the equivalent of a whistle generating the low-pressure needed to form the cavitation bubbles.

 

[3DDave]

See also -

https://www.valin.com/resources/articles/pop-cavitation-bubble-hydraulic-systems

which, among other things, recommends eliminating suction side filters in exchange for better filtration elsewhere.

 

[TugboatEng]

This is a variable displacement pump but I do not know the mechanism of operation. In another type of plunger pump displacement is controlled by uncovering a spill port. There is a pressure shockwave that causes erosion so a replaceable erosion plug is placed at the point of impact.

My problem seems to be that I am getting a similar shockwave on the suction side of my pump.

This system is under warranty so all worn and failed parts are quickly swept away and I don't get to witness anything. The warranty is about to end and I want to fix this once and for all once I own it.

 

[davefitz]

The cavitation occurs when the local pressure drops below the saturation pressure . The items that cause the pressure to drop to that low level downstream of the filter are related to the filter pressure drop which in turn varies by the square of the flowrate . If the flowrate varies depending on what part of the pump's piston stroke , then that pressure can be equalized to a constant pressure by using an inline bladder, implying a tee connection downstream of the filter and a bladder installed.

Another piping element that can cause erosion are sharp contractions /expansions that case a vena contracta to occur- and the typical effective flow area of a vena contracta is 80% of the nominal diameter ( ie 64% of the nominal pipe area) , implying a local drop in pressure below the vapor pressure.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick

 

[TugboatEng]

The flow velocity in this pipe is less than 1.4 feet per second.

I think the OEM's logic behind adding a 6 inch section of braided hose to the line was to act as a pulsation damper or bladder. My trouble here is that there is extremely limited space to add anything to the line.

 

[EdStainless]

You can go to an aerospace supplier and buy some 21-6-9 hydraulic tube.
It will be thin wall because it is 142-162ksi UTS.
1" OD x 0.052" wall is fatigue tested at 4500psi and has nearly infinite life.
Being a high Mn SS, it will resist wear very well.
The most cavitation resistant alloy that there are are soft Co based alloys.
But that is ridiculous.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[TugboatEng]

I do believe a harder stainless alloy will be the solution here. I have done this in centrifugal pumps before, replacing bronze parts that are experiencing mild cavitation erosion.with stainless. I appreciate the suggestion of a wear resistant stainless that is readily available. I will likely persue this route.