Circulating Water Pump Failure (Column break)

[yuswandi]

Hi, I all.
introduce of my power plant 625MW.
there are 3 circulating water pump (CWP A,B,C). medium seawater.
operating since 2010.
last year (2018), on august CWP B fail column break into pieces.
then on november CWP C fail also.
We focused on discusing about column material,Column material Cast Iron Ni Resist.
Is it acceptable pump column fail after 9 years ? (2010 until 2018), i mean is it on the range of lifetime that material?
for note : impressed current for cathodic protection since 2014 the function found not properly.
thank for any feedback

 

[LittleInch]

You really need to ask a good materials engineer or post in the metals and matalurgy forum.

Warm aerated seawater eats most metals, especially if there is no CP!!

A simple search shows there is Stress Corrosion Cracking on large NI resist castings

e.g.

http://cdn.intechopen.com/pdfs/4121...tile_ni_resist_irons_and_stainless_steels.pdf

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Artisi]

LittleInch is correct, you need a full analysis of the material and an engineering investigation as to that caused the failure.
It could be a material failure or a hydraulic problem or a combination of both.

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.)

 

[MJCronin]

This is a good reference for seawater pump material selection.

https://www.911metallurgist.com/blo...01/Materials-Selection-For-Seawater-Pumps.pdf

Bottom line:

1) Seawater is bad corrosive stuff and, as stated above, will eat most any material... be prepared to spend a lot of money on the fix.

2) Premium stainless steels (duplex and super duplex - not 304/316) are a more common modern solution.

3) The complete pump and all wetted surfaces must be carefully engineered. Different materials may be required in different parts of the pump assembly. Some materials are a good choice for parts of only certain fluid velocity ranges ... Higher fluid velocities may cause quick failure. The impeller must be of premium material.

Your picture does not give much information... When you say column failures, do you mean the exterior casing or the the pump shafts ?

Who made the pumps ?

Can you show us pictures of the pump impellers ?

How badly were they chewed up ?

MJCronin
Sr. Process Engineer

 

[Strong]

Was there any high vibrations observed or measured prior to the column failure? Was there any noticeable or measurable performance drop off that might indicate erosion or Cavitation at impeller and result in unbalance or bearing damage? Is the intake structure well designed to minimize vortex formation, sand/silt deposits and to keep debris from entering pump intake? You may have a materials issue, but something else may have contributed to premature failure.

Walt