WKM valve failure

[24hrs]

Trying to do a root cause analysis of a pre 1974 2inch WKM gate valve. Dont really have enough information to help get this completed satfisafcatory.

My question is does any one have any experience with stem failure of this valve and causes.


I have found through research that 2inch valves are made from somekind of brass alloy any reason for that?

 

[gerhardl]

Brass alloy components were at that time quite common as metal price was lower, a lot of foundries available, and machine tooling cheaper and more easy at that times technology with limitation in number and availability of automated machine tools with high technology metal-cutting tools.

Gun metal and other bronse and brass alloys were commonly used for valves and had very good properties for corrosive fluids, and were for instance used for ship-valves exposed to sea-water and sea climate.

More specialized valves and altered ship-technology, along with altered prices and better tooling and material technology have changed the picture.

Stem failure can be caused by anything from lacking maintenance (grease, and regular test operation) to wear or abrasion of stem and gate, damaged gate, sticking gat, excessive forces and or repetitive bending (material fatigue) or any combination of this or other causes.

Much can be seen by demounting and inspection. Please bear in mind that there is normally more than one single cause, but that use of excessive force is normally one of them.

 

[jbeckhou]

Pre 1974?? Do you have any pictures? Markings on stem? Was the valve in service when it failed?


Petrotrim Services, LLC

http://www.petrotrim.com

 

[PeterIgg]

Are you doing a failure analysis or trying to work out how it has lasted so long? Strikes me that any valve that has worked for 40 years has not done too badly!

 

[24hrs]

The valve stem failed during an annual maintenance when the tech was trying to open the valve.

 

[PeterIgg]

Per jbeckhou, we will need some more data in order to give meaningful answers. Pictures would be good else detailed description of the failure. I take it that the valve is rarely operated. Did the valve fail opening/closing? Was the valve difficult to move? Were cheater bars, or similar, used or did the failure happen under normal hand operation? What is the service? Where is the valve situated - inside/outside; offshore/coastal marine/tropical/temperate......So many factors to consider.

 

[sjrfc2]

One of the things we've seen with brass components is reapplying. Brasses with higher zinc or aluminum content in particular. This is something that occurs over time and it's dependent on media through the valve. A quick example is brass with higher zinc in seawater. Zinc is anodic and goes away leaving a porous weak structure. I think I member threshold of about 10-15% zinc but that's memory. MSS specs included some generic guidance for the designer to be aware of.

 

[sjrfc2]

Sorry, should read "de-alloying" like dezincification.

 

[Ehzin]

If you could, specifically define how it failed. Did the valve leak out through the packing or did the valve stem just outright fail/break/crack? Knowing the actual failure is important. A very random comment is that WKM makes a Pow-R-Seal gate valve. I'm not entirely certain if WKM's line of Pow-R-Seal gate valves cover 2" and can comment even less back in 1974 but it's plausible, given the previous information, that these are WKM Pow-R-Seal Gate Valves (Assuming they cover 2". If that's the case, these valves meet the leakage criteria of API-6D which for a soft seated valve is "zero" leakage across the seat and nothing across the stem). The Pow-R-Seal offer no self relieving function to prevent cavity over-pressure protection so if the valve is isolated, with the line liquid full, and temperature begins to rise there is nothing to prevent the cavity of this valve rising considerably (due to liquid full) and over-pressuring the capacity of the stem gaskets/seals leading to leakage. Essentially, more information is needed to provide appropriate feedback to help with this issue but I believe the community as a whole would appreciate helping you with this dilemma.

Thanks,
Ehzin