Seeking Hypotheses for Issue with DN40 Check Valves

[Lolain4238]

Hello,

I'm reaching out regarding an issue we’ve encountered with DN40 straight-way check valves (lift type check valves) and would greatly appreciate your input, as we’re running out of hypotheses to explain the phenomenon.

I reported a sealing issue with two check valves installed in an NH3 system. Check valves are mounted in a discharge pump circuit. I observed that the metal sealing surface on the check valve body was severely damaged after only a couple of months, while the PTFE sealing seat remained in excellent condition—a situation I could not explain.

Upon inspection, we confirmed that the metal sealing surface of the valve body was indeed heavily damaged, whereas the PTFE seat was nearly intact. The damage patterns on the sealing surface matched the diameter of the metal piston, suggesting direct metal-to-metal contact. This seemed incompatible with the pristine condition of the PTFE seat.

The check valves have been replaced (body + bonnet top) twice and the same problem keeps occuring.

Informations :
The fluid velocity is near the maximum allowable limit for the pump.
No vibrations nor shattering.
There are no fluctuations in pump speed or pressure
Check valves are compatible with the operating pressure and temperature.

Let me know if you have any idea, it would be much appreciated.

Lolain4238

 

[mk3223]

It should be no issue for the metallic seat & disc valve by using the proper material for the NH3 system. What's the material of the check valves?

Why to replace the valve body and bonnet top as the sealing surface of the valve seat damaged?

 

[Danlap]

Hello,
Can you share maybe some pictures of the damage, material (metallic) used and flow rate or velocity?
Without those, can only assume either wrong material selection and/or flow accelerate corrosion.
Also, I don't really understand, cmiiw, so Seat is PTFE, Plug is metal and damage indicated is suspected to be 'metal to metal contact'. Which means the Plug is hitting something (not the seat)?
Or is the pattern of damage looks like indentation (metal to metal contact) and not erosion?

regards
D

 

[BEMPE16524]

show us some photos. what's the material?

 

[georgeverghese]

Google tells me water content in anhydrous NH3 must be in the range 0.2-0.5 weight %. Corrosion can be expected when it is outside this range. Check your NH3 water content. See page 4 of this doc.

https://www.ossmaine.com/wp-content/uploads/2017/09/Water-in-Ammonia-Test-Methodology.pdf