<...what is the likelihood of corrosion/scale causing 2 NRVs on two braches of a pipeline to fail simultaneously ?...>

Lower than that of a chunk of wood, a dead bird or an old bucket handle being caught within them, or a broken return spring come to think of it.

What does it look like when it's on the bench?

Since the NRVs have failed and you are going to replace them, open and see what is the likely cause.

I have seen too many NRVs to fail due to different reasons

- The seal matrial on the seating surface (depends on design) if rubber then that degeneration and a few times it simply dislodged from slot and escaped.

- The spring mechanism jammed or as PWS said broken.

- Since you are on water line, the material is likely to be SS ? if not then your corossion/ rusting may jam it

Hi pillayse,

Basically for me base on my experience, the main reason of corrosion and scaling specially base on the folliwng reason:

1. water or medium beig use.

2. what type of application did you use for the cooling tower, because for me there are many reason why scale is being develop base on the application depending on how much temparature do you need to cool, I mean the specially the inlet water temperature after it pass thru the machine itself.

3. you mention 10weeks your valve failed to open. My question is how strong is your preventive maintainance of yuor cooling tower?

thanks,

Larry Oleta

What's an NRV? I hate these bloody acronyms with no definition! Blimey, mate.

What's an NRV? I hate these bloody acronyms with no definition!

Hahahaha million dollar question......Discussion Moderator (If Any) please pay attention to mr. guest.

"Bali"

KINDLY ATTACHED A HAND DRAWN SKETCH TO UNDERSTAND THE SYSTEM AND ITS RELATTION TO NRV FAILURE.

Although, fluttering due to pr. diff. may also cause the valve seat failuire and leakage problem. Did you obserrved any hammering / fluttering sound !!!

When you replaced the valves, did you observed any changes on Valves seat, Spring corrosion etc. Please share all such things to undestand your problem in detail.

with regards,

Nilesh.

Hi I have done a rough sketch ...how do i attach it to the thread ?

scan it convert to jpg file then use the camera button (green- 7th button above) and then link the jpg file to it, submit

Hi All

Thanks for the input.....i took out a permit and opened up the valves on that system....they were passing.....a piece of plastic was stuck in one valve and corrosion was also evident.

Thanks again,mystery solved !

Well done.

A non-return valve with corroded internals can continue to operate provided it seals adequately. Replacing seal surfaces at intervals, or even the whole valve at intervals, ought to be written into the maintenance strategy for the facility in question. That is why maintenance spares are always an important consideration: what is the threat to the facility's operations if this part were to be unavailable <rhetorical question>?

In utility systems, it is often the case that low-value materials are used, and the risks of needing to replace sections of it at intervals become part of the ongoing maintenance budget.

In the end it becomes a question of strategy:

• does one build cheap and improve over time or
• does one build best and struggle to find the investment with which to do it, or
• somewhere in-between?

If the projected lifetime of the facility is short then the first may be the best option.

Thanks, you are one of the few who bothers to post once they get the cause. It helps the others in the field, and of course because of that gets a GA

1. no filters/ strainers in the line?

2. material of contruction of the body and the flaps (as well as spring)

Check these and do the needful, else this will repeat again.

Hi

There were no filters or strainers, because this was an emergency temporary line installed to accomodate the delay in construction of a new plant.

Yes the material spec was not stainless steel it was mild steel, i presume used to cut costs as this was a temporary measure.

The valves have since been replaced with stainless steel since the expected date of the new plant is still far off.

I would bet the corrosion occurred from the valve not being used or static for ten weeks. You may want to have a water analysis done or if the line was drained then consider a nitrogen purge on the system while drained.