Freezing of pilot sensing lines

[Alabaman]

Hello I have a quick question. What effect does freezing of pilot sensing lines have on its operation? Pre mature lifting? or potential for overpressure? Any insight will be appreciated. Thanks

 

[zdas04]

Either one. When water freezes it increases in volume by approximately 4%. If there is a couple of feet of tubing between the freeze point an the pilot, it would be just like shutting a valve and trapped pressure will only increase slightly. If the freeze is very close to the pilot, it can simulate a very high pressure (especially if there is liquid water between the freeze and the pilot.

Heat tracing and insulating pilot lines is a very good practice.

David

 

[Ashereng]

Pilots freezing, plugging, or contamination in general is potentially dangerous. if freezing is a concern, heat trace and insulate is a good idea as zdas04 mentioned.

I am presuming the source of freezing is due to ambient conditions. If the freezing is due to process conditions, heat trace/insulate may not work and you will need to find alternatives.

"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?

 

[Alabaman]

Thanks all. I understand theoriticaly why a pilot valve will open prematurely before reaching its set point if the sensing line freezes.

However, I still dont understand why it will NOT open when it reaches set point due to sensing line freezing up. The operators i spoke to said they haven't seen this before. Can some one explain if this is indeed a likelihoo?

Thanks.

 

[zdas04]

Did you read my post? The freeze can act like a shut block valve which makes it really hard for the control valve to close.

David