Safety Relief Valve Lifting

[JPiii]

I am at a plant working on a few product transfer lines. I transfer from building to building crossing out side containment areas. As part of an environmental project, I had automatic valves installed at each building. Before the operator transfers, he must test the line for leaks by charging it for 5 mins. He shuts one valve, pumps until it is full, then shuts the second valve. During our PHA it was determined that we needed Safety Relief Valves on each line. I had these installed which are set to discharge at 165 psi. There are five lines total, of which one relief valve keeps lifting slightly only discharging about a quart of product. I thought it was a bad relief valve so i swapped it for another. That one again lifted. It seems to only be happening in the very beginning of the charge. I removed the failing relief valve and installed a tell-tale pressure indicator on the same flange. The highest pressure shown on the gauge was 70 PSIG. I do not understand, both relief valves were sized for 165 PSIG. The product temperature is about 62 deg C.

I was thinking I needed an expansion tank to absorb the air that could be trapped in the product transfer line when the operator began charging.

But then why is it not shown on the pressure indicator?

Any Ideas?

 

[BigInch]

Slowing valves will tend to help. Plus in general all valves should open before a pump starts, if possible, and should remain open until after a pump stops.

Sequences are usually converted to programatic events, as is so in your case, so the best way to discuss sequences is LIST EACH STEP ... BY THE NUMBERS. Get in the habit now. I say that because actually your sequence still is not totally clear. You seem to say (you don't say exactly) that the pump stops when set pressure is reached, yet you never say it starts again, so I'm not sure if it actually stops, or not.

1) Open V1 & V2
2) Start Pump
3) Flow Confirmed
4) Close V2 relief event???
"The pump continues to run until" (when exactly?)
5) Pressure Set Point Reached

6) Stop Pump
7) Close V1

8) Wait 5 minutes
9) Pressure Set Point Holds
10) Open V1 & V2
Start Pump I'm not sure if pump started, or not. I assume yes.
11) Transfer Product

I assume the relief event occurs immediately after step 4.
If that is true, I agree that your best bet is to slow down that valve.

Independent events are seldomly independent.

 

[m2609]

Sorry 'JPiii' but i must be reading your posts wrong? You last post stated "If pressure is held, Air Valves #1 and 2 are opened and full transfer occurs". So does this mean you are hydrotesting the line with the process fluid, in this case an acid! The point of doing a hydrotest is to check the integrity of the system and should be done with water! You would be safer not doing the hydrotest at all as your transferring pressure will be lower. What would happen if your test was unscusseful and the line ruptured? Acid spraying everywhere i assume you have a barriers set up around the system when the test is taken place?

Wouldn't it be safer to do routing hydrotests every few months using water?

 

[BigInch]

I understood it as not exactly a hydrotest per say, more like just a quick "leak check", kind of like a pilot looks for fuel leaks every time just before he takes off, and he is using his process pump, so hopefully it's not got the capacity to reach "test pressure".

Independent events are seldomly independent.

 

[Latexman]

"I had access to a lift today and was able to throttle the air supply to Air Valve #2 to slow down the closing speed." A fail open (FO) valve in an acid transfer line? I would say, "that's interesting", but it's not. Why is there a FO valve in this service? To me, a FC valve is a no-brainer.

m2609 touched on an "issue" that I had briefly thought about before, but I ignored it to help stop the acid from coming out where it shouldn't. Unfortunately, many small issues in this post are starting to add up to big problems. Routinely blowing a steam traced and insulated line because the acid is/may be freezing? There's a problem somewhere. Two valves in normal operation that trap acid in a steam traced and insulated line? One valve will stop flow and prevent backflow. Remove the second valve (and possible the pump's check valve) from normal operation; handle non-normal operation administratively to avoid trapping liquid. I've seen "leak checks" every transfer when the containment of the fluid path is compromized each time, but not a hard-piped line at every transfer? I've never seen that before. Now, a FO valve in acid transfer service. These "issues" are complicating the operation and adding unnecessary risk. Take care of these things and you can probably eliminate the PSV.

Good luck,
Latexman