Frequent bursting of rupture disks 2

[GreenHawk]

In our plant, there is a 1" rupture disk combination with a relief valve, along with a redundant unit, which is procured for gas/vapor service (i.e., fire scenario). At a few times when the rupture disk is switched to the redundant unit, the redundant rupture disk bursts as soon as it’s taken in service. The temperature of process stream remains below the specified burst pressure of the rupture disk.

Is the failure due to incorrect fluid service category or due to a possible water hammer scenario which might create a sudden pressure wave? The change over valves between the in-service and redundant unit operate very quickly. The pipe length between changeover valve and rupture disk is less than 5 feet on one side and less than 3 feet on the other side.

I’d be interested in hearing your thoughts on the potential reasons of the frequent failures. Thanks.

 

[don1980]

Is this a liquid-filled system?

 

[GreenHawk]

This rupture disk-relief valve combination is installed on the outlet line of a heater (steam on shell side), and process stream is all liquid. I'd consider that the real purpose of the relief valve (with a D orifice) is thermal relief, but the datasheet says fire scenario. I guess that due to fire scenario being specified on datasheet triggered the procurement of a rupture disk for gas/vapor service.

In normal operation, the process temperature is way below the burst temperature.

 

[LittleInch]

Two things - "The change over valves between the in-service and redundant unit operate very quickly" - Why?? I've never seen a back up relief vale system like that and am curious as to how the change over is performed and why you can't do it slower by opeiing the back up valve first then closing the other one - for what? maintenence??

You keep saying burst and process temperature. This might be me but bursting discs work on pressure not temperature. BDs are quite fragile things and don't have a lot of give once the pressure (not temperature) gets close to it's set pressure. Any schock wave is not good for a bursting disc so I think you've answered your own question.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[GreenHawk]

LittleInch,

Both of the automated valves at inlet of rupture disks have a common actuator and are connected by a mechanical link. When one valve opens, the other one closes simultaneously. This change over happens quite rapidly when we switch to the redundant unit for maintenance, etc.

The existence of water hammer is just my hunch - I'm not really sure whether a sudden pressure wave does occur in our system at the time of change over.

Hope this would help in better understanding of the system.

~GreenHawk

P.S. I was talking about process temperature being below burst temperature setting as rupture disks' actual burst pressure is a function of the process temperature as well. If the process temperature increases above the specified burst temperature, the rupture disks blows off before reaching the burst pressure setting.

 

[LittleInch]

Wow, I've never heard of such a device for isolation of relief system. Most plants I'v seen just have manual Locked open or closed valves and rely on precudures to open on before closing the other. Occasionally you see key systems to prevent both being closed, but for a 1" system a motorised valve seems a bit OTT. Maybe you need to consider a modification...

I can understand why you refer to temperature, but unless pressure is ONLY affected by temperature then it's pressure that counts as you could have lower temperature but higher proessure from a pump or other pressure source, not just temperature.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[don1980]

Here's my perspective......disks are excellent at maximizing long-term cost and unscheduled events. They're also real good at creating safety and environmental incidents while minimizing the plant's on-line reliability.

The best solution is always ... get rid of the disk.

Check to see if the disk is actually necessary.