1 reply to this topic

[hollerg]

I have a maintence supervisor that wants to direct the tail pipe on a rupture disk within the same dike as the tank it protects, because the tail pipe can be shorter and reduce cost. This tank is the only tank in the dike and the disk will be set at 13 psig (15 psig tank). The only source filling the tank is from periodic transfers from a tank truck.

The fire that might result in the overpressure would be from a leak involving that tank or the pumping system associated with that tank. What makes this acceptable or not acceptable?

[pleckner]

You can get a gazillion answers/opinions on this one so here is just one. But the best opinion is your own safety department and insurance carrier. They must be the final say no matter what I or anyone else says.

First, I will assume the rupture disk is mounted on a flange at the top of the vessel. Second, I assume you are concerned that liquid in the vessel will pour into the dike helping to fuel the fire. Third, I assume this is not a hazardous fluid.

In a fire case, the internal contents will boil so there will be very little possibility of liquid relieving through the rupture disk piping (unless it is a two-phase relief). You should not have liquid relieving into the dike helping to fuel the fire. Anyways, if the tank is leaking, then you have that situation with or without the rupture disk. However, if the contents are hazardous in nature then there is no way I would allow the stuff just to flow into the dike. It must go to some type of enclosed containment and processing. If this is pretty benign stuff, you can direct the flow into the dike.

If the scenario is overfilling the vessel, this arrangement is also not a problem (unless hazardous) and is commonly done. After all, the dike is there for containment.

By the way, why set the burst pressure to only 13 psig on a 15 psig tank? You can go right up to 15 psig (watch your Manufacturing Range and burst tolerances).