Atmos column relief valves

[dhdsvr]

Is anybody awaare of installing rupture disc at the upstream of crude distillation column relief valve inlet line, to prevent corrosion of the relief valve internals.

If yes, what is the metallurgy and set pressure selected

 

[EGT01]

Can't say I have specific experience with crude distillation relief but it is not uncommon to use an inlet rupture disc as you suggest. However, the addition of a rupture does add a number of other concerns that will need to be addressed and you should weigh the cost of just upgrading your PSV materials against the addition of a rupture disc.

As for metallurgy, you will have to determine the nature of your corrosion problem and what will work best. Use the PSV internals as a starting point and then select a more corrosion resistant material for the rupture disc. Depending on your application, you might could get your rupture disc with a protective coating or liner to enhance its corrosion resistance. In fact, you may be able to get your relief valve prepared in a similar fashion.

As for set pressure and the number of other concerns that need to be addressed, well, you could write a book about those and I would advise you to seek the advice and direction of a senior engineer in your organization. In regards to books, you should thoroughly familiarize yourself with the discussions in API RP-520 regarding rupture discs and when they are used in combination with PSVs.

Here's a few key points. First, I don't like saying that a rupture disc has a set pressure, it has burst conditions that are very much dependent on temperature. You must select your burst conditions so that your disc is suitable for all possible relief cases not just your controlling case.

Here's a few more....

For inlet rupture discs, API recommends the disc burst pressure to be the same nominal value of the PSV set pressure when installed close coupled.
You need to account for the manufacturing range of the disc when specifying the burst pressure so that the upper limit of the manufacturing range does not exceed the vessel MAWP or other limting factors.
You need to consider the operating pressure approach to your desired disc burst pressure.
You will need to provide some means of ensuring that pressure can not build-up between the rupture disc and PSV.
You will need to account for the additional pressure loss that the disc adds to the PSV inlet line.
You will need to account for the reduction in relief capacity that results from a disc used in combination with a PSV.

and the list continues ....