4 replies to this topic

[lokesh_09]

Dear all,

Is there any specific standard for sizing rupture disk inlet line.
What is criteria to be followed for rupture disk inlet line sizing. we have criteria on API RP 520 for Pressure relief valves inlet line sizing (i.e pressure drop less than 3 % of set pressure),similarly what will be criteria for sizing rupture disk inlet line sizing.?
Please advise.

Thanks and Regards,
Lokesh.

[fallah]

Lokesh,

The 3% pressure drop (based on set pressure) rule is considered for blow-down adjustment of reclosing type PSVs in order to not being chattered.

Thus,IMO,it is not applicable for rupture disc as a non reclosing pressure relief divice.Of course,it is obvious that length,route and diameter of inlet line would affected the rupture disc relief capacity.

APPENDIX E of API 520 part 1 contains an example shows the method of calculating relif capacity of a rupture disc as per flow resistance through the line in which it is included.

Fallah

Edited by fallah, 30 March 2011 - 02:45 AM.

[lokesh_09]

Lokesh,

The 3% pressure drop (based on set pressure) rule is considered for blow-down adjustment of reclosing type PSVs in order to not being chattered.

Thus,IMO,it is not applicable for rupture disc as a non reclosing pressure relief divice.Of course,it is obvious that length,route and diameter of inlet line would affected the rupture disc relief capacity.

APPENDIX E of API 520 part 1 contains an example shows the method of calculating relif capacity of a rupture disc as per flow resistance through the line in which it is included.

Fallah

Dear Fallah,

Thanks for your prompt response. On what basis we have to size the rupture disk inlet line. what is the operating pressure for the rupture disk inlet line. Do we need to use the burst pressure for sizing the rupture disk inlet line or line operating pressure or minimum flare back pressure. what will be the velocity limitation for this line.

Awating for your response.

Thanks and Regards,
Lokesh.

Edited by lokesh_09, 30 March 2011 - 10:41 AM.

[Lowflo]

Once the disk has burst, the relief system is just an open pipe, and the relief capacity is simply the flow capacity of that pipe. The broken disk is treated like any other piping component in that it contributes to the overall resiatance to flow. So, the terms inlet and outlet have no significance.

The physical location of the disk has no impact on the proper functioning and capacity of the relief line. Its location will affect mechanical forces placed on the pipe and vessel nozzle, once the disk bursts, but it's not important from a performance and sizing perspective.

Note that this is true for the common disk applications. It's not true for the rare deflagration services in which disks are used. In those cases the piping is critically important, because too much resistance can cause the deflagration to turn into a detonation.

[fallah]

Lokesh,

If you read the Sec. 3.11.1.3 (Rupture Disc Sizing Using Flow Restricted Method) of API RP 520 Part 1 7th Ed.,you will see when rupture disc used as the sole relieving device,it would be considered along with its inlet/outlet lines as a system and you can use the mentioned method to size the rupture disc itself and its inlet/outlet lines by getting help from vendor information and Crane Technical Paper No. 410.
Of course,Sec. 3.11.1.2 of the same RP may only ber used conditionally when a RD discharges directly to the atmosphere.

Fallah

Edited by fallah, 03 April 2011 - 02:41 AM.