Rupture Disk ASME certified

[StoneCold]

My current employer would like to discontinue the practice of having rupture disks ASME certified for pressure vessels. He would rather just use the graphite ones "off the shelf". I am against the change but can not find in the code where it is specifically stipulated. I see in ASME VIII Division 1 UG-127 where the stamping of setpressure, temperature, lot # and the procedure of testing two disks from a lot to verify accuracy are required for the disk to be certified, but I don't see where use of a certified disk is required? Anyone have any references for this?

Thanks
Brad Stone

 

[psafety]

My understanding based on ASME Section VIII, Div 1 it is required that the disc have the "UD" Code Symbol Stamp a "certified flow resistance factor (KR), and the minimumum net flow area stamped on the RD tag.

 

[StoneCold]

psafety
Do you know where it the code the requirement is called out?

Thanks
Brad Stone

 

[gerhardl]

To my knowledge all producers of rupture disc, and all regulations worldwide will require a certification and stamping/marking of all rupture discs. (In Europe this is a EN - requirement, relatively parallell to the US regulations).

The certification consists of a certain number of discs to be tested for each lot produced. This can lead to a relatively high price if the disc is 'order produced' and in small quanta.

Your employers requirement is undoubtly caused by a wish to get the costs down.

There are only two ways to obtain this.

Commercial: ask several bidders for a larger (optimum) number of discs and alternative solutions.

Technical : Check and control the reason for bursting dics to release too often. Evalute process control and release solution.

This will involve process control evaluation as: trying to keep pressure more even, optimizing set pressure (set pressure too low?, right type of discs? discs with more narrow tolerence, allowing higher operating pressure peaks? other material discs, more solid than carbon (higher price, but more lasting over time), other release diveces than discs (higher price) etc.

As always the real engineering challenge is to check what you have against what is readily commercially available
out there, and find the best cost/lifetime practical solution.

 

[StoneCold]

The costs seem high to him because we change out our disks on a yearly basis. For two reasons. Buildup of material on the inside of the disk, and the fact that the disks are weakened by chemical attack over time.

Thanks for the input.

Regards
StoneCold

 

[psafety]

StoneCold,
In the 2001 Code it was UG 137. Not sure of the current version. The verbiage above I pulled from BS&B.

 

[gerhardl]

Using carbon discs indicates a fairly low set pressure. As you do not mention number of discs, sizes or other technical details it is difficult to advice.

Buildup of meterial and chemical wear indicates that perhaps both some reconstruction of pipelines and/or other types of bursting discs (exotic materials) or relief valves (air-vacuum types) perhaps could be considered on a cost/benifit basis.

Or are the economic cost perhaps, as you indicate, only seemingly high?

Good luck!