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? 

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-Forged Steel Valves).

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.
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!
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.

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