Special Class Valve Ratings

[pipe15]

Is it possible to use working pressures that are above the B16.34 Special Class Table values. the Valves in question are CL1500 special class. If it is possible, what would a vendor or end user have to do to document going to working pressures that are above the special class values

thanks
Mark

 

[gerhardl]

Do I read your question correct if generally formed as:

'Is it possible to use a valve, designed and built to satisfy a certain given pressure class in a certain given norm' with higher pressures (or temperature related pressures) as given in the norm?'

In this case the answer in my opinion is generally 'no'.

As a supplying company my company has always said no to such cases.

The reason is that 'somebody' in this case must take the juridical and practical consequences if anything goes wrong.

I doubt you can find any valve producer that will give such guarantees.

More common is to use a higher class construction and adapt to lower class flange borings. Even this must be done within the counter-flanges technical (proved) limitations. General the wole piping construction must be within approved official regulations locally valid.

Theoretically you could of course construct a valve or prove that a standard valve is solid enough for a given increase above what is given by a pressure class by calculations and tests, .... But again at what cost and risk?

Arguments for increasing pressures 'just a little bit above standard' is always to save often large amounts of money on the endusers side. Far better and safer to select a commercial readily available proven standard product in higher pressure class.

 

[terje61]

Hello Mark,

I assume that you already have the valve operating, otherwise you would just have bought a class 2500 valve. Additionally I expect that you already have checked your piping and flanges, because they are very likely also rated for class 1500.

In case the valve is the bottleneck, you can ask the manufacturer if he can 'upgrade' the valve design pressure. This is sometimes possible in case materials with a high yield strenght were used. Note that the valve no longer complies with ASME B16.34. The manufacturer must use a different design criteria (like DIN standards) and change all valve pressure information (documentation / tagplates).

As the enduser you must thrust the manufacturer to do a good job and agree with the new design criteria.

'Upgrading' is not so easy, especially when you increase the design pressure for more than a few bar.

Good luck,
Terje