Steve,
Finally the client has agreed to use gas accumulators to take the sting out of the surge. Thanks all for the advice. Put on the spot I guess the client didnt want to take the risk after all.
regards
Geoff
Steve McKenzie <Mechproj@xtra.co.nz> wrote: Hi Geoff
I think Dr Nick is referring to a non code situation where engineering judgement may be exercised instead of blind code compliance. If you read it in that context it makes some form of sense. If you read it as a code interpretation, it makes no sense. If you are trying to force this statement into a code context, be prepared for disappointment. However, if your client (or his insurer) is prepared to assume risk of a departure from code, then there might be some money to be saved and a bit of engineering design for you.
Cheers
Steve
-----Original Message-----
From: PipingDesign@yahoogroups.com [mailto:PipingDesign@yahoogroups.com]
On Behalf Of Geoff Stone DD&D Australia
Sent: Monday, October 31, 2005 11:44 AM
To: PipingDesign@yahoogroups.com
Subject: RE: [PipingDesign] Fram Lewis Filters
Steve,
The following paragraph appears in Chapter 8 of Pressure Safety Design for Refinery & Chemical Plants by Dr Nicholas P Cheremisinoff. This appears to fly in the face of the other arguments presented. Is loss of power that causes a surge considered such an event? Does this actually appear in ASME VIII?
Geoff
"In some cases where the ASME Code would not require pressure relief
protection, the 1.5 Times Design Pressure Rule is applicable. This rule is stated
as follows: Equipment may be considered to be adequately protected against
overpressure .from certain low-probability situations i f the pressure does not
exceed 1.5 times design pressure. This criterion has been selected since it
generally does not exceed yield stress, and most likely would not occur more
frequently than a hydrostatic test. Thus, it will protect against the possibility of
a catastrophic failure. This rule is applied in special situations which have a low
probability of occurrence but which cannot be complete& ruled out."
Steve McKenzie wrote:Hi Geoff
Cant find your original question, but am concerned a client may be trying to sway your judgement. If you have a coded system, then they/local authority must be able to produce the validating documentation. If you cant, then the system coding stamps/tags are worth jack. You may not even know the corrosion allowance, and if you donât, there is no record of serviceability limits.
If you have a non coded system then you may be able to apply some judgement: In the 60's, a lot of gear was pressure rated as "non shock". If there was an anticipated shock pressure, then this was added to the operating pressure to arrive at the basic design pressure before correcting for temperature etc. A test of 1.5 times max was almost standard (even outside the good ole US of A, Chris) and 10% overpressure was generally accpeted as the "margin". While this approach worked about 95% of the time, the flaw is obvious in that no allowance is made for fatigue/endurance limit often being lower than yield/proof stress. In occasional surge systems, few problems. In power hydraulics, heaps of problems, although oddly enough we still use (new) burst pressure as the benchmark. In a non coded system, I think that a maximum occasional pressure excursion of up to 10% over design is unlikely to cause a problem. More than this and I would be looking at a few SN charts and material specs. 50% over design and forget it as you are outside the designers wildest dreams. A reverse engineer may be on the cards if the replacement cost is truly high.; have done this on a few hydro power station penstocks, but judgement( in the matter of residual strength), alas, has far more importance than calculation.
Donât put your nuts on the block because your client doesnt keep good records.
Cheers
Steve
-----Original Message-----
From: PipingDesign@yahoogroups.com [mailto:PipingDesign@yahoogroups.com]
On Behalf Of John Luf
Sent: Friday, October 28, 2005 4:28 PM
To: PipingDesign@yahoogroups.com
Subject: Re: [PipingDesign] Fram Lewis Filters
no ASME plate...
well it might have been cooked up by some long dead guy based on one code or another... it might be able to take a limited surge above what its stamped but on the other hand it may actually have less metal in place now then when it was put in service...
I have more maybes than certainties... guess that means go by the name plate...
Going to sleep on it for now!!!
John C. Luf
In the Great Lakes of the U.S.A. and not in Neudorfl... master of unimportant trivia, free agent!
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