RE: Allowables in Stress

From: <Rajesh_V_Balapure@ril.com>
Date: Thu May 09 2002 - 04:34:00 EDT

"Why? We discovered so far

about 4 or more multiple root causes leading to the loss event."

Apart from the material used, not being as per the design specification e.g. m.o.c ,thickness etc.,what are the root causes for the above failures...?..

Regards,
Raj...

"SARE, RALPH H." <SARERH@YANPET.SABIC.com> on 05/09/2002 12:35:21 PM

Please respond to PipingDesign@yahoogroups.com

To: "'PipingDesign@yahoogroups.com'" <PipingDesign@yahoogroups.com> cc:
Subject: RE: [PipingDesign] Allowables in Stress

From: Rao V.T. [mailto:raovt@npcc.co.ae] Sent: 08 May, 2002 3:13 PM
To: 'PipingDesign@yahoogroups.com'
Subject: RE: [PipingDesign] Allowables in Stress

THE allowables on rotating equipment is to avoid misalignment of pump and driver......(so only dia )..

most of the failure associated with piping load is damage to the mechanical seal. For pumps, its not enough that you ensure the that the loads and m oment (which is a function of dia) is below the prescribed limit but also you need to ensure that the magnitude of the resultant load and moment satisfy also the interaction formula (which is a function of both the individual load componet and forces). on turbines and compressor i would agree (strickly dia) but the nema allowables is very unreasonable.

whare as the allowables on the vessels/columns is to avoid stress failure at
nozzle/vessel junction......(so dia and rating....)

it is as simple as that.

i hope its as simple as that but the api 610 has undergone several revision.
the last two are major improvement. vessels and columns (air collers and tanks exempted since they're covered by specific API std) nozzle load are evaluated using the wrc rules (or fea). wrc rules if i remember it right does not have a rating. if your refering to the flange rating, then what it satisfies is only a leak-free joint. ive repaired/replaced/relocated a couple of nozzle on columns, api tanks, silos, heat exchangers, vessels for the pds, etc. During the design stage and rca ive have always reviewed the stress calc for both the vessel and piping (particularly at the nozzle junction) aside from the ndt/incident report and operation log. Guess what? the stress level are well below the allowable and yet failure at the nozzle still occurs (production loss = revenue loss). Why? We discovered so far about 4 or more multiple root causes leading to the loss event.

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Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ Received on Thu May 09 04:34:00 2002