RE: [PipingDesign] Rigid Hangers with Clevis'' on Thermally Cycling Piping

From: <James>
Date: Fri Apr 04 2008 - 04:04:00 EDT

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From: PipingDesign@yahoogroups.com [mailto:PipingDesign@yahoogroups.com] On Behalf Of Christopher Wright
Sent: 03 April 2008 18:26
To: PipingDesign@yahoogroups.com
Subject: Re: [PipingDesign] Rigid Hangers with Clevis' on Thermally Cycling Piping

On Apr 3, 2008, at 7:54 AM, James, Barbara wrote:

> > It is not uncommon to find main steam and hot reheat systems in
power
> > stations that are hung entirely on rods, constant effort supports
and
> > springs.

> How stiff is the system overall, compared to other types of piping? I
> do a fair amount of seismic analysis (although not a whole lot of
> piping) and lateral loading with soft supports really makes for huge
> displacements and stresses in soft structures.

Main steam piping is inherently stiff, typical dimensions are of the order of 250mm ID with 70mm walls. Not too far from thick wall cyclinder criteria.

Hot reheat is typically 400mm ID with 30mm walls, again its big stiff piping.

System layout obviously varies from station to station, though most UK boilers in the 500 - 600 MW output are around 40m tall. Horizontally the boiler to turbine is around 60m.

> Am I right in assuming that you're trying to keep the piping fairly
> soft (structurally) to mitigate thermal stress?

Yes. In general, seismic events are not a consideration on conventional power plants in the UK. Largest recorded seismic event in the UK measure 6.1 on the Richter scale. Water hammer is sometimes a consideration, though whether we are asked to undertake analysis for it depends on the boiler design and operating modes.

> Might you have sufficient fixity from flanged connections at the ends

> to provide support without the need for stiff intermediate supports?

At typical main steam design conditions of 170barg and 550 deg C there aren't any flanged connections! But yes, the turbine is certainly sufficiently rigid enough to be modelled as completely fixed. Different turbine manufacurers will place limits on the loads that can be imposed which may necessitate guiding the pipe local to the turbine. Boiler headers are usually well supported albeit on hot structures.

  Barbara

.

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[Non-text portions of this message have been removed] Received on Fri Apr 04 04:04:00 2008