Re: Repair of Piping In-Service

Flow requirements on in-service piping repairs, depends upon several variables. API-570 does address this issue, but it also refers to their companion standard API-RP 2201 (no surprise). The 2201 std. does tell you in detail why in some cases you would want low flow rates and/or higher flow rates. My Sept. 1995 version of 2201 Sect. 3.3 explains this very well. Maintaining flow on metal thickness less than 1/4" minimizes overheating of the liquid contents, burn through caused by elevated metal temperatures and fluid thermal expansion in closed systems. But higher flow rates increase the weld cooling rate and the risk of cracking. And they go on talking about various ranges of metal thicknesses etc.. API 570 sect. 'Repairs, Alterations, and Rerating of Piping Systems', tells you the patch size and configuration requirements among other things.

• Original Message ----- From: Paul Bowers <pbowers@pipingdesign.com> To: <PipingDesign@yahoogroups.com> Sent: Thursday, May 31, 2001 9:35 PM Subject: Re: [PipingDesign] Repair of Piping In-Service

> > AWS Pipeline Welding and Inspection (page 77), ASME B31G and the
> API 570 is
> > your best source on this subject. One of the FAQ's is why does
> one have to
> > ensure a flow when welding on a live line (say to install a
> patch to fix
> > leak or do a hot tap or stopple plugging). Almost always, the
> answer is that
> > it helps to cool the weld area. I don't agree. What says you?
>
> That's always been my understanding.
>
> Paul
>
>
>
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Received on Sat Jun 02 14:28:00 2001