Randy:
Following up on your comments: hot tapping is usually a response to try and
avoid shutting down a flowing line, to avoid disturbing a process. And a
hydro test would by definition be an interruption of the process. So my
comment is "how are you going to hydro? You might do a maximum pressure
test, but anything beyond that would involve blanking/shutting off relief
valves - not at all recommended for an operating process"
George McKinney
Augusta Engineeering & Design
> I am not an expert in the hot tapping field but am learning from the many
suggestions in this thread. I noticed among the suggestions, "Before
cutting, hydro the hot tap connection." I certainly understand the intent of
this (to assure the quality of the new connection with a hydrostatic test);
however, I wonder if whoever is designing and/or conducting this
installation or test should probably also consider any very high
differential pressure effects against the outside of the uncut pipe
coupon/existing pipe wall, also if they exist in this procedure? It would
seem that some level of differential pressure could conceivably inversely
buckle etc. particularly a large coupon of low existing wall thickness, even
though this coupon is in the shape of a circular arch if the differential
pressure happened to be large enough? However, I suspect this consideration
would require some experience and/or knowledge of the sizes,
effective/existing thickness and mechanical properties o!
> f the in-service pipe and/or necessitate some rather fancy calculations
or FEA etc. appropriate to the specific circumstances.
>
> Randy Conner
> Research Department - Technical Division
> American Cast Iron Pipe Company
> 1501 31st Avenue North, Birmingham, AL 35207
> P. O. Box 2727, Birmingham, AL 35202
> ph 205-325-7946
> fax 205-325-8095
>
> -----Original Message-----
> From: PipingDesign@yahoogroups.com
> [mailto:PipingDesign@yahoogroups.com]On Behalf Of tomcruz55
> Sent: Wednesday, December 14, 2005 1:53 AM
> To: PipingDesign@yahoogroups.com
> Subject: [PipingDesign] Re: Hot Tapping
>
>
> > --- sattar hkan <pip04bbi@y...> wrote:
> >
> > > Hi,
> > > Are there any constraints or limitations for Hot
> > > Tapping :
> > >
> > > In the Process Plants?
> > > In the size of Header & Branch ( is it possible
> > > to make a connection with same size of header)?
> > >
> > >
> > > ---------------------------------
> > >
> Are there any constraints or limitations for Hot Tapping?
>
> Yes as Shannon stated. Things like burn-thru and cracking, minimum
> pipe header wall thickness, maintaining some flow during hot tapping,
> presence of lamination, mixture near explosive/flammable range, its a
> definite no no when hydrogen s d commodity or when PWHT is required.
> See Section 3 of API RP 2201 for details.
>
>
>
> In the Process Plants, is it possible to make a connection with same
> size of header/branch?
>
> Yes. TDW does it all the time . The important thing is to ensure that
> the isolation valve is full-port and that the actual thickness of the
> header is assured. How you may ask - well the use of full
> encirclement is one solution. You also want an assurance of course
> that the coupon can be retracted/recover and that the hot tapping
> machine can be removed. Before welding, check for lamination. Before
> cutting, hydro the hot tap connection. Use also a qualified weld
> procedure and material that is suitable for the service - with
> traceability. When there is a doubt about safety, dont proceed.
>
>
>
>
>
>
>
>
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>
>
>
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Received on Wed Dec 14 11:15:00 2005
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