RE: minimum base metal thickness for hot tapping

From: <THOMAS>
Date: Sun Apr 18 2004 - 10:50:00 EDT

Dear Tanmoy,

We have done hottaps over many years.

In a normal hottaps, you need to mark up the spot for hot tapping. Inspectors take UT thickness reading yo ensure there is no unusual corrosion. ( Some co. dictate a minimun of 5 mm before hottaping is allowed).
You calculate min. wall thickness based on design pressure. Add 2.4 mm as suggested by API RP 2201 or in absence of any code use 1 mm for every 100 ampere of welding current used. As a first root pass, you would normally used 3.2 mm size wedling electrode and current less than 150 amp. ( melting thickness less than 1.5 mm ).

Have not seen or come across any melt thru based on above procedure for hottap.
You may howver more likely to encounter other issues like loss coupon, etc but not this issue.

>From: TANMOY SABUD <tsabud@yahoo.com>
>Reply-To: PipingDesign@yahoogroups.com
>To: piping <pipingdesign@yahoogroups.com>
>Subject: [PipingDesign] minimum base metal thickness for hot tapping
>Date: Fri, 16 Apr 2004 23:18:37 -0700 (PDT)
>
>Dear members
>
>As per API RP-2201 (refer clause 3.4) the actual
>minimum base metal thickness for a hot tapping is a
>“function of the thickness required for strength, plus
>a safety factor, usually 2.4 mm, to prevent burn
>through.”
>Now what does it mean by “strength”?
>Is it the strength to sustain the internal pressure?
>Or is it the strength to sustain the load generated
>during hot tapping? Or is it both?
>If it is both, then how we can calculate the load
>generated during hot tapping operation and also the
>required thickness.
>I want the valuable suggestion from the group.
>
>With best regards
>Tanmoy sabud
>
>
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Find love on MSN Personals http://personals.msn.com.sg/ Received on Sun Apr 18 10:50:00 2004