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Subject: four welds meeting at a point

Date: 09/19/02 at 10:49 PM
Posted by: dorios
E-mail: dorios2001@yahoo.com
Message Posted:

We have designed a large pipe bend (under high pressure).Just imagine an U bend made out of two large elbows united, we placed the plug in the inner side of U, in the "trough" where they meet.

When we join the bend together we come up with 4 welds meeting at a point. We suggested the insertion of a plug 100 mm dia in order to avoid 4 weld to come together and comply with AS 1210.
> AS1210 states that inter alia Welded joints should be
> located:............to avoid more than two welds meeting at a point.
> Where the above is not practicable, the reader is referred to AS4458 which
> in Cl 8.3.3 clearly allows for a crucifix type connection
> provided appropriate NDE or PWHT is performed.
> AS4458 states ......
> Location of Joints and in section (b) Staggering of Longitudinal Joints
> which states that consideration shall be given to PWHT where more than
> welded joints meet and all of the following conditions are met:
> - Longitudinal joints in adjacent strakes or rings are not
> staggered by a distance equal to or greater than five times the thickness
> the thicker plate.
> - Material in Groups A to M (yes)
> - Material thickness exceeds 50% of that required by code for
> - Specified min UTS exceeds 490Mpa
> In the event that the joint is not PWHT, the area 100mm either side of the
> joint shall be subjected to 100% RT or UT.
Where the design code is ASME B31.3, I find no reference to avoiding
> crucifix type welds and sight the case of two large diameter 90 elbows
> longitudinal welds brought to together- fitting to fitting" in an "S"
> configuration - typically change of rack height.
> In this instance the elbows would not have a pair of plugs inserted.

I believe that the plug design is saffer due to change in stiffness at that point. Any comments?

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