Even on new construction a WOL is considered a branch connection.
http://www.pipingdesigners.com/Training%20-%20section%201c.htmhttp://www.topazinc.com/tappingtees.htmhttp://www.tdwilliamson.com/hottaptdw/fittings/SSWelding.htmThe myth a branch weld is illegal is not exactly right. You cannot have a UNSUPPORTED branch connection and they may or may not be approved for certain DOT regulated pipelines. On new construction you can get into a cost issue. A 12 X4 reducing tee is quite expensive and can have a long lead time. The piping designer may decide to use a 4 inch o let instead of a reducing tee. Sometimes on header fabrication you may need center to center distances less than than a reducing tee will allow.
While the branch test is a endurance test and for most firing line welders on a pipeline useless, if you are on a firing line and pulled off to tie-ins you have to have that branch qualification.
BABRT's
Just did one of these tee saddle's on a live 36" water line a few weeks ago, never seen one before. Then they came in and bolted up to the flange and taped into it with a huge holesaw and valve it off, pretty cool stuff.
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