Re: [MW:15331] hot tap welding-branch weld

Dear Rajampalli,

 

Just to add to Mr. Sudhakar response, Shell standard refers and recommends - " No Hot Tapping is allowed for thickness below 5mm." The reason is well explained by Mr. Sudhakar.

 

This is for information.

 

Thanks & Regards

Vino P Varghese 

 

On Mon, Sep 17, 2012 at 12:41 PM, sudhakar kuppuswamy <mechsudhakar@gmail.com> wrote:

Dear Rajampalli,

 

Reply for your query 1.

 

SMAW process is low heat intensity process when compared with other Site useable welding arc process .During hot tapping, since welding is carried out on LIVE lines it is always advisable to weld with less heat input to avoid danger of puncturing the main live line.

 

Small branch 1" 4mm thick is really used in top tapping.?!

 

Reply for your query 2.

 

During SMAW welding arc initiation may lead to undercuts and burn through if OCV, open circuit Voltage is high. So to avoid such risk of burn through on live line welding, one electrode run out is used.

 

Regards

Sudhakar.K

 

 

 

On Mon, Sep 17, 2012 at 11:43 AM, Rajampalli <rajampalli.rao@gmail.com> wrote:

Please clarify the following.

Query 1

Clause 1.1 of DEP 30.10.60.30 quoted as below.

"This DEP specifies requirements and gives recommendations for the welding of fittings,

sleeves, branches or attachments onto pressurised carbon steel pipelines (X70 or lower

strength) and on-plot piping using SMAW welding only."

Why welding process is limited to SMAW only. In case of  small branch(1" dia x 4mm thk)  why can't  be  GTAW process  applied?

Query 2

For welding of set-on type branch weld in  new construction, hot pass will be deposited after completion of root pass for entire circumference, where as for same in hot tapping , the first pass in the throat of fillet shall not be extended beyond one electrode  run out length  before being reinforced by deposition of hot pass.  What could be the reason?

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