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Re: [MW:32046] In -service welding on HP Gas line, prior to Hot Tapping. Need immediate suggestions.

By Materials & Welding
Dear Mr. Venkat G,

I have a doubt, is the vapour cloud mentioned in your mail is it the welding Fumes formed during Hot Tap.

Thanks & Regards

J.Gerald Jayakumar



On Thursday, 11 March, 2021, 08:45:32 am IST, Venkatachalam Govindan <vinisaa@gmail.com> wrote:


Attn: J.Gerald Jayakumar

Dear Sir, 

Thank you so much for your sincere response. We are worried about no flow in the pipe because isolated by check valves on both sides. Another worry the client doubt about valve may have passing so. 

Anyhow have decided now, one line can do with Nitrogen purging and another line with a minimum of at least 10% of the crack opening flow. Hope things will be better. 

We afraid of the vapor cloud but there is flow now so it could be safe we believe and planning the execution next week. 

Still, we are looking for a suggestion from anyone on their own experience about in-service welding can be possible without flow inside the pipe? in such an isolated pipeline. 

Best Regards, 

Venkat G. 

On Wed, Mar 10, 2021 at 9:32 AM 'james gerald' via Materials & Welding <materials-welding@googlegroups.com> wrote:
Few steps to consider as below.

1. First determine the actual thickness existing on the pipe where 2' ventilate to be attached by performing UT Thickness Gauging.
2. Based on the thickness consider the viability of performing an Hot Tap, Normally 6.5mm minimum is considered viable.
3. Based on the AWS formula calculate the Peak temperature attained at the inner side of the pipe.
4. Another option is to conduct a Mock-up test using the same condition and measure the inner side peak temperature by attaching a Thermocouple.
5. Based on the actual process fluid scale, consult the process engineer the effects of Flash point of the actual Fluid with respect to the inner side peak temperature calculated or simulated.
7. Also consult your process engineer with respect to the vapour cloud.


With respect to the effects of welding,

1. Higher thickness helps in fast heat conduction and hence inner side peak temperature may increase.
2. This can be combated by increasing Heat Input during welding or preheat if permitted.
3. Normally hot tap mockup would provide you with actual situation

Thanks & Regards

J.Gerald Jayakumar




On Wednesday, 10 March, 2021, 08:46:47 am IST, Venkatachalam Govindan <vinisaa@gmail.com> wrote:


Dear Respected ones, 

We are planning a hot tapping on the HP gas line, which is 30" dia, and thickness 15mm, and carbon steel material. 

Around 15-meter length, where both the ends are closed by check valves. 

The line is isolated, we want to weld a 2" dia ventilate on the 30" pipe.

There is no flow is possible. We have to complete this work at any cost, the client says. Is this okay for you? it can be safe? 

Due to 15mm thickness, we are planning to do by 2.5mm, E 7018 electrode by the lower current. 

Please advise, any vapor cloud will be an issue inside the pipe? or we can do it because thick ness is high?  or shall we ask for at least a minimum flow so the vapor cloud will not be there. 

Looking sincerely your support friends. 

For your information, we regularly do such hot tapping works, at 800PSI pressure, but, with the flow. 04m/s. 

--
Venkatachalam Govindan
QHSE Lead | Auditor | Trainer
(API U Trainer | IRCA Lead Auditor | Exemplar Global MS Specialist |CQI Practitioner)
Mobile +965-97604989

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