Hot Tapping Pressure Limitation 2

[uaepiping]

Dear All,
Shell DEP 31.38.60.10-Gen. Section 3.3.3.1 Item 1 states:
“For general safety reasons, at any time during the hot-tap operation the pressure of fluid inside the run-pipe shall not exceed 7000 kPa (ga) (1000 psig)"

So apparently it seems that hot tapping shall not be performed on run pipes having pressures more than 7000 kPa.

DEP 31.38.60.10-Gen (Informative) does not list any reason or clarify this limit.
I am in search of the logic behind this limit of pressure and under what conditions we can exceed this limit. Kindly share if you know.

 

[XL83NL]

You'd need to ask Shell, who at ome point came up with this number. Probably, and usually, for a reason no one knows anymore, but keeps on finding it's way into the company specs.

 

[uaepiping]

Agreed!
Even TOTAL Spec GS EP PVV 172 section 4 states (Hot tapping is prohibited for the following cases):
"Pipe operating at 70 barg and above, unless otherwise agreed with HSE discipline and site representative"

 

[MJCronin]

Unfortunately, the old guy that developed this Shell DEP has gone on to his final reward ...

MJCronin
Sr. Process Engineer

 

[weldstan]

Due to hot tapping of pipelines using cellulosic weld metal electrodes in the 60's 70's and early 80's, flow rates were reduced (pressure reductions), to mitigate rapid quenching and resultant hydrogen cracking. There were many reports on this subject by Battel and others during this time period and published by both the AGA and API.

At 1000 psi many large diameter pipelines were operating under a 72% of SMYS design with thickness generally of 3/8" or less and it was considered somewhat unsafe to permit a welder to make the weld under those conditions should he weld too slowly and create a blowout or have the weld crack due to weld quenching.

 

[LittleInch]

Hot tapping is an inherently hazardous operation.

Reduction in pressure is recommended to reduce risk.

However an experienced qualified contractor can provide further data and input into e.g. heat input, welding procedure, cooling of welds etc. to allow tapping of much higher pressure pipelines than 70 bar.
talk to those specialist contractors and get their track record. This is not something for your common contractor to try. Pay the money for the proper people.

You might need to do some small scale testing to prove the method on a similar size and wt to prove it to the requirements of those signing this off.

Then watch from a distance when they do it.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[uaepiping]

All responses appreciated with thanks!
It is a fact that hot tapping on pipes having much higher pressure than 70 bars is being done.
We need to find the good expert hot tap specialist.

 

[Dhurjati Sen]

Dear uaepiping,

Follow the guidelines of API RECOMMENDED PRACTICE 2201 "Safe Hot Tapping Practices in the
Petroleum and Petrochemical Industries".

Regards.

DHURJATI SEN

https://www.nace.org/people/dhurjatisen

 

[mk3223]

IMO, form the operation point of view, the pressure limit for the hot tapping construction could be a business risk concern in additional to the safety issue, even though there is no engineering difficulty to perform the work.