Hot Tapping of Natural Gas pipeline

[ibrahim]

Can any one tell me how to hot tap a natural gas pipeline. What hazards involves and precautions should be taken? Is there any size limitation?

[ashfaqanwer]

Special considerations are required in order to hot tap a natural gas line:
1. Nitrogen purging arrangement shall be made available on the entrance and exit of the head (assembly).
2. Open both the purging valves to purge the head. This will ensure no oxygen is present inside the assembly.
3. Close the outlet purging valve and perform the tapping operation with inlet purging valve open.
4. After tapping, open the outlet purging valve till you ensure that there is no natural gas now.
5. Remove the tapping equipment and close the branch piping valve.

Notes:
1. Ensure that the area in which this operation is being performed shall be free of any fire hazard.
2. Fire fighting squad shall be made available during the operation.
3. Main header shut off valves shall be made accessible.
4. O-rings / seals of hot tapping equipment shall be replaced with new ones.
5. Hydrotest / air leak test of the assembly shall be made.
6. All precautions / requirements mentioned in API 2201 shall be met.

Regarding size limitation, a branch connection of 0.8 main header size is possible.

Hope this would help.

[ibrahim]

thanks ashfaq, can you further clarify the inlet gas flow requirements and maximum hot tap size. Appreciate if you can exactly tell me the maximum size i can hot tap in a 12" line; SCH 80.

[ashfaqanwer]

Ibrahim,
Do you need to know about the inlet purging gas flow requirement or the natural gas flow in the pipe to be hot tapped?
The purging gas flow must be maintained with reference to the flow of natural gas in main line; must be enough to sustain natural gas flow. However, a minimum flow of 0.4 m/s is recommended in gas lines during welding operation.
API 2201 does not specify any size limit for hot tapping.
For 12" NPS pipe, you can take a hot tap of 8" NPS branch connection easily and safely but now a days size on size taps are also practical.

Hope this would help.

[tosif]

Ibrahim, maximum tap size can be upto the ID of that pipeline, but usually drill size is slightly smaller than pipe ID. It will act as a big flow orifice, with a T-type flange connection of almost equal size as of pipeline. As shown in figure below;

[Zahid]

There is also an advance technique called "STOPPLING" to do hot tapping and even rerouting gas lines online (with out any shutdown).
There is company TD Williomsons who provides STOPPLING services.
For more clarity you can see the below link or visit
http://www.youtube.com/watch?v=9oIQk4fa ... re=related
http://www.tdwilliamson.com

[ibrahim]

thanks guys. last question that popped out of my mind was the cutting residue. Actually the pipeline we planned to hot-tap is the suction of a compressor. Strainer is installed, but a courser one. So during the drilling, the iron particles will damage the compressor impellers. Or there is some technology that will eliminate that problem?