Definition of Hot Tapping: The process of adding nozzle or valve to a line or equipment without removing contained material on live line. Hot tapping is the last option when it is not possible to isolate the process line at any cost.
It is method of making connection to existing piping or pressure vessel without interruption or emptying that section of the vessel. This means that pipe is continuous in operation whilst maintenance or modifications are being done to it.
The hot tapping process consist of two phases,
1. The welding process in which nozzle part has to fix on line.
2. The mechanical cutting of the hole onto the pipe/equipment.
Procedure for hot tapping safety:
1. Hot tapping work shall be carried out by specialized contractor.
2. Risk assessment shall be carried out by specialized consultants who are having the required expertise and knowledge.
3. Contractor shall obtain approval from company for specialized contractor/consultant for hot tapping.
4. Once work has started, it should proceed without interruption until the hot tap has been completed and valve closed.
5. Determination of metal thickness- the area to be hot tapped shall be visually and physically identified. An ultrasonic thickness test measurements of the metal must be made, within 48 hours before to work, at the exact location s of the proposed hot tap.
6. Prepare all the materials as approved specification for tie-in.
7. Bench test on all valves prior to installation shall be carried out. It is nothing but hydro test of valve body and steam in presence of PD.
8. QC approval shall be taken prior too fitting.
9. Hot-Tapping is not applicable for stress relieved pipelines.
10. Flow in Lines- such as flare line it is necessary to continuously purge or flood the line with steam, inert gas, hydro carbon gas to ensure line does not have gas pockets of flammable mixture during the welding process, suggested product velocities during welding
Ø Liquid- 0.4 m/s (minimum)
-1.75 m/s (maximum)
Ø Gas-0.4 m/s (min) and max having no limit.
Ø Product temperature during actual welding.
Max- 370, min 7 *c
11. At any time during hot tapping operation pressure of fluid inside pipe shall not exceed 7000 kpa and hot tapping shall not carried out on sub atmospheric pressure.
12. Hot tapping shall not be carried out on pipes which contains:
Ø Vapor/ air or oxygen/vapor mixture.
Ø Chemical such as acid and chlorides.
Ø Caustic and amines.
Ø Unsaturated hydro carbon such as ethylene.
Ø Oxygen enriched atmosphere or chlorine.
Ø Compressed air.
Ø Equipments and piping under vacuum.
Ø Sulphuric acid.
Ø H2S above toxic level.
13. Welding shall be qualified and expert in butt welding joints and pass muck up test.
14. Parameter, operating techniques, electrode shall be detailed in procedure must be adhere.
Concept of hot taping: