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Southern African Gas Association case study on hot tapping and line stop technical specification

Southern African Gas Association case study: Hot tapping is a means by which access is made to the inside of an operational pipeline, using either a drill or a circular cutter, it is the process of drilling a hole in an on-stream operational piping system without pouring its contents or interrupting its flow. A hot tap is performed when it is not possible or impractical to take piping or equipment out of service.

Hot Tap Applications include:

  • Attachment of a branch connection to the line,
  • Installation of an internal probe or monitor,
  • To stop or redirect flow in a line for maintenance or repair purposes.
  • Implies positioning a branch fitting on an operating pressurised line, flowing or stagnant. Followed by cutting a hole in the header through the branch to allow connection to the flowing media. Normally implies using a welded fitting,
  • Can also be applied as a repair method to remove defects, i.e. dents.

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Hot work

Hot Tapping is classified as Hot work, an operation that can produce heat from flame, spark or other source of ignition with sufficient energy to ignite flammable vapors, gases, or dust. Hot Work includes electric arc and gas welding, chipping, flaming, grinding, cutting, abrasive blasting, brazing and soldering. Special procedures and permits are required when hot work is to be performed in certain areas.

Due to the process of Hot Tapping being potentially harmful, it may only be performed by a competent and qualified person i.e.

  • “One who is capable of identifying existing and predictable hazards in the surroundings or working conditions which are unsanitary, hazardous or dangerous to employees and who has the authorization to take prompt preventative and corrective measures to eliminate them”
  • A person found competent by the employer, by way of his expertize, gained through training in the procedure to execute a hot tap, who by extensive knowledge, training and experience has successfully demonstrated the ability to solve problems relating to Hot Tapping subject matter. It is the responsibility of the employer to ensure that their employees have the skills and knowledge to perform their tasks safely.

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 Obtaining Clearance for doing a Hot Tap:
  • The hydro test shall be witnessed and signed off by the AIA
  • Before signing off the Certificate of Conformity (COC), the contractor and client shall do a visual inspection of the Hot Tap stub and all associated attachments, such as studs, nuts, gaskets, new piping, blind flanges etc. to ensure that it conforms to all the requirements.
  • A defects list shall be compiled and all defects shall be rectified before the COC may be issued.
  • The COC shall be signed off before a Hot Tap may be done

The scope of hot tapping involves the attachment of welded branch fitting to piping or equipment in service, followed by creating an opening in the piping by means of drilling or cutting inside the attached fitting, without upsetting the process or spillage of the content

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 Hot Tap Fittings

Hot Tap fittings are either bolted or welded to the existing header pipeline. A tapping/drilling machine is attached to the valve, which is attached to the hot tap fitting. A cutter, attached to the tapping machine is inserted into the hot tap fitting through the valve and the tap is made. In the case of a permanent valve, a branch connection can be made, allowing flow through the outlet.

Selection of Hot Tap Fittings

For reduced-branch taps, weld neck flanges on a weld-o-let can be used, but the size of the branch must not exceed 50% of the header diameter, to ensure remaining strength is not compromised. It also compensates for the material that is cut out of the header and provides strength to support the Hot Tap valve and Hot Tap Machine.Where the branch will exceed 50% of the header diameter, Hot Tap fittings are full-branch or reduced-branch split tees, designed for use with Tapping Machines.

Where unlisted material under ASME is used to manufacture a Hot Tap Fitting. Where listed ASME Material is modified, there shall be an Approved Mechanical Design. An Engineer and AIA signs off in accordance with the applicable ASME code. For South African Legislative Compliance the Pressure Equipment Regulations under the OHS Act No 85 of 1993, as well as SANS347 shall comply. A registered Professional Engineer must sign off the design.

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CST29(Pty)Ltd. has been performing Hot Tapping and Line stopping in the Petrochemical Industry. Particularly at Sasol since 2004,  for the replacement, abandonment, additions and modifications of pipe work from 1/2“ up to 60” diameter without the need for shutdowns or interruptions to consumers or critical services, in accordance with, but not limited to, the following Industry Standards:

  • API RP 2201 Safe Hot Tapping Practices in the Petroleum & Petrochemical Industries.
  • ASME IX Welding to the ASME boiler and pressure vessel code or the ASME pipework codes
  • ASME B31.1 Power Piping
  • ASME B31.3 Chemical Plant and Petroleum Refinery Piping
  • ASME B31.4 Pipeline Transportation Systems for Liquid Hydrocarbons and Other Liquids
  • ASME B31.8 Gas Transmission & Distribution Piping Systems
  • ASME VIII Boiler and Pressure Vessel Code
  • API 510 Pressure Vessel Inspection Code
  • API570 Inspection, Repair, Alteration, and Rating of In-service Piping Systems
  • API 578 Material Verification Program for New and Existing Alloy Piping Systems
  • API 653 Tank Inspection, Repair, Alteration and Reconstruction
  • API 1104 Welding on Pipelines and Related Facilities
  • API RP 582 Welding Guidelines for the Chemical, Oil and Gas Industries
Hot taps and and Line stops successfully completed by CST29 (Pty) Ltd;

 

  •   Petrol
  •  Fuel Oil
  •  Light Oil
  •  Diesel
  •  Ash Water
  • Crude Oil
  • Natural Gas
  • Flocculated Water
  • Instrument Air
  • Plant Air
  • Plant Air
  • Processed Water
  • Gas Oil
  • Syngas
  • Foam Water
  • LP and MP Steam
  • Flare Lines
  • Cooling Water
  • Methane Gas

 

  • Hydrogen Rich Gas
  • Nitrogen
  • Demineralized Water
  • Fire Water
  • Gas Liquor
  • Methane Rich gas
  • Gas Liquor
  • Catalyst

 

 

The option to adequately perform abandonment, additions and modifications of pipe work without the need for shutdowns or interruptions to consumers. However, critical services is a more efficient way of altering pipe work today.

Critical Considerations before doing a Hot Tap

  • Design and Construction code used to manufacture the Header Line
  • Legal requirements
  • Header Material and Hot Tap Fitting Material selection compatibility, as well as weld procedures and welding consumables
  • Heat Input and Run Out Rate of filler material deposited in the weld during Welding
  • Operating Pressure, temperature and flow rate of the product in the header
  • Possibility of spontaneous combustion of the product in the line in the absence of oxygen (Refer to case studies of welding done on in-service ethylene lines)
  • Remaining wall thickness of header before welding, to prevent burn-through, obtained by means of wall thickness and lamination scans at the weld area on the header line
  • Carbon Equivalent of the header material, as excessive carbon content can lead to excessive hardness and cracking of welding
  • Health and Safety and applicable plant and product specific PPE
  • Approved Hot Tap Procedures
  • Permit Requirements and Authorizations
  • Risk Assessments- Hot Tapping is a high risk task. Successful Hot Tapping is about eliminating, mitigating and controlling of risk
  • Tapping Machine and cutter selection for product, temperature and pressure
  • Product Handling, relating to protection of the environment, surrounding area and safety of Hot Tap personnel, where hot taps are completed and equipment must be depressurized before removal of the Hot Tap machine from the Hot Tap Valve
About SAGA

We promote the safe and efficient use of methane based gas within Southern Africa through:

  • Educating in safety and standards
  • Providing qualified gas practitioners
  • Assisting industry to comply with relevant legislation
  • Administering a safe gas equipment scheme
  • Ensuring a climate conducive to safety
  • Advocating the efficient use of gas and equipment
  • Interface with government on regulatory issues
  • Upholding sound environmental practices

For more information on SAGA visit www.sagas.co.za

 

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Dennis Ayemba
Country/ Features Editor, Kenya

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