Pipeline Hot Taps
Summary
Hot tapping is a procedure used to make a new pipeline connection while the pipeline remains in service, flowing natural gas under pressure. The hot tap procedure involves attaching a branch connection and valve on the outside of an operating pipeline, and then cutting out the pipeline wall within the branch, removing the wall section through the valve, and closing the valve for future connection. Hot tapping allows an operator to make a new connection without having to shut down the pipeline or vent gas to the atmosphere. This practice allows for uninterrupted service to customers, as well as reduced emissions of methane. Hot tapping is an alternative to the practice of “pipeline blowdowns” which entails shutting down a portion of the system and purging the line of gas before beginning any work.
Description
Hot tapping is a technique that allows a pipeline connection to be made without shutting down the system and venting gas to the atmosphere. Hot tapping is also referred to as line tapping, pressure tapping, pressure cutting, or side cutting. The process involves attaching branch connections and cutting holes into the operating pipeline without interruption of gas flow, and with no release or loss of product. Hot taps permit new tie-ins to existing systems, the insertion of devices into the flow stream, permanent or temporary bypasses, and constitute the preparatory stage for line plugging with inflatable, temporary balloon plugs (known as stopples).
Hot tapping equipment is available for almost any pipeline size, pipe material, and pressure rating found in transmission and distribution systems. The primary equipment for a typical hot tap application includes a drilling machine, a branch fitting, and a valve. Hot tapping equipment is described here:
- Fitting: the connection to the existing pipe is made within a fitting, which can be a simple welded nipple for a small (e.g., one inch) connection to a larger pipeline, or a full-encirclement split-sleeve tee for extra support when the branch is the same size as the parent pipeline. The tee wraps completely around the pipeline, and when welded, provides mechanical reinforcement of the branch and carrier pipe.
- Drilling machine: the drilling machine generally consists of a mechanically driven telescoping boring bar that controls a cutting tool. The cutting tool is used to bore a pilot hole into the pipeline wall to center a hole saw that cuts out the “coupon,” or curved section of pipeline wall. The pilot drill includes a “catch” to withdraw the cut-out pipe wall (coupon) and withdraw it past the valve.
- Valve: the valve on a hot tap connection must allow the coupon (the section of pipeline wall cut out by the drilling machine) to be removed after the cutting operation. Suitable valve types include ball or gate valves, but not plug or butterfly valves.
The basic steps to perform a hot tap are as follows:
- Connect the fitting on the existing pipeline by welding (steel), bolting (cast iron), or bonding (plastic) and install the valve.
- Install the hot tap drilling machine through the permanent valve.
- Perform the hot tap by cutting the coupon from the pipeline through the open valve. A special device retains the “coupon” for removal after the hot tap operation. Withdraw the coupon through the valve and close the valve.
- Remove the tapping machine and add the branch pipeline. Purge air from the branch pipeline, open the valve, and the new connection is put into service.
Applicability
Hot taps can be vertical, horizontal, or at any radial angle around the pipe as long as there is sufficient room to install the valve, fitting, and tapping machine. Current technology allows for taps to be made on all types of pipelines; at all pressures, diameters, and compositions; and even older pipes merging with new. Lightweight tapping machines are also available that allow a small hot tap to be performed by a single operator, without additional blocking or bracing.
In preparation for a hot tap project, operators will need to determine the maximum operating pressure (during welding of a fitting and the hot tap), type of pipe material (i.e., steel, cast iron, plastic), and condition of the parent pipeline (internal/external corrosion, wall thickness) to ensure a safe project. A hot tap connection can be made on a pipeline only where the parent pipe material is in good condition. Other conditions to evaluate include the flow of fluid in the pipeline to carry away the heat of welding, location of nearby valves for emergency isolation in the event of an accident, the desired tap diameter, working space around the connection, location of other pipeline welds, and imperfections or obstructions. Operators should also determine if the line is “looped,” as many gas transmission companies avoid operational disruptions by shifting the load to a parallel line. It is advisable to develop and follow a written plan to ensure full and proper evaluation of a future connection.
Methane Emissions Reductions
Methane emission reductions can be determined by taking the difference in emissions from the source before and after the specific mitigation action was applied. The emissions reductions achieved by implementing this mitigation option (i.e., hot tapping) can be estimated by calculating the volume of natural gas that would have been vented as follows:
ER = A × L × PC
Where:
ER = Emissions reduction estimate (Mcf gas/yr)
A = Cross sectional area of pipeline (in2)
L = Length of pipeline between tapholes (feet)
PC = Pressure correction factor (unitless)
The cross sectional area of the pipeline (with a conversion to square feet) is calculated as follows:
A = π × D2/4 × [1 ft2/144 in2]
Where:
A = Cross sectional area of pipeline (in2)
D = Pipeline diameter (inches)
The pressure correction factor is calculated as follows:
PC = LP/AP
Where:
PC = Pressure correction factor (unitless)
LP = Line pressure (psi)
AP = Standard atmospheric pressure (psi) (14.7 psi)
After combining all numerical constants into a conversion factor (CF), the initial equation can be rewritten in terms of pipeline diameter (D), pipeline length (L), and line pressure (LP) as follows:
ER = D2 × L × LP × CF
Where:
ER = Emissions reduction estimate (Mcf gas/yr)
D = Pipeline diameter (inches)
L = Length of pipeline between tapholes (feet)
LP = Line pressure (psi)
CF = Conversion factor (0.000371) (i.e., π/[4 × 144 × 14.7])
Other Benefits
In addition to reducing emissions of methane, employing hot tapping procedures may:
- Reduce service interruptions: Allows for continuous system operation by avoiding shutdowns.
- Maintain pipeline structural integrity: Avoids cutting, realignment, and re-welding of pipeline “T” sections.
Lessons Learned
References
American Petroleum Institute. (2003, July). Safe hot tapping practices in the petroleum and petrochemical industries (Recommended Practice 2201), Fifth Edition (reaffirmed March 2020). https://www.api.org/oil-and-natural-gas/health-and-safety/refinery-and-plant-safety/occupational-safety/rp-2201
American Petroleum Institute. (2021, July). Welding of pipelines and related facilities (Standard 1104), 22nd Edition.https://www.api.org/products-and-services/standards/important-standards-announcements/1104
American Society of Mechanical Engineers (ASME). (2021.). Gas transmission and distribution piping systems, ASME B31.8-2020. https://www.asme.org/codes-standards/find-codes-standards/b31-8-gas-transmission-distribution-piping-systems
McAllister, E. W. (Ed.). (2013, September). Pipeline rules of thumb handbook: A manual of quick, accurate solutions to everyday pipeline engineering, Eighth Edition. Gulf Professional Publishing. https://doi.org/10.1016/C2013-0-00277-0
McElligott, J. A., Delanty, J., & Delanty, B. (1998, November 30). Use of hot taps for gas pipelines can be expanded. Oil & Gas Journal. https://www.ogj.com/home/article/17226609/use-of-hot-taps-for-gas-pipelines-can-be-expanded
Transportation of Natural and Other Gas by Pipeline: Minimum Federal Safety Standards; Design of Pipeline Components. U.S. Code of Federal Regulations. Title 49, Subtitle B, Chapter I, Subchapter D, Part 192, Subpart D (2022). https://www.ecfr.gov/current/title-49/subtitle-B/chapter-I/subchapter-D/part-192/subpart-D
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