Pipeline Hot Tapping

Hot tapping is an alternative technique that allows the 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, and 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 is the preparatory stage for line plugging with inflatable, temporary balloon plugs (stoppels).

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 below and shown in Exhibit 1.

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 in order to center a hole saw that cuts out the “coupon,” or curved section of pipeline wall.

Fitting. Connection to the existing pipe is made within a fitting, which can be a simple welded nipple for 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.

Valve. The valve on a hot tap connection can be either a block valve or a control valve for the new connection, and must allow the coupon (section of pipeline wall cut out by the drilling machine) to be removed after the cutting operation. Suitable valves include a ball or gate valve, but not a plug or butterfly valve.

 

Exhibit 2 provides a general schematic of a hot tapping procedure. The basic steps to perform a hot tap are:

1. Connect the fitting on the existing pipeline by welding (steel), bolting (cast iron), or bonding (plastic) and install the valve.
2. Install the hot tap machine through the permanent valve.
3. 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.
4. Remove the tapping machine and add the branch pipeline. Purge oxygen, open the valve, and the new connection is put into service.
5. Hot taps can be vertical, horizontal, or at any 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, even older pipes merging with new. New, lightweight tapping machines are also available that allow a hot tap to be performed by a single operator, without additional blocking or bracing.

Safety manuals and procedural outlines are available from the American Petroleum Institute (API), American Society of Mechanical Engineers (ASME), and other organizations for welding on in-service pipelines for all sizes, flow rates, and locations. These manuals provide information on what to consider during welding, including burn-through prevention, flow in lines, metal thickness, fittings, post weld heat treatment, metal temperature, hot tap connection and welding design, and piping and equipment contents.

Vendor manuals and equipment catalogues are also good sources for determining which size and type of equipment is most appropriate. Several vendors have published comprehensive outlines and guides for performing hot tap procedures, including information on tapping on various materials, job-site evaluation and preparation, selection and installation of fittings and other equipment, and safety precautions. Most importantly, because this is a hazardous procedure, each potential hot tap must be evaluated on a case-by-case basis and a detailed, written procedure should be prepared or reviewed before starting each job to ensure that all steps are taken properly and safely.

References:

http://www.epa.gov/gasstar/documents/ll_hottaps.pdf

https://edarikahiki.wordpress.com/2013/02/04/pipeline-hot-tap/

Dega Damara Aditramulyadi

Student ID : 15512046

Course      : KL4220 Subsea Pipeline

Lecturer   : Prof. Ir. Ricky Lukman Tawekal, MSE, Ph. D.

                  Eko Charnius Ilman, ST, MT

Ocean Engineering Program, Institut Teknologi Bandung

http://www.ocean.itb.ac.id/en/