Preparation for Repair

Once the damaged area has been located, the next step is to prepare the pipeline for the repair. This includes the following steps:

• Identify pipeline materials since they will dictate the repair method.

• Secure all pumping stations and tag out equipment. If the flow cannot be stopped then reroute the flow or reduce flow to lowest rate.

• If the pipeline contains explosive, toxic, or flammable material, then determine the proper mitigation method for specific material.

• If the pipeline cannot be flushed and it contains flammable or explosive materials, then welding or thermal cutting techniques should not be used because of the danger of explosion.

• Remove all obstructions around the damaged pipe section.

• Measure and draw a diagram of the pipe, identifying damaged areas. Sketches, photographs, and/or videos can help topside personnel assess the damage and plan for repairs. Some commercial repair couplings require reasonably round pipe for an effective seal. Refer to manufacturer's directions. Measurements should include wall thickness and out-of-roundness.

• Clean all marine growth from the pipeline to at least 2 to 3 feet on either side of the damage.

• Cut, grind, or bend protruding material from the damaged area to provide a smooth contour for the patch or coupling.

• For severely damaged pipelines it may be necessary to add new sections of pipe. In this case, remove damaged pipe sections and measure/sketch a layout for a replacement section. Elevation changes as well as horizontal distances and bearings of remaining pipe ends will be needed to fabricate replacement pipe sections.

5.3.4 Pipeline Repair

A number of techniques are available to repair damaged pipelines. Selecting the method and the equipment to be used will depend on factors such as: nature of material carried in the pipeline (flammability, environmental compatibility, health hazard); the diameter and material of the pipeline; nature and extent of the damage; site conditions; permanency of the repair; and operating pressure of the pipeline.

Manufacturers of commercial products for conducting pipeline repair are listed in Appendix A. Available repair products vary from simple clamps to complex couplings capable of sealing and tapping into pressurized pipelines. The categories of commercially available equipment for both land and underwater pipeline repair applications are:

• Clamps and Couplings: Both flexible and rigid clamps for repairing leaks.

• Misalignment Flanges: Specifically designed to accommodate angular misalignment.

• Bolted Couplings: Gasketed couplings for attachment to pipe and joining pipe sections together.

• Transition Couplings: For joining pipes of different diameters, or where there is a separation between pipes.

• Hot Tap Couplings: Provide a means of tapping into active pipelines for diverting flow or plugging the line without leakage. Primarily designed for tapping into oil and gas production files.

• Welded Flanges and Couplings

• Compression Flanges

The discussion below considers the following techniques:

• Expedient on-site fabricated patching techniques.

• Commercial patches.

• Concrete encasement.

• Replacing damaged pipe with new pipe sections.

5.3.4.1 Clamps and Fabricated Patches (for minor repair to low-pressure noncriti-cal pipelines). In some applications it may be appropriate to make repairs using patches that are fabricated on site. In most cases these repairs should be considered temporary but may be made more permanent by encasing the patched pipe section with concrete or wrapping with fiberglass tape impregnated with a water-activated resin. Figure 5-7 shows some simplified on-site, fabricated patch configurations.

Any of these techniques may be useful depending on the size of the hole, internal pressure in the pipeline, and required final integrity of the seal.

In all cases the pipe surface to be patched must be thoroughly cleaned of marine growth. Jagged material and protrusions should be smoothed before applying the patch.

• For temporary patches on small holes in low pressure pipes where a seal is not critical, use a clamp or clamps in combination with a patch and an elastomeric gasket or other sealing material such as an underwater setting epoxy.

• The clamp should be a minimum of 1-1/2 inches wide. The repair may be made permanent by encasing the damaged section in concrete as discussed later. Small piping may be wrapped with fiberglass tape impregnated with a water-activated resin (Appendix A). For large diameter pipes, chain binders and wire rope in combination with turnbuckle binders and other cinching mechanisms may be used to hold the patch in place.

• On steel pipelines the most permanent repair is made by welding the patch to the pipe. However, underwater welding requires considerable experience and skill, and is not recommended unless experienced personnel are available. Consult the U.S. Navy Underwater Cutting and Welding Manual, NAVSEA S0300-BB-MAN-010.

Clamps with gasket over small leaks

Gasket

Clamps with gasket over small leaks

Gasket

Clamps with patch and gasket

Clamps made of barstock

Band clamps

Double bolt band clamp

Clamps made of barstock

Banding strap

Band clamps

Band clamps

Double bolt band clamp

Banding strap

Figure 5-7. On-site patches and clamps used in conjunction with various materials (steel, plastic, etc).

• On metal pipelines, the pipeline repair patches and clamps should be reviewed to determine potential problems with corrosion.

• Estimating Patch Thickness - If the steel pipeline carries pressurized gas or fluid then it is necessary to select the thickness of the patch and strength of the clamp or attachment method so that it will not rupture under pressure. The patch should be formed to fit the contour (diameter) of the pipe.

Thickness of a steel pipe patch, either welded or clamped, may be approximated by the following formula:

where:

p = anticipated pressure in pipeline d = outside diameter of pipeline

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