Repair Methods

Dressing

Dressing involves carefully removing metal from around the defect with a low-powered angle grinder to produce a smooth profile, thereby eliminating stress points. It is a highly skilled operation that must be carried out in accordance with strict guidelines to avoid removing too much metal. Careful continuous measurement of the defect during this process, followed by the full reinstatement of the pipeline coating and/or cathodic protection measures on completion, constitutes an acceptable permanent defect repair method. Typical defects repaired by dressing are gouges, corrosion, spalling, very low-level cracks and manufacturing faults.

Weld Deposition

An application that deposits replacement weld metal into a defect area, weld deposition is generally used for low-level defects including general corrosion, pitting corrosion and limited mechanical damage. It has strict limitations relating to the weldability of the pipe material, the remaining wall thickness and the need for highly qualified welders to perform the operation.

Welded Patch Repairs

Normally circular in shape and made from a material that is as strong as or stronger than the pipeline material, these repairs are used for non-leaking defects. They provide only protection and containment, not support for the defects. Their limitations are much the same as for other welded repairs.

Snug-Fitting Shell

A snug-fitting shell is a full encirclement split sleeve whose main function is to provide support for the defect area. It is constructed to form a close fit around the defective area, leaving little or no annular gap. The longitudinal seams are welded, and if total containment is required, fillet welds are performed at each end. The need to carry out this 'live' welding is the main drawback to this repair. This operation has obvious inherent dangers, and highly skilled, experienced and coded technicians are required. Badly fitting snug-fit shells, or shells that have been fitted using external force to achieve contact, can create 'pinch points' causing stresses in the pinched areas.

Stand-Off Shell

Stand-off shells are used when snug-fitting shells cannot be used because of pipeline distortion or where the pipeline is not straight. This repair is far more complex in the installation process, as each repair is made in stages and can require many pieces. If the defects are extreme or at the point of failure, the pipeline in the repaired area must be drilled through the repair, thereby pressurizing the annulus between the pipe and shell and removing the hoop stress from the damaged area. This requires that the top half of the repair shell be fitted with a connection that can take a standard drilling machine and plugging device. After installation of the shell, the drill is passed through the fitting and the pipewall, withdrawn and the fitting plugged using proprietary drilling and plugging equipment. While perfectly valid, this method has the usual limitations with regard to live welding, but the requirement when necessary to perform the drilling procedure adds cost and risk and is another highly specialized operation.

Epoxy Sleeve Repair^® (ESR)

It has long been acknowledged that filling an annular space between the pipe and steel sleeve with stiff material provides excellent support to a defective area. This fact, together with the inherent problems with the more traditional methods, prompted the development of ESR. ESR is an excellent, well-proven, permanent repair system for pipelines.

• Learn more about Epoxy Sleeve Repair

Hot Tapping

Hot tap fittings are proprietary products that serve the same function and have the same limitations as the modified stand-off shell described above. They allow the defective area to be drilled, pressurizing the annulus and removing the hoop stress from the defect area.

Temporary/Leak Repairs

Usually proprietary bolted clamps, their pressure containment relies on the installer achieving a good seal by tightening the bolts joining the two halves together. If the product is leaking, the top half of the repair is fitted with an offtake, allowing the product to be routed away and removing any pressure buildup during the sealing process. The repair provides only containment. Movement is still allowed in the defect area, and susceptible defects may still be prone to subsequent failure, at which point the repair again relies on its quality of seal. Temporary repairs should be removed from the pipeline and replaced with a more permanent alternative as soon as possible.

Replacement Pipes (Cut Outs)

This is the preferred method of repair. It removes the defective section, replacing it with new, problem-free pipeline, but it is one of the most expensive options, especially when considering environmental issues and lost production. Replacement pipes may be impossible to achieve on pipelines that are strategically uninterruptable.

StrongBack Master Wrap^®

This product is a resin-impregnated tape wrap that is applied directly to the prepared damaged pipeline area. The wrap is activated by immersion in, or external application of, water and thus has the advantage of being applicable to wet lines. This is a good reinforcement application and is used on relatively low levels of corrosion and/or mechanical damage.

Armor Plate^® Pipe Wrap

Armor Plate is very similar to StrongBack, except that the hardening agent is a chemical rather than water. Again, this method is a good reinforcement application and is used on relatively low levels of corrosion and/or mechanical damage.

Wrapmaster

The Wrapmaster repair system is a coil of high-strength composite material with a configuration that allows it to wrap tightly around pipe of almost any size. The layers of wrap are sealed together with a strong adhesive. The defect is filled with adhesive filler to assist with support and load transfer prior to the Wrapmaster installation. This method of repair is ideal for blunt-type defects. It is not suitable for internal defects, sharp crack-like defects or girth weld or circumferential defects. The Wrapmaster repairs are magnetic pig detectable and are available in a range of widths.

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