When a pipeline operator discovers a defect or anomaly that poses a threat to the integrity of their pipeline, they repair the pipeline employing techniques that will restore the pipeline to its original design specification. If the repair technique cannot restore the pipeline to its original design specification, the operator must reduce the Maximum Operating Pressure of the pipeline.
Repairs can be required due to a leak or release from a pipeline, or because the operator has become aware of a defect or anomaly that poses a threat to the integrity of the pipeline. The operator can become aware of the latter through an integrity assessment as required by the Integrity Management rule.
When an operator becomes aware of the need to repair a pipeline, the operator first identifies the location of the repair. Depending upon the location, the operator may have to obtain permits, notify property owners, prepare a dig plan, and let contracts to outside firms as necessary. Since the majority of pipe is underground, the operator first must excavate the repair site. Once the repair location is uncovered, the operator will inspect the pipeline for the general condition of the pipeline coating. The pipeline coating will be removed to expose the exterior of the pipe. If the defect or anomaly is on the exterior surface of the pipe, the pipe will be cleaned. Once the defect or anomaly is exposed, the operator may perform an ultrasonic test, a dye penetrant or magnetic particle test, or take an etching of the anomaly. Dimensional data such as, depth, width, length, and exact location on the pipe, will be taken to compare with the information provided by the in line assessment tool. At this point the operator is ready to repair the pipeline.
There are several methods that may be used to remediate pipeline defects and anomalous conditions that can present a potential threat to the integrity of the pipeline. These include:
- Removal and Replacement of Pipe
- Deposited Weld Metal
- Full-Encirclement Sleeves
- Mechanical Bolt-on Clamps
Removal and Replacement of Pipe
Removal and replacement of defective pipe is always considered a good alternative to repair. Most industry standards suggest that, where practical, pipeline repairs should be made by replacing sections of pipe. Many operators will replace a complete section of pipe - weld to weld – rather than cut out and replace a smaller section. This requires more excavation, but it minimizes the number of circumferential or girth welds in the pipeline.
Grinding may be used to repair the pipeline if the defect is a shallow crack or gouge of the pipe wall. Removal of material by hand filing or power disk grinding constitutes a repair of a defect or imperfection if the stress-concentrating effect of the defect or imperfection is eliminated and the amount and distribution of metal removed does not significantly reduce the pressure-carrying capacity of the pipe. Many operators do not permit grinding to be used as a method of repair.
Deposit of Weld Material
Depositing weld metal on a pipeline attempts to eliminate the defect by replacing lost or damaged metal and restoring the continuity of the pipe. Deposition of weld metal is simple, direct, and can be applied where the use of a full-encirclement sleeve is impossible (such as for the repair of fittings and field bends).
Full Encirclement Sleeves
Sleeves are probably the most important and widely used method of general repair of pipeline defects. Sleeves may be steel, Type A (reinforcement) or Type B (pressure retaining reinforcement), or composite material.
Type A sleeve – a Type A sleeve is used to reinforce the area where a defect exists. The defect cannot be a through wall defect. The type A sleeve is a full encirclement of the pipe. The sleeve halves are normally welded together while the sleeve ends are not.
Type B sleeve – a Type B sleeve can be used to contain a leak or to reinforce an area where a defect exists. The Type B sleeve is similar to the Type A except the sleeve is completely welded to the pipe.
Composite material – a fiber material is wound around the pipe in the area of a defect. This material can be used in lieu of a Type A sleeve and has proven quite effective in remediating defects.
Mechanical Bolt on Clamps
Mechanical bolt on clamps are as the name indicates. Defects are reinforced by the application of a full circumferential clamp where the two halves are bolted together. An elastromeric seal is placed between the pipe wall and the clamp to contain any leaks that might develop.
Date of Revision: 12012011