When a defect or anomaly jeopardizes the integrity of a pipeline, it necessitates repairs using techniques that bring the pipeline back to its original design specification.
If the repair method fails to restore the pipeline to its original specification, two options are available: either the maximum operating pressure of the pipeline must be reduced, or the pipeline system must be taken out of service.
Repairs may become necessary due to a leak or product release from the pipeline, or upon discovery of a defect or anomaly posing a threat to the pipeline's integrity. The latter may be identified through an integrity assessment mandated by the integrity management rule.
Various methods are available for addressing pipeline defects and anomalous conditions that pose potential threats to pipeline integrity. These methods include:
1. Removal and Replacement of
Pipe
2. Fillet Welded Patch
3. Half Repair Sleeves
4. Weld Overlay or Weld Deposition Repair
Removal and Replacement of Pipe
The removal and replacement of defective pipe is often viewed as the preferred method for pipeline repair, as recommended by most industry standards. This approach involves replacing entire sections of pipe, weld to weld, rather than patching smaller sections. Although more labor-intensive, it reduces the number of round or circumferential welds in the pipeline, enhancing overall integrity.
Fillet Welded Patch
Fillet Welded Patch is utilized for temporary repairs on pressure vessels, covering damaged areas with a patch plate and welding it to the vessel using fillet welds. This method is suitable for addressing damage caused by corrosion or erosion, resulting in localized wall thinning.
Half Repair Sleeves
Half Repair Sleeves are widely recognized as one of the most essential methods for repairing pipeline defects. These sleeves, which can be made of steel or composite material, come in two types: Type A and Type B.
(1). Type A Sleeve: Used to reinforce areas with defects, but not through-wall defects. It fully encircles the pipe, with the halves typically welded together while the ends remain open.
(2). Type B Sleeve: Similar to Type A, but completely welded to the pipe, making it suitable for containing leaks or reinforcing defect areas.
Composite material sleeves involve wrapping fiber material around the pipe in the defective area, serving as an alternative to Type A sleeves and proving effective in defect remediation.
Weld Overlay or Weld Deposition Repair
Weld Overlay/Weld Deposition Repair involves depositing a suitable metal layer onto the pipe surface or fittings through welding. This technique enhances pipe strength and surface protection against corrosion while maintaining the base structure's strength.
Weld overlay utilizes various welding methods like shielded metal arc welding, MIG/TIG welding, submerged arc welding, CO2 welding, or Plasma Transferred Arc welding. It's ideal for complex pipe configurations and offers improved corrosion and wear resistance compared to sleeves, particularly for galvanic, crevice, and fretting corrosion.
To prevent metallurgical defects during weld overlay, selecting compatible electrodes and suitable welding procedures is crucial. Techniques like temper bead welding minimize heat-affected zone hardening by alternating layers of deposited metal with low and high heat input, akin to an annealing process. This control over heat input helps maintain pipe integrity during repair.
Composite Sleeves
Composite sleeves or full composite wraps represent a cutting-edge solution for repairing pipeline defects before leakage or spillage occurs. These wraps are particularly suitable for contoured pipelines and sections with installed fittings, such as small take-off points or metering points.
Capable of restoring damaged pipelines to their original Maximum Allowable Operating Pressure (MAOP), composite sleeves offer the added advantage of coating pipes to shield them from corrosion.
Currently, there are two types of commercially available composite sleeves: prefabricated sleeves and wet sleeves.
(1). Prefabricated sleeves: These sleeves are designed and cured in a factory for rapid on-site installation.
(2). Wet sleeves: These sleeves are wrapped and cured on-site as needed, providing flexibility and adaptability in repair applications.
