Repair Leak – Different Type of Pipe Leak Repair Clamps and Their Effectiveness
One of the fundamental aspects of a damaged/deteriorated pipe that dictates the type of pipe repair component to be applied is the external pipe surface condition. If the external surface is damaged to the extent that an elastomeric seal cannot provide sufficient sealing forces in the immediate vicinity of the damage, or in the relatively unaffected areas adjacent to the major damage (these areas being used to effect the sealing of ‘stand’-off repair clamps), the external pipe surface may need to be re-instated using some form of filler material. Products comprising of composite wrap and rebuilding materials have been shown to accommodate such areas of extensive damage and have applications for a whole range of defects, including corrosion, non-propagating cracks, dents or gouges in both axial and circumferential orientation, and girth weld associated anomalies.
Types of Repair Clamps
The simplest form of repair component is a metallic patch which may be applied to cover a small, non-leaking defect. The repair involves the welding, by fillet welding to the pipe, of a suitably curved patch. The pipe wall in the weld regions, which are away from the defect area, must be of sufficient pipe thickness and must be defect free. This type of repair of leaks is very rarely applied to high integrity applications and offers no major advantage over a simple patch clamp – a bolted clamp that holds a patch of elastomeric material adjacent to the defect area. An example of a patch clamp in shown below.
Figure 1 Patch clamp
In the case of a small pin-hole leak on a section of pipe, a simple patch clamp may be used or a special pin-hole leak repair clamp may be used. The pin-hole leak repair clamp utilises a locator pin which guides a pointed cone seal into the leaking hole. Pressure is then applied to the cone seal by a force screw and once the seal is compressed the pin may be removed thus completing the seal. This type of repair of leaks is capable of withstanding working pressures of up to 138 bar (2000 psi). An example of a pin-hole leak repair clamp is shown below.
Figure 2 Pin-hole leak repair clamp
A defective section of pipe may be simply reinforced by the use of simple encircling sleeves. The sleeves are in the form of two halves and are a close fit to the outside diameter of the pipe. The two halves are welded together longitudinally (backing strips are used for the longitudinal welds to prevent weld induced damage, or mechanical property changes, at the pipe surface). For pressure containing applications, the sleeve must also be fully seal-welded to the pipe. An example of an encircling sleeve is shown below.
The most common form of pipe repair component is the ‘stand-off’ repair clamp. These repair clamps are usually cylindrical in shape and are formed in two half shells. Low pressure clamps, however, may be furnished in the form of a flexible one-piece assembly that can be ‘sprung’ over the defective pipe. Stand-off repair clamps are sometimes referred to as ‘enclosures’ by virtue of the fact that they totally enclose the defective area within a sealed pressure containment vessel. The sealing of the enclosure is typically by elastomeric seals at the longitudinal joints of the two half shells and seals at the ends of the ‘cylinder’. These seals may be energised by the compression forces caused by the tightening of the two halves or can additionally be energised by any leakage of the pipe contents – acting on a lip-type seal, commonly referred to as a ‘self-seal’ arrangement. Examples of typical cylindrical stand-off repair clamps are shown below.
Figure 4 Medium duty ‘stand-off’ type repair clamp
Enclosure type repair components are also capable of repairing leaks, sealing damaged flanges and bends/elbows, as illustrated below.
Figure 6 ‘Self-seal’ type repair enclosure
In the case of repairing leaks for a flange, special enclosures, which seal on the outside diameter of the flange halves, are available as illustrated below.
Figure 7 ‘Outside diameter’ type flange repair enclosure
Unlike the ‘self-seal’ type repair enclosure illustrated at Figure 6 that totally encloses the flange assembly, the ‘outside diameter’ type flange repair enclosure needs to, additionally, seal at the flange’s bolt holes. For this reason, the above illustration features an additional sealant injection port at the centre of the fitting (the other screwed ports are used for injecting sealant should the seal between the outside diameter and the clamp be ineffective). Figure 8 below illustrates the sealing of the flange bolt holes.
Figure 8 Sealant injection at flange bolt hole area
Considerations When Applying Different Type of Repair Techniques
|Applicability of repair components to repair scenarios (straight pipe sections)|
|Repair Scenario||Patch||Encircling Sleeve||‘Stand-off’ clamp/connector||Epoxy-filled sleeve|
|External metal loss – localised||Yes||Yes||Yes||Yes – consider cost effectiveness|
|External metal loss – extensive||No||Yes||Yes – c/w new pipe section||Yes|
|Internal metal loss – localised||Yes||Yes||Yes||Yes – consider cost effectiveness|
|Internal metal loss – extensive||No||Yes||Yes – c/w new pipe section||Yes|
|Leak||No||No||Yes – consider seal material suitability||Yes|
|Temperature, size and longevity capabilities of various repair components|
|Repair method/component||Maximum pressure rating||Temperature range||Size (normal diameter) range||Temporary or permanent repair|
|Patch clamp (see Figure 1)||7 bar (100 psi)||Depends on seal material 1||½’’ to 42’’ (13 to 1000mm)||Temporary|
|Pin-hole clamp (see Figure 2)||140 bar (2000 psi)||Depends on seal material 1||½’’ to 48’’ (13 to 1200mm)||Temporary|
|Encircling sleeve (see Figure 3)||Same rating/size as the original piping||Permanent|
|Complete circle clamp c/w 360o patch gasket||16 bar (230 psi)||Depends on seal material 1||Up to 30’’ (800mm)||Permanent|
|One-piece stand-off clamp (see Figure 4)||20 bar (300 psi) 2||Depends on seal material 1||2’’ to 48’’ (50 to 1200mm)||Permanent|
|Stand-off type (enclosure) clamp (see Figure 5)||ASA Class 9001b 3||Depends on seal material 1||4’’ to 48’’ (100 to 1200mm)||Permanent|
|Flange repair enclosure (see Figure 6)||ASA Class 6001b 3||Depends on seal material 1||½’’ to 12’’ (13 to 300mm)||Permanent|
|Outside diameter flange clamp (see Figure 8)||ASA Class 6001b 3||400oC 4||½’’ to 24’’ (13 to 600mm)||Temporary|
|One-piece stand-off connector (see Figure 12)||16 bar (230 psi) 2, 5||Depends on seal material 1||Up to 30’’ (800mm)||Permanent|
|Heavy duty connector (see Figure 13)||ASA Class 25001b 3||-50oC to +230oC 6||All diameters||Permanent|
|Epoxy-filled sleeve (see Figure 14)||100 bar (1450 psi)||3oC to 100oC||Same size as the original piping||Permanent|
|Composite repair||50 bar (725 psi)||-20oC to +60oC 8||All diameters||Temporary 8 and permanent|