On-Line Leak Sealing

Composite Repair

Composite Repairs: Mechanism and Standards

Mechanism: Composite wrap repair systems utilise high strength fibre (e.g. glass or carbon) and polymer resin to create a reinforcing wrap or sleeve over a damaged pipe or vessel. After surface preparation and defect filling (with an epoxy putty for load transfer if needed), layers of resin saturated fibre are wrapped around the equipment, then cured in place. The composite wrap acts like a permanent external sleeve, taking up hoop stress and reinforcing or replacing the lost wall strength of the component. Because the composite is bonded to the substrate, it transfers load from the weakened metal to the strong fibre, the equipment integrity when properly engineered. Notably, composite wraps are suited for non-leaking defects – e.g. corrosion thinning, dents, gouges, or crack reinforcement – rather than aggresive leaks. They can be applied on in-service equipment without shutting down flow, as long as the defect is not actively leaking product.

Governing Standards: Composite wrap repairs are governed by demanding industry standards to ensure they provide reliable long-term performance. The primary standards are ISO 24817 (Petroleum, petrochemical and natural gas industries – Composite wrap repairs for pipework – Qualification, design, installation, testing, and inspection) and ASME PCC 2 (Post Construction Code, Article 4.1, for Non-metallic Composite Repair). These standards specify requirements for material qualification, design calculations (e.g. required wrap thickness and length based on defect size and loads), installation procedures, curing, and inspection/testing of the completed repair. For example, ASME PCC 2 and ISO 24817 require that composite wrap repair systems be qualified through burst tests, environmental exposure tests, and long-term creep/pressure testing to validate their performance over the intended life. Composite manufacturers must provide data on tensile strength and elastic modulus of the composite, bond strength of the adhesive, and demonstrate chemical compatibility with the service environment. It is expected that any composite system used has third party certification of compliance with ISO 24817 / ASME PCC 2, and that engineers design the repair in accordance with these codes.

Design and Installation: Designing a composite wrap repair involves assessing the defect and design/operating parameters, then determining the wrap geometry needed. Important design inputs include pipe diameter, wall thickness, defect geometry (length, depth of corrosion, etc.), operating pressure, temperature, external loads (axial/bending), and pressure cycling data. The required safety factors and thickness of the composite are calculated such that the repaired section can safely carry the hoop stress and any axial or bending loads for the desired design lifetime (which could range from a few months to 20 years). Installation is a critical stage – the pipe surface must be thoroughly prepared (usually bristle blasted to near white metal with specified roughness ) to ensure strong adhesion. Trained and validated technicians then apply the resin and fibre wrap according to a prescribed procedure, ensuring correct fibre orientation, proper overlapping and tension, and elimination of air bubbles. Curing time and conditions must be respected (some systems cure at ambient temperature, others may require heating). Quality control checks (like resin cure hardness tests) are done before the line is returned to full service. Once cured, a composite wrap effectively becomes a structural part of the pipe – it can restore the pipeline’s MAOP (Maximum Allowable Operating Pressure) to original levels when designed and installed correctly. Composite wrap repairs are considered “cold work” – no welding or cutting is involved – which is a safety advantage and means they can often be done on a live line with minimal risk (provided the line pressure is moderately reduced for safety during application).

Compliance and Inspection: Because composite wrap repairs are often classified as permanent or long-term repairs, they must meet code compliance and owner specifications. ASME PCC 2 and ISO 24817 both outline inspection and testing regimes. For instance, a repaired pipe might be pressure tested or at least leak tested at a percentage of operating pressure to verify the integrity of the wrap before declaring the repair complete. Visual inspections are typically required periodically (e.g. during routine maintenance) to check for signs of delamination, cracking of the composite, or new underlying corrosion that could manifest as swelling or moisture ingress. Some operators also add monitoring devices. (such as a ferrous layer detectable by smart pig, or thermography to spot delaminating).

Advantages of composite repairs: Composite wrap repairs offer several technical and practical advantages:

• Structural Reinforcement: They restore or enhance the structural integrity of the component. A properly designed composite wrap repair can carry hoop stress and even some axial loads, effectively returning a thinned pipe to its design pressure capacity. This makes composites true strengthening repairs, beyond just leak plugging.
• No Hot Work and Minimal Downtime: Composites are applied without welding, which means no hot work permits and no risk of heat affected zone issues. Repairs can often be done with the equipment in service (no shutdown required for non-leaking defects). This minimizes production loss.
• Code Compliance and Longevity: When engineered to ISO 24817 / ASME PCC 2, composite repairs are considered long term solutions. They can be designed for a specified service life of up to 20 years and with proper maintenance can remain in place indefinitely.
• Versatility in Application: Composite wrap systems can be applied to a wide variety of geometries and base materials. They are used on pipes, elbows, tees, flanges, valves, and even irregular vessel surfaces, where steel sleeves or clamps might not fit well. They can also be tailored for different environments – e.g. there are wet curing composites for underwater repairs, and high temperature resin systems for hot piping.
• Corrosion Resistance: The composite materials (epoxy, polyurethane, etc. with glass or carbon fibre) are generally immune to corrosion. Once applied, they can also serve as an outer coating, preventing external corrosion of the underlying pipe. This can extend the life of the equipment by not only restoring thickness but also halting further external degradation (assuming the wrap remains intact and bonded).
• Weight and Installation Benefits: Composites add minimal weight compared to bolted clamps or metal sleeves, and they conform to the profile of the pipe surface. Installation can often be completed in hours for smaller repairs, and cure times can be as short as a few hours (fast setting resins) to 1–2 days for full cure. This rapid turnaround and ease of handling (no heavy cranes needed, etc.) can be cost effective.

Limitations and Risks: Despite their benefits, composite repairs have important limitations:

• No Active Leaks: Composites cannot be applied over an actively leaking defect without first stopping the leak. The surface must be dry and clean for the resin to bond. If a pipe has a through wall hole, it is plugged (e.g. with a fast curing epoxy putty or by temporary clamping) prior to wrapping. Attempting to wrap over a leaking hole will result in the resin being washed out and a failed repair. Thus, composite wraps are limited to non-leaking anomalies or leaks that have been stopped by other means.
• Temperature Limits: Composites are constrained by the thermal limits of their resin matrix. Standard systems are designed for moderate service conditions, while specialized high temperature variants can extend the usable range. If exposed beyond their qualified limits, the resin may soften or degrade, reducing the repair’s strength. Resins are not suitable for very high temperature applications unless a system specifically designed and tested for those conditions is used. Each composite wrap repair must be verified against its qualified operating envelope, as applying it outside that range can result in premature failure
• Environmental/Chemical Compatibility: The resin and fibres must be chemically compatible with the external environment and any fluids that may contact the repair. For instance, if used on a pipe carrying aggressive chemicals, there is a risk that a through-wall leak could expose the composite to that chemical from the inside. Standards require evaluating chemical compatibility – some composites might need a protective topcoat or use specific resin chemistry to resist acids, solvents, or UV exposure. If not, the composite could blister, delaminate, or lose strength.
• Surface Prep and Installation Sensitivity: The performance of a composite wrap repair is highly sensitive to proper installation. Inadequate surface preparation (poor cleaning or insufficient roughness) can cause weak bonding and potential delamination under pressure. Likewise, improper mixing of resin, incorrect fibre orientation or not achieving the required thickness will reduce strength. Installation is done by trained technicians following detailed procedures. A mistake like wrapping fewer layers than designed, or contamination of the surface, may result in a repair that does not meet its intended strength. Because these are “field fabricated” repairs, quality control is crucial. Poor installation is the highest cause of failure rather than inherent material issues.
• Inspection and Hidden Issues: Once a composite wrap is installed, the underlying substrate is no longer directly visible. If internal corrosion continues under the wrap (from the inside of the pipe), it could progress undetected. Operators need to include composite covered areas in inspection plans – techniques like ultrasonic thickness gauging through the composite, or monitoring tell tales, might be needed to ensure the defect isn’t growing beyond what was designed for. If a composite wrap repair is expected to be in place for many years, periodic assessment is required to ensure the bond is intact and the defect has not worsened. ISO 24817 provides guidance on inspection intervals based on the risk and design life.

In summary, composite repairs are best suited for non-leaking, structurally significant wall loss or defects where a long-term fix is needed without cutting or welding. They must be engineered and installed correctly, but when they are, composites can permanently restore a component’s integrity to code requirements. Composites are an attractive alternative to steel sleeve welds or replacement, especially for complex geometries or when hot work is undesirable

Temporary Online Leak Sealing: Mechanism and Standards

Mechanism: Temporary Online leak sealing refers to methods of stopping or containing an active leak while the system remains pressurised and in service. The classic approach involves installing a mechanical enclosure (clamp, or box) around the leaking area and injecting a sealant compound into the enclosure to plug the leak path. The sealant is typically a specialized injectable resin or polymer (sealant compound) chosen to cure or solidify in the presence of the process fluid, thereby sealing off the leak. Meanwhile, the clamp or enclosure provides a pressure tight cavity to hold that sealant and also, in many cases, takes some structural load. Essentially, the clamp forms a mini pressure vessel around the leak The two key functions of an online leak sealing clamp are: (1) a mechanical clamping mechanism that grips the pipe or equipment and contains the pressure, and (2) an injection system that delivers sealant into the leak area to fill the void and seal the leak. Common types of online leak sealing setups include flange leak enclosures (halved clamps bolted around a leaking flange, with injection adaptors), valve bonnet leak sealing (injecting sealant into a leaking valve gland or bonnet), and pipe leak clamps for pinhole leaks or cracks. In all cases, the goal is to stop the leakage of fluid without isolating or depressurising the equipment, buying time until a permanent repair or replacement can be scheduled.

Governing Standards: Online leak sealing has historically been considered a temporary or emergency measure, and as such it is not “designed” into the original equipment and falls outside normal construction codes (indeed, regulators note that online leak sealing is outside the scope of ASME BPVC since it’s a post construction activity). However, there are industry standards and guidelines that cover best practices for these repairs:

• ASME PCC 2: This post construction repair code includes guidance on various leak sealing techniques. For example, ASME PCC 2 suggests injection of sealant compound as a solution for online sealing of flange connections and provides design considerations for engineered enclosures (sometimes referenced in PCC 2 Article 2.12 or similar for clamps/enclosures). It emphasizes using proper materials and verifies that the clamp can contain the pressure.
• ASME Section VIII and VIII Div.2 (Analysis): Although not formally covered by repair codes, well-engineered leak repair clamps are typically designed in line with ASME Section VIII, Division 1 pressure vessel requirements. In practice, reputable leak sealing providers manufacture clamps as code rated enclosures, and for more complex geometries, Finite Element Analysis using Division 2 methods is applied to validate performance. Seal components such as O rings and injected compounds are chosen with the same rigor as gaskets in pressure vessels—ensuring compatibility with the service fluid and operating temperature. Taken together, these practices give temporary clamps a level of mechanical integrity that closely parallels permanent pressure equipment.

Design and Installation: The process for online leak sealing generally proceeds as follows. First, the leak site is surveyed and measured. A custom clamp or enclosure may need to be fabricated to fit the specific geometry (pipe diameter, flange type, etc.), unless a suitable off-the-shelf solution is on hand. For flange leaks, a typical enclosure will have injection ports strategically placed. For straight pipe pinhole leaks, a split clamp with sealant grooves or an internal filled void may be used. The clamp is then bolted around the leak area, forming an encapsulation of the leak. Sealant injection is performed using high pressure sealant guns through adaptors on the clamp. The sealant is pumped until the leak stops and the cavity is full and pressure tight. The sealant will cure or solidify, forming a plug. The result is that the fluid leakage is contained within the clamp. Importantly, the clamp is non-structural (just meant to seal), and the underlying pipe still carries pressure loads). Strong back systems are installed to provide axial restraint, ensuring the clamp can safely absorb thrust loads and prevent pipe movement under pressure.

Safety Considerations: Online leak sealing is an operation that requires strict adherence to safety procedures, as it involves working on pressurised, leaking equipment. Key safety points include:

• Assessment First: As emphasized by HSE (Health Safety and Environment), a thorough assessment of the defect and conditions must be done before clamp installation. The team must know the leak size, type (gas or liquid, flammable or toxic?), pressure, temperature, and whether the pipe wall around the leak is still sound. There is a risk of clamp failure or blowout if, for instance, the pipe wall is so weakened that it can’t even hold the clamp or the remaining ligament fails.
• Specialized Personnel: Typically, online leak sealing is done by specialist technicians. They often wear protective gear (for chemicals or high temperature spray) and use custom equipment. The procedure may involve risks like handling high pressure injection guns – improper use could cause injection injuries or cause the sealant fitting to become a projectile. Therefore, training and following a proven procedure is critical. The work area is usually cordoned off and, if flammable, fire guards or fire suppression is on standby until the leak is sealed.
• Monitoring: During injection, one must monitor that the leak has indeed stopped and that pressure on the clamp does not exceed its rating. After sealing, some clamps require periodic re-injection – if a small weep reappears over time, additional sealant can be injected to reinforce the seal. The HSE warns that needing to re inject a clamp can indicate ongoing pipe degradation and should be a red flag to reassess the situation urgently.
• Structural Support: A major safety concern is ensuring the clamp provides structural support if the pipe’s strength is compromised. A clamp that only seals but does not brace the pipe against pressure thrust can be dangerous: if the pipe wall yields or cracks further, the entire section can eject from the clamp. To avoid this, an additional restraint, or strongback, should be installed.

Advantages of Online leak sealing: Online leak sealing’s primary advantage is immediate leak mitigation without shutdown:

• No Process Downtime: It allows plants and pipelines to continue operating when a leak occurs, avoiding the enormous costs and logistical challenges of an emergency shutdown. Leaks – whether a pinhole spraying fluid or a flange dripping – can often be sealed within hours by a mobilized crew, meaning production loss is minimal. This is especially valuable for continuous process industries and critical pipelines.
• Versatility of Application: A wide range of leak scenarios can be addressed. Specialized clamps exist for flanges, tees, elbows, valve bonnets, pump casings, tanks, etc. For example, a flanged joint leaking at a gasket can be enclosed by a clamp that seals around both flange OD’s and injects sealant into the gasket gap. A valve stem leak can be fixed by injecting sealant into the packing gland area. Onshore, leak sealing is commonly done on steam lines, hydrocarbon lines, acids – virtually any fluid, as long as an appropriate seal material can be used.
• Avoiding Emissions and Spills: Sealing leaks online has environmental and safety benefits – it stops the release of harmful or flammable materials. This reduces facility emissions (important for volatile organic compounds or greenhouse gases) and eliminates slip/trip hazards or fire hazards from leaking fluids. Temporary leak seal devices achieve that by containing the fluid. In pipelines, deploying a leak clamp can prevent a small defect from growing into a rupture by relieving the leak and reinforcing locally.
• Emergency Response: Online leak sealing is essentially a form of emergency response and is fast. Experienced crews are often on call 24/7. This rapid response can prevent a minor leak from escalating or causing a prolonged outage. Many large refineries and gas companies maintain contracts with leak sealing services for this reason.

Limitations and Risks: By design, online leak sealing is usually considered a temporary or interim fix, and it has several limitations:

• Temporary Nature and Monitoring: Regulators and industry best practices treat leak seal clamps as short term. The industry mandates that such temporary repairs be removed and replaced with a permanent repair at the next available maintenance window. The reasoning is that a clamp with injected sealant is not as reliable in the long run as a welded repair or composite, and it may deteriorate (sealant can age/harden or get washed out if pressure fluctuates). Thus, while leak sealing buys time, one should plan to permanently fix or replace the component at the earliest opportunity. In many cases, clamps are left in place only until the next scheduled shutdown or turnaround, and indeed operators track all such temporary repairs in their MOC (Management of Change) system to ensure none are forgotten.
• No Significant Structural Reinforcement: Basic leak sealing clamps are primarily designed to seal a leak, not to restore full structural strength of a severely weakened pipe. If a pipe is heavily corroded or cracked, a clamp without special design features may not prevent propagation of damage. Using a simple clamp on a pipe that can no longer carry load is inadequate and can fail catastrophically. Therefore, leak clamps are best for situations where the wall still has reasonable integrity aside from the leak defect.
• Maintenance and Monitoring: A sealed clamp may require periodic attention. For example, if a small amount of leakage reoccurs, technicians might need to re inject the clamp by injecting more sealant. Each injection can only do so much if the underlying defect worsens. Clamps left on live systems can also hide active corrosion or cracking beneath – if not monitored, the pipe could corrode through elsewhere or the clamp bolts could loosen due to vibration/thermal cycles. Thus, temporary repairs increase the inspection burden – operators should include them in operator rounds and ensure they are not unknowingly left in unsafe condition.
• Compatibility and Limits: Just as composites have compatibility limits, so do sealant compounds and clamp materials. A given sealant might only be rated up to a certain temperature or incompatible with certain chemicals. The sealant must also cure properly – some seal under pressure, others need a pressure/temperature change to set. If the wrong material is used, the consequences can be dire. Additionally, leak sealing is not well suited if the leaking area is too large or if the pipe is grossly deformed. There is a practical size limit – a clamp can fix a pinhole or small crack readily, but something like a long longitudinal seam leak or a large section of porous metal may require either multiple clamps or another approach (at some point, replacement is the only safe option).
• Residual Stresses and Load: Attaching a clamp can sometimes introduce local stresses. Bolting it on too tight on a thin wall pipe could collapse the pipe slightly (ovalization). Also, clamps are rigid; if placed on a thermal expansion sensitive line, they may induce expansion stresses. Good practice is to evaluate if the clamp needs a flexibility or if the pipe is free to expand elsewhere. In high vibration service, bolts can loosen unless secured. All these mechanical considerations mean a clamp must be designed and installed by competent engineers who consider the overall system, not just the leak in isolation.

In summary, online leak sealing is an invaluable stop gap solution to manage leaks safely while operations continue. Its role is generally to control the situation until a permanent repair can be executed, though in some cases (small leaks on otherwise healthy pipe) a well designed clamp can essentially become a permanent fixture. Operators must treat each online leak seal as part of a temporary repair program – subject to risk assessment, regular monitoring, and timely replacement. When used appropriately, leak sealing drastically reduces unplanned downtime and improves safety by eliminating active leaks, but it is not a substitute for proper replacement or comprehensive repair of the underlying problem.

Comparative Overview: Composite Repairs vs. Online Leak Sealing

Leak status:

• Composites – require a dry, non-leaking surface; ideal for reinforcing or preventing leaks.
• Leak sealing – designed for live, pressurised leaks; can be applied without depressurisation.

Structural integrity:

• Composites – restore full strength and pressure capacity; become part of the pressure boundary.
• Leak sealing – mainly seals leakage; only structural if designed with reinforcement (e.g., strong backs).

Codes and compliance:

• Composites – covered by ISO 24817 and ASME PCC 2, accepted as permanent repairs.
• Leak sealing – treated as temporary; best practice follows ASME VIII/PCC 2 guidelines, but regulators expect permanent replacement.

Service life:

• Composites – long term, potentially asset life repairs when designed correctly.
• Leak sealing – inherently short term; should be removed or replaced at the next shutdown.

Operating limits:

• Composites – handle high pressures but limited by resin temperature tolerance.
• Leak sealing – clamps with compatible seals can handle higher temperatures (e.g., steam service).

Geometry and access:

• Composites – conform well to irregular shapes and broad surface defects.
• Leak sealing – effective for flanges, valves, and joints where wrapping is impractical.

Cost effectiveness:

• Composites – lower lifecycle cost; competitive vs. replacement.
• Leak sealing – high immediate cost but avoids costly downtime; serves as a bridging solution.

Regulatory expectations:

• Composites – treated as permanent repairs, fully documented.
• Leak sealing – tracked as temporary repairs; must be justified, monitored, and replaced with a permanent fix.

The table below summarizes key selection criteria and how composite repairs compare to online leak sealing: