FormaShield

October 24, 2017
Repair your Pipe: Fixing High-Risk Leaks in Process Piping

Posted by: Casey Whalen

Leak Repairs on process piping can be one of the most challenging composite repair scenarios. These types of repairs must address a much wider set of variables versus typical pipeline repairs including initial defect cause, design temperatures, pressures and the chemical makeup of the product in the pipe itself. 

A leak is typically considered “high-risk” in situations where pressures are over 150 psi, temperatures over 120°F and products considered Immediately Dangerous to Life and Health (IDLH) fluids. To ensure a consistent high quality repair, Milliken Infrastructure treats all leaks as high-risk when utilizing a designed repair.

How did we get here?

The first mistake one can make in the repair process is to assume that all leaks behave the same.  Before considering repair options, understanding the cause of the leak is vital to a successful repair. The most common defect comes from external corrosion. Typically occurring due to chipped or neglected coating, further growth is easily stopped by applying a new coating or a composite repair. However, if the corrosion is allowed to proceed to the point of either a near thru-wall condition or a complete thru-wall condition resulting in a leak, a designed repair will be required.

Additionally, leaks can result from internal wall loss through various means. Ideally, internal wall loss defects have a composite repair installed prior to becoming a  thru-wall condition. In either case, the design of the composite repair is performed at the anticipated end-of-life conditions. This typically means that the expected hole is much larger than the hole at installation. Additionally, certain geometries, such as elbows or tees, can create ideal locations for internal wall loss due to internal fluid flow.

Other potential leak contributors are bad welds, chemical attack, microbial induced corrosion (MIC), stress corrosion cracks (SCC) or abrasive wear caused by passing particulates. Each scenario for a leak implies a different root cause failure mode and may result in small variations on the final design solution to address these challenges.

Repair design concerns

Due to the diverse characteristics of the resulting damage, a one-size-fits-all leak repair option is seldom a sufficient answer. This is where the customization capability of our composite repairs stand out as a far superior and effective solution. To adequately address unique leak scenarios, it is important to examine some of the factors that are taken into consideration during the design process. Topping the list of importance are the potential failure mechanisms of the solution that need to be considered in order to create a successful repair.

Failure Mechanism

Cause

Solution

Other Considerations

 

 

Chemical Attack

Chemical incompatibility between the product flowing through the pipe and the composite repair results in the corrosion thru the pipe and the eventual failure of the composite.

Select a resin matrix for the composite and primer that is chemically resistant to the product passing through the pipe.

Chemical compatibility is highly driven by the chemical % concentration as well as temperature.

 

 

Thru Thickness Failure of the Composite

Fluid pressure forces its way through the thickness of the repair composite creating a void in the composite resin.

Select a composite with either an appropriate fabric structure (i.e. a multi-directional weave) so to create a tighter architecture of the repair and design a sufficient thickness that can provide greater resistance to pressures being emitted from the leak.

Proper installation minimizes voids in the repair. The repair needs to be applied as tightly as possible; A loose fitting repair is more susceptible to through thickness failure.

 

 

 

Adhesive Failure

Fluid pressure acting perpendicular to the composite fabric attempts to peel apart the pipe and composite. This creates a crack in the adhesive that fluid pressure tries to propagate until the edge of the repair is reached.

This failure mode is the primary design concern in the repair standards. To overcome this peeling force and eliminate crack propagation, the repair must be thick enough to provide adequate stiffness toward peeling forces.

Aside from composite thickness, surface preparation of the pipe is key to the success of the repair. A correctly prepared pipe surface will bond better with the adhesive providing a higher resistance to crack growth.

 

 

Active Repair

An active leak acting on a un-cured repair can cause the resin to wash away. This creates a leak path in the repair already present before the composite can set and cure.

A stop gap or emergency repair option must be used to stop the leak and provide a 30-minute window prior to installing the repair where there is no active leak.

Milliken Pipe Wrap does provide several temporary methods to stop leaks prior to installing a longer term composite repair.

 

Other aspects of the repair to take into consideration are preparation and installation time. For example, on a repair of a six inch pipe with a one-foot repair zone, a two-hour preparation and set up time can be expected. The actual composite installation can be achieved in about 45 minutes.

With each leak situation being so unique, each repair requires a certain degree of customization. Part of this customization includes geometry, for example, elbows and tee intersections. Due to varying shapes, sizes and dimensions of these geometries, a form-fitting (non-rigid) repair system is ideal for application to ensure intimate contact around the entire pipe geometry. Utilizing a wet lay-up system is also beneficial for repairing leaks at flanges, reducers or other common piping components.

Product considerations

From low- to high-risk process pipe leak repairs, Milliken Infrastructure can provide a product uniquely engineered to handle the design specifications required of your situation.

  • FormaShield®: This fiberglass based repair system is meant for aggressive leak environments and is available with four different polymer systems: General use, High Temp (HT) and two forms of Chemical Resistance (CR & CR2). This system has a multi-directional woven fabric to maximize leak containment potential.
  • A+ Wrap®: A fiberglass based repair system commonly used to quickly and temporarily repair lower risk leaks scenarios. This system is ideal for applications in wet environments (offshore, underwater, etc.) as it is water-activated.
  • Atlas™: A high-strength carbon repair system used to repair process pipe damages suffering from large mechanical damage. The Atlas™ system is also commonly used to address leaks with large thermal fluctuations.

All of these products require similar steps for preparation and application. Once a stop gap has been put in place on the process pipe or the pipeline has been depressurized and no fluid is present for 30 minutes, repairs can begin. Before installing the repair system, a surface profile must be applied in order to increase the adhesive strength of the adhesive primer. This can be performed either by mechanical prep or media blasting. A NACE 3 minimum surface prep is typically required with a NACE 1 finish preferred.

Load transfer filler must then be applied to the damaged area to create a smooth transition zone between the area being wrapped and the continuation of the pipe length. This process helps prevent voids from occurring between the composite and the pipe. The load transfer filler should also be applied over any stop-gap, welds, “tented areas” or other potential obstructions. An adhesive primer is then applied to the entire repair zone followed by the repair composite. A constricting layer is applied over the repair to tighten and compact the repair to minimize voids. Finally, the repair is perforated to release any CO2 (for the A+ Wrap™) and to allow excess resin to drain. The repair is then allowed several hours to cure before topcoat is applied as needed.

Performed properly and under normal conditions, the leak repair design range is between two to five years depending on the estimated wall loss rate. All composite repairs for potential thru-wall conditions should be considered temporary repairs and should be replaced when the next opportunity presents itself. The repair’s topcoat should be monitored over time to assess any external degradation, and it may require recoating for UV protection. In short, it’s typically safe to say that if there is no longer any leaking then the repair is still working. There are advanced inspection methods to evaluate the integrity of the composite.

Finally, since no two leaks are equal, it goes without saying that high-risk leaks of process pipes should be repaired with a solution intentionally designed and engineered to repair that specific challenge. Repair systems that claim they are the one-size-fits-all solution offer nothing more than a subpar repair.

Next in our Repair Your Pipe series, we’ll look into solving transmission pipeline dents and the specific considerations for an effective solution. Be sure to subscribe to our News and Thought Leadership Blog to catch that and more infrastructure repair insight from Milliken.

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Category: Pipe Wrap

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