The most critical step for any composite repair is the installation. In accordance with the standards, composite repairs can only be installed by trained individuals. The standards also dictate a variety of requirements, including coursework, hands-on training and a test.
To assure the best possible chance of success, the training programs need to be taken more seriously by the operators, trainees and the trainers. Although many manufacturers tout “quick and easy” to install, every system has numerous trivial details that can cause a repair to go awry.
Highlighting potential problem points during training is almost as important as learning how to apply the material itself. Instead of only listing over-simplified installation steps, installer manuals need to provide a list of common issues, concerns and limitations that will help technicians and supervisors make the right calls in the field.
Individuals newly trained on a product need to be closely monitored for the first several repairs. A recommendation for newly trained crews is that a manufacturer representative is present to supervise the first several repairs until a crew has shown a level of expertise deemed sufficient. Additionally, tests should be taken seriously — senior personnel or a relevant engineer should take the test, perhaps beforehand, to ensure the legitimacy of it.
Site and Pipe Preparation
Once the first resin is mixed or the first pouch opened, a timer has started on the installation process. Some general guidelines for site preparation include ensuring that all tools are ready and accounted for. Solvent to clean the pipe needs to be on hand; it is recommended that only Acetone M.E.K. or Toluene are used because they do not leave behind residue as they flash off. All individuals need to be donning proper personal protective equipment (PPE) to minimize the amount of oily residue left on the pipe or fabric due to touching. Additionally, all materials to be used need to be checked for expiration dates and to ensure that an appropriate quantity is present.
Before beginning any application, the pipe also needs to be properly prepared. All soft coatings, rust and sharp edges should be removed unless otherwise specified by the manufacturer. Ideally, media blasting is used to bring the pipe to a NACE No. 1 standard with an anchor profile higher than 2.5 mils, which can be measured using replicant tape. Ensuring a clean, rough surface will allow the adhesive primer to adhere to its best potential. Depending on the defect, additional work, such as removing sharp edges, may be needed. After all surface work and measurements have been performed, the repair area needs to be marked according to the design package and cleaned using an approved solvent. Achieving adequate surface prep is extremely important for any leak repair scenarios or if axial loads are significant.
Load Transfer Filler and Adhesive Primer
The load transfer filler and adhesive primer are used here to describe the components used to fill in the defect, reshape the pipe as necessary and be the initial adhesive boundary between the substrate pipe and composite repair material. Load transfer filler can come in many varieties but ultimately needs to fulfill one purpose: Provide a path for stress distribution from the pipe to the structurally reinforcing composite.
A filler material should be relatively sag-free, easy to apply and can be applied to various defects and obstructions without creating voids or air pockets. Filler material should be applied in any corroded areas or dented regions and should further be applied over any welds. When applying the filler material, the goal is to create a surface that is as flat on a round pipe as possible and will not create any hollow spots or voids when a wrap is applied tightly over the region.
With the load transfer filler installed correctly, the next step is to apply an adhesive primer. It should be noted that not all composite repair manufacturers use an adhesive primer — if this is the scenario with a repair being considered, make sure that appropriate testing has been conducted and that the method being used will provide adequate adhesion and moisture ingress protection if needed. The adhesive primer should be applied over the entire repair area that is to be immediately wrapped and then allowed to set until it begins to thicken. The purpose of waiting is to ensure that a composite wrap does not squeeze out all the adhesive primer if it is being applied tightly.
There are many types of composite wraps available and many have unique steps. The following section is only intended to highlight critical aspects that should be common across all composite repair systems.
Generally, the different systems can be split into three categories.
Rigid coil systems are composites that have already been cured containing a fabric and resin. These systems have been pre-stressed and shaped for specific pipe sizes within a tolerance. Intended for straight pipe segments, rigid coil systems typically use a starter pad to assist with initial placement and then are stretched and wound onto the pipe. As the layers in a rigid coil system are solid, an additional adhesive is applied between each layer to ensure that the system does not uncoil. Rigid coil systems are not naturally form-fitting and need to be compressed to ensure that a tight fit exists. Pipe that has been deformed or has a high degree of ovality may prove to be a challenge.
Water-activated, pre-impregnated repair systems contain a fabric that has been impregnated with a base resin but has not cured yet. Sealed in an air-tight pouch, these pre-preg systems can be opened on-site and activated with water, which eliminates the need for any epoxy measuring and mixing. Once activated, the composite can be applied to many geometries and defects tightly to ensure form-fitting contact. The composite is comprised of polyurethane, so it is highly recommended that an adhesive primer is used to ensure a good bond between the composite and the pipe. Most of these systems have testing and a history of underwater repairs as well.
With field-impregnated repairs, fabric and resin are shipped separately, allowing for custom resins and fabric sizes if needed. To minimize potential human error, it is recommended that when pre-measured resin kits are used that smaller fabric sizes are implemented. If too much resin is mixed and not used quickly enough, the exothermic process of polymerization may cause the resin to overheat and smoke, potentially causing a flammability issue. Field-impregnated repairs allow for the largest use of on-site customization, but this comes at the cost of installation speed. One last note of caution for these systems is regarding how much resin should be used during the wet-out process. Too much resin will cause the tensile strength and modulus to be reduced and may interfere with stress transference.
Regardless of the system style used, all composite repairs follow a few basic principles:
- Need to be applied tightly to the composite and ideally in compression while it is curing.
- Intimate contact between layers to allow for adequate stress distribution.
- The systems each need to be installed in such a way to prevent potential water ingress.
- Need to be chemically compatible with the environment.
- If multiple pieces are used, they should be installed in a way to allow stress to be transferred appropriately and avoid sagging materials.
Specific documentation is ultimately the responsibility of the pipe operator, but the creation and distribution of it should rely heavily on the composite designer. A quality verification form or something similar should be provided for every repair performed and linked to the design documentation. If allowed, take photos at various steps in the installation process because a trained expert may be able to identify issues missed by the site supervisor.
Basic information that should be recorded for every job:
- Installer and supervisor names, roles and ID (if applicable).
- Pipe prep work such as recording surface roughness, cleanliness and measured repair zone.
- Environmental conditions such as humidity, temperature and weather.
- Batch numbers for every component used, including rigid-coil systems.
- Verification at every major installation step.
- Installation time and cure profile.
- Inspection report.
Having this documentation will not only help ensure that a repair is properly installed, but should the repair integrity ever be questioned, this information can also greatly assist in determining the cause.
Casey Whalen is engineering supervisor for Milliken Infrastructure Solutions.