David Futch, PE
In the presence of non-leaking defects, such as dents, gouges, crack-like features, or corrosion, there are two main options for pipeline repair: steel sleeves and composites. In these situations, there are multiple consideration factors that must be taken into account for selecting the right pipeline repair technique. To start, operators should have a comprehensive understanding of the similarities and differences between the two options.
Steel Sleeves Repairs
Steel sleeves repairs are a common option for repairing pipeline features and have been used for a considerable amount of time. Steel sleeves use steel to repair the sections of the pipeline. In the most basic sense, steel sleeves are adding more material of the same characteristics to the base pipe over a pipeline section to prevent leaks or failures at the point of the defect.
Today’s steel sleeves can be created from split pre-tested pipe or rolled plate. During steel sleeve repairs, welding is required as two split pieces of the steel sleeve are joined together to encircle the pipe. As such, the process for steel sleeve repairs can be lengthy, as the welding process may take several hours, and there is a necessary inspection period after the repair is complete to ensure the safety of the repair.
Composite Repairs
Composite repairs are a relatively new repair method for pipelines. Different brands of composite repair products use different materials. The basic components of composite repair material include fiber, polymer matrix, and load transfer filler material.
Composite repair installation depends on the product used, but most, if not all, composite repairs do not require welding. Composite repairs can typically be installed in a couple of hours after the pipeline is ready for repair. After installation, the composite will be left to cure, which can take anywhere from one hour to 24 hours, depending on the temperature. On a hot Texas day, the composite repair may be installed in just one day.
Introducing the 5 P’s of Pipeline Repairs
The best repair method largely depends on the situation. Either composite or steel sleeve repairs may prove to be better suited for the repair needed, the demands on the repair site, the availability of resources, and the economic benefit. The defining factors for choosing one over the other come down to the base pipe material, the availability of qualified personnel, the price comparison, the ability to procure materials, and the product being transported in the pipeline.
Pipe Material
The material properties of the base pipeline, including the thickness and the chemical composition, are key consideration factors in selecting a repair material.
Thickness. If the pipe material is thin, the risk of burn through during welding increases. Therefore, in some cases, composite repairs may be better suited for the repair.
Chemistry. Depending on the material of the pipeline, including the carbon content and carbon equivalent (CE), welding may pose too high of a risk. Higher CE of the pipe and/or sleeve increases the risk of hydrogen cracking. In this situation, a composite repair may be the best course of action.
Personnel
Whether you are installing a composite or welding a steel sleeve, both require trained and qualified personnel to complete the repair. The qualifications and expertise of the available staff should be considered when making a pipeline repair selection.
Price
The economic benefit of one type of repair over the other largely depends on the situation. The diameter and length of the base pipe that must be repaired will define the demands of the repair system.
For shorter lengths, it may be better suited to use composite repairs. Composite materials are typically provided in shorter segments, provided in kits that cover approximately one foot of pipe. For smaller features, composites can be better suited to meeting repair needs.
For longer lengths, steel sleeves may provide greater economic benefit. Steel sleeves generally come prepared to repair longer lengths of pipe, with some providers offering products that repair up to ten feet of pipe. For large repairs, steel sleeves may be overall more cost-effective.
Procurable
Depending on the urgency, severity, and demands of the feature itself, the availability of repair materials can be deciding factor for which repair material you should use. Operators may have more access to one type of repair over the other, and for features that require fast reactions, ordering a new product not currently on hand may be infeasible.
Product
Finally, operators should have a comprehensive understanding of the effect of the repair method on the product being transported. Under conditions of high pressure and heat, the product can decompose. If there is a risk of the product becoming unstable due to the heat of welding, then composites are a better option.
A Third Option: Carbon Fiber Repairs
Carbon fiber repair systems are a newer technology that is advancing pre-existing composite repair systems. In carbon fiber repair systems, the composite’s structural materials embedded in the polymer matrix are replaced with high-performance carbon fibers[1].
These repair systems have the potential to expand beyond the typical applications of traditional composite repairs.
How to Pick the Right Repair Method
The 5 P’s provide a framework for understanding the different elements that can have an effect on selecting the best repair system for the feature at hand. The key to selecting the right repair method is sound engineering judgment based on rigorous testing and analysis. Without an adequate understanding of each of the 5 P’s, selecting the most cost-effective, resource-efficient, and sustainable repair solution will be much more difficult.
Originally published on June 28, 2022