Composite repair systems are continuously improving. Technology advances are enabling the introduction of more composite products to the market, and more installations are improving industry understanding of the range of applications for composite systems. The growing number of installations is contributing to increased confidence in composites for both emergency and long-term repairs. These repairs generally can be carried out without negatively impacting operations, encouraging more potential users to take a closer look.
Taking the leap
In some cases, offshore companies have chosen a composite solution as a last resort.
For an operator offshore Thailand, a composite repair was made to avoid a traditional solution that could not be carried out without seriously impacting project economics. The asset owner had discovered wall loss on a 32-in. riser, but cutting the riser and replacing the pipe would have required production to be shut in, resulting in a loss of approximately $125,000/hr, or more than $3 million per day. Replacement also would have required the logistics of sourcing the pipe and a vessel to transport it to the rig as well as engaging qualified welders to carry out the work, a process that could have taken months.
Instead, the riser was evaluated to determine the extent of the corrosion so a composite solution could be designed. Experts examined the pipe details, noting that the riser had lost significant wall thickness at an area where the riser transitioned through a concrete floor on the rig and was on a long radius elbow joint. The decision was made to use a unique pre-impregnated, bi-directional composite system that would reinforce the riser. This wet-applied system ensures the proper fiber-to-resin content ratios that are essential for reliable performance on transmission and distribution pipelines, oil and gas risers, process piping and is appropriate for complex geometries such as elbows, tees, flanges and girth welds.
Installing the composite repair
To promote adhesion, the technicians cleaned the riser with power tools to remove rust, paint and other foreign particles. The pitting and corrosion defects on the pipe were filled with two-part, high-compression strength epoxy putty. Using filler to address defects before applying the composite has two purposes: it restores the pipe to its original geometric shape and helps in transferring the load from the riser to the composite system.
Once the filler was applied, technicians coated the riser with the high-compression strength two-part Kevlar reinforced epoxy. Like the filler, the epoxy has two functions. It arrests corrosion and promotes the bond between the riser and the composite wrap, and it provides a load transfer medium engineered to cycle and work under extreme pressure strain and aggressive pressure cycling. Finally, the line was wrapped with a high-strength, fiberglass composite wrap to provide structural integrity to the repair. The materials were applied over a length of about 3 m (10 ft) to restore the riser to its original design pressure of 1,580 psi.
By using this high-quality composite repair system, the riser was repaired in less than 36 hours. A full hydrostatic pressure test of the cured repair at 1,700 psi (117 bar) for 4 hours provided confidence that the riser could be returned to service. It was restored to full operation later that afternoon, and production resumed, eventually reaching full capacity of 17.8 MMcm/d (630 MMcf/d).
Testing reliability over time
The riser had been in service for five years when the decision was made to remove the repaired segment. The intent was to perform inspections and tests to gain a better understanding of how the composite had withstood five years of wear. It is important to note that there were no issues with the performance of the repair during this time.
Part of the process involved a full review of the product testing and compliance information to verify the long-term values used in the original design. This review, coupled with the full site inspection and product tests of the original repair, would serve as proof of the composite repair’s effectiveness for long-term use. The results would be used in the development of subsequent composite system designs.
As the contractor removed the composite repair system on location, adhesion testing and coupon inspections were made on the original repair system. These tests showed that the composite repair not only functioned as expected, but that there was no noticeable degradation of the adhesion of the system, which meant the composite would have continued to function as designed had the riser remained in service. Full inspection of the pipe wall thickness also revealed that the riser had experienced no further corrosion, which proved the composite also functioned successfully as a corrosion coating.
These test results, combined with the performance of the repair during five years of field service, established the composite repair as a viable option for the owner, which not only reinstalled the composite repair on the original section of the riser but installed similarly designed composite repairs on other areas of the same pipe. These sections also will serve as test/inspection points to provide further field testing of the composite system.
Testing during product development
Composites materials used in structural strengthening are multicomponent systems that include a reinforcing fiber (glass, carbon, aramid, etc.), a saturating resin, a primer polymer and a filler compound. Understanding the role of each component (on both microscopic and macroscopic scales) in the system and its performance behavior is critical to ensuring a design that is based on limit state analysis. Thorough material performance analysis requires an understanding not only of the molecular behavior of the material but also an understanding of how that translates into a macroscopic performance.
Usually, microscopic and macroscopic studies constitute different fields of research. Most R&D groups do not pursue them concurrently. However, when a technical team understands the connection between them and explores the two fields together, the knowledge of the materials is more complete, and there is much greater confidence in the products that are designed. This is a costly process, but R&D is vital to designing composite repairs that perform under exacting conditions on critical components.
The performance of this composite system in the field is a testament to the R&D process, validating the design as well as the design process.
Efficacy and efficiency drive adoption
Composite technologies are changing the way corrosion repairs are carried out offshore. Developed specifically to contend with corrosion, composite technologies have been used to repair a range of offshore defects, producing results that prove their value in extending the service life of offshore rigs.
As companies in the offshore industry work to contain costs, more will begin using composite solutions that reduce risks and deliver reliable and durable repairs without compromising project economics.
Contact E&P's Executive Editor Jennifer Presley at firstname.lastname@example.org for comments or questions about this story.
This story first appeared in E&P magazine's "2019 Offshore Technology Yearbook" issue, which published in May. Read the other "2019 Offshore Technology Yearbook" articles:
Operators Foresee Vast Potential
Composites Gain Ground (story above)
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