Steel sleeves have been a mainstay pipeline repair method for well over a century.
Composites have made significant inroads as a repair method in the last 20 years.
But what about compression sleeves?
Compression sleeve technology has been a viable repair method for corrosion, lamination-like features, and longitudinal crack-like features in gas and liquid pipelines for several decades but remains a relatively obscure avenue of repair. Even the regulatory requirements of compression sleeves are somewhat murky.
A compression sleeve is similar to a conventional Type A repair sleeve—which provides structural, but not pressure-containing reinforcement to a pipeline—except that it is designed to also apply compression to the carrier pipe. A compression sleeve relies on thermal expansion and contraction of the steel repair sleeve, which results in a compressive hoop stress in the carrier pipe.
The Risks of Introducing an Open Flame to a Jobsite
Until recently, the sole method of prompting heat expansion of a compression sleeve was through utilizing a heating torch and putting it in direct contact with the sleeve. The flame from the torch heats the sleeve directly and prompts elongation in the circumferential direction. This method presents several challenges:
- An open flame is a hazard to any job site and should be treated with caution.
- A single heating torch operator is likely to face difficulty applying consistent heat to the entire surface of the sleeve. Several torches would be required simultaneously (again, introducing more risk), and the margin for error is high. Because it is difficult to manage or control heat distribution in this way, a chance of insufficient, excessive, or uneven sleeve growth is present.
- Manual operation of a heating torch increases the likelihood of error. If too much heat is focused on one area of the sleeve for too long, the pipe itself may become heated, weakening the pipe wall and increasing overall risk.
The above issues suggest a general unpredictability of the repair, a somewhat dubious scenario in a high-stakes and hazard-ridden industry.
Prioritizing Purpose Over Product
When Allan Edwards developed the Compression Sleeve, we began by defining the need in the market, working first to understand current gaps and then a product that would meet that need.
As we worked through this process, two prerequisites became abundantly clear: a new and improved compression sleeve product must be both controllable and measurable before additional “bells and whistles” were considered. Given the unpredictability that an open flame introduced to a jobsite, we knew these basic requirements must hold true throughout the installation, specifically during the heating process. So, we challenged ourselves with a question:
What if you could achieve compression of a Type A repair sleeve while maintaining absolute control over the entire heating process?
It was by leaning into this simple idea that the Allan Edwards induction-heated Compression Sleeve was born.
Why Induction Heating?
The classic example of an induction heating system is the induction stovetop. Induction stoves use an electromagnetic field to heat up a pan while leaving the cooktop surface cool to the touch. Compared to electric or gas cooktops, an induction stove is:
- Energy Efficient: 60% more so that a flame stovetop
- Safer: Heat is transferred only to the pan, leaving the cooktop cool to the touch
- Faster: Heats food 40% faster than other cooktops
The benefits of the Allan Edwards Induction-Heated Compression Sleeve are just as applicable as an induction stovetop – with the end result being a measurable & controllable heating process that enables a highly efficient, safer, and faster compression sleeve repair.
The Compression Sleeve System
The Compression Sleeve heating process is automated using induction coils positioned throughout a specialized heating blanket. The heating assembly for the Compression Sleeve is composed of:
- (2) Induction Blankets w/ Induction Heating Coils
- (4) Temperature Thermocouples
- (2) Hydraulic Sleeve Clamps with Hand Pumps
- Gap Measuring Tool & Temp Measuring Tool
The heating process is both quick and efficient. The induction blanket assembly is placed around a 3-ft long Type A steel sleeve that has been coated with an interior epoxy layer. Hydraulic clamps hold the sleeves halves together. Once the entire Compression Sleeve assembly is in and a “cold gap” measurement of the distance between the sleeve halves has been recorded, the induction heating process is initiated. The sleeve is heated to a target temperature of around 400 degrees Fahrenheit– this carries out all while the heating coils and blanket remain cool to the touch.
During the heating process, circumferential growth is prompted in the sleeve halves, shrinking the long seam gap between the sleeves. Once target growth is confirmed by the gap measurement tool, the sleeve is tack welded. The blanket assembly and clamps are removed, and a final weld is performed across the long seam, locking the sleeves into final position. As the sleeve cools, it contracts, putting the pipe into a state of compression that prevents further crack growth and reduces the hoop stress on the pipe.
Considerations For Use of The Compression Sleeve
As stated above, the primary advantage of the Compression Sleeve is the ability of the system to provide measurable & controllable heat input, a critical benefit of the system. The computer-controlled induction heating process leaves little margin for human error to disrupt the repair. Furthermore, the elimination of an open flame from a jobsite certainly reduces the likelihood of jobsite injuries or other potential hazards. Finally, the Compression Sleeve involves the use of a Type A sleeve, which requires no circumferential end welds. By avoiding direct contact to the pipe, the Compression Sleeve can be installed over pipe laminations without concern. , this is another important benefit of the Compression Sleeve system.
The development of the induction-heated Compression Sleeve system was solely rooted in the identification and execution of a market need. By evaluating current gaps in the industry and producing a product to meet a real-world need, this system is truly engineered with purpose.
About Allan Edwards
Since 1947, Allan Edwards has leveraged our first-hand experience and trusted expertise to steer advancements in pipeline performance. We engineer, manufacture & distribute products that optimize throughput wherever product flows. Our duty is paramount: to deliver risk mitigation you can count on while partnering with you every step of the way. Let’s partner.