In the pipeline industry, repairs do not often have the luxury of slow response times. To ensure that efficiency is maintained and production quotes are met, repairs must be both timely and cost-effective. Extended loss of productivity can have a catastrophic impact on the operator’s bottom line. Due to their ease of use and versatility, full encirclement steel sleeves have been a popular repair solution among pipeline operators for over a century.
Two variations of full encirclement sleeves are typically used as repair methods, each with important differences. The first is a manufactured repair sleeve. Manufactured repair sleeves are die-formed or rolled from ASTM-grade plate. They are purpose built to reinforce in-service pipelines and tend to be both cost-effective and ensure proper fit-up is achieved. However, a lack of universal specification for manufactured repair sleeves means that any quality assurance for this product falls squarely on the shoulders of the sleeve provider or operator specification, with no regulatory standard of compliance.
The second repair sleeve variation is one constructed from pre-tested steel pipe. Sleeves formed from pre-tested pipe utilize line pipe that has been qualified for service through hydrotesting and other engineering tests. The pipe is initially split into two half pipe sections and the edges are ground down to the approximate size and shape of a repair sleeve. Because of their stringent testing requirements — and the lack of a minimum sleeve manufacturing standard – some operators prefer split half pipe sleeves to repair sleeves manufactured from plate. However, split pipe sleeves come with their own set of drawbacks.
A fundamental issue with constructing sleeves from split pieces of half pipe is the inevitable waste it generates. This waste occurs because the split pipe sleeve does not have a big enough inner diameter (ID) to be able to fit well over the outer diameter (OD) of the same size pipe. For example, attempting to fit a 24” split pipe sleeve over a 24” pipeline will result in a fit-up gap—with the sleeve being too small—since the pipe OD is larger than the ID of the split pipe sleeve. This occurs because the split pipe was manufactured according to pipe size dimensions – its ID is too small to fit properly over the OD of the same size pipe. It is being used to suit a different purpose than was intended when produced. This fit-up differential does not occur with manufactured repair sleeves because the sleeve is manufactured so that the sleeve ID matches the pipe OD.
Consider a practical example: If one were to take a pair of size 10 tennis shoes and attempted to fit one of the shoes inside of the other shoe, it would not fit without significant distortion. While both shoes have been manufactured to fit a size 10 foot, the inside of the shoe is not designed to fit a size 10 shoe because of the size differential of the inside vs the outside of the shoe. The same is true for a split pipe sleeve attempting to reinforce a pipeline of the same diameter.
To account for this ID/OD differential, both sleeve halves for a pre-tested pipe sleeve must be cut with an overlap of at least 185 degrees of the pipe surface, or 370 degrees of the total circumference, to ensure enough coverage for welding across the center seam.
However, because both the top and bottom halves of the split pipe sleeve must be “overcut,” the undercut half of the sleeve (175-degree half) is rendered useless and must be discarded. Practically speaking, this means that twice the amount of pipe is needed to complete a full encirclement split pipe sleeve repair compared to ordering an exact amount of manufactured repair sleeves. Even if a larger-diameter split pipe sleeve was used, it would require extensive re-rounding to fit the smaller pipeline – a labor-intensive scenario not realistic in the field.
When waste levels are high, costs will inevitably be high as well. Furthermore, apart from the considerable usage required for split pipe sleeves, the cost to produce and install these sleeves mounts extremely quickly. Some, but not all, costs associated with split pipe sleeves are detailed below:
- Hydrotesting equipment, labor and materials (welding end caps, TOR fitting)
- Hydrotesting costs (8-hr test)
- Cut costs: splitting section of pipe in half and removing weld caps post-testing.
- Grind time labor to shape sleeve edges after splitting to ensure proper alignment.
- Material waste (half of the split pipe sections are discarded)
- Third-party inspection of hydrotest
- Downtime spent waiting on test results
- Installation time
Fit Up Issues
Perhaps the most significant shortcoming of pre-tested pipe sleeves is their pervasive fit up issues. This primarily occurs because of the ID/OD differential mentioned above. The “overcut” section of sleeve must be matched with another “overcut” sleeve half to ensure enough coverage to adequately fit over the pipe.
As displayed above in the left figure, this creates a visibly distorted fit over the pipe, which must be corrected during the sleeve installation. A sleeve with fit-up issues like this will likely not sit in close contact with the pipe even after extensive fit-up manipulation. With gaps present, the sleeve cannot effectively “take load” away from the pipe from the pipe, hampering its effectiveness as a reinforcing agent. When a repair sleeve is installed over a pipe, it is critical to ensure that at least 90% of the sleeve is in direct contact with the pipe to enable the sleeve to provide optimal reinforcement. This direct sleeve-to-pipe contact is essential to reduce the hoop stress of the pipe and transfer it to the sleeve. See Allan Edwards testing program on the critical importance of sleeve fit-up when reinforcing pipeline defects. Fit-up issues resulting in gaps between a steel sleeve and the carrier pipe increase the chances of poor long-term reinforcement.
While both manufactured sleeves and pre-tested pipe sleeves have merit, there are a handful of factors that negatively impact the performance of steel sleeves constructed from pre-tested pipe. While this sleeve type incorporates an extra layer of validation through hydrotesting of the original pipe, issues with inflated costs, extreme waste, and pervasive fit-up difficulties hamper its overall viability as a repair method. Manufactured sleeves, despite having no recognized regulatory manufacturing standard, are better positioned to grow as an effective repair sleeve method through increased regulatory standards, proactive participation by sleeve providers in full-scale validation testing programs, and widespread adoption of a universal sleeve specification.
See what Allan Edwards is doing about it: Allan Edwards has been in the repair sleeves business for over 75 years. If you would like to learn more about how we are working to close the manufacturing standards gap for repair sleeves, contact us here.