During the last decade, GL Noble Denton has been working to develop an alternative solution which removes the need for welding to a live pipeline, and is both rapid and safe. Over 240 of its trademarked Grouted Tees have now been installed on a range of both high and low-pressure pipelines of varying diameters, and this solution has provided many advantages over other techniques.
The Grouted Tee was originally developed to overcome issues of welding connections onto gas transmission pipelines. Since then, GL Noble Denton has worked with a number of pipeline operators to develop the technology further to accommodate thin-wall pipelines, high flow rates and numerous pipeline products.
The Grouted technology does not require any site welding, and full pressure and flow can be maintained during installation and hot tapping. The tee’s half-shell construction is simple, and GL Noble Denton says that it can also accommodate much larger ovalities in the main pipeline than alternatives.
Installation to a Tee
Installation is carried out with minimal pipe preparation; all that is required (after the pipe has been exposed and the excavation rendered suitable for the equipment) is for the existing coating to be removed and the pipe surface grit-blasted to ensure it is both clean and has a suitable “÷key’ to which the subsequently injected grout can adhere.
The tee is made up of several equally important components. For each application, the tee piece is custom-manufactured to the appropriate size as half shells that are clamped by bolts around the host pipe. The tee can be set at any position around the host pipe to suit the configuration of the pipework.
A special hydrogenated nitrile rubber (HNBR) seal is installed at the position where the branch line will meet the host pipeline, and is retained in position by a steel containment ring inside the half shell within the tee piece. Opposite the branch in the other half shell, spreader plates are located to allow seal compression during tightening of the bolts and subsequent compressive load to be spread over the pipe and not to act as a point load (for which the host pipe would not have been designed).
Once the half shells have been clamped around the host pipe and the bolts tightened to the predesigned load, the gaps between the ends of the half shells and the host pipe are filled with a rapid-setting epoxy putty which – within approximately 60 minutes – provides a seal to prevent escape of the epoxy grout that is injected as the next part of the operation.
The three-part epoxy grout is injected to fill the space between the inside of the tee piece and the host pipe, and has the effect of both adhering to both surfaces to keep the tee securely in place and of transferring the load from the main pipe to the newly-installed outer shell. Tests have shown that even without the bolts to hold the two halves of the Grouted Tee in place, the epoxy grout’s adhesive properties ensure that the pressure-bearing capacity is retained.
The liquid grout is pumped into the space between the tee piece and the host pipe from the bottom. A number of “÷tell-tale’ points are used, both to allow the air in the annulus to exit and to ensure an even progress of the injected grout as it fills the space. These points are sealed subsequently with set screws.
The grout is then left to harden, which usually takes 24 hours, after which the tee is pressure-tested to line pressure, and released for service.
Teeing up projects
UK high-pressure gas pipeline operator National Grid has installed many of the 240 Grouted Tees that have been used to date; GL Noble Denton has licensing agreements with both Furmanite and Subsea 7 to also use the technology, onshore and offshore respectively. In addition to the UK, the tees have been installed successfully in Brazil, Norway and Kazakhstan.
The components of the tees, designed by GL Noble Denton, are not manufactured by the firm, so suitable third-party engineering companies are used for this purpose. The special HNBR seals are supplied by FTL Technology and are imported from a specialist manufacturer in Italy. Rotabolts are specified for the half-shell bolts because of their simplicity and ease of installation, and most importantly to ensure accurate tensioning is applied.
Apart from providing a straightforward and elegant solution to the problem of attaching a tee piece to an operating pipeline, the Grouted Tee has a further advantage over other methods, as it requires only a very small team to complete its installation.
While welding a tee onto a high-pressure pipeline can require upwards of eight to ten welders and support staff, a Grouted Tee can be installed at any size by a team of only five. GL Noble Denton says that a total elapsed time onsite of two days is normally required (after completion of the necessary excavation), much of which is required solely for the curing of the epoxy grout. Ordering and manufacturing time for pipeline sizes from 4-12 inches is between four to six weeks; larger sizes can take up to 12 weeks to manufacture and deliver to site.
GL Noble Denton has developed solutions using this technique for installing two tees of similar or different sizes, and for diver-installed use of the technology subsea. A clever double-Y branch fitting has also been developed, one application for which could be to provide a pig launcher or receiver.
The Grouted Tee is suitable for operations with numerous pipeline fluids and gases in the temperature range -50å¡C to +125å¡C, and can be manufactured to suit a host pipe diameter range of 2-56 inches and diameter-to-wall-thickness ratios of 120 or less.
Live pipeline intervention is hazardous, but essential for maintaining product supply. Pipeline operating companies often need to install tees to allow new lines to be connected or to divert flow for repairs, and it is both convenient and economic to maintain throughput in the main line while such operations are undertaken.
About GL Noble Denton
GL Noble Denton is a global independent provider of technical services and software to the oil and gas industry. The company works with some of the sector’s best-known corporations to provide a wide range of services across the lifecycle of their assets.
GL Noble Denton’s expertise spans upstream operations, such as onshore and offshore exploration, production and delivery storage; midstream import, storage and processing; and downstream distribution. With over 3,500 employees and a presence in more than 80 countries, GL Noble Denton plays a key role in helping to design and develop, operate and execute, and assure some of the industry’s most innovative solutions.