A Houston refinery recently required rehabilitation of 16,000 ft of 6-in. ductile iron pipe as it was experiencing multiple leaks at the pipe’s joints and pinholes. This refinery — also a tank terminal — is one of the most sophisticated chemical tank terminals in the world, and the hub for global and regional trades to and from the U.S. Gulf.
This particular terminal operates a 6-in. processed water line that carries treated wastewater to a treatment facility located about three miles north of the refinery. This 35-year-old line experienced multiple failures and leaks that forced the terminal to suspend use of the processed water line. The owners of the terminal were forced to truck the material down to the treatment plant at an exorbitant cost.
Facility engineers sent out an RFP for cured-in-place pipe (CIPP) in order to rehabilitate the line. Complicating the process was the fact that the line went underneath railways, waterways and went through a corridor, which has a network of pipelines through it making conventional dig-and-replace impractical.
A Primus Line certified installer responded to the RFP and met with the client to discuss potential solutions. The client quickly recognized that CIPP was not the best solution, and that Primus line was the correct choice as a rehabilitation method. Primus Line’s solution was one third of the cost and one third of the project duration time, compared to that of conventional CIPP methods. It is important to understand how this product is different than CIPP or conventional sliplining. Typical length for CIPP is about 1,000 lf maximum. While some of the larger installers have equipment that is capable of longer runs, the average run proposed by the CIPP contractors to the owner was average of 750 lf; whereas the Primus Line is capable of 8,200 lf in one run.
This Flexible Kevlar liner, which is a composite system consisting of the liner itself and the end fitting or connectors, this system was originally designed for the gas market and is incredibly durable and capable of high pressure as a result of the combination of Kevlar sandwiched between polyethylene outer and inner sleeve providing protection of Kevlar weave from any damage during the insertion process. The inner coating of polyethylene produces a factor of 150 and increases the volume of water moving through the pipe. The liner is stored on spools, pre-folded and taped ready to be pulled into place, this reduces the friction during the insertions and allows us to navigate multiple changes in direction and inclination. Once the liner has been pulled into place, crews utilize air pressure at roughly 7 lbs to inflate the liner and break the tape. It’s at this point the pipe takes on the round shape it will maintain the rest of its service life. The connectors are then installed providing a monolithic and guaranteed leak-free pipe for years of trouble-free service. This process truly mitigates all risk of a problem during the installation. The installation process is generally simple and not lengthy since: (1) there is no curing process during installation and (2) one installation section can be up to 8,200 ft; reducing the number of construction pits required. The installation process generally involves several steps as described below:
- Accessing the pipe.
- Cutting the pipe.
- Camera inspection of old pipe prior to cleaning.
- Pipe cleaning
- Liner insertion. The originally folded line is spooled onto transport reels at the starting point. A winch is then placed at the destination pit, where the winch rope is pulled through to the pit at the starting point to insert the liner;
- Liner inflation. The liner can be inflated using the compressed air or water;
- Connector installation
- Pressure or leak test.
After significant evaluation of all proposed technologies by the engineers of the pipe owner, it was determined that Primus Line was the best solution for this project when compared to the alternative technologies submitted. This decision was based on performance of the product, installation time (one-third that of CIPP) and overall cost savings ($1.5 million cheaper than CIPP), a smaller footprint and the ability to work in the 103 F average daily temperatures and heavy rains that where present during the install.
The material buildup in the line was significant. The installer utilized a pigging method for cleaning and was fairly aggressive; this process took a bit longer than originally anticipated. Once the line had a free inner diameter, a soft pig was sent through the line to verify the pipe was in fact ready for the liner
The challenges associated with this particular project included the long runs, as well as several runs inside the active refinery itself, with multiple bends including two runs with 90 degree vertical turns. Complicating the installation process was that the refinery could not be shut down during the project. The installation consisted of nine pulls of DN150/6-in. low pressure flexible liner. Two pulls were in excess of 4,000 ft of continuous liner, one pull was exceeded 3,000 ft, and there were multiple shorter runs with 90-degree bends. The project duration was only four weeks.
One section that was located outside the perimeter of the refinery in what’s called “Exxon corridor.” This posed an even greater problem for conventional methods of rehabilitation as multiple pits on this location would require coordination with multiple property owners to grant permission to dig and work in the pits creating greater overlay of safety security and doubling the cost for work in this area. The one section here consisted of 4,300 lf, along this section are 3 to 30-degree bends. To use conventional CIPP would require at least four runs with five pits; conversely Primus Line was pulled into place in one section in one hour. Once the two end connectors where attached, the pipe was ready for service within six hours.
Two of the sections, approximately 850 ft long, run under an active rail system and had two 30- and one 45- degree and ended by a 90-degree transition vertically to the surface. This was accomplished with no problems with flexible Kevlar liner.
Final Pressure Test
All lines were successfully pressure tested at 300 psi, with an operating pressure of 200 psi. Along with a successful installation, the client also reported a significant increase in flow rate.