HDD-Assist: A recently installed gas main is replaced
When things don’t go according to plan at a jobsite, quick action is required. Trenchless technology is primarily used for underground pipe installations while protecting the surface above. But also, when pipes, which have already been installed, need to be removed again – for example due to damage – the pipe rammer then becomes the drillers best friend. Especially when it is immediately available.
Within the framework of an infrastructure project expansion project near Houston, Texas, HDD company Directional Service South faced an unexpected challenge: A sizable section of a recently installed gas transmission main had been damaged by obstacles in the ground during the installation. Jake Gautreaux, founder and co-owner explained: “For this project, we were tasked with the installation of Ø 500 mm steel gas pipes with installation lengths ranging from 150 m to 920 m. Pipe welds were wrapped in ScarGuard® – to help protect them – a total of 30 HDD crossings over several miles.” On an especially long section over 360 m they noticed some damage on a pipe. The pipe had to be removed and replaced.
For Rick Melvin, specialist for the GRUNDORAM ramming technology at TT Technologies, pipe extraction is an evolution of existing HDD assist methods: “Based on this experience, we were able to develop a method for a full-scale pipe extraction.”
The pipeline project in Houston would put this method to the test.
Pipe extraction: the balance of forces counts
These pipe rammer HDD assist methods have been developed cooperatively between HDD contractors, engineers and trenchless equipment manufacturers for several decades. Pipe extraction has been part of this process. “If, for example, a drill stem breaks or a segment of pipe needs to be removed, we can use the rammer to retrieve or remove these items from the ground,” according to Melvin. It’s about using the right balance of force: “The percussive force of the rammer is combined with the pulling force, which can be an excavator or a direction drill.” That’s where the complexity of the process lies. How to balance and apply the forces in a way to remove the pipe from the ground.
Percussive force of the rammer sets the pipe in motionack to Houston: A very large scratch ran the visible length and breached the coating of the pipe, which had just been installed. Gautreaux: “Now we had to make an urgent decision regarding the future of that section.”
HDD Assist & Rescue
HDD-Method(Static tensile strength)
+ Ramming technology (Dynamic stroke)
= Additional strength for pipe pulling
When problems arise on an HDD project, quick action is required. The ramming method offers proven solutions to avoid costly problems. The so-called HDD Assist & Rescue technologies with GRUNDORAM include:
Drilling inside a protection pipe:
Installation of a casing pipe for the start of a HDD drilling operation
support during pipe pulling
Drill rod retrieval:
loosening jammed drill rods
retrieving jammed product or protection pipes
There was no way of knowing the extent of damage to the pipe underground. After reviewing with the project owner, a decision was made to remove and replace the pipe. Furthermore, the replacement pipe would be completely wrapped in ScarGuard® to prevent any possible damage.
When the extraction work started, the pipe had been in the ground for two months. “The wrapping on the welds is abrasive and creates friction and made it extremely difficult to pull out the pipe,” according to Gautreaux. Initial attempts to use static pull force to remove the pipe failed. Furthermore, we wanted to pull in the 360 m replacement section of pipe at the same time. That’s when we brought the TAURUS rammer in as a support.
For an optimal configuration of pulling and percussive force the rammer was placed at the rear end of the pipe string, to generate percussive force. A 150-ton, 6-part block system was used to channel the static pull force from a crawler track unit, which was doing the pulling, to the lead end of the pipe. The percussive force of the rammer, in this case, is used to get the pipe moving, so the static force can be used to pull it out. After ten minutes of ramming and pulling, the pipe finally started to move. It took the crew two 12-hour working days to remove the damaged pipe and install the new one. The damaged 360 m pipe was pulled out in two separate 180 m sections.
“It was only thanks to the rammer that we were able to get the pipe moving again at all and eventually retrieve it. It proved to be extremely useful”, Gautreaux sums up. “That’s why we bought the GRUNDORAM – to always have it ready for use at a jobsite. When problems arise, time is of the essence.”
The percussive force of the rammer helps, not only with complete pipe extraction, but also to avoid other costly problems, which can occur in HDD projects.