As part of its network system between the three production sites of the Werra plant, K+S relies on a pipeline that crosses under the River Werra in the middle of Germany. This pipeline had been installed using horizontal directional drilling. The length of bore was 365 metres, with a diameter of the pipeline being DN 500. Testing of the pipe insulation revealed damage to the coating, which leads to corrosion of the buried pipeline. The work Visser & Smit Hanab performed included running first a survey of the pipe and second the survey of the borehole, retrieving the pipe, analysing and refurbishing the existing borehole (since drilling a new one was not an option due to spatial restrictions), welding and installing a whole new pipeline.
We deployed a wide range of equipment to complete the job, such as a complete drilling spread, pipeline equipment, several special reaming tools, and gyro tools. One particularly indispensable tool was the 140-tonne pipe thruster, which is often used to apply extra pushing force during a standard HDD project. In this case, the pipe thruster actually provided the necessary pulling force for retrieving the original pipe. The thruster was set up on one side of the river (the pipe side), while a pneumatic hamer was attached to the pipe on the other bank (the rig side). This was also where the drill rig was located. After a few hits with the pneumatic hammer, the pipeline moved. The pipe thruster was then able to pull the pipe out of the borehole, with a pulling force of 25-30 tonnes. As the pipe was pulled out, the quality of the coating was inspected along its entire length. The string was then cut into sections and transported off-site.
Engineering & craftsmanship
This left the borehole filled with drilling mud and thus available for various measurements and cleaning runs to better survey and evaluate the situation inside. After the cleaning run, which is a run with a barrel to wash out the borehole, the borehole was surveyed in a so-called gyro run. Our engineers subsequently documented the situation. This information was used by Visser & Smit Hanab to formulate a plan, in close consultation with the client, for conditioning the borehole adequately, so that the pending pullback operation would proceed smoothly.
Conditioning the borehole was challenging. The upper layer of the subsurface consists of a combination of sand and gravel followed by sandstone at deeper levels of the drilled route. We used a variety of specially equipped reamers, barrels and buckets pulled through the hole in both directions to improve the borehole.
In the meantime, the new pipeline was welded and coated. Before pulling in the pipeline, we installed an extra PE pipe in the pipe casing. This pipe was filled with water to allow the pipeline to 'float' in the drilling fluid during the pull-in operation. It was important to ensure that the pipeline had the lowest possible effective weight in order to minimise friction. That kept the chance of damage to the coating during the pull-in to a minimum.
Visser & Smit Hanab used its HDD drill rig and ancillary equipment for refurbishing the borehole and during the pull-in operation. To stabilise the borehole, V&SH used a special drill mix according to the client's specifications.
Once the pull-in operation was complete, the drill crew removed the PE pipe and ran a pressure test on the installed pipe at 168 bar. After a coating check of the pipeline was performed and approved by the client, we linked it to the rest of the pipeline on each side of the river, so that K+S Kali GmbH could start using it again.
The project was completed on schedule to the client's full satisfaction.