Construction department 

For the mud transfer from pipe site to rig site a mud transfer pipeline is required. For this purpose a HDPE pipe OD 200, SDR 11 has to be installed in one of the existing steel pipes DN 500. This preparation has to be ready, before the pilot drilling is completed. During reaming the drilling fluid, which emanates from the HDD hole at the exit point will be pumped via this HDPE pipeline back to the rig site where it is recycled and can be used again.

The DN 700 steel pipe string has to be prepared in the extention of the HDD. There is only approx. 1000m length available between the exit point and the main street. As such it is not possible to prepare the complete steel pipe string in one single length but two strings have to be prepared. Therefore it will be necessary to stop the HDD pullback installation for a so called “golden joint”. To reduce the stop time for the HDD the welding procedure has to be prepared as easy as possible. It is therefore necessary to make the golden joint not in the area of the overbend construction.. The overbend is approx. 200m long. The string length should therefore be 800m (1000m -200m) for string no. 2 and 710m for string no. 1. A large difference in length and a preparation as far as possible behind the exit point is an advantage, because in this case, the pulling can be continued during coating works.

This helps to reduce the risk involved in the interruption. Both strings have to be pressure tested and coated. Then a HDPE pipe OD 110mm SDR 11 has to be pulled into the steel pipes. This HDPE pipe will be used as filling line for the buoyancy control. On the front end of the steel pipe string 1, the pulling head has to be welded.