Press Release
On the morning of December 27, 2022, the successful completion of the 3# Line crude oil HDD crossing work for Yongzhou Expressway Project was confirmed as the pull-back process was completed and tested successfully. This project, located on Cezi Island in the Dinghai District of Zhoushan City, Zhejiang Province, involved transporting crude oil at normal temperature with a design pressure of 6 MPa. The pipeline has a diameter of φ813 mm and a wall thickness of 17.5 mm. The HDD crossing has a horizontal length of 1108 meters, a curved length of 1118 meters, an entry angle of 14°, and an exit angle of 8°. The entry elevation was +11.3 m (after excavation), and the exit elevation was +3.78 m.
Based on geological survey report, the soil conditions at the entry side primarily consist of strongly weathered tuff with some moderately weathered tuff, making the strata relatively hard (the rock’s maximum uniaxial compressive strength ranging is 142.95MPa, the minimum is 72.46 MPa, and the average is 108.24 MPa). The exit side mainly consists of silty clay and mud clay, making the layer relatively soft. The HDD project crossed approximately 900 meters of rock and 200 meters of mud.
Construction began on June 8, 2022. The entry point is located 17 meters from the Taoyao Gate Road, on a mountain. To maintain the stability of the mountain and minimize excavation, only necessary slope reductions and leveling were done at the entry point. To lower the entry point elevation and ensure the pipeline's burial depth under Taoyao Gate Road, an excavation pit was created for the drilling rig, with installation of anchor bolts and shotcrete support. Drilling conditions were met on July 16, 2022.
To improve efficiency in rock layer, drilling a pilot hole was first carried out on the rock section at the entry side, followed by the use of a power reamer to complete the rock section reaming. After completing the rock section, drilling pilot hole and reaming were conducted on the clay section. This method facilitated mud circulation, avoided mud loss in soft layer at the exit, and enhanced construction efficiency.
In terms of pipeline prefabrication, due to the site conditions with the exit point located about 55–65 meters from the rear mountain, overall pipeline welding was not feasible. The "24-in-1" method was used for pull-back, with prefabricated segments of 48 meters each. Pipeline prefabrication began on October 22, 2022, and was completed on December 11, 2022.
To ensure construction safety and reaming efficiency, a 7-5/8" large drill rod was used throughout the project. After drilling a pilot hole and reaming at the rock and mud sections, measuring, washing & repairing hole, a test tube pull-back, and segmental pipeline prefabrication, pull-back conditions were met on December 20, 2022.
During the pull-back period, a 500-ton pipe jacking machine was installed at the exit side to assist with the process and ensure successful pull-back in one attempt. At 10:45 a.m. on December 20, under the traction of an HY-6000(D) electric drilling machine at the entry side, the first prefabricated pipe with UV-curing coating slowly entered the hole, marking the beginning of the pull-back process.
The pull-back of this pipeline took place during a cold spell in Zhoushan, with extremely low temperatures. Together with the high number of COVID-19 infections, the construction turned to be very high tense. Despite these challenges, all construction staff from Huayuan persevered and successfully ensured a one-time pull-back.
We extend our gratitude to the Zhejiang Petrochemical crude oil pipeline project department and the China National Petroleum Corporation Langwei supervision department for their support and assistance. With the strong support from the owner and the supervisors, our Huayuan team meticulously planned, organized, and controlled the project, following the detailed construction plan and risk prevention measures. Despite various challenges, we successfully completed the 3# Line HDD crossing work for Yongzhou Expressway Project.
The successful completion of this project once again demonstrates the company's mature capabilities in non-excavation crossing construction and adds valuable experience in pipeline crossings through complex geological conditions.
