Sea outfall pipeline for Egyptian petroleum company
Egypt is a big producer and exporter of oil and gas and has an important role in the worldwide oil- and gas industry. It is the country, which connect North-East-Africa with Asia and has also a high political and economically position in the region. Egypt has one of the longest histories of any country, tracing its heritage along the Nile Delta back to the 6th–4th millennia BCE. The ancient Egypt is considered as the cradle of civilisation.
Nowadays the oil and gas industry are very important for the Egyptian economy and secures the energy supply of the strong growing population in Egypt. Egypt has around 100 Million inhabitants and owns 1 Million square Kilometres. The El Nasr Petroleum company (N.P.C) belongs to the local oil- and gas industry and is located in the port of Suez. The El Nasr Petroleum company was already founded on 1911 by the British company Abar Solutions Petroleum. The actual production of N.P.C reaches 6.5 million tons per year. To improve the environmental sustainability the N.P.C. has planned the construction and installation of two outfall pipelines to dispose the treated industrial water into deep sea. Last year also the environmental minister issued a law to regulate the discharge of treated water into the sea. A big environmental progress, because for many years the treated water was discharged on the shore-line, which cause pollution and destroying the marine life.The considered minimum discharge flow is 3000 m3/hr and the maximum discharge flow is 9000 m3/hr. As result of the hydraulically calculation both pipelines are designed with an internal diameter of 1500 mm. For the maximum pressure load capacity 2,5 bar was defined. After presentation of different solutions and pipe materials to N.P.C. the Krah pipe concept was selected as most cost-effective and durable solution and because of the technical properties, meeting the requirement for the project.
All pipes are produced in Egypt at KRAH MISR by using high quality Polyethylene PE100 rawmaterial “Borouge HE3490 LS”. The raw material has a Minimum Required Strength (MRS) of 10 MPa and provide a high resistance against external loads. For the pipes a profiled wall structure with adequate inner wall to handle the inner pressure was designed. Following the standard DIN 16961 and considering PE100 and Design Coefficient of 1,25 (acc. ISO 12162) the pressure class PN 2,5 is correlating with SDR 65, what means 24 mm solid wall at diameter DN/ID 1500 mm. The additional profiled wall structure ensures highest grade of pipe stiffness and buckling resistance. The pipes fulfills a higher stiffness than SN 16 [kN/m²] (calculated with flexural modulus of 1000 MPa.
All pipes are produced with integrated spigot and electrofusion-socket. For homogenous jointing of outer wall an additional Krah Electrofusion coupler is manufactured. Due to this technology the axial pulling load during installation could distributed to total axial wall thickness of inner and outer wall. Further the bending resistance could be increased, what was an advantage for the selected installation procedure. Because of the site conditions, especially the native very soft soil, the planner preferred an installation of the pipe string on piles. The pipes are fixed in special clamps every 6 m and weighted by concrete ballast to ensure the necessary uplift safety. The deflection between the piles has to be minimized, what is ensured by using the double wall profile and double wall jointing of the pipes. Regarding pipe design and detailed calculation of load capacity of the pipe system during handling, installation and operation KRAH MISR cooperated with the German engineering and consulting companies Selle Consult GmbH and Plaspitec GmbH.
Krah pipe flange connection during Krah pipe flange connection during pressure test
This kind of third party support was helpful for all stages of the project, especially because of changing conditions for installation-process during the project proceeding. So, all different szenarios for installation could be verified and confirmed in time. The pipes are produced in 6 m length and jointed to 12 m length in the Krah factory before delivery. Each pipe and joint are inspected by QC department and each joint is additionally leak-tested with special joint-testing-device before shipment the 12 m length. The weight of the shipped 12 m length is around 3 tons and for transport small trucks could be used. The low weight simplified also the handling at site, where firstly the pipes are jointed to 100 m strings with flange joint at the ends. The pipes strings are pressure tested with 1,5 times the maximum design pressure (1,5 x 2,5 = 3,75 bar). Instead of using flat gaskets or simple O-rings, special rubber sealings were developed to maintain the pressure and simplify assembling in marine environment. The used stub-ends are produced out of solid wall Krah pipes and machined on a turning machine to get the final shape and sealing-surfaces. The design corresponds to the GRE Krah Pipe flanges and the GRE Krah Pipe screws. The GRE flanges, screws and nuts, produced in Germany, are chemical resistant against marine water and well-proven for this application. Long term tests under marine water environment document the distinguish properties.
The usage of GRE flanges avoids the installation of complex cost-intensive cathodic protection or usage of super duplex steel. That reduces costs and the effort for maintenance significantly.
Lifting and pushing into the sea Pipe on wheel carrier
Easy handling off-shore Wall penetration
Because of local situation at site the pipe strings could be prefabricated not directly at the place for launching, but has to be lifted on wheel-carrier and transported to the shore. String by string the pipes are transported and lifted and pushed into the sea. Because of this special launching process an additional artificial ramp and special railway could be avoided. The final installation and sinking process is done after the pipe strings are pulled to destined position. The maximum installation depth is around 6 m because the range between the water level at rising and falling tides is more than 2 m, the installation is conscious planned to start during lowest tide level. The controlled sinking process by using 3 ton concrete ballast blocks and controlled water filling let the sink into the projected position. Hydrostatic test is made for complete pipeline (500 meter each) to guarantee leakage free pipelines. The pipes are connected on shore with the outfall chamber by using Krah pipes wall penetration fittings. Due to the special design of the wall penetration, the pipe gets radial and axial anchored in the concrete wall. The tailormade design ensures leak-tightness penetration of the chamber wall. The integrated EPDM puddle flange and the additional installed swelling material guarantees perfect sealing and maximum safety. The integrated flange joint allows total closure in case of maintenance and also pressure tests of the string after installation.
Author: Peter Youssef, KRAH MISR, Egypt
Dipl.-Ing. Stephan Füllgrabe, Plaspitec GmbH, Germany