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PE100 Solid wall for marine pipeline

The following abstract provides a brief description of the Al Ghubrah Project with information regarding installation of Large Diameter Marine Intake and Outfall Pipelines, especially regarding the typical work phases: Survey, Design and Construction.

The Al Ghubrah Desalination Project is formed under the Independent Water Project Scheme in Muscat, Sultanate of Oman. The project is sponsored by Muscat City Desalination Company SAOC (MCDC); contracted to the joint venture M/s International Water Treatment Co LLC (formed by WABAG, CADAGUA, & GALFAR). The project is located approximately 20 Kms on the eastern side of Muscat city. The Intake and Outfall Pipelines are produced locally as solid wall Krah-Pipes at United Gulf Pipe Manufacturing Co LLC based in Rusyal Industrial Estate, Muscat, Sultanate of Oman.

Google Earth Top view March 2014 during Installation

The project highlights are as follows:

1 Seawater
1700mm ID
PN 6
1600 m 2

Pneumatic pressure testing (0.2 bar) afterlaunching in sea

Fitted with pig entry and exit elbow for cleaning based on hydraulic performance of pipe during its operation

2 Seawater
1900mm ID
PN 6
1100 m 1  -
3 Chlorination lines PE 100 PIPE
110mm OD
PN 16
1600 m 2  Installed parallel to intake pipeline
4 Air Bust
200mm OD
PN 16
1600 m 2

Further characteristics and details of the Al Ghubra project

  • Thrust boring of tunnel (3 nos) to underpass existing outfall duct of neighboring desalination plant. Tunnel size – 3mtr OD and 2.4 ID of length 33 mtrs
  • Intake passive screen (4 nos) placed on intake pipelines (2 nos)
  • 1 multi port uni-directional diffuser placed in 1 outfall pipeline
    (65 m length diffuser with 30 ports - 24 working & 6 standby)
  • Bathymetry survey to analyse the sea bed profile and to determine the sea bed contour on the site, by using single beam echo sounder and Differential global positioning system. (Sea bed profile is in a slope of 1:110)
  • Offshore geo-technical investigation: Sub surface materials in site maximum constitute if silty sand, followed by gravelly sand. Natural repose slope of the above subsurface material is in the range of 1:3. Cutter section dredger is recommended for the above soil type.
  • Results of MET oceanographic survey:
    • Wind: 38.61% - 0 to 30 degree and balance 61.39% - 30 to 360 degree. Maximum speed 9.73m/sec. Predominant wind direction – NE and NW directions
    • Temperature 82% - 26 to 35 degree C.
    • Relative humidity of 46.69% occurrence - 56% to 76%
  • Sea profiling
    • Current speed found in the range of 0.25m/sec (Predominant current direction – NE)
    • Significant wave height: 90% occurrence record below 0.5m height with peak wave period of 14 second.
    • Salinity at surface 36 PSU, at bottom, 2 meter above sea bed 25 to 30 PSU.
    • Temperature of sea water found Predominant in the range of 25 degree C.
    • Turbidity converted to Total Suspended Solid found in the range of 3-5 mg/l. (Used to decide the pre-treatment requirement of plant)

Pipe design for Al Ghubrah Project

As a result of the hydraulic design under consideration of the calculated intake (5.890 m³/s) and outfall (3.657 m³/s) flow, the inner pipe diameter is chosen. The pipe material used is High Density Polyethylene (HDPE) and especially the chosen grade PE 100, guarantees perfect properties and provides the necessary durability. The wall structure has to be selected to carry all loads during installation and long-term operation. 

Selected Intake Pipeline:

  • Internal diameter (mm): 1700
  • External diameter (mm): 1842
  • Wall thickness (mm): 71 (SDR: 26)
  • Pipe Material: HDPE, PE 100 (Krah pipe)

Internal pressure

  • Working pressure at 1.294 bar against 6.4 bar pipe pressure

External pressure

  • Buckling pressure due to unsupported length caused will be 13mwc against 18.21mwc pipe capacity

Buckling pressure due to Soil in trench caused will be 12.53mwc against 33.76 mwc pipe capacity.
Allowable pressure surge for pipe 6.4mwc (0.6bar), for gate operation at intake sump location.

Selected Outfall Pipeline:

  • Internal diameter (mm): 1900
  • External diameter (mm): 2058
  • Wall thickness (mm): 79 (SDR: 26)
  • Pipe Material: HDPE, PE 100 (Krah pipe)

Internal pressure

  • working pressure at 0.98 bar against 6.39 bar pipe pressure

External pressure

  • Buckling pressure due to unsupported length caused will be 9.8mwc against 20.13 mwc pipe capacity
  • Buckling pressure due to Soil in trench caused will be 12.53mwc against 33.76 mwc pipe capacity
  • Allowable pressure surge for pipe 6.4mwc (0.6bar), for gate operation at outfall sump location

The pipes are produced as Solid Wall Krah Pipe according to DIN 16961 and technical requirements of ISO 4427. The pipe wall structure is helical extruded and each layer is homogenously jointed to guarantee the required mechanical and physical properties. The highly automated pipe production process and the implemented quality system convinced every partner involved in this project.

This project shows, once again, clearly in all tests conducted in the laboratory and in handling the pipe strings at site as well, that a helical extruded Krah pipe is in all points comparable with a standard direct extruded pipe. The pressure rating is the same. In contrast to the direct extrusion method, the wall thickness for fittings or flanges can be increased easily. United Gulf Pipe Manufacturing is able to produce Krah pipes in Sultanate Oman with an ID 4000 mm.

The pipes for the Al Ghubrah Project are produced in length of 6 meters and welded to 18 meters in length before shipping to construction site.

Hydrostatic Pressure Test in QC lab
Hydrostatic Pressure Test in QC lab
Launching pipe string
Launching pipe string
Butt-fusion at site
Butt-fusion at site
Concrete ballast
Concrete ballast

Eng. Mohammed Al Hashani
United Gulf Pipe Manufacturing
Rusayl Industrial Estate
Sultanate Oman