Krah MISR has been producing Krah pipes in Egypt for decades, mainly for water and wastewater pipelines. Krah MISR reports on his first marine project experiences and gives advice on what needs to be considered in advance.

First of all, there is basic marine survey information that needs to be considered in order to make the ideal pipes with their connections for these conditions. To begin with, a bathymetric survey is carried out. Bathymetric data is used to create models that can calculate currents, tides, water temperature and salinity in an area, and what forces will act on the pipes. Then a soil survey is done for the seabed. It is important to know how loose or firm the seabed is in order to find out what subsidence will occur along the pipeline and what forces will act on the joints and the pipe body. The installation method also plays an important role. Here we look at whether the pipes will be laid in S-curves or whether the lowering of the pipes will be carried out using concrete, or whether other laying methods are more suitable. Again, this must be considered as it will affect the forces that will be applied to the pipe and joints. Finally, the pipe profile must be considered. The pipe profile must be adapted to the depth of the water, because the depth is an important factor with regard to the load-bearing capacity of the pipe. The deeper the pipes are laid, the more stable the profile of the pipe must be to withstand the increasing pressure.

   
After these points had been worked through, there were other things that had to be considered in advance. The first question was how to transport the pipes from the welding point to the sea. Then it was necessary to find out how to best build the inlet and outlet chambers. Fixing the pipes to concrete ballast bases and fixing two adjacent pipelines were also issues that Krah MISR had to address in advance before the project started.

Connection of the pipes is particularly important

The connection of the pipes is one of the most important points to be examined in the marine application, as the forces usually affect the weakest point of the pipeline, which is always the connection. The pipe joint in the marine application is subject to strong tensile and compressive loads, and a special construction must be built for the installation period. The finite element method is the best way to find out whether the joint can withstand the load or not. The finite element method is a simulation method that uses small areas of a component or calculation area - the finite elements - to predict the physical behaviour of the component. Other points to be considered are the length of the pipeline section, the distance between 2 concrete ballastings, the swell, the water depth, and much more.

A lot of calculations had to be done, among others:

• Profile of the main pipeline
• Cross-section of the connection
• Recommendation for the length of the pipeline sections
• Recommendation for spacing between concrete ballast
• Design of the butt end
• Flange material and dimensions
• Load cases and safety considered therein
• Verification of the installation method

What also needs to be considered for marine applications is the material of the pipes. A material must be found that does not interact with the seawater. GRE material is often used for this purpose. GRE is a mixture of high-strength glass fibres and epoxy resin as a base material. Due to its chemical and corrosion resistance, it is often used as a lining material in the marine industry. A combination of HDPE spigots and GRE flanges was chosen to connect the pipes together, which is reliable due to its long service life and low maintenance requirements. The bolts, nuts and washers are also made of the same material and can therefore maintain the high pressure. To be on the safe side, the GRE material was tested at 1.5 times the working pressure required by the customer (there is NO PRESSURE in shipping as the pipeline is open at its end), but to meet the customer‘s requirements, it was tested.
After everything was calculated and the perfect materials and connections were found and all tests were passed, nothing stood in the way of the first marine application. The pictures speak for themselves, the project worked perfectly and left happy customers and suppliers.

Peter Youssef,
Krah MISR