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

Infrapipe is a leading New Zealand manufacturer and supplier of PE 100 profile pipe technology throughout New Zealand. Using the latest European technology from Krah, Infrapipe manufactures the largest size range in New Zealand of up to DN/ID 3200mm.

Infrapipe continuously grows and enhances its market presence as a manufacturer and supplier for various applications. Examples of applications include sewer, stormwater, and low pressure. Our ability to create manholes and tanks from any Infrapipe PE pipe is in continual high demand.

In the New Zealand marketplace, we are one of the only companies in the industry that manufacture culverts for forestry and rural use. We guarantee our products are one of the strongest engineered culvert pipes on the market, with the bonus of using recycled materials in our manufacturing process to promote closed-loop cycles. Infrapipe continuously increases its presence at the forefront of any industry space it operates in.

Guarantee of reliability and durability

As a business, we continuously gain certifications and approvals to guarantee our products‘ reliability, durability, and industry-leading standards. Infrapipe Spiral and Ecopipe are manufactured to the highest quality and comply with all the terms and conditions stipulated by the governance of the ISO Type 5 Scheme‘s operating rules that meet or exceed standards requirements AS/NZS 5065:2005.

Our knowledgeable sales team is continuously increasing our market presence with councils, merchants, and engineering consultants, to name a few. As a company, we promote transparency and regularly provide factory tours to engage more with our market and clients and demonstrate our expertise. As a cohesive sales team, they provide hands-on knowledge with the technical assistance of our engineering team to meet any project‘s exact specifications and requirements.

Picture 1 demonstrates a project recently completed in September 2023 in Hawkes Bay, highlighting the impressive magnitude of Infrapipe‘s operations. This project required multiple HDPE DN3200 SN8 spiral wound culvert pipes. Using our latest technology, we supplied the necessary lightweight PE pipes while performing static calculations to determine the appropriate SN rating.
Picture 2 illustrates our second large-scale project completed in September in Hawkes Bay. Infrapipe manufactured large DN/ID3200mm SN7.57 culverts for a forestry application. The culverts were PE100 spiral wound CPR pipes.

Fynn McDonough,
Infrapipes

What does the need to change a storm sewer in the city of Joliette, Quebec have in common with an innovative European HDPE pipe design and manufacturing process? Soleno’s expertise in meeting a major engineering challenge by reaching overseas for technologically advanced product to solve a complex situation.

At a time when a marked increase in the frequency and intensity of rainfall events has prompted various levels of government to impose more restrictive regulations to avoid the risk of sewer overflows that could have consequences in terms of human health, as well as the health of flora and fauna, the City of Joliette needed to repair and bring into compliance a portion of its stormwater drainage infrastructure that would be called upon to carry a greater volume of water caused by new residential developments. To fulfill this contract, the construction firm Sintra Inc., along with the engineering firm Parallèle 54, needed a versatile pipe capable of meeting the specifications required by the circumstances. They called on Soleno to provide them with a HDPE product that would meet their particularly high expectations.

The City of Joliette, Sintra Inc. and Parallèle 54 chose to trust Soleno to supply the products needed to upgrade the storm sewer system under Saint-Pierre Street South. The work site, active from June 2019 to November 2019, offered limited space between neighbouring homes to carry out the work, which involved replacing 350 metres of pipe at the bottom of a 7 metres deep trench. The pipe had to be able to carry a significant flow of water, while withstanding the combined pressures of the weight of the overlying fill and the water table.

In order to meet the requirements of the engineers’ specifications, Soleno’s technical team proposed the use of DN/ID2200 mm and DN/ID2400 mm HDPE pipes manufactured by the German company Krah in its factory in Estonia, a North American first for these products, which have been renowned in Europe for over 40 years.

350 Meters of DN/ID2200 mm and DN/ID2400 mm HDPE Krah pipes

Indeed, Krah’s HDPE pipes were perfect for the particularly complex specifications of the project. Their light weight made them easy to install, as they did not require a crane, as would be the case with a concrete pipe of similar diameter. A simple excavator was all that was needed, greatly speeding up the operation, therefore cutting down cost drastically. Also, the high compressive strength of the pipes made it possible to withstand the high pressures that would be exerted on their external surface. Their large diameter and excellent roughness coefficient allowed them to easily accommodate the high water flow that would be required to pass through the storm sewer system. Krah’s HDPE manhole had the same advantages as the pipes themselves. In addition, an HDPE manhole does not need to be oversized for the diameter of the pipes, unlike an equivalent concrete product.

Once the proposal was approved, Soleno took charge of all the logistics and technical support required for the project to proceed smoothly. Soleno’s Quebec ingenuity and international vision enabled it to provide an affordable and sustainable solution to a local municipality’s problem.
Thanks to Soleno’s proposal, the City of Joliette was able to complete the workwithin its budget and schedule. HDPE structures and pipes are much lighter than comparable concrete products, making their installation quicker and more affordable. In this project, Krah’s DN/ID2200 mm and DN/ID2400 mm pipes were on average 15 times lighter than the outdated concrete products being replaced. A unique feature of Krah’s technology is its method of manufacture, which allows the product design to be tailored to the unique specifications of a project. The range of possibilities is vast in terms of diameter, product size, durability and hydraulic properties. Krah’s DN/ID2200 mm and DN/ID2400 mm diameter pipes were smaller than their predecessors but could handle the same amount of water flow. Capable of withstanding the pressure of the overfill, the water table and the frequent passage of cars on the roadway above, as well as corrosion, abrasion and the effects of de-icing salts, Krah’s products will ensure the durability of the storm sewer system on Saint-Pierre Street South. Soleno supported its clients in the design, procurement, delivery and implementation of this project with a dedicated technical team and a constant presence on the site.

Soleno

Why should you do a pipe stiffness test, regardless according to which standard, constant speed (ISO9969) or constant load (DIN16961)? As a part of a paper related to stiffness testing this little article will answer the upper mentioned question.

The pipe stiffness or a stiffness class will not give any confirmation for a pipe that it is suitable for a specific pipe project.
The only proof that a pipe is suitable for a specific project is a structural calculation (or in some cases experience).
The stiffness test will only prove that the produced pipes are correct according to given specifications. To be specific, the proposed specific bending stiffness is proven as the product of the short-term Modulus of Elasticity E for the used material and the specific area moment of inertia I with dimension mm4/mm. It is an integrated part of the production quality!

To explain it on a short example:
A given project (gravity pipeline for drainage, DN/ID1600mm installed under a hard shoulder of a highway, with certain installation conditions, short term ground water, traffic load, etc.) required a structural calculation regarding the American AWWA M55 standard. The idea of this calculation is to be sure that the proposed pipes-material combination will take all load of the project. A structural calculation will always check and proof multiple load-cases and not only deflection/stiffness.
The result of the calculation (considering all site conditions and installation conditions) is a profile type in combination with a raw material, in our example it should be Profile No. PR75-011.95 (profile distance 140mm, waterway wall thickness 6mm and profile height 83mm, etc.) with a theoretical area moment of inertia of 11.95mm4/mm and a raw material PE100 with a short-term E-Modulus of 1.100N/mm2 – for a pipe diameter of DN/ID1600. So, the manufacturing company knows exactly what to produce.
The product EI is called specific bending stiffness of the profile, where the area moment of inertia is normalized with respect to the profile width.
The corresponding stiffness (according to ISO9969) is given by the specific bending stiffness divided by the third power to the mean diameter of the pipe. So that the testing machine can do a proper quality control test.
The theoretical pipe stiffness for this combination of profile, material and diameter should be approximated.

SN 2.8 (rounded)

Remark: A SN2 lass pipe would be too weak, whereas a SN4 class pipe would be over-designed.
Now, this theoretical approach should be “re-checked” by a physical stiffness test according to ISO9969. Following the test procedure of ISO9969 three pipe samples should be checked by the constant speed method, where the average value should be taken as result. Note that the pipe need to be exposed to a proper temperature within the test as well as before the test. Moreover, a correct storing of the pipe is of most importance to avoid ovality.
The actual testing result (SN-value), according ISO9969, will be compared with the theoretical value.
If the measured SN-value is greater or equal to the theoretical value – the real pipe fulfilled the theoretical approach (in this specific case it was 3.1 and all was more than ok).
If not, problems could be:

• usage of unsuitable material
• improper temperature condi- tions within the last 24 hours
• deviating dimensions of the pipe
• improper storage of the pipe
• incorrect cutting of the pipe sample
• incorrect placing and testing of the pipe

The problem needs to be analysed using another raw material test as well as a detailed measurement and check of the profile geometry.
Checking the production settings to exclude e.g., an overheating of the material.
Depending on above mentioned issues, for spiral wound pipes like Krah-Pipes especially the cutting and positioning of the pipe sample allows a variation of -5% which can appear and is not critical. Note that due to the profile structure of standard double wall corrugated pipes which are not spiral produced, these tolerances do not appear.
Other solutions and problem finding methods are available. One is sending a thin cut of the profile to Krah Germany making a real analysis of the actual profile to certify the actual area moment of inertia.

Conclusion: The basis of the decision which pipe can fulfil the requirements on a real project, is never a stiffness test, or even a stiffness class, it is always a structural calculation (e.G. AWWA M55 or ATV A127). A stiffness test only confirms that the theoretical values of material properties in terms of E and the profile geometry in terms I are reached. A stiffness test is only a quality control test for the production, additional tests according to the standards should be checked, too. In our example the theoretical approach was approved by the physical deflection/stiffness – test.

Alexander Krah,
Krah GmbH