Comprehensively tested safety
Mannesmann Line Pipe has now supplied over 4,000 HFI-welded steel pipes for the WarmtelinQ district heating network operated by Gasunie. Each individual pipe underwent comprehensive full-body ultrasonic testing to ensure smooth operation to the highest safety standards.
Pipeline operator Gasunie has been building an extensive district heating network in Rotterdam since April 2022. WarmtelinQ makes use of previously unused residual heat from industrial companies based in the port to provide sustainable heating for private households and industrial and commercial customers.
Already in 2023, Mannesmann Line Pipe supplied around 900 tonnes of HFI-welded steel pipes for the first pipeline section between Rotterdam, Vlaardingen and The Hague.
Ongoing progress
Following completion of the first section, work is currently underway among other things on the 25.6 km section between Rijswijk and Leiden. The aim is to also supply parts of the city of Leiden, population 125,000, with sustainable heat.
Mannesmann Line Pipe also supplied various sizes of HFI-welded steel pipes from DN 300 to DN 600 for this part of the project. Around 4,300 tonnes of pipes were produced in Siegen and Hamm to the strictest manufacturing tolerances (EN253) and delivered to FW-Fernwärme-Technik and, through ms concept GmbH, to isoplus GmbH for further processing.
Network plan of the WarmtelinQ district heating network.
Laying of a pipe bridge to the Uniper power plant, The Hague, in June 2025. Photo: © WarmtelinQ, Vincent Basler
Open grid strategy with further carbon savings potential
In order to link up further local heat producers and consumers going forward, the network is being implemented as an open grid. Ideally, up to 500,000 residential units in the densely built-up Rotterdam region could be connected to WarmtelinQ at a later date. The utilisation of unused process heat from industry and commerce thus opens up scope for tapping vast extra carbon savings potential.
Cooperation with big-name systems producers
As a supplier of media and jacket pipes, Mannesmann Line Pipe has decades of experience of working with big-name systems producers of district heating pipes. The decisive factors here are technical expertise, top quality and reliability, and the ability to meet strict customer specifications. This also includes the full-body ultrasonic testing of every single pipe.
Photo: © WarmtelinQ, Vincent Basler
Special customer requirement: full-body ultrasonic testing
Product Manager Kevin Kroh explains the background to and procedure for this elaborate test.
Mr Kroh, why did the pipes have to be fully tested in addition?
For safety reasons, the network operator Gasunie stipulated compliance with the manufacturing standards EN 10217-2 and EN 10217-3 for the delivery of the pipes. The test category ‘TC2’ was required in each case for steel grades P235GH and P265GH as well as for steel grade P355NH, making it mandatory to perform full-body ultrasonic testing on each pipe.
What exactly is the test procedure?
Each pipe is first placed in or under the ultrasonic testing system. The testing heads are then automatically aligned in the ‘12 o'clock position’ above the pipe and the pipe is then rotated very slowly. At the same time, the testing head carriage travels along the length of the pipe to inspect the weld seam and the base material of the entire pipe for longitudinal defects and doublings. In addition, this method also permits measurement of the wall thickness over the entire pipe body.
What are the benefits of this test?
In addition to inspecting the weld seam, the test also rules out defects in the base material of the pipes. This ensures the durability and highest safety standards of our steel pipes ‘Made by Mannesmann’. Each pipe produced is given its own production number and is recorded and documented in our ERP system together with the test certificate.
Photo: © Wolfram Schroll