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Interim pipelines in ductile cast iron are the best

When supply pipelines or sewage systems still in operation need to be replaced, renovated or even repaired, the engineering involved for ensuring a secure supply or disposal service in the meantime is not to be underestimated. In branched local networks supplying drinking water, the section concerned can usually be closed off and the water diverted away from the area affected by a bypass. But shutting down and diverting is often not possible, and pipelines laid below ground (e.g. in gravity sewers) or above ground, referred to as “flying” or interim pipelines need to be constructed so as to be able to continue transporting the media in question while the work is being carried out.

Interim pipelines

The route of the DN 800 interim pipeline over the dike between the pipe bridge over the River Mulde and the Canitz waterworks

Rules and practical examples for interim pipelines

To date there are no generally applicable requirements for the planning, construction, operationand deconstruction of interim pipelines, meaning that as a rule technical solutions have been worked out as each individual case arises. Information on the construction of pipelines above ground and on special requirements for piping systems constructed above ground can be found in DVGW W 400-2, chapter 15.2, EN 805, chapter 5.4 (protection of systems) and in the draft of prEN 598. Basically, the requirements described there are to be observed when planning interim pipelines.

But also, different network operators have many years of experience in the use of ductile iron pipe systems as interim pipelines which can be drawn on in order to formulate requirements for interim pipelines.

  • The setting up of an emergency supply at Maifeld during the conversion of the Olympic stadium in Berlin using DN 250 ductile iron pipes and BLS® restrained push-in joints. Because angular deflections of 3.5° are possible with the BLS® joint, it was possible to install the interim pipeline along the curve of the stadium wall
  • The use of a 2,000 m long DN 600 interim pipeline for theSouth Saxony water supply association. The ductile iron pipe sand fittings were used a total of three times in order to allow the renovation of a 6,000 m long section of pipeline
  • The installation and reuse of a DN 150 interim pipeline with BLS® restrained push-in joints to maintain the supply of water to the districts of Eimelrod and Hemminghausen in Willingen/Upland by the Upland water supply association


Interim pipeline between the Canitz waterwork and a pipe bridge

The communal waterworks of Leipzig renovated two DN 1000 grey cast iron water transport pipelines running in parallel which supply the city of Leipzig with fresh water from the waterworks at Canitz and Thallwitz, by pulling in DN 800 ductile iron pipes with BLS® restrained push-in joints. The two waterworks at Canitz and Thallwitz feed their water into the two strings of the 23 km double transport pipeline in the direction of Leipzig.

The section of the double transport pipeline to be renovated is located between the pipeline junction at Thallwitz/Canitz in the immediate vicinity of the Canitz waterworks and a pipe bridge over the River Mulde. At this point the pipelines run underneath the flood prevention dike. The first step was to construct a DN 800 interim pipeline with BLS® push-in joints between the Thallwitz/Canitz junctions and the pipe bridge and put it into operation. Then this new pipeline was put into operation and the interim pipeline was decommissioned. The pipes and fittings of the interim pipeline were then used again so that the second DN 1000 could be renovated.

In all cases, drinking water pressure pipes with restrained BLS® push-in joints, DN 800, wall thickness class K 9, with cement mortar lining and a 400 g/m² zinc/aluminium coating plus a blue epoxy finishing layer were used. In addition, various fittings in ductile cast iron, nominal size DN 800, were installed.


Renovation of a wastewater pressure pipeline in Berlin Tegel Forest

An old DN 1000 wastewater pressure pipeline in asbestos cement along the external West and North fence of Berlin Tegel Airport was to be replaced by DN 800 ductile iron pipes with BLS® restrained push-in joints. The new pipeline was to be installed along the same route. This meant that wastewater from the old pressure pipeline had to be routed parallel to it through an interim pipeline constructed above ground. The removal and relaying of the waste-water pressure pipeline was done head on in a number of installation stages.

In the first stage of the work, an approx. 870 m long section of the interim pipeline was constructed along a forest road. In the 2nd stage of the project, the interim pipeline above ground was first of all dismantled and assembled again in the same way at the new section of pipeline. Because of the tight space conditions in this section of the were, constructing the interim pipeline parallel to the route of the wastewater pressure pipeline was not possible and so the pipeline was laid along an existing forest road. Once complete, the interim pipeline was 1,300 m long.

No disruptions in operation occurred throughout the entire construction phase. Also the construction and dismantling of the pipelines was, as usual, uncomplicated, however, in 2017 the Berlin city area experienced the effects of local bad weather events on many occasions. Heavy rain resulted in flooding and squalls took away roofs and uprooted trees and dozens of trees were uprooted in Jungfernheide Forest and a decades-old oak fell onto the interim pipeline. Once the oak had been removed from the pipe-line then, as expected, it was seen that the pipeline in robust ductile cast iron had withstood the powerful impact of the tree without damage. There were not even any detectable alterations to the surface of the pipe.

Interim pipelines

An uprooted oak tree which fell onto the interim pipeline did not result in any operational disruptions

Requirements for interim pipelines

  • the choice of a piping system consisting of pipes, fittings and valves
  • a robust, non-flammable, impermeable piping system with a high level of resistance to external influences (e.g. fire and mechanical stresses)
  • able to be supplied in a wide range of nominal sizes
  • suitable for delivery even under restricted site conditions
  • thrust-resistant joints connecting all pipeline elements parts
  • the possibility of flexible routing of the pipeline which can be adapted to e.g. struc-tural and/or topographical conditions
  • fast, easy and secure assembly, as well as dismantling, even under the worst weather conditions (temperatures in the minus range) without additional expense
  • the possibility of using system components again once dis-mantled without any particular preparation work
  • efficiency and environmental compatibility

Authors: Uwe Hoffmann and Lutz Rau

The article was slightly shortened by the editors. You can find the complete article with various illustrations as a PDF in the download area under Downloads Annual Issues EADIPS FGR.