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 under-estimated. 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.

After a new construction however, it must be borne in mind that the time windows for connecting up a new section are small. 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.

In normal usage, these interim pipelines are often seen as workarounds. However, the term is more appropriately interpreted as temporary engineering works which need to be planned, constructed and operated in their own right.

Rules and practical examples

To date there are no generally applicable requirements for the planning, construction, operation and 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 [1], EN 805 [2], chapter 5.4 (protection of systems) and in the draft of prEN 598 [3].

DVGW work sheet W 400-2 applies to the construction and testing of water distribution equipment for drinking water supply. Chapter 15.2 describes additional requirements for the construction of pipeline systems above ground. There are descriptions of the requirements for pipe joints, the installation of pipeline components, thermal insulation, corrosion protection etc. through to pressure testing and commissioning. Basically, the requirements described there are to be observed when planning interim pipelines.

In EN 805 [2] from the year 2000 there is the following statement: With respect to terrorist attacks, vandalism and other illegal acts, keen attention is to be paid to the protection of water supply systems. Underground systems are safe in general, but particular attention needs to be paid to sections of pipeline above ground.

As a possible consequence, the fire behaviour of structures has been included as an essential characteristic in the die EU regulation for determining harmonised conditions for the marketing of construction products. This also relates to pipe systems which, in future, must be assigned to fire classes [4].

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.

Documented examples are:

• 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 [5].
• The use of a 2,000 m long DN 600 interim pipeline for the South Saxony water supply association. The ductile iron pipes and fittings were used a total of three times in order to allow the renovation of a 6,000 m long section of pipeline [6].
• 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 [7].

In addition, there are two current practical examples from Leipzig and Berlin. The experiences from these projects can also be used in order to formulate requirements for interim pipelines.

Interim pipeline between the Canitz waterworks and a pipe bridge

A flood prevention dike runs between the River Mulde and the waterworks at Canitz which has been protected against future floods by the regional reservoir administration by means of sheet pile walls. The communal waterworks of Leipzig took this work as an opportunity to renovate 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 (commissioned in 1912) and Thallwitz (commissioned in 1943) 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.

Once the interim pipeline had been commissioned, one of the two DN 1000 pipelines to be renovated was taken out of operation and the DN 800 pipe was pulled in. Then this new pipeline was put into operation and the interim pipeline was decommissioned. The pipes and fittings of the interim were then used again so that the second DN 1000 could be renovated.

When this pipeline was reassembled, the used TYTON^® DN 800 sealing rings were replaced with new sealing rings of the same type. The interim pipeline was 208 m long. The section of the Thallwitz pipeline which was pulled in was 178 m, with a total length of 199 m, and the length of the pipe pulled into the Canitz pipeline was 185 m, with a total length of 203 m.

In all cases, drinking water pressure pipes with restrained BLS^® push-in joints, DN 800, wall thickness class K 9, with cement mortar lining to EN 545 and a 400 g/m² zinc/aluminium coating plus a blue epoxy finishing layer to EN 545 and DIN 30674 were used. In addition, various fittings in ductile cast iron, nominal size DN 800, were installed.

The joints of the newly constructed pipelines were produced in each case with restrained fittings and valves at the Thallwitz/ Canitz junction and on the West side of the pipe bridge.

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 to EN 598 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 wastewater 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 addition to the steel inserts at the beginning and end of the wastewater pressure pipeline, pipe bridges in steel pipes were used where paths or roads branched off or crossed the route, in order to allow extinguishing vehicles unhindered access to the forest in case of fire.

In the 2^nd 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. It is planned that the pipes of the interim pipeline will also be used again for securing the receiving water course in the next stage of construction. While the interim pipeline through the Jungfernheide Forest was in operation it was shown that the sentence formulated in EN 805 – “but particular attention needs to be paid to sections of pipeline above ground” – proved to be true, although in a future revision of EN 805 this should be supplemented with a reference to effects due to climate change.

The specific case occurred while the interim pipeline was in operation. 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.

During the latest storm in October 2017, dozens of trees were uprooted in Jungfernheide Forest and a decades-old oak fell onto the interim pipeline. But this did not cause any interruptions to the operator’s services. Once the oak had been removed from the pipeline 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.

Requirements for interim pipelines

Based on many years of experience in the planning, construction and dismantling of interim pipelines of ductile cast iron pipes, fittings and valves, the following general requirements can be formulated for interim pipelines constructed above ground:

• 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. structural 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 dismantled without any particular preparation work
• efficiency and environmental compatibility

Interim pipelines of thrustresistant cast iron pipe system

For ductile iron pipe systems, pipes, fittings and valves are available in a wide size and pressure range for different liquid media such as fresh water (see EN 545 [8]) or wastewater (see EN 598 [9]). The individual components of the robust, non-flammable and impermeable pipe system are protected against contamination during transport and can be transported on e.g. open trucks and unloaded by excavators.

The 6 m long pipes are delivered direct to the construction site by truck where they can be taken off the back of the low-loader by excavators. The pipes can then simply be stored on timbers, sealed in the socket area. Once the sealing ring is in place, the pipes are assembled using pipe-laying equipment/ chain hoists or construction machinery.

Then locking bars or segments are inserted via the openings in the crest of the BLS^® socket which are arranged around the circumference in the thrust resistance chamber of the socket in front of the weld bead at the spigot end and then quickly adjusted and the joint is extended slightly.

After this, the pipe joint can be angled horizontally and vertically, depending on its nominal diameter, in order to adapt it to the contours of the route.

In the event that directional changes are necessary which exceed the bending capability of the socket joint, socket fittings with BLS^® push-in joints are used. If necessary, it is possible to resort to the diverse range of flanges. When it comes to dismantling the pipeline, the pipe joints are easily released and the locking bars or segments for thrust resistance are pushed up to the opening in the crest of the socket and removed from there. They do not come into contact with the medium in the pipeline and can be handled from outside in front of the socket.

Environmental compatibility is also a decisive criterion for the general framework conditions. A robust cast iron pipe system not only offers security against damage and fire as already mentioned. The fast assembly of an interim pipeline required for a specific time, along with the small amount of space needed for site equipment means minimal disturbance of fauna and flora. Low noise levels (no power generators necessary) and no additional fire prevention regulations to be observed add to the list of arguments, so that even from the point of view of those responsible for woodland and countryside preservation, ductile iron pipe systems should be used.

Outlook

Interim pipelines are temporary engineering works which enable fluids flowing through the sections of pipeline under renovation to be diverted during the construction phase, so enabling the renovation to be completed without disruption to the service. No general requirements are available for the planning, construction, operation, dismantling and reuse of interim pipelines and this can lead to uncertainty among planners and operators. This is exacerbated by current political development (risks of terrorism), the effects of climate change and changes in the requirements for piping systems (fire regulations).

Against this background, some requirements for interim pipelines have been formulated on the basis of experience and these should be able to be included e.g. in future regulations.

Bibliography

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