by Linda Bertelsen
Logstor. Foto: © Michael Bo Rasmussen / Baghuset. Dato: 02.09.10

This article will focus on a new opportunity for qualifying recycled HDPE from external sources to produce the casing on new pre-insulated pipes so that the product will consist of 100% recycled plastic material. An opportunity which today is possible.

By Peter Jorsal, Product & Academy Manager, LOGSTOR

The Journey towards a Circular Economy and Recycling

The demand to move towards a circular economy, making sure that materials are recyclable at the end of a lifetime and that we can produce new products from recycled materials, has come to the business for pre-insulated products for district heating and district cooling projects.

The main components in pre-insulated pipe systems are steel as the service pipe, polyurethane (PUR) foam for the insulation, and HDPE for the outer casing.

At the end of the lifetime of a pre-insulated pipe system, the different materials can, in principle, be separated and handled in different ways:

  • The steel pipe can be handled as scrap steel. Scrap steel has been traded for years and has value. 
  • PUR foam is today mainly handled as waste material burned in waste-to-energy plants.
  • HDPE is today either burned in waste-to-energy plants (this will often happen if PUR foam is not separated from the casing) or, in the best case, cleaned and recycled for different purposes.

When it comes to the production of new pre-insulated pipes with the use of recycled raw materials, the situation today is in general as described below:

  • New steel pipes include some percentage of scrap steel with the right quality.
  • We produce PUR foam only by using new-produced chemicals, Polyol and Isocyanate. It is still on the research level to recycle PUR foam and use the recycled material to create new PUR foam – more about this later in the article.
  • Manufacturers have, until lately, only been using HDPE rework from their productions in producing new HDPE casing.

Environmental Advantages

We use HDPE (High-Density Polyethylene) for the casings of pre-insulated district heating (DH) pipes. Recycling HDPE waste instead of using new HDPE reduces the CO2 emission because the energy spent to produce HDPE granulate for our production is higher when the granulate is made from oil rather than when the granulate comes from waste HDPE, including transport. 

If the recycling material is from Europe, we save 1.6 kg CO2 per kg HDPE. Reference is made to the life cycle database Ecoinvent 3.5.

At the same time, we save the Earth’s natural resources by avoiding extracting oil from the underground as far as possible. 

What’s in it for the Energy Company?

For the energy company, the DH distribution network owner, it is a decisive condition that the use of recycled plastic in casings does not compromise the quality of the finished product and the service life of the distribution network. 

Therefore, the documentation that the casings produced from recycled plastics meet the exact requirements as those made from new plastics and consequently have the same long-term properties is crucial.

Once this fundamental requirement is met and, using products produced from recycled materials will strengthen the environmental profile of the energy company:

  • To consumers
  • With authorities
  • Concerning other ways of heating the housing stock, and a strengthening of the competitive position of DH

And then, of course, there will be a documented CO2 saving.

The use of recycled materials is a hot issue, and in the future, demands from governments, organizations, DH companies, customers, and citizens will arise.

The European Standard EN253:2019

The European standard EN253:2019 poses a challenge to set off the journey towards using recycled plastics from external sources.

EN253:2019 requires the following of the casing material: “Only clean, not degraded, rework material, generated from the manufacturer’s production, shall be used.”

The purpose of this requirement is, of course, to make sure that only HDPE material of the proper quality is used, which of course is a good intention, but it is this requirement that LOGSTOR wants to challenge and have changed. What must be important is that when you use recycled plastics, you make sure the casings are of good quality and meet all other requirements in the standard.

LOGSTOR has therefore initiated the process of changing the standard, allowing the use of recycled plastics from external sources. So earlier this year, we filed a proposal regarding this with the technical committee of the European standards for pre-insulated pipes. This subject is now an active work item within the Technical Committee for European standards for pre-insulated pipes (TC107).

The possibility to document that the quality and lifetime of the pre-insulated pipe is the same by using external recycled HDPE of excellent quality as with new HDPE material produced from oil is essential.

I will describe this in the next part of the article.

Requirement Specification to Externally Recycled Plastics and Qualification of Suppliers

The first step to securing the recycled HDPE’s right quality is to define a material specification, describing the minimum requirements to recycled plastics from external sources. In the material specification, the minimum rate of recycled plastics is PE80 or PE100, and the recycled HDPE shall fully comply with the requirements in EN253:2019. Suppliers of recycled HDPE must document that they live up to these requirements with a so-called 3.1 certificate.

Type test of the casing produced from recycled HDPE

In compliance with the European standard requirements, the casings of each production line using recycled plastics from external suppliers mandatorily must pass a so-called type test.

The type test is concerning the requirements to the following parameters described in EN253:2019:

  • Carbon black content
  • Carbon black dispersion
  • Melt flow rate
  • Thermal stability (OIT)
  • Dimensions of the casing (nominal outside diameter, wall thickness)
  • Appearance and surface finish
  • Heat reversion
  • Stress crack resistance
  • Impact resistance

Production Units Qualified for using Recycled Plastics from External Sources

LOGSTOR has qualified two production lines in the factory in Løgstør, thereby being able to use HDPE from external sources:

  • Axial Conti pipes in casing dimensions ø90 – 315 mm. In this production line, you find both single pipes and TwinPipes. The pipes are produced with aluminum diffusion barriers to ensure that the low lambda value and the heat loss properties are not deteriorated and aged during the service life of the pipes.
  • Traditionally produced pipes in casing dimensions ø90 – 710 mm. In this production line, you find both single pipes and TwinPipes.

We have carried out type tests according to the requirements of EN253:2019 on the casings of pipes with casings made of 100% recycled plastics from external sources. All tests were performed by the German test institute IMA, Dresden.

Test reports from IMA, Dresden on pipes 

The test reports document that we meet all requirements in EN253:2019 on pre-insulated pipes with casings made of 100% recycled plastics from external sources by the two production lines in the factory in Løgstør: Axial Conti production and traditional production.

So far, the approved recycled plastics have been qualified for use in the production of straight pipes. Casing joints and fittings will come later.

Quality Inspection of Recycled Plastics from External Sources before Production Release 

The next step to secure the right quality of casing produced of externally sourced recycled HDPE is to implement in-depth quality control of the recycled HDPE before it goes into production.

We test all recycled plastics from external sources following the requirements in the material specification and do not release the batch until all requirements in the test are met and documented.

The supplier must deliver a 3.1 Certificate for every batch, documenting the results of each test and that the pack complies with the material specification. Some of these tests last four weeks, and until all tests are approved, we do not take the recycled HDPE material into production.

Test of elongation at break
Test of elongation at break
Test of stress crack resistance
Test of stress crack resistance

Pilot Project at Aalborg Forsyning

In March 2020, LOGSTOR and the utility Aalborg Forsyning entered an agreement about a project that delivered pre-insulated pipes with casings, produced 100% recycled plastics from external sources.

The project comprises the pre-insulated pipe system, the entire distribution network, and branch pipes, supplying the houses in two small Danish towns. All homes supplied with individual natural gas as their heating source will convert to DH supply in these two towns.

Aalborg Forsyning has had the highest focus on choosing a pipe system with the lowest possible heat loss during the service life of the entire system. So, the whole district heating distribution network is established as a TwinPipe system, and the project comprises more than 30 km TwinPipes in series 3 insulation class in dimensions ø33.7×33.7/180 – ø168.3×168.3/560.

Pipes in casing dimensions up to ø315 are Axial Conti pipes with diffusion barriers to ensure good heat-insulating properties during the service life of the pipe system, and larger dimensions are traditionally produced pipes.

Branch pipes for house connections will be made as flexible branches with Alupex service pipes.

Casing joints are in all dimensions BandJoint weld joints.

The delivery period of the project is March 2020 – March 2022.

We use 100 tons recycled plastics from external sources to produce the casings on the straight pipes for the entire project.

Until the standard change, we will handle casings produced of recycled plastics from external sources like in the project with Aalborg Forsyning, where we entered a specific agreement about delivering pre-insulated pipes with such casings.

What will be the future opportunities?

In 2021, more Danish energy companies have followed this green journey and are installing pre-insulated pipe systems where the casing is produced from external sourced recycled HDPE:  

  • Lemvig Varmeværk, 2 km of TwinPipe ø26×26/140 – ø139×139/500
  • Din Forsyning Esbjerg, 2 km of TwinPipe ø273/500 and ø323/560
  • Hinnerup Fjernvarme, 6 km of TwinPipe ø33×33/180 – ø168×168/560
  • Frederiksberg Forsyning, 0,5 km of SingePipe 219/355
  • Løsning Fjernvarme, 9 km TwinPipe ø26×26/140 – ø139×139/500

There is an increased interest from Danish energy companies about pre-insulated pipes with casing produced from recycled plastic.

The question is when we will see this movement start outside of Denmark. All energy companies have green agendas, so the new green product should be an exciting opportunity.

For further information, please contact: Peter Jorsal, pjo@logstor.com

Download and print the article from here:

Meet the author

Peter Jorsal
Product & Academy Manager