Development of a new high performance PE pressure pipe system, from design phase to reality
Apr 10, 2008
Since the introduction of the first PE pipe more than 40 years ago, PE raw material producers and pipe producers have continuously joined their efforts to propose better and better pressure pipe solutions to the end-users and installers. The development of modern installation techniques, in particular trenchless technologies, has created a need for improved systems, with enhanced insensitivity to installation conditions. Rehau and Borealis, have gathered their respective long expertise and knowledge in PE pipes and raw materials to develop a new pipe system with outstanding crack resistance to meet new market expectations and needs. This paper will describe the different steps the two companies have passed together, from analysis of the market needs to the first actual projects of the newly created RAUPROTECTII solution.
Since the first pipe productions almost 50 years ago, PE has developed an impressive successful track record, and is today the preferred choice for these applications. Ease of installation, low maintenance and corrosion free are some of the well-known reasons for this success story.
Another key reason is the constant efforts of both raw materials producers and pipe producers for improved quality and reliability.
After the development of HDPE pipe materials like PE63 and then PE80, the first PE100 materials arrived on the market at the end of the 1980s. These materials were a real milestone in the development of HDPE pipe materials because they facilitated the use of higher service pressures or pipes having thinner wall at the same service pressures and at the same time they also offered the end-user other advantages such as high resistance to Slow Crack Growth and high resistance to Rapid Crack Propagation.
|Pipe installed since||1965||1975||1990||1990|
|Design stress||5.0 MPa||6.3 MPa||6.3 MPa||8.0 MPa|
|Stage II knee point 80°C||100-300 H||1000-3000||> 10 000||> 10 000|
|Notch test, 4,6 Mpa/80°C||10||100-200||> 1000||> 1000|
|Rapid crack propagation/Pc 110SDR11||< 3 bar||< 3 bar||> 10 bar||> 10 bar|
But these techniques can happen to be more aggressive and demanding to pipe materials, which can be in contact with hard or sharp objects.
There is also a clear trend, over different European countries, in the case of installation in open trenches, to move from the traditional sand-bed laying to sandless bedding and to re-use as-dug material as backfill material to fill-up the trench after installation of the pipe system. Depending of the type of soil in the specific area of installation, higher stresses can be created to the pipes.
In a practical way, two main situations can initiate slow crack growth phenomenon in a pressure PE pipe:
- The first one is scratches or notches created at the outside surface of the pipe before installation with improper handling or storage, or during installation when the pipe can be accidentally damaged.
- The second main cause is “point-load”: an external local stress is created at the surface of the pipe for example by a rock pressing directly against the pipe wall.
4.1 Optimizing the raw material: the polymerization process
- Independent control is applied to the reactors to steer comonomer distribution and to tailor molecular weight distribution (MWD).
- Flashing between the reactors guarantees independent reaction mixture compositions. A wide density range, from LLDPE to HDPE can be produced.
- Different comonomers can be incorporated according to needs, e.g. butene or hexene.
- The MFR2 of the different reactors can be varied across a very broad range, from <<0.1 to more than 1000 g/10min.
- The process offers great flexibility with regard to the type of comonomer which can be incorporated into the correct regions of the polymer. For example, the use of the comonomer hexene in the bimodal Borstar process results in polymers having extremely high resistance to Slow Crack Growth.
With the help of the Borstar process and according to the description in the previous section, it has been possible to create a material which enables the pipe producer to make any dimension from 20mm to up to more than 2000mm and wall thicknesses of >100mm. Not only does this material provide the possibility to make any pipe dimension, it also possesses an excellent resistance to impact failures e.g. Rapid Crack Propagation, and excellent resistance to internal pressure manifested by the PE100 designation according to ISO 9080 standard extrapolation method.
We have seen before that SCG is a key parameter when in comes to lifetime of the pipes; we are now able to demonstrate that this new material has taken yet another step of at least one decade in the resistance to slow crack growth in the notched pipe test. However we can show not only that but also an unprecedented resistance to SCG in all of the tests to which the material has been subjected until now.
|NPT (a)||ISO 13479||80°C / 9,2 bar||> 18000 h||165 h1 |
|FNCT (b)||ISO DIS 16770-3||80°C / 4 MPa / Arkopal||ca. 6000 h||3500 h3|
|ACT (c )||90°C / NM-5||ca. 4000 h||330 hrs4|
|PENT (d)||ASTM F-1473||80°C / 4,4 MPa||>10000 hours||50 hrs|
1 = EN 1555 and EN 12201 requirement
2 = PE100+ association requirement
3 = DVGW requirement for sandless bedding
4 = Provisional DVGW requirement for sandless bedding
Figure 7: Summary of test results for Borsafe™HE3490-LS-H (Source: Kania et al.)
- the demonstrated technical fact that higher stress concentration is located at the opposite inner surface of the pipe while external point loads and internal pressure are combined during the whole lifetime of the pipe system.
- The requirement for this new pipe to keep the traditional key benefits of PE pipes, e.g. flexibility, ease of installation and weldability .
To achieve an outstanding crack resistance meeting new market expectations and needs, REHAU have then chosen to use Borsafe™HE3490-LS-H , the best available PE100 VRC-Quality (VRC= Very Resistant to Crack) available on the market for the co-extrusion of a thick inside layer of a smooth pressure pipe dimensioned according to the the established European standards EN 12201 / EN 1555 / EN 13244.
This material combination of best PE100+ association-grades for the outside layer with Borsafe™HE3490-LS-H on the inside layer brings a cost-effective, technical superior pipe system quality to the market that fulfills all the market expectations. The well-know testing institute “Dr. Hessel Ingenieurtechnik” in Roetgen-Germany confirmed that the RAUPROTECT II RAUSISTO system solution based on Borsafe™HE3490-LS-H showed best results against point loads and can therefore be used without risks for trenchless technologies and in trenches without sand embedding. Another advantage worth mentioning for the installer and end-user is that RAUPROTECT II RAUSISTO pipes, can be installed as standard PE pipe: in particular, they can be butt-fused or jointed with standard-fittings and welding parameters. No expensive special tooling for the removing of outside protection layers is necessary.
Together with long life-time expectation , traceability and easy identification of the pipe after installation are becoming to be perceived as highly important. To improve the traceability of that heavy-duty pipe system, REHAU has decided to marks all RAUPROTECT II RAUSISTO pipes with durable, laser-marked traceability-Barcode according ISO 12176-4 (Code 128, type C) and ISO 13950. Every produced meter of RAUPROTECT II RAUSISTO can now be easily tracked and welded with modern welding equipment to make pipe laying in the trench more easy and safe than ever before.
Gas pipe installation in Holzthaleben / Germany One of the first important projects using the new developed RAUPROTECT pipe system was in Holzthaleben in Germany.
The gas distribution company E.ON has chosen this system for a new gas distribution system, installed in very demanding conditions: the pipes had to be installed in very tough rocky soil , using horizontal drilling and ploughing-in installation techniques. 2,4 km of pipes diameter 63 SDR11 and 2,3 km of diameter 110 SDR 11 have been successfully installed for that project.
They have proven, since several decades to offer a safe solution for gas and drinking water distribution, contributing to protect these precious fluids. They are in particular showing the best leakage statistics among all pipe materials. One of the key reasons for this success is the innovation potential shown by both PE raw material producers and pipe producers; recently, a new market need for tougher materials for installation in demanding conditions has pushed for the development of a new generation of pipes.
The new RAUPROTECT II RAUSISTO system, based on the combination of BorSafe™HE3490-LS-H, a new PE100 material with outstanding resistance to slow crack growth and modern state-of-the-art pipe-design will continue to secure the safe transport and distribution of potable water and gas for generations to come!
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Guido Kania (REHAU Senior Manager R&D, Civil and Underground Engineering)
91058 Erlangen, Germany
+49 9131 92-5546
+49 9131 92-51-5546