Experience with Higher Performance PE Compounds [PE]

Polyethylene technology is advancing continuously. In the pipe sector, SOLVAY has led the way in the development of the third generation compounds of polyethylene classified MRS10 or PE100 materials.

The advantages of PE100 are PE100 enables pipes of a given wall thickness to withstand higher pressure; or

• PE100 may be used with thinner walls for a given diameter and pressure, thereby reducing the costs per meter of pipe; or
• PE100 provides maximum safety standards provided by PE today without changes of pipe dimensions and operating pressures; and
• PE100 is safely weldable using the traditional fittings and butt welding methods; and
• PE100 is flexible and coilable up to 160 mm reducing the installation cost and reducing the number of on-site welds needed.

Consequently, the third generation PE for pipe developed by SOLVAY has been approved and is used by many gas and water distribution companies throughout the world.

P£100 compounds has significantly extended the application range of polyethylene pipes against traditional materials, especially for large diameters and high pressure systems.

With sales since the beginning of more than 100,000 mt in Europe, PE100 is considered the reference product for  : 

• gas application in the pressure range from 4 to 10 bars;
• water application in the pressure range from 10 to 16 bars and diameter between 110 mm and 400 mm. For lower pressure, pipe with a diameter as large as 1200 mm have been routinely produced.

PERFORMANCE PE
COMPOUNDS L. CASTIN Y. TAVERN/IJER September 1995


Polyethylene technology is advancing continuously. In the pipe sector, SOLVAY has led the way in the development of the third generation compounds of polyethylene classified MRS10 or PE100 materials.The advantages of PE100 are PE100 enables pipes of a given wall thickness to withstand higher pressure; or
PE100 may be used with thinner walls for a given diameter and pressure, thereby reducing the costs per meter of pipe; or
PE100 provides maximum safety standards provided by PE today without changes of pipe dimensions and operating pressures; and
PE100 is safely weldable using the traditional fittings and butt welding methods; and
PE100 is flexible and coilable up to 160 mm reducing the installation cost and reducing the number of on-site welds needed.Consequently, the third generation PE for pipe developed by SOLVAY has been approved and is used by many gas and water distribution companies throughout the world.P£100 compounds has significantly extended the application range of polyethylene pipes against traditional materials, especially for large diameters and high pressure systems.With sales since the beginning of more than 100,000 mt in Europe, PE100 is considered the reference product for  : gas application in the pressure range from 4 to 10 bars;water application in the pressure range from 10 to 16 bars and diameter between 110 mm and 400 mm. For lower pressure, pipe with a diameter as large as 1200 mm have been routinely produced.



Plastic pipes have steadily increased in importance in the design of piping systems for water and gas transport throughout the world. This trend reflects the development of plastic materials and the world-wide knowledge and experience of its advantages versus the traditional pipe materials.The manufacture of plastic pipes began with PVC. PVC was largely used for water supply in medium diameter pipes. Low price per unit length as well as simple handling and jointing techniques have contributed towards PVC pipes gaining a substantial market share.Polyethylene has been used as a pipe material for more than 40 years. Conventional LDPE was initially proposed for small diameter pipes and low pressures.Since the late 1950’s, HDPE and subsequently MDPE have been used in pipes for carrying pressurized gas and water with a current diameter range from 40 to above 250 mm. Easy jointing and handling have been keys in the success of this plastic material PE also has the advantage of flexibility.In the late eighties a new PE type - third generation material - with noticeably improved mechanical properties has been offered for pipe production. This new generation pipe material first manufactured by SOLVAY allows  : e higher pressure of the transported medium; e thinner pipe walls; e higher safety margin.The excellent properties exhibited by polyethylene depend largely on the structure of their molecular structure.Long term mechanical properties mainly depend on the resistance of the longer chains to disentanglement.In the eighties, SOLVAY has developed a polymerisation process which enables higher co-monomer incorporation in the amorphous portion. This considerably increases the entanglement of the molecular chains and therefore affects the properties of the product. The first consequence of this new approach is to reach a higher portion of incorporated co-monomer in relation to the density or rigidity.This leads to significant improvements of the normal ESCR/stifiness compromise. [hus, giving higher hydrostatic pressure resistance, a really good resistance to stress cracking, plus an exceptional resistance to rapid crack propagation. This explains why MRS10 classification was attainable.PE100 PIPE PROPERTIES PE pressure pipes for the transportation of gas and water must meet very stringent requirements.The most important improvements provided by the PE100 materials are discussed here.1. Higher long term strength Long term strength 1s demonstrated by pressure testing of pipes at different temperatures (20, 40, 60, and 80°C).
Based on these results, regression calculations make it possible to find the permitted maximum wall tension in the pipe (hoop stress) by extrapolation at 50 years at 20°C.
For this new generation material, the minimal wall tension extrapolated at 50 years at 20°C (LCL : lower confidence limit) is above 10 MPa. Consequently, the material is classified MRS10.2. Better Stress Crack Resistance Pipes in service may contain surface defects caused, for example, during site handling or relining of defective metal pipes. These defects can act as initiation points for slow crack growth ultimately leading to failures. In order to evaluate this phenomenon pipes are tested.The standard tests consequently aim at measuring the sensitivity of material to notching.Accordingly, pipes containing 4 notches to a depth of 20 % of the wall thickness are tested at 80°C.Medium density compounds of the second PE generation normally pass these tests, while standard high density types usually fail.
Although the third generation material from SOLVAY is a high density PE, it easily passes this test.3. Higher resistance to fast fracture propagation Standard polyethylene, although normally a high ductile material, does exhibit brittle characteristics under adverse combinations of high strain rate and low temperature. In the network, such brittleness can emerge as a fast running longitudinal through-wall crack which propagates in a wavy manner at speed of above 200 m per second. This is called rapid crack propagation.
In service, the initiation of a propagation fracture may arise accidentally as a result, for example, of an impact. Therefore any propagation of fracture must be self-arresting within a distance as short as possible.
Different tests have been proposed to tackle this critical phenomenon  : e The Full Scale Test (developed by British Gas and used in UK, also listed in the ISO and CEN drafts as a material type test);
e The Small Scale Steady State Test (known as S4 and proposed in the new ISO and CEN standards as a QC test).At a temperature of 0°C, a traditional high density or medium density PE pipe having a service pressure of 3 to 4 bar may, depending on the diameter and the thickness, potentially face a rapid crack propagation problem. Meanwhile, with the third generation resin from SOLVAY, this may be possible only when the line pressure reaches a value over 20 bar. Therefore PE100 resins can be safely used in higher pressure applications.The high performances of the PE100 resins extend the application range of PE pipes against other traditional materials and also increase the safety standards of piping systems.Advantages of pipes made of third generation resins — Increase of pressure Since PE100 resins have a design stress of 10 MPa, fluids can be transported at higher pressure, provided the dimensions of the pipes and the safety factor remains the same. As a result of excellent resistance to fast and slow fracture propagation and other improved properties, the required safety factor is lower than for second generation material types.
As example, pipeline systems for gas are operating at 7 bar and those for water at 16 bar. The corresponding safety factors are 2.9 and 1.25 respectively.— Reduction of wall thickness If the currently used operational pressures and safety factors are maintained, pipes with thinner walls may be used. The costs per meter of pipe are thus reduced.While mechanically stronger, PE100 resins still maintain the principle installation advantages of PE. The installation cost of the pipes is significantly reduced since pipes with a diameter up to 160 mm are available on winding drums. Additionally this reduces the number of on-site welding.The outside diameter reduction is also an advantage in connection with the relining of used metal pipe.— Improving safety If no change of pipe dimensions, operational pressures, or installation 1s desired, switching to PE100 resins material offers the best safety standards provided by PE piping today. The list of advantages includes  : e higher safety margin; e higher resistance to fast fracture propagation; e higher resistance to notching.The new PE types are particularly suitable for piping systems targeted for countnes with high average temperatures, or for the disposal of warm waste water. At the same time, excellent resistance to fast fracture propagation makes it possible to use the pipes made of PE100 resins at extreme conditions (temperatures < 0°C).— Competitiveness with other materials The many advantages of polyethylene pipes made from PE100 resins provide a new competitiveness of PE against traditional materials. It consequently broadens the field of polyethylene pipe applications, especially in larger diameters and higher pressures.In fig1, the competitiveness of the PE100 resins against ductile iron and the second generation PE material for water distribution at 10 bar is presented.
The competitive analysis is based on the future CEN standards and the existing conditions on the UK market for price of pipes and installation cost. The results shown in fig] demonstrate the significant competitive advantages provided by the PE100 material against standard PE80 material and ductile iron, especially in the diameter range from 250 to 400 mm. Additionally, in aggressive soils, ductile iron like steel needs a costly anti-corrosion treatment that is not required for PE pipes thanks to the good chemical stability of PE.Price Competitiveness of PE Pipe Estimated Installed Cost (10 bar network) 2,4 aD <a 18 1,6 1,4 120,8 0,6 0,4 0,2
 
160
180 Diameter (mm) ~#- MRS 100 -«- MRS 80 -<- Ductile Iron The fig2 shows the penetration of PE100 pipes on the UK water market. Starting with the diameters 90 mm, PE100 pipes are significantly used today upto 630 mm diameters.Market Share by Product and Diameter Water Market in UK 1994 BE MRS 8 MRS 10 8D! B PVC MGRP| 
 
 63 90 125 180 250 315 355 490 S300 360 630 £710 PE equivalent diameter 
 PE100 pipe now hold about 30 % of the PE water pressure pipe market in UK.Another analysis conducted on the Italian water market shows the difference in percentage of water transportation costs in a PE100 pipe compare to ductile iron and steel pipe.Water transportation costs per m3 (Comparison to PE100 pipe) ‘% Extra Cost Compared to PE100
 
 
 
sats Diameter (mm)
(fig 3)
rT
300
 The graph clearly shows the significant advantage of PE100 for a diameter range upto
400 mm.Currently, pipe diameters as large as 1200 mm and fitting diameters as large as 500 mm have
been routinely produced.PE100 resins produced by SOLVAY have been approved by various organizations including | British Gas, Gaz de France, Electrabel, Italian Institute of Plastic (IP), Laboratoire National d’Essais (NF), Institut Belge de Normalisation, WAA Sewers and Water Mains Committee (WRC - UK), DVGW, Drinking Water Inspectorate (DWI - UK), Department of the Environment (DoE - UK), SVGW, Miljostyrelsen and Kontrollradet for Plastor (KP), etc ...Offered first on the market in the year 1987 with the objective to expand the range of application of the PE pipe for the larger diameter and higher pressure application, PE100 resin have today been used for more than 100.000 t in Europe.To put the impact of PE100 materials on Europe piping systems more in perspective, we can compare the overall growth of PE for pipe systems (forecast 94-95) which is about 8 to 10 % to the growth of PE100 which is about to 25 % per year. This growth of PE100 resins is expected to continue in the future with the increased availability of fittings and larger diameter pipes.When compared to traditional materials, PE100 compounds offer a variety of advantages. In combination with the traditional advantages of PE piping systems (no corrosion, high flexibility, ease of jointing, simple installation, good water quality), the features provided by PE100 materials represent an excellent technical and economical solution for pressurized transportation and distribution systems.This family of PE100 resins has firmly established itself as a competitive piping material by providing users with a number of possibilities for developing higher performance piping networks  : increased pressure capabilities; resistance to rapid crack propagation; enhanced safety factor potential; reduction in cost ....Subsequentiy, PE100 pipes are gaining a significant market share against other traditional material in Europe’s piping systems.Sold today for more the 100.000 mt, PE100 can be considered as a reference product for the following application  : Gas application e diameter above 110 mm, e pressure from 4 to 10 bars.Water application e diameter between 110 mm and 400 mm, e pressure from 10 to 16 bars.For lower pressure, pipes with a diameter as large as 1200 mm have been routinely produced.Reference GAS- EN WATERDISTRIBUTIE, Toepassingen van kunststofbuizen; Het Ingenieursblad 1990, 9.H. BOCKER. R DEWITT Hochleistung-PE gibt mehr Sicherheit bei Rohrleitungen; Kunststoffe 82 (1992) 9.A. McDIARMID, L. EWING UK EXPERIENCE WITH 7 BAR POLYETHYLENE DISTRIBUTION SYSTEMS; IGUCECOR Workshop session at 18th IGU World Gas Conference, 11 July 1991 Berlin.THE USE OF PE PIPES IN THE GAS INDUSTRY UP TO 10 BAR; 18th IGU World Gas Conference, July 1991.G. MA JONES THE CHALLENGE FOR WATER PIPE SYSTEMS IN THE 21st CENTURY