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Butt-Fusion of Glass-Fiber Reinforced Polyethylen Pipes (PE-GF)

General:

Since some years helical extruded pipes made of PE-GF are used in the market for pressure application.
Worldwide many projects have been realized in various diameters and for pressure applications up to 16 bar. The pipes are produced by the Krah Comtruder®-Technology, what guarantees a homogenously distribution of the chopped glass-fibers and the coupling-agent in the polyethylene-matrix. The international available standards for pipes DN/ID 400 until DN/ID 4000 are ASTM F 2720/ASTM 2720M, DIN SPEC 19674 and ISO/CD 29561 is still in process.
Mostly used in the market is the PE-GF 200 with a MRS-class 20 MPa, based on 20 % Glass Fibers, 2 % Coupling agent and 78 % polyethylene matrix of PE 100.
Joining of this kind of pipes is done either by the typical Krah-Electrofusion-Technology or by Butt-Fusion.

 

The Butt-Fusion-process

For standard Polyethylene Pipes the Butt-Fusion process is standardized in DVS 2207. Also the Butt-Fusion process for helical extruded PE-GF-pipes is following the rules of DVS2207 in general issues, especially regarding preparation of welding, quality control and general requirements for training and equipment.
The welding parameters itself, must be adapted regarding temperature-and pressure profile:

Process stages of heated tool butt welding 

 

Welding factor

BECETEL, the international well-respected institute in Belgium was instructed and authorized to verify the short- and long-term behavior of the butt-fusion-joints.

  • Test Product is a helical extruded pipe (Krah-pipe) with solid pipe wall.
  • The used Polyethylene Raw Material is PE 100 (Hostalen CRP 100, Lyondell-Basell)
  • Internal Diameter / Nominal Diameter = 500 mm
  • Wall thickness = 33 mm
  • Pipe Producer = Krah AG
  • Place and Date of Production = Schutzbach, Germany, 2013
  • Butt-Fusion = Henze GmbH, Germany, 2013
 

The measured welding factors by BECETEL are:

Short term fz = 0,83
Long term fs = 0,79

Conclusion:

The butt-fusion process is proper for welding of PE-GF pipes. The Butt-Fusion process fulfills the requirement to take the load of pipe under internal pressure.

The axial stress in pipes because of inner pressure is 50% of the circumferential stress.
PE-GF (MRS 20) pipes acc. DIN SPEC 19674 are designed with a safety factor of 1,6 for inner pressure.

  • The circumferential stress in PE-GF pipes by inner pressure is 12.5 N/mm²
  • The axial stress in PE-GF pipes by inner pressure is 6.25 N/mm²
  • The axial strength in butt-fused joints of PE-GF pipes is more than 22 N/mm² and provide a lot of safety!

The members of the committee for DIN SPEC 19674 have already signalized to integrate the mentioned welding parameters to the new and updated DIN SPEC 19674.

Furthermore you will find the detailed test report soon in the News of the Krah Community.

 

Author:

Dipl.-Ing. Stephan Füllgrabe
Managing Director of
Plaspitec GmbH, Cologne, Germany
Plaspitec is an international operating
Consulting and Engineering Company for
Large Diameter Plastic Pipe Systems