Papers
Plastic Pipes Conference Association # 2016 Berlin
Karin Jacobson, Daniel Ejdeholm, Rikard Kärrbrant, Kenth Olsson
IT IS WELL KNOWN THAT IT IS NECESSARY TO SCRAPE OFF A 0.2 MM OUTER LAYER OF A POLYETHYLENE (PE) PIPE SURFACE AT THE LOCATION FOR THE ELECTROFUSION WELD PRIOR TO WELDING. THE REASON FOR THIS PROCEDURE IS SAID TO BE REMOVAL OF AN OXIDIZED LAYER WHICH CAN RESTRICT MOLECULAR DIFFUSION ACROSS THE WELDING INTERFACE LEADING TO POOR WELDABILITY. SWEREA KIMAB HOWEVER, QUESTIONS THE EXISTENCE OF AN OXIDE SKIN, PARTLY SINCE IF THE PE WAS THAT EASILY OXIDIZED THAT IT NEEDS TO BE RE-SCRAPED AFTER A DAY DUE TO OXIDATION, THEN THERE WOULD BE A REAL PROBLEM WITH THE SERVICE LIFE OF THIS MATERIAL. THE ACTUAL REASON BEHIND THIS BEHAVIOR HAS BEEN STUDIED AND IS BELIEVED TO BE DUE TO MIGRATION OF STEARATES ADDED AS A PROCESSING AID IN PIPE PRODUCTION RATHER THAN OXIDATION.
It is well known that it is necessary to scrape off a 0.2 mm outer layer of the PE pipe surface at the location for the electrofusion weld prior to welding. The reason for this procedure is said to be removal of an oxidized layer (caused by UV degradation and/or the extrusion process) which can restrict molecular diffusion across the welding interface. It is also generally recommended that the welding is performed directly after scraping. However, Swerea KIMAB has questioned the existence of an oxide skin, partly since if the polyethylene was that easily oxidized that it needs to be re-scraped after a day due to oxidation, then there would be a real problem with the service life of this material. The actual reason behind this behavior has been studied and is believed to be due to additive migration in the pipe rather than oxidation. Better understanding about this will lead to possibilities to improve weld procedures and weld performance. The study has comprised both mechanical testing of pipes with and without scraping. Different time intervals from scraping to welding have been investigated and a thorough study on the chemical and physical properties of the material has been performed. In addition, pipes with an outer PP layer have also been studied to investigate if the weldability of this pipe after the removal of the PP layer is the same as for a scraped pipe.
Related papers
Author(s) : M. Eckes & Dr. B. Baudrit, Dr. M. Troughton & D. Wylie, H. van Laak & J. Fritz
Unplasticized polyamide 12 (PA-U12) is increasingly being used in pipe applications, especially in the gas sector. However, the material behavior in the usual quality tests for pipe welds has not yet been thoroughly investigated. For this reason, two research institutes, worked in cooperation with a manufacturer of...
Author(s) : Jörg Wermelinger, Sunwoong Choi
In the development of an international standard on non-destructive test for polyethylene electrofusion socket (EF) joints, the inspection capability of the phased array ultrasonic test (PAUT) in assessing flaws in the joints was needed to establish procedure qualification of the test method. For this, a worldwide...
Author(s) : Yilaing He, Tianjun Zhang
A new electrofusion PE belt is developed by reinforcing it with various layers of steel mesh. It’s of sandwich structure, consisting of steel mesh reinforcement, heating wire and polyethylene. One or more layers of steel mesh is encapsulated in the middle, and heating wire is embedded onto “inner side” of the belt....
Author(s) : R.J.M. Hermkens, H. Colmer, H.A. Ophoff
To investigate the suitability of PE pipes for the transport of hydrogen on a specific industrial site, three topics were investigated. These topics are: the chemical resistance of PE to hydrogen, the permeation rate of hydrogen through PE and the electrofusion of PE pipes exposed to hydrogen. It can be concluded that...
Author(s) : Dr. Love Pallon, Dr. Karin Jacobsson, Daniel Ejdeholm, Marie Allvar, Rikard Kärrbrant
This work presents the development of the Full Length Tensile Test (FLTT), a method that enables an objective judgement of welding quality of electrofusion welds by measuring the energy to break (J/mm2 ). In this way a brittle, ductile and transitional mode failure can be differentiated without subjective visual...
Author(s) : Mark Yu, Dongyu Fang, Peck Tze Kang, Amos Tay , Fan Liu
Large diameter pipe was introduced in refineries and petrochemical plant, desalination plant and power plant for water intake and sea out fall in the past decade. PE100-RC material was selectedfor its excellent balance of superior bi-modal stress crack resistance and consistent high stiffness modulus. Under the...
Author(s) : Juergen Wuest, Benjamin Baudrit, Frank Dorbath, Christopher Pommer
A testing apparatus for determining the mechanical properties of electrofusion and heated tool sleeve welded joints with the mechanized linear shear test (LST) was developed. The LST-apparatus allows the recording of the force as a function of the extension / shear length. It has been proved that the linear shear test...
Author(s) : Peter Postma
On request of the Dutch DSO’s and in cooperation with all important Dutch stakeholders (producers, suppliers, contractors and the regulator), Kiwa Technology investigated the relevancy of defects found with Phased Array Ultrasonic Testing (PAUT) and if it was possible to determine acceptance criteria. The project...
Author(s) : Mats Bergman, Karin Jacobson
The Swedish Water & Wastewater Association (SWWA) has funded a R&D project to investigate different methods suitable for installation inspection of PE joints in field. Methods like phased array ultrasonic testing (PAUT), microwave technology and digital radiography were studied. Digital radiography shows promising...
Author(s) : Predrag Micic, Cliff Mure
An extensive investigation was conducted into the electrofusion compatibility of pipes produced using a PE100 resin with an MFR5 value below 0.2 g/10min. The electrofusion (EF) joining program included pipes up to 800 mm in diameter and the use of electrofusion couplers and saddle type fittings as well as varying...
Members of the Association
