Polytec Systems

The Development and Validation of Non-Destructive Testing Techniques for Electrofusion Joints in Polyethylene Pipes

Strategic Objectives

1. To reduce the cost of repairs of polyethylene (PE) pipe systems by developing effective non-destructive testing (NDT) systems.
   
   
2. To reduce the risk to the environment through leakages of dangerous chemicals from PE pipe systems due to incorrect jointing procedures and techniques.
   
   
3. To develop an inspection standard, which will allow flaws to be assessed based on their effect on the performance of the welded joint.

List of Participants

TWI Ltd - Project Co-ordinator (UK)
Egeplast Werner Strumann GmbH & Co. KG (Germany)
Horton Levi Ltd (UK)
Isotest Engineering S.r.l. (Italy)
NDT Consultants Ltd (UK)
Simplast S.p.A (Italy)
Vermon S.A. (France)
Consorzio Catania Ricerche (Italy)
Hessel Ingenieurtechnik GmbH (Germany)
Italgas S.p.A (Italy)
Northumbrian Water Ltd (UK)
South West Water Ltd (UK)

Total Cost 1,815,000

Commission Funding 939,500

Project Main Goals

• To develop ultrasonic phased array and thermographic NDT techniques for the inspection of electrofusion (EF) joints in PE100 pipes.
• To determine the limits of detection for the above two techniques, for all possible flaws in EF joints.
• To compare the various short-term and long-term destructive tests that are currently used to assess the quality of EF joints in order to determine the critical defect sizes and contamination levels, which cause a reduction in the integrity of the welds.
• To produce and assess prototype NDT equipment that can:

  - detect and size defects in EF joints in PE100 pipes, both during installation and retrospectively;

  - compare the size of these defects with the critical values;

  - advise the operator whether to reject or accept the weld.

Key Issues

PE pipe offers significant advantages over other materials, such as cast iron, steel and concrete, for the distribution of fluids such as natural gas, water and corrosive liquids. It has a longer predicted service life, leading to less frequent replacement; it is less expensive to install due to its light weight; it doesn't fracture in the event of an earthquake or other earth movements due to its flexibility; and it has significantly lower leakage rates. However, its more widespread use is being restricted by the lack of a reliable NDT method for the welded joints.

Pipeline leakage does not only cause high repair costs but can also result in disastrous environmental consequences and even in loss of life. The development of a reliable NDT method for welded joints in PE pipes will result in both lower leakage rates in these systems and also in lower overall pipe leakage rates, due to an increase in the usage of PE over other materials for pipelines.

Technical Approach

Earlier work at TWI has suggested that manual ultrasonic and immersion C-scan NDT techniques can detect flaws such as lack of fusion, incorrect positioning and particulate contamination in EF welds, after the completion of the welding process. In addition, thermographic NDT techniques may be able to detect the aforementioned flaws during the welding process.

This Framework VI Co-operative research project, carried out with the financial support of the European Community, has developed these techniques further to provide a practical and reliable detection of flaws both under laboratory and field conditions. The development was made on welded samples in 125mm and 250mm diameter PE100 pipe containing manufactured defects of known size and quantity, and the NDT data was analysed to determine the limits of flaw detection.

In parallel with the NDT developments, the significance of defect types and sizes was established in relation to service requirements. This was achieved by both short-term and long-term mechanical testing on welds containing known flaws, and comparing with the results for welds containing no defects. In the final inspection systems, the NDT results will be compared with the defect significance data to allow those welds that are not acceptable to be identified.

Two prototype systems were manufactured for this project; 1) a thermography system which records the temperature at various positions around the joint during the welding process, and 2) a phased array probe and scanning frame specifically designed for use on completed EF joints. Both the above were developed on the basis of the results of the development of the NDT techniques and acceptance criteria. This equipment has been assessed under both laboratory and field conditions.

Co-ordinator Contact Details

Dr Mike Troughton
TWI Ltd
Granta Park
Great Abington
Cambridge CB21 6AL (previously CB1 6AL), UK

E-mail: mike.troughton@twi.co.uk
Fax: +44 (0)1223 891284 Copyright © 2006 TWI Ltd