Weld Testing for Quality Assurance
Weld Testing for Quality Assurance – One piece of the puzzle
Unlike HDPE membranes, which allow for a series of both patented destructive and non-destructive tests, the manufacturers of bituminous geomembranes only recommend non-destructive testing to verify the integrity of installed geomembrane materials. In this article, I introduce two methods applied by Groupe Alphard to test welds in bituminous geomembranes, and provide a reminder that weld testing is only one part of a quality assurance program that guarantees the material and environmental integrity of geomembrane materials.
The vacuum chamber method is used to ensure that geomembrane welds are leakproof
Vacuum Chamber (ASTM D5641-94) – The first line of defence
The vacuum chamber method is used to ensure that geomembrane welds are leakproof, but only provides limited information on the mechanical strength of the weld. Firstly, the test portion of the weld is moistened with a soap solution. Next, a rigid transparent chamber is placed over the test weld. This chamber is lined with a leakproof neoprene seam and fitted with a gasket, allowing a quality control technician to pump air out of the chamber and create a vacuum directly above the test weld. If the weld leaks, the vacuum chamber will draw air through the leak, creating bubbles in the soap solution and allowing the quality control technician to verify whether the test area is leakproof by eye. The vacuum chamber method is normally applied to all welds on-site. The frequency of tests is decided through a statistical analysis performed by the project’s quality control lead.
Ultrasonic testing (ASTM D7006-03) - Technological approaches
Ultrasonic testing is significantly more technologically advanced than the vacuum chamber method, requiring trained technicians and dedicated ultrasound equipment. However, it allows technicians to precisely identify a wider range of possible faults at an extremely high resolution. Ultrasonic testing begins by passing sonic waves into the test weld material, recording the amplitude of the waves as they enter and exit the material. If the weld is free from faults, the entry and exit amplitudes will be the same. If the weld is faulty or incomplete, or if it is compromised with air bubbles or foreign bodies, a third amplitude reading will be present alongside the amplitudes of the entry and exit waves. A trained technician can then establish the depth and size of any faults by comparing these readings. Like the vacuum chamber method, ultrasonic testing is usually applied to all welds on-site and test frequency is determined by the project’s quality control lead through statistical analysis.
Weld Testing – Limitations and the importance of leak location
The tests described above are only applicable to welds between geomembrane panels. The frequency of these tests is decided on a case-by-case basis by the quality control lead and can vary between companies and projects. Whilst they remain extremely effective within their range of applications, these tests should always be accompanied by a thorough leak detection program to ensure that installed geomembrane materials are 100% leak proof. Groupe Alphard’s industry-leading leak detection team plays a central role in our quality assurance program, applying a variety of leak detection methods over the entirety of installed membrane materials.