QUALITY CONTROL TESTING
EPL-SA Quality Control Procedures
The importance of on-site Quality Control Testing cannot be over exaggerated. Quality Control (QC) procedures and testing entails the implementation of a detailed QC Plan which includes among others weld testing during the entire installation process. On site testing offers peace of mind in terms of the methods utilised to install a lining system and to test the integrity of such a system whilst installing. The reasoning behind such prescribed methods of installation and testing is that in the unlikely event of a defect, it is quickly identified and immediate remedial or corrective action can be taken to resolve potential future issues.
Installation and composition specifications are defined in terms of the internationally accepted GRI-GM13 (GRI GM29) specification, as well as the SANS 10409 and SANS 1526 specifications for thermoplastic geomembranes. These specifications set forth a set of minimum physical, mechanical and chemical properties that must be met or exceeded by the geomembrane being manufactured. Together with the prescribing methods of manufacturing, the specifications also sets forth installation, sampling and testing procedures.
Engineered Plastics and Linings – South Africa (Pty) Ltd abides by these international specifications and commits to follow these specifications without exception.
The two predominant methods for welding/joint seaming polyethylene geomembranes are the Double Hot Wedge Welding and Extrusion Welding methods. Both these methods require different approaches to testing, depending on the specific application. Seam testing is carried out at agreed intervals during the installation of the geomembrane to ensure that any seaming faults are detected, and corrected at an early stage. Seam testing comprises both destructive and non-destructive tests.
EPL-SA tests our welding installations by means of the following:
1. Trial Weld Testing
Prior to undertaking production welding it is specified that a trial weld test be completed to determine the functionality of the welding machinery at the specific current site conditions. A test strip is welded using the same material that will be welded, at the intended joint weld and a destructive sample is cut from the test strip. A tensile test is completed on the sample to ascertain whether or not the machine is calibrated correctly for the climatic conditions. This test ensures the equipment functions effectively for production weld and also serves as a calibration test.
2. Air Pressure Testing (Non Destructive)
Double Hot Wedge Welding/Seaming is defined as the controlled thermal bonding process of two sheets of geomembrane. This is achieved by means of an electronic, self-driven, machine welding the sheets together in a controlled manner. The result of this method of welding is two thermally bonded seams with a small un-welded cavity formed between the two seams. The channel between the two bonded seams is then pressurized by pumping air into the channel itself. The pressurised channel is monitored by means of a pressure gauge over a defined period of time. Should the pressure in the channel dissipate it would be fair to conclude that a defective weld might be the cause. The EPL-SA QC Manual sets out a specific repair procedure, which would be actioned as remedial work to the above potential issue.
3. Vacuum Box Testing (Non Destructive)
Vacuum box testing is used when the Extrusion Welding method was utilised for welding purposes. A perspex box is placed over the welded seam and using a pump a negative pressure is created inside the box. A soapy solution is applied over the weld prior to the box being placed over the weld. If there are any defects in the weld itself or any hairpin holes penetrating the lining, it will be visible in the form of bubbles bubbling outwards. This method is used in instances where Pressure Testing or Spark Testing is either impossible or impractical.
4. Spark Testing (Non-destructive)
When joint welding is done using the Extrusion Welding method and Vacuum Box testing is not possible or practical, it would be necessary to test these welds by means of the Spark Test method. The Spark Test method entails the inclusion of a small conductive wire into the extrusion weld itself. EPLSA utilises a small copper wire into the overlapped edges of the weld. The extrusion bead is laid over the wire, in addition to thermally bonding the two sheets of geomembrane. Once the weld has set a spark tester is manoeuvred over the weld and if there are any hairpin holes present, it would manifest itself in the form of an arc. This method of testing extrusion welds is widely utilised for patches and intricate work.
5. Destructive Testing
Once the lining system is installed, samples are cut from the welded seams for testing purposes. This method of cutting installed portions must be kept to a minimum as it deals with installed product and the repair of these test samples results in more jointing that could itself be vulnerable. The frequency of testing is defined in the SANS and GRI specifications. These samples can be tested by the engineer, a 3rd party QC Consultant or EPLSA, depending on the site specific requirements.
All Quality Control Testing is set out in the EPLSA Quality Control Manifest and more detailed descriptions are available upon request. Premium quality installations are a function of the implementation, documentation and control of testing, both during manufacturing of the membrane as well as the installation process. Following completion of the installation, EPLSA will issue the client a Quality Control Document, indicating all testing completed in a detailed format. This provides peace of mind that the integrity of the installed lining system is intact, which is of significant importance especially in hazardous fluid containment structures.