Thermoplastic tanks are an attractive alternative to metal tanks for the containment of many products, including hazardous chemicals. At present there are no established procedures for inspecting the welds in these tanks, either following manufacture or during service. With an expected lifespan of between 15-25 years, thermoplastic tanks are susceptible to failure through cracking due to chemical degradation, fabrication flaws or elevated operating temperatures.
TWI is combining expertise with eight European project partners, to develop a new approach for testing welded joints in thermoplastic storage tanks using automated non-destructive evaluation (NDE). The PolyTank project, launched as part of the European Seventh Framework Programme, began in November 2012 and will last for two years.
The inspection technique will involve ultrasonic examination of the full weld volume, from the outside surfaces of the tank. This means it will not be necessary to open up a tank to prepare the inside for examination. Until now, full volumetric examination of tank welds has not been possible.
The project team proposes that as well as ensuring the safety of thermoplastic tanks in specific or corrosive environments, the development of a volumetric NDT and inspection technique will result in new confidence for their use in demanding applications across many industries, as well as extending operating life, and allowing cheaper installation and maintenance.
Part of the PolyTank project will be to develop acceptance criteria for different types of flaws in welded joints based on both short-term and long-term testing. NDE and mechanical test data will be brought together in a database to highlight critical defect sizes that cause a reduction in the long-term integrity in different types of welds. The data will be put forward to CEN as the basis for producing a European Standard.
The PolyTank project team comprises: Chem Resist Group Ltd, UK; TWI, UK; Technology Assistance BCNA 2010 SL, Spain; HESSEL Ingenieurtechnik GmbH, Germany; Acutech Ltd, Greece; InnoTecUK, UK; HSE, UK; UNIVAR Ltd, UK.
The PolyTank research project receives funding from the European Union Seventh Framework Programme (FP7/2007-20013) 'Capacities' programme under the call for 'Research for SMEs' grant agreement 313950.
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