> Home > Case Studies > Saint Gobain Gypsum Saint-Gobain Gypsum Added 14.03.2017 At Manthorpe Engineering we have been manufacturing multi tubes for what was at the time British Gypsum, and has since Changed hands and is now known as Saint-Gobain Gypsum, on a build to print basis since the mids 1980's. The multi tube is made up of a dished end that has a flange welded all around with a series of tubes welded into the dished end in concentric rows and is used to heat up gypsum powder in the 400° to 800° temperature range. The flange weld is subject to radiographic examination to ensure there are no defects in the weld zone whilst the tube welds and tie start welds are only subject to dye penetrant inspection. When we first started manufacturing the multi tubes the average life span of the product was only around two years, with failing due to cracks in the tubes after only eighteen months of service whilst others were lasting up to three years before any failures. During 2002 we were approached by the head of the British Gypsum technical department based in East Leake to see if they would be prepared to work with their technical engineers to try and obtain the reason behind varying life span before failures occurred. Collaborating with British Gypsum, together we decided on approaching Comech Limited, who are a metallurgical testing facility. They carried out a full detailed analysis on the mechanical and chemical properties of a multi tube that had failed earlier than its life expectancy, this was to try and gain an understanding of what was causing the failures, and whether a solution could be found to increase the life expectancy. Upon their initial visual examination, Comech Ltd found that the majority of the cracks where the multi tube failed, were located on the centre two rows of tubes whilst the remained of the tubes were all intact with no visible cracking evident. Further investigation showed that the cracks were all located on the toe of the welds where the tubes were welded on the outside face of the dish, in what is known as the heated affected zone. Samples were then taken from the fractured area and subjected to fractographic and metallographic examination which revealed that fatigue cracking had taken place at multiple starting points within each tube weld, which may be attributed to the heat affected zone of the welds having a hardness value that was significantly higher than the tube material hardness. Upon analysing the Comech Ltd report a joint decision was made to carry out heat treatment of the next multi tube upon completion of manufacture, which would remove the heat affected zone around the tube welds and therefore create a uniform hardness throughout the whole of the multi tube and thus eliminate the potential fracture points. Thermal Hire in Hartlepool were selected to carry out the stress relieving process as they were one of the few companies that were capable of heat treating the stainless steel products of this size. Since the investigation was carried out in 2002, our fabrication department have refined their welding sequences and procedures and now heat treat every multi tube, resulting in a life span that has increased to between five and seven years. The results of this collaboration has led to a significant saving for Sain-Gobain due to the difference in life span of the product. Although this has reduced the amount of potential work for us at Manthorpe in the short term, our commitment to the customer led to us being nominated as the European supplier of multi tubes to Saint-Gobain, and have also manufactured multi tubes for both north and south America. We are still manufacturing multi tubes for Sian-Gobain and hope to continue to do so well into the future. 123 Back to Archive © Copyright Manthorpe Engineering 2021 Home Industry Sectors News About Us Services Contact Case Studies Contact T +44 (0)1773 514 200 E engineeringsales@manthorpe.co.uk Connect