Sassda is investing in the future of the South African stainless steel industry thanks to its year-long sponsorship of 28-year-old Wits University Masters student Abiola Ladenika. His thesis concerns stainless steel thin wall pipe welding, in sectors subject to more stringent health legislation. This is because practically it is far more difficult to achieve healthy joints than to meet structural integrity criteria, particularly with site welding. The work will factor in changing health legislation in the food and beverage industry and provide benefits for the maintenance and fabrication of new stainless steel pipes in process plants.
Nigerian-born Ladenika, who hails from the Yoruba tribe, will see a year of study sponsorship provided by Sassda to complete his thesis which focusses on ‘the effect of pipe-end forming and alignment in ensuring better fit up, thereby limiting the bacterial count in weld joints’.
Of relevance to Sassda members, the project aims to find a means of managing the fabrication of stainless pipes in new plants while also maintaining older plants to accommodate the changing health legislation and operational conditions, which will go a long way to easing operating costs.
Commenting on his studies, Ladenika says; “I am very environmentally conscious. I have a background in metallurgy and a willingness to find a solution that is going to save people money. My thesis will focus on an approach to the hygienic fabrication of process plants subject to health legislation.”
Wits School of Chemical and Metallurgical Engineering, Adjunct Professor Tony Paterson, BSc(Eng), BEngHons, Meng, PhD, PrEng, MSAIIE, MSAICE comments; “The applications for stainless steels in engineering is vast, particularly in the process industry sectors. The department formulates courses to teach students in identifying appropriate applications and the data to support the use of stainless steels in, for example high-temperature or corrosive environments that may be encountered across diverse needs.
“Abiola was chosen because the focus of this particular study will facilitate a better procedure for site welding of stainless steel pipes for the pharmaceutical industry and food and beverage process plants, and will contribute valuable information to the stainless-steel community.”
Professor Paterson, who has worked in joint ventures with Sassda and its members since the 1980s, oversees post graduate students who are exposed to the discipline of stainless steel welding as part of their studies.
Paterson has also previously worked with stainless steel welding applications – and its problems – specifically within brewery process plants. These include factory made tanks, heat exchangers or columns linked by site welded pipes. Process plants where the product is ingested by humans, are subject to health legislation and hygiene procedures required to guarantee food safety.
“The reality of the situation is that following recent health legislation, replacement piping in breweries is now faced with an emphasis on health requirements which they didn’t have to meet when the plant was built. Most problems in thin wall pipe welding are found at the joints. Pipe manufacturing tolerances allow a deviation in diameter, wall thickness and bowing. These have a significant impact on fit up and alignment for onsite welders.
According to Paterson for the external welding of pipes, the overlap at the join needs to be near perfect with a minimum 80% overlap. However, the manufacturing tolerances of thin wall pipes preclude good overlaps. The weld material creates an uneven root surface on the inside of the pipe. The geometrically uneven joints together with cracks in the weld is where bacteria lodges, causing both health concerns and corrosion. Borescope investigations post welding, show the difficulty of achieving even inside finish geometry at the joints.
Paterson adds; “It is one area where not a lot of attention has been given in process plants and the costs of poor welding is significant in the long term. The process of thin wall welding is hard to control onsite and hard for the welders when working with different pipe tolerances by manufacturers.
“Ladenika’s thesis will look to a new method of expanding the end of the pipe mechanically beyond the elastic limit then ironing the pipe end back, to lie parallel with the pipe. The purpose is to resolve residual stresses and to achieve a circular pipe. Then the onsite pipe welder can get a good weld. This process also allows for pipes to be modified while in storage awaiting application, with both ends of the pipe modified to suit the purpose.
Ladenika’s studies expose a more coherent principle to achieve thin wall pipe ends suited to welding. This means pipes can be joined onsite with the orbital pipe welding able to overcome both structural criteria and meet health and corrosion requirements