A multimillion-dollar order for the man- ufacture and supply of high-tempera- ture tube supports for a Middle East oil refinery has seen local stainless steel foundry Steloy Castings rise to new challenges.
Steloy sales and marketing director Wynand Labuschagne says the supports, which include spun cast tubes, as well as static castings, comprise over 10 000 individual items ranging in weight from 100 g to 500 kg.
The combined weight is more than 200 t and the contract stipulates staggered supply, with the last components scheduled for delivery by December this year.
Manufactured for use in a fired heater, where temperatures are in excess of 800 °C, the supports are cast in two variants of heat-resistant HK40 stainless steel. American Society for Testing and Materials (ASTM) A351, popularly known as 310H, is used for the static castings and ASTM A608 for the centrifugally cast tubes.
“The company has a 25-year track record in the supply of critical stainless steel components to the global petrochemicals industry. However, intricate manufacturing requirements, combined with the sheer size of this contract, have seen the foundry enter new territory.
“The major challenges are on the manufacturing side, where gas tungsten arc welding of the tubes, with a diameter of 23 mm and up to 23 mm walls, is required. “Dedicated weld procedures have to be implemented for the high-quality welds, which have to pass level 1 radiographic inspection,” Labuschagne says.
Steloy states that thousands of support bars and hundreds of tubes are cast in its Chamdor plant, which incorporates South Africa’s only stainless steel centrifugal casting facility. Components are subjected to 100% liquid penetrant examination according to the American Society for Mechanical Engineers V specification and radiographic inspection in line with ASTM E446, and the tubes also undergo pressure or bubble testing.
The tubes are then transported to the company’s Bronkhorstspruit machining facility, where the required weld preparation is machined and some mounting holes are drilled in both the tubes and the bars.
The tubes are then mounted four at a time in a 9-m-long jig fitted with a 150 A plasma cutter mounted to a computer numerically controlled frame to cut 176 slots of varying sizes into each tube. Components are then sent for final fettling and finishing before final assembly.