SANDVIK Materials Technology has developed a production method for internally, longitudinally finned, cold finished tubes for use as pyrolysis tubing in the demanding environment of ethylene furnaces.
With supply approvals having been obtained from key contractors, Sandvik has become an approved industry supplier.
As a result, a major order has been obtained from Russia's largest oil company, Luk Oil Europe Holding Ltd, for the supply of furnace radiant tubes for four furnaces at the Luk Oil ethylene plant in Burgas, Bulgaria.
A previous order had been delivered last year to Borealis AB, Sweden's only ethylene producer.
In the ethylene process, steam and hydrocarbon are mixed together and heated, resulting in a tube metal temperature of between 900° and 1150°C and extremely aggressive and corrosion conditions.
In order to extend the life of tubes in such an environment, Sandvik produces the required 50mm-76mm outside diameter finned tubes in a modified high temperature steel grade Sandvik 353MA (UNS S35315) - an austenitic, chromium-nickel steel alloyed with nitrogen and rare earth metals.
The chemical composition of Sandvik 353MA is optimised to provide a material with excellent carburisation and oxidation resistance. It has a high creep strength and maintains a very good structural stability in the temperature range required for service in ethylene furnaces.
Longitudinal fins increase the inside surface area of a tube by up to 25% and this enlargement of the tube's inside area improves heat transfer, which in turn, means increased productivity for ethylene producers.
The new tubes from Sandvik require a lengthy production route which includes extrusion followed by cold working.
Johan Josefsson, product manager for ethylene furnace tubes, said the project group responsible for the process development of finned tubes had to create a manufacturing route.
“In this respect, Sandvik Steel benefits from close control of its tubemaking processes - from steel melt throuah to the finished product.
“Finned tube production places large stresses on machines and to achieve successful results, we drew heavily on our processing skills and knowledge of production methods.
“The result is we are now approved and the market for ethylene furnace tubes is open to us,” he added.
Sandvik 353MA is manufactured under licence from AvestaPolarit.