[ Petrochemicals ]
[ Petrochemicals ]
0.5 % niobium, 0.45 % carbon and a balance of iron. That a wide range of alloys may be required for an ethene cracker is amply demonstrated by a project report from Mantis. A contract award from a PVC complex in Louisiana called for pipe, fittings, flanges, and forged fittings, in materials including Nickel 625, Nickel 200, duplex S31803 / 2205, and titanium. Finally, readers might like to peruse a very interesting article from Asset Optimization i, which outlines a methodology to manage the reliability of ethane crackers based on API standards. The authors state that a well implemented and managed reliability program incorporating these processes can identify potential damage mechanisms, optimize maintenance and inspection, reduce risks and improve the governance in managing ethane crackers. It is sadly beyond this editor’ s capabilities to provide a reliable summary, but this article does include a wealth of information about materials including corrosion resistant alloys such as 304H, 347H and 800HT as well as 25Cr / 35Ni and 35Cr / 45Ni alloys.
Global research As might be expected, considerable research efforts are underway worldwide to understand and address the effects of corrosion, coking, etc, on materials used in steam crackers. In China for example, a team recently presented a failure analysis of 304H convection section tubes in an ethene cracking furnace ii. Based on numerous experiments, the team determined that the cause was metal dusting as a result of the protective oxide layer on the inner wall being destroyed by overheating. The article indicates that“ There were dense circular corrosion pits on the fire side inside the furnace tubes, loose metal oxides and carbide particles were filled in the corrosive pits. Severe carburization occurred on the surface of the pits, the furnace tube experienced metal dusting. The metal dusting resulted in the decomposition of the surface layer of the metal alloy into metal particles and graphite to thin the wall thickness. Then the furnace tube cracked because of the stress concentration appeared in the furnace tube with reduced wall thickness.” In another article detailing the premature failure of a 304H convection tube( expected to last for over thirty years), researchers investigated cracks on the
Polythene has become part and parcel of daily life. Image: DreamsTime.
second convection tube and noted severe bulging deformation around the cracking area iii. Following analysis including stereoscopic inspection and scanning electron microscopy analysis, the team concluded that the cracks were caused by localized overheating. They further suggest the root cause for such localized overheating may be due to inadequate steam flow and uneven heat distribution within the convection tube during service.
“ failed tubes had a thick layer of coke adhered to the inner wall”
304H was also the focus of a team from the Department of Chemistry at the University of Calgary in Canada, who set out to understand the effects of sulfur compounds on the formation of coke in the ethane / steam cracking process iv. After setting up a laboratory-scale quartz reactor heated by a horizontal tube furnace, the team exposed stainless steel 304H coupons and stainless steel 304L powder samples to ethane−steam or dry ethane with varying hydrogen sulfide contents at 700 ° C. The samples were then analysed using scanning electron microscopy. The 2018 article states that this work‘ demonstrates the importance to maintain optimized pO2 and pS2 levels in order to reduce catalytic and pyrolytic carbon formation and corrosion of stainless steel-304H tubes by sulfidation’. Meanwhile, an article by other researchers considered the degradation of 25Cr35NiNb radiant tubes in an ethene cracking furnace v. The tubes were investigated after seven years of service using microstructural analysis, chemical composition analysis, hardness testing, and mechanical testing. The results were compared between uniaxial and small punch tests. Apparently, the small punch test indicated serious damage to the outer surface of the tube. The team further suggests that the small punch test can replace the uniaxial test for performance testing of ethene cracking furnace tubes in service. Finally, the need to be aware of coking was amply presented by experts from Argentina, who investigated the failure of radiant coil tubes in an ethene cracking furnace vi. With an expected lifespan of five years, tubes failed after just three and a half years. Tensile testing showed severe in-service degradation of material mechanical properties. Longitudinal cracks on failed tubes were said to be brittle and have originated in the inner wall. Tellingly, all failed tubes had a thick layer of coke adhered to the inner wall; this layer was easily broken by bending
www. stainless-steel-world. net Stainless Steel World June 2026 47