TPI July 2013

duplex stainless steel products include super duplex stainless steel Sandvik SAF 2707 HDTM, super duplex stainless steel Sandvik SAF 2507TM, duplex stainless steel Sandvik SAF 2205TM, and economical duplex stainless steel Sandvik SAF 2304TM. Sandvik SAF 2707 HDTM is an example of Sandvik’s constant efforts to develop innovative products. This hyper duplex stainless steel was developed by Sandvik in 2009. Sandvik SAF 2707 HDTM has strong corrosion resistance to organic acids including formic acid and acetic acid, and maintains corrosion resistance in contaminated acids. Within a certain concentration range, the steel has equivalent or even higher corrosion resistance to inorganic acids than high alloy austenitic stainless steel. Therefore, Sandvik SAF 2707 HDTM can effectively replace high alloy austenitic stainless steel and nickel base alloy in environments where standard austenite is subject to severe corrosion. A German oil refinery provides a good example. The refinery experienced corrosion problems in the overhead condensation unit of its crude distillation column. Heat exchanger lifetime was short and processing had to be shut down to replace the carbon steel pipe bundle twice a year. When it learnt of this problem, Sandvik recommended that the refinery replace the carbon steel tubes with its next generation duplex stainless steel, Sandvik SAF 2707 HDTM. This hyper duplex stainless steel has good resistance to chloride induced stress corrosion cracking and its minimal thermal expansion makes it easy to install in a carbon steel construction. Due to the duplex stainless steel’s increased anti-corrosion properties, the wall thickness of the tubes could be reduced from 2.77mm to 1.65mm. The German oil refinery installed Sandvik SAF 2707 HDTM tubes in 2006. The new tube bundle was inspected after six months and showed only slight erosion corrosion. A shutdown check after four years showed no further erosion corrosion. After cleaning, eddy current testing and hydro testing, the bundle was reinstalled to run for another four years. Over a four-year period the number of shutdowns was reduced from eight to just one. The substantially reduced frequency of steel bundle replacements improves working safety. In terms of operation, it has meant large savings in terms of material replacement, manpower and lost production. Conclusions Oil refineries are constantly improving their awareness of key equipment material selection in response to the crude degradation trend. It is believed that with increasing development and promotion of duplex stainless steel technology, more refineries will apply duplex stainless steel material in key equipment to meet the demand for high strength and anti-corrosion products. Sandvik will remain innovative to satisfy the tough requirements placed on materials across a range of applications.

operation of subsequent processes. As part of the vacuum distillation plant, the overhead condensation system is most seriously exposed to corrosive substances. Corrosive media in the overhead condensing system include hydrochloric acid, chloride, ammonia chloride and hydrogen sulphide. The corrosive media form a corrosive HCI+H 2 S+H 2 O- based environment in the overhead low-temperature light oil location and condenser cooling system. Types of corrosion include general corrosion and uniform thinning of carbon steel parts, pitting corrosion of ferritic steel and chloride stress corrosion cracking of austenitic stainless steel. Therefore, a lack of effective anti-corrosion measures may result in severe corrosion of the overhead condenser cooling system and affect the normal operation of the equipment. Under these circumstances, refineries are seeking a more corrosion-resistant material to replace highly corrodible materials such as carbon steel and high alloy steel. Duplex stainless steel is a good solution. By combining the toughness and weldability of austenitic stainless steel with the high strength and resistance to chloride stress corrosion of ferritic stainless steel, duplex stainless steel has become the preferred material for key equipment for many refineries. Moreover, duplex stainless steel’s long service cycle makes the cost to the user much lower than competing products. The applications of Sandvik duplex stainless steel in equipment corrosion prevention Since the advent of duplex stainless steel in the 1960s, Sandvik has always been at the forefront of duplex stainless steel development. Today, Sandvik has become a major global supplier of duplex stainless steel based on its extensive product range, high quality products and uniform product criteria. Taking advantage of its technical expertise in smelting, Sandvik has made constant breakthroughs in duplex stainless steel production and added more specialised and better performing products to its product family. Currently, Sandvik’s

Sandvik – China Email: sara.liu@sandvik.com www: www.sandvik.com/cn

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Tube Products International July 2013

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