Solving problems in process plant heat exchangers

Solving problems in process plant heat exchangers

Keywords Sandvik Steel, Heat exchangers, Stainless steel

In the last few years, super duplex stainless steel grade Sandvik SAF2507 from Sandvik Steel is reported to have found increasing use in shell-and-tube heat exchangers in the refining, petrochemical and chemical process industries.

According to Sandvik its excellent resistance to localised attack, such as stress corrosion, cracking and pitting, combined with high general corrosion resistance in hydrocarbon process fluids and various other chemicals, has made SAF2507 the optimum material for a wide range of processes and applications. In addition to its material properties, the increasing use of SAF2507 has been a result of increased availability. Today, all necessary components for heat exchangers such as tubes, tubeplates and welding consumables are believed to be readily available in the marketplace.

In service, heat exchanger tubes are often the most critical part of the construction. The use of seamless Sandvik SAF2507 tubes can reportedly be shown to increase operating reliability. A good example cited of the use of SAF2507 in chloride containing media is in seawater cooled heat exchangers. Retubing the exchangers with SAF2507 seamless tubes has solved erosion problems found on lower strength materials such as brasses, bronzes and Cu-Ni materials.

The high erosion resistance, low thermal expansion and ease of fabrication claimed of SAF2507 is considered to make it an ideal material in such cases.

Another example quoted by Sandvik of the successful use of SAF2507 can be found in the refining industry. An Italian refinery has been using SAF2507 tubes in an overhead condenser system in the crude distillation unit – an application where the corrosive conditions can be severe and unpredictable. Previously, carbon steel tubes were used, with a life limited to less than two years. By using SAF2507, with a longer operating potential, the lifetime has reportedly been extended meaning less downtime and maintenance costs. The first SAF2507 exchanger was installed in 1995 and, based on its good results, four new heat exchangers have now been purchased and installed at the same location.

In the petrochemical industry, SAF2507 has created interest as a construction material for EDC/VCM plants. One example is said to be in a Brazilian EDC/VCM-reboiler, where general corrosion and pitting was experienced on lower alloyed stainless steels. SAF2507 was recently specified as the problem solver for this application. In organic acids, also SAF2507 claims a long and proven record of test results, showing very good properties – in some cases considered equal to considerably higher priced Ni-based alloys. Recently the major US chemical company DuPont specified SAF2507 seamless tubes for use in acetic acid service.

Details available from Sandvik Steel, Tel: +44 (0)1922 728800; Fax : +44(0)1922 728827; Web site: www.steel.sandvik.com