Battle against corrosion

As part of the annual conference of NACE International held in New Orleans, nine corrosion specialists recently presented their views on the technical challenges facing the global chemical process industry. About 200 chemical process engineers from around the world attended a session titled “Process Industry Corrosion in the New Millennium.” Stewardship of chemical process equipment is needed to reduce the release of hazardous chemicals from processing plants, according to Robert E. Smallwood of Det Norske Veritas (USA) Inc. Equipment stewardship would result in better corrosion-resistant alloys being selected for vessels, and those vessels would not have to be designed so that an operator can gain access to them for inspection, he said. Chak M. Wong (Bayer Corp.) said that nickel-containing alloys are being specified more often for critical chemical process equipment. Tubing in equipment such as condensers and heat exchangers at Bayers’ operations in the USA has been upgraded to S31603 stainless steel to solve various corrosion-related challenges. Josef Heinemann of UTP Schweissmaterial GmbH showed that one nickel alloy (N06059) gives the best corrosion test results in a series of tests when used to weld a wide variety of base materials. Thomas Ammann of Linde AG revealed that the welding of nickel-base alloys using the GMAW/MAG processes could be improved simply by using multi-component shielding gases rather than pure shielding gases, such as pure argon. Rudolf Morach of Ciba Specialty Chemicals expressed his views that the removal of heat tint is a must. He developed a test showing that pickling gives a major improvement. Four new nickel-based alloys were described: Martin Caruso explained how Haynes International developed alloy N06035, a high chromium, high molybdenum nickel base alloy. Larry Paul of ThyssenKrupp VDM discussed a number of field test results for R20033. The alloy, with about 33% chromium, 33% nickel, 0.5% nitrogen, but only 1% molybdenum, was developed for highly oxidizing conditions, which occurs with nitric acid and certain sulphuric acid applications. Another paper by ThyssenKrupp VDM, this one by Helen Alves, included a case study for the production of Vitamin C. Tests showed that N06059, a nickel-chromium-molybdenum alloy in the upper end of the “C-type” alloys, was the most suitable. Lee Pike and Dwaine Klarstrom of Haynes International described a new high-strength alloy called C-22HS [TM]. It is comparable to N06022 in terms of corrosion resistance, but can be age-hardened to produce nearly double the yield strength.

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