Conference Report: The Battle Against Corrosion
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THE MAGAZINE DEVOTED TO NICKEL AND ITS APPLICATIONS |
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STEWARDSHIP of chemical process equipment is a process whereby authority is given to someone whose
responsibility it is to make sure that the equipment operates properly.
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NICKEL ALLOY N06059, has now reached the stage of full commercialization and is used here to
transport hazardous waste.
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ALLOY R20033, is used in this pickling tank. The alloy was developed for highly
oxidizing environments.
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WELDING NICKEL ALLOYS can be done at a rate that is two times faster than normal by using
so-called multi-component shielding gases.
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For more information from the Nickel Institute on the use of nickel-containing
materials in the chemical process industry, |
Chemical processors meet to discuss corrosion, welding and the use of new alloys.
Nickel Magazine, July 2004 -- Nine corrosion specialists recently presented their unique perspectives on the technical challenges facing the global chemical process industry. The venue was a conference in New Orleans, Louisiana, U.S.A. where about 200 chemical process engineers from around the world attended a session titled "Process Industry Corrosion in the New Millennium." It was part of the annual conference of NACE International, the largest gathering of corrosion specialists in the world. The following, are highlights from the event, which show how nickel-containing materials are playing a leading role in the chemical process industry.
Equipment Stewardship Needed
Stewardship of chemical process equipment is needed to reduce the release of hazardous chemicals from processing plants.
This is just one of the ways chemical plant operators can reduce the number of injuries to plant operators and members of the public that can result from such releases, according to Robert E. Smallwood of Det Norske Veritas (USA) Inc.
Equipment stewardship means that someone has authority to make sure that equipment operates properly. "If responsibility and authority were delegated more often to individuals," Smallwood says, "mechanical integrity would play a more important role in process equipment design." At least 10-15% of process equipment is not built to code, according to Smallwood.
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. This would offset the higher cost of the corrosion-resistant alloy.
Alloy Upgrade
Nickel-containing alloys are being specified more often for critical chemical process equipment. Take, for example, the experiences of Bayer Corp., one of the largest chemical processing companies in the world. Tubing in equipment such as condensers and heat exchangers at Bayers' operations in the U.S. has been upgraded to S31603 stainless steel to solve various corrosion-related challenges, according to Chak M. Wong of Bayer.
"One of the biggest problems in the Gulf Coast area of the U.S. is legionnaires' bacteria," Wong says. "Therefore, most plant operators use a lot of chlorine [in their process streams] to kill the bacteria. Operators would rather have some corrosion than have these bacteria. But this leads to various maintenance consequences."
He presented four cases in which tubing in critical pieces of equipment was upgraded to S31603 stainless steel to solve the corrosion challenges resulting from the use of chlorine.
High Standards vs Low Cost
Can large chemical process companies save money by stocking just one type of welding consumable rather than a whole range as required for specific corrosion requirements?
This is not a question that Josef Heinemann of UTP Schweissmaterial GmbH set out to answer. However, he did show 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.
In New Orleans, he reported the results of a series of ASTM corrosion tests he performed on various different base materials that had been welded together with four different welding filler metals ( N06022, N06059, W86022 and W86059 to be exact). He concluded that N06059 was the best weld metal for his particular combination of base materials. But he went one step further, saying "N06059 and W86059 can be applied for the welding of all the other base materials of the NiCrMoFe alloys and for higher alloyed austenitic stainless steels."
Clearly, choosing this particular weld filler material may give the best corrosion results, but whether or not it would result in cost savings if it were the only material used in a large company remains to be answered. Of course, each company would require new welding procedures to qualify this filler metal for use for the various combinations of base materials.
Weld Two Times Faster
The welding of nickel base alloys using the GMAW/MAG processes can be dramatically improved simply by using multi-component shielding gases rather than pure shielding gases, such as pure argon.
This conclusion emerged from work done recently by Linde AG.
Thomas Ammann of Linde AG explained how the company designed and tested a multi-component shielding gas that results in a stable arc, produces excellent wetting characteristics, and permits welding at higher speeds.
The gas is commercially available in Europe and can be obtained on special order in the U.S. It consists of argon (as the base gas), 0.05% carbon dioxide for arc stabilization and 30% helium to provide a heating effect that also provides excellent wetting characteristics. It also contains 2% hydrogen to facilitate travel speeds as high as 50 centimetres per minute -- double the speed that is possible when pure argon is used. Argon-helium gas mixtures are commonly used for production welding of nickel alloys, but this gas appears to be a further improvement.
The gas is not recommended for welding stainless steels.
Still Not Sure About Heat Tint?
It is still not perfectly clear in the minds of most corrosion engineers whether or not heat tint, that slight discolouring of a metal around a weld where the metal has been affected by the heat of welding, negatively affects the corrosion resistance of stainless steels and nickel alloys.
There are simple, commonly available methods to remove the heat tint (immersion pickling, spray pickling and pickling paste, for example), but they use quite hazardous chemicals. But is it necessary to do so? Would a requirement to remove it be worth the cost? And how can you check if the passive layer has been disturbed?
One corrosion engineer who is now convinced the removal of heat tint is a must is Rudolf Morach of Ciba Specialty Chemicals. He developed a simple pen-type electrochemical sensor that can measure the local reduction in corrosion resistance around a weld because of the heat tint. He used this sensor to conduct a large testing program on heat tint on welded pieces of stainless steels and nickel alloys.
His results were unequivocal: pickling gives a major improvement. The Nickel Institute has never argued that pickling of heat tint is always necessary, but that in many (but not all) corrosive services, it is advantageous. Thank you, Rudolf Morach.
Newer Alloys
It is interesting to follow the developments of new alloys as they go through the various stages of development from a laboratory idea to full commercialization and four such nickel based alloys were described in New Orleans.
High temperature chloride-containing phosphoric acid, especially when containing abrasive solids, is a very aggressive media, but one that is an integral part of phosphoric acid production from phosphate rock. Acid producers are constantly seeking alloys that will give them improved equipment life. Martin Caruso explained how Haynes International developed alloy N06035, a high chromium, high molybdenum nickel base alloy, for that purpose. Autoclave tests confirmed its suitability and there are now plant installations. The alloy might find applications in other acids too.
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. However, it has been successfully used for weld overlay of boiler tubes, a high temperature application, and one that was not originally considered when developed.
Another paper by ThyssenKrupp VDM, this one by Helen Alves, included a case study for the production of Vitamin C. It involves a cocktail of chemicals, and laboratory tests were required to help choose the most suitable alloy. Their tests showed that N06059, a nickel-chromium-molybdenum alloy in the upper end of the "C-type" alloys, was the most suitable. N06059 has now reached that stage of full commercialization.
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.
PHOTOS: Tim Pelling/Nickel Institute, ThyssenKrupp VDM.
Additional information on the above news items can be obtained from the
full-length technical papers that were presented at Corrosion NACExpo 2004. These are available in PDF
format from NACE International. For your convenience, catalogue numbers are given in
brackets. 2. Corrosion and Damage in Cooling Water Systems - Some Case Histories (04216), by Chak M. Wong. 3. A New Nickel Alloy Resistant to "Wet Process" Phosphoric Acid (04221), by Paul Crook and Martin Caruso. 4. Investigation Concerning the Application of the Weld Filler Metals FM 59 and FM 22 for Welding of Nickel Alloys of the C-Series (NiCrMo Alloys) in Chemical Process Industry (04224), by Josef Heinemann. 5. Alloy 33: A versatile Alloy for Concentrated Mineral Acid and Other Applications (04226), by Larry D. Paul. 6. Analysis of Welded Stainless Steels and Nickel Base Alloys Using a Locally Resolving Electrochemical Sensor (04232), by Rudolf Morach and Markus Buechler. 7. Alloy Selection for Organic Environments with Small Additions of H2SO4 or HCl (04235), by Helena Alves and Helmut Werner. 8. Influence of Shielding Gases on Corrosion Properties of Nickel Alloy Weldments (04237), by Josef Heinemann and Thomas Ammann. 9. A New Corrosion Resistant Ni-Cr-Mo Alloy with High Strength (04239), by Lee M. Pike and Dwaine L. Klarstrom. |
