Chemical and Process Industries
MTA has broad experience in the chemical and process industries. This begins with the design of the chemical plant, selection of materials of construction, inspection of equipment such as heat exchangers, pressure vessels, expansion joints, piping during fabrication, and the final plant erection. Follow up work includes inspection of equipment at plant shutdowns, as well as ongoing corrosion monitoring in service. Failures, often related to corrosion, are analyzed in the laboratory to determine root cause such as stress corrosion cracking, hydrogen embrittlement, microbiological corrosion, pitting, and crevice corrosion.
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Chemicals manufactured include:
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Ammonia and Urea
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Sulfuric, Nitric, and Phosphoric Acid
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Chlorine and Caustic
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Chlorine Dioxide
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Sodium Chlorate
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Hydrogen Peroxide
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Ethanol
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Sodium Carbonate
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Sodium Sesquicarbonate
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Sodium Cyanide
Example One: Chemical Reactor
When materials such as stainless steels, high nickel alloys, or even titanium or zirconium cannot handle corrosive acids, then a practical option is to use glass lined carbon steel equipment.
Glass Lining a Chemical Reactor
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The carbon steel reactor has to be manufactured to strict quality requirements so that the glass lining can be applied to a uniform surface.
All welds have to be full penetration with the penetration beads ground flush to the interior surface. Nozzles welded to the vessel have to be generously radiused to avoid sharp edges.
The initial layer of glass is deliberately made semi porous to provide some ductility between the steel surface and subsequent glass layers. After spraying onto the carbon steel surface the vessel is heated to allow melting and surface bonding. Successive layers of dense glass is applied by spraying and heating until the desired thickness of glass has been achieved
A careful visual inspection of the glass lining is made, followed by a search for pinholes with an electrical tester.
Failure in Service
The glass lined steel reactor shown above had been successfully installed, and the system hydro tested, and brought on line to handle hot sulfuric acid. Unfortunately, a leak at the flange between reactor nozzle and glass line steel pipe caused attack of the exterior carbon steel surface and catastrophic failure of the vessel occurred.
Quick replacement was not possible as this was not a standard “off the shelf” vessel.
Care of glass lined steel vessels requires not only a good exterior protective coating, but warnings such as “glass lined vessel, do not weld or hammer on this surface”.
Example Two: Storage Tanks
Collapse of two 316L Stainless steel storage tanks containing 65% phosphoric acid.
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These tanks had survived for many years without losing integrity.
Due to a loss of cooling capacity in the phosphoric acid plant, the acid was pumped to the storage tanks at 70C, instead of the usual 50C.
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At the elevated temperature, chlorides present in the phosphoric acid caused stress corrosion cracking in the heat affected zone of the welds where high residual stresses were present.
Widespread stress corrosion cracking in the heat affected zone of the weld caused the parent plate to separate from the circumferential weld, which remained intact.
