Open AccessCOATINGS FOR PROTECTION OF EQUIPMENT FOR BIOCHEMICAL PROCESSING OF GEOTHERMAL RESIDUES: PROGRESS REPORT FY 97
Author(s) -
M. Allan
Publication year - 1997
Language(s) - English
Resource type - Reports
DOI - 10.2172/757096
Subject(s) - geothermal gradient , environmental science , waste management , engineering , geology , geophysics
Thermal sprayed ethylene methacrylic acid (EMAA) and ethylene tetrafluoroethylene (ETFE), spray-and-bake ETFE and polyvinylidene fluoride (PVDF) and brushable ceramic-epoxy coatings were evaluated for corrosion protection in a biochemical process to treat geothermal residues. The findings are also relevant to other moderate temperature brine environments where corrosion is a problem. Coupon, Atlas cell, peel strength, cathodic disbondment and abrasion tests were performed in aggressive environments including geothermal sludge, hypersaline brine and sulfur-oxidizing bacteria (Thiobadus ferrooxidans) to determine suitability for protecting storage tanks and reaction vessels. It was found that all of the coatings were resistant to chemical attack and biodegradation at the test temperature of 55 C. The EMAA coatings protected 316L stainless steel from corrosion in coupon tests. However, corrosion of mild steel substrates thermal sprayed with EMAA and ETFE occurred in Atlas cell tests that simulated a lined reactor operating environment and this resulted in decreased adhesive strength. Peel tests to measure residual adhesion revealed that failure mode was dependent on exposure conditions. Long-term tests on the durability of ceramic-epoxy coatings in brine and bacteria are ongoing. Initial indications are that this coating has suitable characteristics. Abrasion tests showed that the ceramic-epoxy had good resistance to the abrasive effects of sludge. Thermal sprayed EMAA coatings also displayed abrasion resistance. Cathodic disbondment tests in brine at room temperature indicated that EMAA coatings are resistant to disbondment at applied potentials of {minus}780 to {minus}1,070 mV SCE for the test conditions and duration. Slight disbondment of one specimen occurred at a potential of {minus}1,500 mV SCE. The EMAA may be suited to use in conjunction with cathodic protection although further long-term, higher temperature testing would be needed