A couple of years ago a lot of work was done on anchor corrosion from experiences in the cement industry where increased use of waste-derived alternative fuels leads to high levels of alkali chlorides and sulphates. The problem in the field still exists today. One issue is that the steel grades that apparently exhibit the greater resistance are those with the lower service limits i.e. generally too low for the environment in which we want to use them. Our current strategy is to modify the lining construction, limiting the possibility of gas tracking and minimize insulation to avoid dew point conditions and problems at the interface with the working lining. As a result of this ongoing problem, there is an increasing movement back to brick, contrary to the high tech monolithics available today.
There is strong momentum however behind the idea of ceramic coatings on anchors. We have been promoting our high temperature ceramic coating, ITC 213, which is specifically designed as a ceramic coating for metals. Aside from cement we are also getting involved in waste to energy and power applications, where there are similar issues.
ITC COATED ANCHOR CORROSION SAMPLES
Castable pots made of silicon carbide (SiC) were core drilled and filled with 40g of a 60:40 molar mix of NaSO4 and NaCl respectively. Fourteen anchor samples were cut (two of each grade), half were coated in the ITC 213 alkali resistance coating, and all of the samples were placed into an individual pot covered with a SiC incineration tile lid. The ITC coating was easily applied; the anchors were rubbed with emery paper then rinsed in bleach. A sponge was used to lightly coat the anchor with the ITC 213 coating and the samples were left for 24 hours to dry. The pots were transferred to a furnace set to 900o C for 5 hours, the pots were removed once they had cooled and were visually inspected.
As expected the samples with the higher content of nickel have corroded the greatest. The ITC 213 coating appears to have offered alkali corrosion protection to all the grades. For example theuncoated Inconel 601 has completely corroded however the ITC coated Inconel 601 still posses some of its original structure. From outward appearances it would appear that the ITC coating has been highly beneficial. A more detailed evaluation of the test pieces should reveal the full extent of the alkali resistance that the coating imparts to the stainless steel.
The images below show the outward appearance of the test samples.