CHROMIZING AND SOME OF ITS APPLICATIONS
Chromizing is a metallurgical process where one or more elements are diffused into a base material. Sage has successfully applied this technology to Recovery Boilers studs for almost a decade. Several other applications have been tested and proven to be effective. The great advantage granted by chromizing is that the material may be treated to withstand tough conditions at its surface whereas the core material presents other desirable properties. For instance if the material is exposed to chemical attack and thermal shock, the chromium at the surface will withstand thee chemical attack whereas the core material handles the thermal shock..
The main advantage of the process is that chromium goes into the base metal and therefore it does not chip off the base. Depth of the chromium rich layer is controllable and thus can be customized to meet the requirements of each particular application.
Chromium content at the surface is around 40% and the depth of the chromium "skin" can be controlled to reach the desirable effect.
Sage started using a dual metal approach to fight corrosion in Recovery Boilers back in 1990 and chromizing followed as an evolutionary step.
Both concepts are shown below.
Panels requiring rather frequent replacement as smelt spout "six packs" are an excellent application which grants much longer cycles in operation.
In refineries and other chemical industries chromized tubes have demonstrated to withstand corrosion in different environments far better than stainless steel and other alloys. In Recovery Boilers its main advantage over Composite Tubes derives from the fact that the mechanical interface is eliminated. Besides the heat transfer which is greatly jeopardized in the case of Composite Tubes, suffers no measurable variation.
Chromizing can be done internally, externally or on both walls of the tubes, depending upon its application.
Sage performs its own chromizing operation in its facility in Ooltewah, Tn.
Chromized parts treated are not affected dimensionally as shown below. After chromizing the parts fit as before treatment.
The metallurgical bond between the diffused chromium and the substrate metal also prevents the chromium "skin" to be chipped off by mechanical impact or any other means.
Chromized smelt spouts can last at least twice as long than non chromized ones. We address each user individually to define the right approach to implement this goal. Individual characteristics may call for improvement in the erosion resistance or to emphasize corrosion resistance. Most common variables affecting each case are user's experience, limitations in available water flow or pressure, angle of slope and requirements for special connections.
Lockerbie and Hole from Canada and Sage are teamed up to offer superior performance smelt spouts designed to last for user's maximum acceptable life cycle.
Generating Bank "Bottles", SH Loops
Generating bank tubes are replaced mainly due to near drum corrosion. We have the solution to this problem.
The swaged tube ends or "bottles" are chromized with a proprietary process that prevents chromium diffusion to the portion to be rolled into the drum wall. We can supply either the chromized bottles or the services to chromize the user's parts.
For comparative corrosion tests between chromized tubes and 420 SS and 4140 tubes click here