On-stream cleaning of tubes to remove scale may be beneficial to improve the accuracy of infrared scan or to improve the heat transfer (heater efficiency). Some techniques used include blasting with walnut hulls, crushed dry ice and water. Course walnut hulls have proven effective in removing loose scale; however, the user should recognize that refractory damage can occur where the hulls affect the wall. One benefit of the hulls is that they burn up in the firebox and most of the ash leaves the heater through the stack. Another technique is to water blast the tubes, which removes scale by thermal contraction/shock. Consideration needs to be given to the water type and the spray type so that tube damage won’t result. In this instance as well, refractory damage can result where the water impacts.