Interpretation of Deposit Weight Density Analytical Results as a Measure of Boiler Tube Cleanliness, 2002 Fall Technical Conference

Boiler tube overheat failures can often be avoided via a testing program whereby the accumulation of waterside deposition is quantified via an analytical procedure known as Deposit Weight Density (DWD) testing. But there are three widely recognized DWD test procedures in use today, and there is enough variation in the results that different decisions might result, depending on which test procedure is used. The three current analytical procedures in use are:

Mechanical Removal: A vibrating tool is used to physically remove the waterside deposition from a measured area of tubing. The scraped deposit is collected and weighed.

Acid Etching: An acid is used to dissolve the deposition from a measured area of tubing, with the final tube weight being compared to the initial.

Glass Bead Blasting: Non abrasive glass beads are used to dislodge deposition from tube surfaces, with the tube being weighed before and after removal to develop the correlation.

A frequently used evaluation of DWD testing results has been developed by Babcock and Wilcox Company, a foremost US boiler manufacturer, and used for many years in the industry. Depending on the boiler’s operating pressure, a DWD result may or may not suggest the need for deposit removal. Certain critical boilers, such as paper mill kraft process recovery boilers may be judged more conservatively, with lower DWD results seen as requiring deposit removal.

The problem as it currently exists is that the different testing procedures may result in different conclusions being reached as the whether cleaning is required, based on the fact that different test procedures yield different results. The purpose of this paper is to discuss the three procedures in current use, and suggest a way of interpreting the results so that accurate operating decisions about the need to chemically clean the boiler can be made.