When disinfecting a new pipeline using the chlorine tablet or granule methods, it cannot be used on which pipe type?

• A. CIP
• B. Screwed joint steel
• C. Solvent welded plastic
• D. Both b and c

Answer: (D)

The chlorine tablet or granule method works by dissolving solid chlorine and letting it circulate evenly through the new pipeline to establish a uniform disinfectant residual. Screwed joint steel has threaded joints that create crevices where a tablet can lodge and dissolve unevenly, making the disinfection unreliable and potentially increasing corrosion risk at the joints. Solvent-welded plastic pipes use joints that can trap debris or be sensitive to solid chlorine residues, which can hinder proper dissolution and distribution. Cast iron pipe typically offers a smoother interior and joints that allow the disinfectant to mix more uniformly, so this method is suitable there. Therefore, the method cannot be used on screwed joint steel or solvent-welded plastic pipes.