There are many bends in the superheater and economizer of high-pressure wall-hung boilers. Since the superheaters are mostly installed vertically, it is very easy for water to accumulate when the boiler is shut down. Based on multiple inspections and pipe cutting situations, for all wall-hung boilers that have undergone drying treatment, there is no water in the vertical bends of the superheater; whereas if drying measures are not adopted, there will be 400-500mm of accumulated water in the vertical bends. This accumulated water mainly comes from the condensation of steam during the shutdown process of the wall-hung boiler. In this way, if maintenance lasts for 20 days, the superheater will corrode for 20 days. If the wall-hung boiler is a standby one, the corrosion time will be even longer. Bosch wall-hung boilers need to pay attention to the corrosion caused by water accumulation during the shutdown period.
Source: http://blog.tianya.cn/blogger/blog_main.asp?BlogID=3778593