SURFACE PROTECTIONSSURFACE PROTECTIONS

Water tube membrane walls with no refractory lining protection are subject to erosion and corrosion by hot flue gas and deposit of dust.

Because they cannot be neither easily nor quickly cleaned, contrary to heat exchanger units, some solutions to grant a long life also to these parts of the boiler are suggested:

1. 1. – Welded cladding with nickel-chrome materials, 1.5÷2 mm thickness. This cladding is suggested for areas in which flue gas temperature is over 900 °C.
A typical application in a grate integrated type boiler is immediately above the refractory lined zone, that is the upper part of the first rising chamber.

2. Plasma thermal spray producing a metallic nickel-chrome layer of 250÷350 µm thickness.
This coating is suggested for those zones in which the flue gas temperature is less than 900°C.
In integrated grate type boilers this usually concerns the second radiant chamber (descending); on the contrary, it concerns the first radiant chamber in rotary kiln or adiabatic furnace type boilers.

In both cases coatings must be applied in the workshop during manufacturing and should be followed by thermal treatment.
Coatings carried out on site can only be made for repairs or in an emergency situation.