Corrosion Resistance of Lining Materials

The thickness of the liner is a factor affecting permeation. For general corrosion resistance, thicknesses of 0.010-0.020 in. are usually satisfactory, depending on the combination of lining material and the specific corrodent. When mechanical factors such as thinning to cold flow, mechanical abuse, and permeation rates are a consideration, thicker linings may be required. 

Most of the lined pipe have loose fitting liners (the lining material is not bonded to the inside of the pipe). Although the lining provides the advantage of corrosion resistance to the material being conveyed, there are some disadvantages... 

Table 3.2 General Corrosion Resistance of Thermoplastic Lining Materials...

In a tank lining, there are usually four areas of contact with the stored product that may lead to different types of corrosion. These areas are the vapor phase (the area above the liquid level), the interphase (the area where the vapor phase meets the liquid phase), the liquid phase (the area always immersed), and the bottom of the tank (where moisture and other contaminants of greater density may settle). Each of these areas can, at one time or another, be more severely attacked than the rest, depending on the type of material contained, the impurities present, and the amounts of oxygen and water present. In view of this it is necessary to understand the corrosion resistance of the lining material under each condition, not only the immersed condition. 

External and internal corrosion resistance of the pipe material itself and the sealing material or the external and/or internal corrosion protection External corrosion protection according to DIN 30674, Part 3 or Part 1, 2 or 5. Internal corrosion protection with cement mortar lining according to DIN 2614 or with a special lining. 

CF8C (cast equivalent of 347) contains columbium to stabilize the material against chromium carbide formation. A narrow line of attack adjacent to a weld can occur if the casting is not properly heat-treated. CF8C must be solution heat-treated at 1950-2048°F (1066-1120°C) and stabilized at 1598-1652°F (870-900°C). The corrosion resistance of CF8C is about the same as that for CF3 and CF8. 

A common form of representing the corrosion resistance of materials is what is known as isocorrosion diagrams. The use of the prefix "iso" refers to lines (or regions) of constant corrosion behavior across variations in concentration and temperature. The diagram shown in Fig. 11.2 illustrates how some stainless steels compare to... 

---