Base materials

For wetted parts, stainless steel SS316, mainly SS316L or SS316Ti, is the most common material. Depending on the aggressivity of the mixed media, lower grades like SS304 or higher grades like SS 904, duplex grades or titanium are often applied. The surface roughness of wetted parts varies simple cold/ hot rolled steel to highest surface grades Ra0.2 to 0.8 grinded or polished or even electropolished depending of cleanability requirements. Normally, carbon steel and cast iron are applied for non-wetted parts, but in special conditions stainless steel can be applied.

Linings

For the most aggressive conditions, wetted parts are protected against corrosion or wear by rubber or other polymer lining. In addition, a high-grade steel lining may be used to take advantage of the mechanical properties of the large carbon steel shaft pipe as the base material plus highly resistant special material for wetted parts.

Materials are selected based on the corrosion and abrasion conditions inside the tank. Mechanical properties in relation to the required agitation forces also play a role when selecting materials. Ideally, solid materials are applied, but sometimes linings have to be used due to the availability, cost or a poor combination of wear and mechanical strength of the base material.