Piping and Valves

Piping and valves available for electroless nickel systems are of four principal types: stainless steel, polyvinylidene fluoride, CPVC plastic, and polypropylene. The advantages and disadvantages of each of these materials are summarized in Table 9.

Table 9 Comparison of piping and valve materials for electroless nickel plating systems

Material

Resistance to plating temperatures

Resistance to plate out

Relative cost

Availability

Pipmg

Stainless steel

High

Low

High

Good

Kynar

High

High

Moderate

Poor

CPVC

Moderate

Moderate

Low

Good

Polypropylene

Low

High

Low

Limited

Valves

Stainless steel

High

Low

Moderate

Good

CPVC

Moderate

Moderate

Moderate

Good

Polypropylene

Moderate

High

Moderate

Good

Piping components in electroless nickel plating systems are used for air agitation spiders, tank outlet, pump inlet, and discharge pipes, solution manifolds, and deionized water fill lines. These pipes must be sized to minimize restrictions and provide proper agitation and filtration. The diameter of the tank outlet piping should be at least as large as the pump inlet connection to avoid cavitation and increased pump wear. CPVC plastic is normally used for pipe exposed to the plating solution.

Although CPVC or other plastic pipe may be joined by solvent welding, threaded joints are preferred. Threaded connections are easier to make and more trouble-free, allowing repairs or modifications to be accomplished quickly. When threading plastic pipe, a plug should be inserted inside the pipe end to support the pipe and prevent collapse or thread breakage. Threads should be wrapped with Teflon tape before joining to prevent potential leakage from the galling of the plastic.

Valves. Almost all of the valves used for electroless nickel systems are a ball and seat design. Because of prolonged exposure to stagnant plating solutions, inertness or resistance to deposit plate out is of primary importance with these valves. Accordingly, polypropylene is used most often. The reduced strength of polypropylene at plating temperatures is not a problem with valves, because of their compactness and greater thickness.

CPVC plastic valves are also used occasionally for electroless nickel systems, although their reduced resistance to deposit plate out makes them more prone to seizure and failure due to deposit buildup than polypropylene. Because of their somewhat higher cost and tendency to activation and deposition, stainless steel valves are not normally used. For valves in agitation air supply lines, plain PVC plastic valves may be used if they are mounted at least 200 mm (8 in.) away from hot plating solution. Valves and piping for steam services should be steel or stainless steel.

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