Modeling of Component Lifetime Based on Accelerated Life Tests and Gas Permeation Measurements
Gary Van Schooneveld, Dennis Chilcote, Don Grant – CT Associates, Inc.
Metallic parts in chemical handling systems are potentially subject to corrosion by acid gases like hydrogen chloride (HCl) and hydrogen fluoride (HF). In addition, ozonated solutions are finding increasing application in semiconductor manufacturing processing. Ozone can accelerate corrosion in metallic parts. Examples of metallic parts at risk include springs in valves and magnets in mag-drive pumps. Fluoropolymers, like PFA, are often used to isolate these parts from acid gas containing liquids to prevent corrosion. Acid gases and ozone in these liquids can permeate through fluoropolymers and corrode the parts.
Multiple studies were undertaken to understand and predict the impact of HCl and ozone gas in liquids on Levitronix pump impellers. The first study determined the HCl permeation rate through the PFA used in Levitronix pump impellers as a function of coating thickness, HCl concentration and temperature. The second study, measured pump impeller life under controlled operating conditions. The combined results of these two studies have been used to predict impeller life under different pump operating conditions. The third study measured the permeation rate of ozone through PFA films of varied thicknesses.
The life-prediction model developed during this study indicates that the life expectancy of the Levitronix pump is greater than 10 years for concentrated HCl and much longer for pumps operating in diluted HCl mixtures. Long-term life studies in concentrated HCl continue to support the model. The study further indicates that ozone accelerated corrosion can be eliminated by increasing the PFA thickness of the impeller.
CTA publication #103: 2011 CMP and Ultrapure Users Conference