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Gold plated heat exchange pipes

Hi
We are trying to find a replacement for very expensive titanium heat exchange pipes for cooling and heating of a sulfuric acid tank. We were wandering how well a hard and 24K gold plating on copper tubing will work?
Obviously we will put a barrier of nickel in between. If you guys think that it may work, how thick will the gold have to be for it to last. It's a clean sulfuric acid bath with a low liquid flow and the cooling pipes are just off the floor with a protective sheath.

Thanks Wayne

Wayne Gaybba
- Cape Town, WC, South Africa
2003

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Forget it. Stick with the titanium. Gold plating will foul well before the passive oxide of the titanium. One small scratch and the solution will drill a hole clean through the copper being accelerated by galvanic catalysis on the gold. Incidentally, copper by itself is quite passive in warm sulfuric, as are most grades of stainless. But they are quite sensitive to chloride if it is a contaminant in your system. If the cost of Ti is simply unbearable, you may try 317 stainless. It has a bit of Moly which effectively passivates it even in chloride contaminated Sulfuric.

Dave Kinghorn
Chemical Engineer
SUNNYvale, California
2003

With out knowing the details of your application the following may be of assistance (based on H2SO4 @ approx. 60 °C) You may want to consider the use of Teflon (PTFE) Tubing or replacing the HE units totally with PTFE HE units in this application, the downside to this is the heat transfer rate (approx. 12 times lower than lead) requiring extra tank space but the upside is that PTFE is highly resistant to chemical attack and has a relatively good heat resistance, attaining and maintaining 70 - 80 °C is generally not a problem and due to its excellent non stick characteristics does not have the fouling problems associated with Iron Oxide build up prevalent in standard HE units. Please bear in mind that Teflon tubing is now available with a corrugated surface tube to increase contact surface area.

Jeremy Gray
- Melbourne, Australia.
2003