We have done descaling of heat (tube in tube) exchangers used for processing fruit pulp with a commercial chemical (known as "PICLEWELD" ) made up of HCl acid (17%), nitric acid (2%), corrosion inhibitor (30%) and the remainder water. After passing this chemical through the heat exchangers at ambient temperature for 3 hours, the liquid is drained out from the system and left like this for 24 hours before passing passivation chemical into the system and heat exchangers. Will the residual (remnants of descaling chemical) liquid in the tubes (which are placed horizontally) cause any corrosive or pitting action which can lead to pin holes? Tube wall thickness is 4 mm.
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Brian Dalder Forum Moderator 179 Posts
Re: Will descaling with HCl acid cause corrosion?8 April 2011 at 1:29pmBased on what you have said, I assume the material of construction of the heat exchangers is an austenitic stainless steel like 304 or 316. I am not a fan of putting anything that contains HCl into austenitic stainless steel systems even if it contains corrosion inhibitors. HCl is very corrosive to austenitic stainless steels and should not be in contact with these materials at any concentration. If you continue descaling with this chemical, the risk of corrosion can be minimized by neutralizing any residual HCl. I would suggest rinsing with a dilute base like sodium bicarbonate and then thoroughly flushing the system with water.