Pressure vessels (MOC:CS) are showing rust deposits inside. It is understood that water ingress or moist air could be the reasons to cause electrochemical reactions and that resulted in the formation of hydrated iron compounds. My question is how to clean the rust and its further prevention. Kindly suggest standard methodology to remove rust, any NDT checks required thereafter and how to prevent its reformation.
Have an insight or suggestion?
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Brian Dalder Forum Moderator 169 Posts
Re: How do you remove rust and prevent its reformation?15 February 2010 at 1:29pmI will try to answer your question, in general, since many details of your specific application are lacking. According to ASM Specialty Handbook - Carbon and Alloy Steels, protection against corrosion can be done by: (1) providing an impervious barrier between the steel and the corroding medium, (2) introducing a substance that inhibits the chemical action, or (3) introducing a galvanic activity that counteracts the corrosion that is occurring. The form of protection may be a coating, an inhibitor, or a galvanic device coupled to the steel and some protection methods combine two or more forms. The usual methods for rust removal from carbon steel include abrasive blasting (wet or dry), brushing, acid pickling, salt bath descaling, alkaline descaling, and acid cleaning. The selection of the rust removal method depends on many factors as well including the thickness of rust, the composition of the metal, allowable metal loss, surface finish tolerances, available equipment, and cost. If moist air is the cause of your problem, you might consider purging the tanks with dry nitrogen and using a nitrogen conservation vent. This will permit the tanks to "breathe" while preventing the ingress of moist air. If you are trying to detect small rust deposits, the easiest NDT test may be visual testing. This can be done by the naked eye via periodic internal inspections of the pressure vessels themselves or with the aid of cameras, borescopes, etc. If significant areas of rust are constantly being formed and flaking off, ultrasonic thickness testing may be useful.