Corrosion Section 6 - YILDIZ Technical University

YILDIZ TECHNICAL UNIVERSITY CHEMICAL ENGINEERING DEPARTMENT CORROSION SECTION 6 PROF. DR. EMEK MÖRÖYDOR DERUN RES. ASSIST. ENİS MUHAMMET GÜL 1 CORROSION PROTECTION Measures Taken In Plant Transportation under temporary protection and measures taken during storage Measures Taken In Environment Changi...

YILDIZ TECHNICAL UNIVERSITY CHEMICAL ENGINEERING DEPARTMENT CORROSION SECTION 6 PROF. DR. EMEK MÖRÖYDOR DERUN RES. ASSIST. ENİS MUHAMMET GÜL 1 CORROSION PROTECTION Measures Taken In Plant Transportation under temporary protection and measures taken during storage Measures Taken In Environment Changing Temperature Changing rate Measures taken at the design stage Removal of corrosive components Changing concentration Inhibitor addition Measures Taken for Materials Material selection Coating (Metallic or non-metallic) Metallic coating: Immersion Electrolysis Cementation Metal spraying Cathodic and Anodic Protection Non-metallic Coating INORGANİC COATİNGS Organic CoatinİNG Chemical Coating Painting Asphalt or Rubber Coating Plastic Coating ....................................... Chromate Coatings Oxide Coating Anodic Oxidation Ceramic Coating Glass/Enamel Coating............................................... Measures Taken in Plant  Temporary protection is applied as coating of parts to be protected. Coatings must be capable of easily remove from the surface. Therefore the preferred coatings should be removed by solvents or stripped from the surface easily.  Grease type oils commonly used for temporary coating. Also plastic materials can be used because they can be separated from the surface easily.  The metal piece can be stored by wrapping in inhibitor impregnated paper (e.g. wax). Further, the temporary protection is provided by applying zinc oxide consisting coatings. Measures Taken at the Design Stage  To avoid galvanic corrosion,.................................................................................................................................... If possible the same type of material should be used for all parts of structure different metals should be insulated from each other...................................................................................................................................  Using simple designs can be reduced corrosion. There must be as few as possible corners, edges, inner surfaces and complex structures in the design. Tube profiles should be preferred if possible.  For the design of equipments such as tank, emptying and cleaning ease should be considered. The discharge opening of tank should be inclined to ensure no accumulation of water in the tank bottom after flushing. Measures Taken at the Design Stage  Welding should be preferred to combine metals and should be avoided to use bolts and rivet. If it is necessary to use bolts and rivet, they must be more cathodic than the material. Should not be allowed gaps that may occur during the connection and should be isolated. In welding the welding component must be more cathodic.  Parts of a system which are expected corrode quickly should be should be designed to allow easy replacement. excessive concentration of stress and mechanical stress  Need to avoid........................................................................................................ sharp bends in the piping system (To avoid erosion corrosion )  Need to avoid........................................................................................................  During heat transfer process hot spots must be avoided. Heat exchangers and other heaters must be designed to ensure a uniform heat distribution. Measures Taken at the Design Stage Metin Measures Taken in Environment  Changing Temperature Oxygen solubility decreases with increasing temperature. The deccreased solubility cause lower corrosion rates........................................................................................................................ But in some cases this situation can change according to the environment conditions. For example the boiling sea water is more corrosive than hot sea water.  Changing Rate decrease in flow rate of corrosive A........................................................................ liquid cause decreasing erosion corrosion. But passive materials and alloys such as stainless steel are more durable in moving medium than standing environments. Measures Taken in Environment Removal of corrosive components ........................................................................... Na2SO3+1/2O2→ Na2SO4 N2H2 + O2 → N2 + H2O 3N2H4 → N2 + 4NH3 Removing hardness of water by react oxygen with additives or addition inhibitors can be the done to control formation of protective precipitate layer in heating and cooling water. It is possible to remove oxygen of water by heating or adding hydrogen. Changing Concentration .......................................................................... Reducing the concentration of corrosive substances generally affects corrosion rate. The oxides (HNO3, H2SO4, H3PO4) which have high oxidizing properties are rendered less harmful by increasing their concentration. After a certain concentration metal would win a passive attitude so a great decrease occurs in corrosion rate. The only way to reduce corrosion rate in non-oxidizing conditions is reducing concentration of acid. Measures Taken in Environment INHIBITOR ADDITION .................................................. Inhibitors which are added both atmospheric and aqueous medium will be effective on metal surface in wet conditions and discourage anodic reactions (anodic inhibitor) or cathodic reactions or both of anodic and cathodic reactions (mixed or double effecting inhibitor). Anodıc inhibitors........................................... They are effective in anodic regions. For steel anodic inhibitors are silicates, nitrates, chromates and benzoate. The effects of these type inhibitors on the anodic surface stand out by passivation......................................................................................................................................... Some of these inhibitors make passivation by themselves. For example the surface react with oxides and other parts react with O2. Less than enough presence these inhibitors in the environment accelerate corrosion Measures Taken in Environment Cathodic inhibitors: Cathodic inhibitors PRECİPİTATE ON THE CATHODE REGİONS CHEMİCALLY OR ELECTROCHEMİCALLY AND BE EFFECTİVE BY BLOCKİNG THESE REGİONS..................................................................................................................................................................................................... They have cathodic structures. For example arsenic (As+3), antimony (Sb+3) ions which are added to the solution medium for decreasing corrosion of iron in acid solutions are reduced by cathodic regions on iron surface and formed a thin film with a low electrical conductivity. Also components which are found in water content like CaCO3 and ZnSO4 have the same effects. These components form films in alkaline medium as a result of cathodic reactions. CaHCO3 ZnSO4 CaCO3 Zn(OH)2 Measures Taken in Environment MİXED (DOUBLE EFFCTİNG ) İNHİBİTORS.............................................................................. They are organic based and show their effects by adsorption. Most pf them contain N, S or both of them. Mixed inhibitors are adsorbed to all metal surface and obstructed both anodic and cathodic reactions. CATHODIC PROTECTION  Cathodic protection is the most powerful and common measures taken against. It is defined as changing potential of anode –the corroded metal in the corrosion system- and forcing it to act as the cathode.  It can be applied by addition a more active metal to the protected metal or applying current from the outside. Cathodic Protection with Sacrificial Anode..........................................................  It is used to protect the structures from corrosion which have good-quality coatings and do not have high current requirement. Cathodic Protection with Sacrificial Anode  The current which is needed for cathodic protection is provided with the metals disposed within anode bed and corroded in low potentials (Zn, Mg or Al-Zn alloys).These compounds corrode instead of the structure when prevent the structure so it is called as Sacrificial Anode.  Anodes are embedded at appropriate intervals along the buried pipes to provide a uniform current distribution.  This protection method is very common for ships, water tanks, and the systems buried in the soil.  The mostly common used metal is Mg which has low potential and provides high current although it has low yield. CORROSION OF CERAMIC MATERIALS  Ceramic materials are exceedingly immune to corrosion by almost all environments, especially at room temperature.  Corrosion of ceramic materials generally involves simple chemical dissolution, in contrast to the electrochemical processes found in metals.  Ceramic materials are frequently utilized because of their resistance to corrosion.  Refractory ceramics must not only withstand high temperatures and provide thermal insulation but, in many instances, must resist high-temperature attack by molten metals, salts, slags, and glasses.  Ceramic materials are.............................................................................................................................................. MUCH BETTER SUİTED TO WİTHSTAND MOST OF HİGH TEMPERATURES AND PRESSURE CORROSİVE ATMOSPHERE FOR REASONABLE TİME PERİODS THAN ARE METALS............................................................................................................................................................................................................................................................................................ CORROSION OF POLYMERIC MATERIALS  Polymeric materials experience deterioration by means of environmental interactions. However, an undesirable interaction is specified as degradation rather than corrosion because the processes are basically dissimilar.  Whereas most metallic corrosion reactions are electrochemical, by contrast, polymeric degradation is physiochemical; that is, it involves physical as well as chemical phenomena. BY SWELLİNG AND DİSSOLUTİON  Polymers may deteriorate...............................................................................  Covalent bond rupture, as a result of heat energy, chemical reactions, and radiation is also possible, ordinarily with an attendant reduction in mechanical integrity. It should also be mentioned that because of the chemical complexity of polymers, their degradation mechanisms are not well understood. CORROSION OF POLYMERIC MATERIALS Polyethylene, if exposed to high temperatures in an oxygen atmosphere, suffers an impairment of its mechanical properties by becoming brittle. The utility of polyvinyl chloride may be limited because this material may become colored when exposed to high temperatures, although such environments do not affect its mechanical characteristics THANK YOU FOR LISTENING…