galvanization – What Is Piping: All about Piping Engineering

Definition of Galvanization/ Galvanization Meaning Galvanization or Galvanizing is one of the most widely used manufacturing process of applying a thin zinc coating over steel or iron material for the purpose of protecting them from corrosion or rusting. Once this is done the steel or iron is called galvanized steel or galvanized iron. That zinc coating (silver color) in galvanized material shield (barrier) the metal from the surrounding environment. Thus galvanization extends the life of the base metal (Steel) to a considerable extent. That zinc coating is applied in several layers as per requirement. In corrosive environment, Galvanized Steel is one of the cost effective alternative solutions to avoid using costly materials like SS or DSS. Galvanizing also prevent the metal from “galvanic corrosion” as the Zinc layer acts as an anode and slowers the corrosion tendency of the base metal. Methods of Galvanization/ Galvanizing Methods Galvanization is achieved by various methods as listed below: Hot-Dip GalvanizationElectro-galvanizationPre-galvanizationGalvannealing Hot-Dip Galvanization Fig. 1: Hot-Dip Galvanization Process Hot-dip galvanization process provides long-lasting, maintenance-free metal at cheap cost and the process is quite simple. In the Hot-Dip Galvanizing process, the base metal is dipped into a pool of molten zinc. Fig. 1 shows the steps involved in the complete process. There are three major steps that are followed in the hot-dip galvanizing process. Surface PreparationDegreasingStrippingRinsingFluxing andDryingGalvanizing andPost-Process Treatment. Electro-galvanization In the Electro-galvanizing process, Zinc ions are transferred to the base metal bu utilization of an electrical current source in an electrolyte solution. Electro-galvanizing is normally applied continuously. Pre-galvanization Pre-galvanizing is performed at the steel mill, usually on materials that already have a specific shape. After cleaning, The metal is passed through a pool of hot molten zinc similar to hot-dip galvanization process and then recoiled. This method offers large scale galvanization. Galvannealing Galvannealing is basically a combination of two methods; hot-dip galvanization and annealing. This method produces a specialized high quality coating on steel. The process involves hot-dipping and then instantaneous annealing, to produce a matte gray finish. Galvanization Standards The codes and standards those govern the galvanization process are listed below: ISO 1461EN ISO 14713-1 & 2BS 7371-Part 6EN 10348‑2BS 3083EN 15773ASTM A123/A123MASTM A153/A153MASTM A767/A767MCSA G164ASTM B6ASTM A143/A143MASTM A384/A384MASTM A385/A385MASTM A780ASTM D6386ASTM D7803ASTM E376 Need for Galvanized Steel Pipes There are various services where care should be taken to avoid rusting of the pipeline as it might be hazardous to personnel, cause damage, malfunction of equipment, instrument, etc. so for that reason, the piping is galvanized. Galvanized pipes can work satisfactorily for up to 70 years. The other advantages that galvanized steel pipe (Fig. 2) offers are Reduced cost as compared to stainless.Very Less maintenance which results in the lowest long term cost.Highly Durable. Hence, Long life expectancy.Reliable performance.Resistance to mechanical damage.Good protection for rusting and galvanic corrosion. Fig. 2: Galvanized Steel Pipes However, for piping application only one disadvantage is that galvanized pipes can not be welded. So, clamped supports are used for galvanized piping systems. Difference between Hot-dip Galvanization and Electro-Galvanization Below are the differences between Hot-dipped galvanization and Electro-galvanization. And the advantages of one over the other- Hot dip galvanizationElectro-galvanizationStringent cleaning procedure is followed (usually termed as 7-bath process: cleaning in alkaline solution, water rinsing, pickling, water rinsing, pickling, water rinsing, fluxing).Cleaning Procedure is not Stringent.Governing codes and standards are ASTM A123; ISO 1461; IS 2629 or BS 729IS 1573 governs the Electro-galvanization processHighly Durable; of the order of 20-50 yearsComparatively low lifeProduces a Fe-Zn alloy layer on the steel surface and leaves a coat of pure zinc on the outer surface. The alloy is very hard. Usual abrasion does not damage the coating although it may damage the soft pure zinc on the topProduces a layer of Zn on the surface which is not continuous with steel metallurgicallySteel is dipped into the molten bath of Zinc @460ºC for achieving the coatSteel is made the cathode in the electrolytic cell there by forming the coating by Electroplating processThe surface finish is not smooth, dull finish.Good surface finishDepending on the dipping duration, the coating thickness is 80-100µm. It is also affected by the composition & roughness of steelNormally coating thickness is 10-12 µm.Coating thickness depends on current density and temperature of the electrolyteWith normal coat thickness about 40% expensive than electro-galvanizingWith normal coat thickness cheaper in comparison to hot dip galvanizing. However at higher coating thickness the cost increases proportionately and hence become exceptionally expensive.Non-uniform coatingUniform coatingSuitable for any sizeSuitable for small componentsHot-dip galvanization vs Electro-galvanization Hot-Dip Galvanization Video Tutorial The following hot-dip galvanization video tutorial by American Galvanizers Association clearly explains the Galvanization process. https://www.youtube.com/watch?v=kwCyq06aatA Hot-Dip Galvanization Video Tutorial