Corrosion Audit Essay, Research Paper
TOPIC: CORROSION AUDIT
AT IIT CAMPUS
2.Main materials used in IITK
5.Life of a material and remedies provided
Corrosion is the electrochemical deterioration of a metal because of its chemical reaction with the surrounding environment. While new and better materials are continuously being developed, this progress is offset, in part, by a more aggressive operational environment. This problem is compounded by the fact that corrosion is a complex phenomenon. It can take many different forms and the resistance of materials to corrosion can drastically change with only a small environmental change.
Corrosion is most often thought of as a slow process of material deterioration, taking place over a significant period of time (examples being general corrosion, pitting, exfoliation, etc.). Other forms of corrosion degradation can occur very quickly, in days or even hours, with catastrophic results. These forms (such as stress corrosion cracking, environmental embrittlement, and corrosion fatigue) depend on both the chemical and mechanical aspects of the environment and can cause catastrophic structural failure without warning.
Some of the data of losses due to corrosion follows. In the United Kingdom the Paint Research Association has estimated that metallic corrosion costs developed countries some up to four per cent of gross national product (GNP) annually.
In the UK this would equal about ?30 billion. In the United States, various reports put the cost of corrosion slightly higher at four to five per cent, equating in that country to about US $300 billion, of which it is claimed that around one-third could be prevented.
In India approximately 5% of the GDP is lost due to corrosion, of which again it is claimed that around one-third could be prevented.
CORROSION AUDIT: There is no clear definition of corrosion audit. It mainly contains inspecting the corrosion sites, analyzing the reasons of corrosion, suggesting methods of prevention, doing the cost analysis of prevention and losses due to corrosion.
2.Main Materials Used in IITK:
· Centrifugally cast iron (CI)
· Galvanized iron (GI)
· Stainless steel
· Cast iron
· PVC (Poly venyl chloride)
· RCC (Reinforced concrete council)
Centrifugally cast iron vs. Galvanized iron: CI is more resistant to corrosion in soil and water environment as compared to GI. But CI cannot be threaded much frequently, as it will corrode very fast near the threads and thus will lead to breakage and leakage. So CI is used only, where long pipes are needed. For small length pipes, like those in houses, GI is the better option. Thus CI is majority used for pipelines for water supply, and GI is also used where small length pipes are needed.
In most of the cases corrosion is recognized by visual inspection.
Corrosion of steel is easily recognized because the corrosion product is red rust.
RCC(Reinforced Concrete Council) is used in all the building constructions. There are always voids present in the structure. In these voids moisture will collect and will lead to corrosion. But this corrosion is usually not spotted out till 10-15 years. It is noticed when after 10-15 years cracks appear on the surface.
· Electric power supply pillars:
The power pillars get corroded very soon in top region, where two different metals are joined.
In some cases inspection can not be done on regular intervals, e.g. underground pipelines.
There can be many reasons of corrosion. In different systems there can be different mechanism of corrosion.
· Iron based alloys:
When iron base alloys corrode, dark corrosion products usually form first on the surface of the metal. These products are protective. However, if moisture is present, this ferrous oxide coating is converted to hydrated ferric oxide, which is red rust. This material will promote further attack by absorbing moisture from the air.
Except this the presence of some chemicals (acids) in laboratory make the metal corrode very fast.
· In water supply pipelines corrosion is not observed very soon. In fact, corrosion does not occur till there is water filled in pipes, because metal is not in contact with atmosphere (oxygen). So whenever the water supply is stopped, due to reasons like maintenance etc, metal start corroding.
Note: It can be observed that as supply is again started, first few amount of water is red colored.
Thus metal in pipeline corrode only when pipeline is empty. So pipelines in IIT does not corrode very soon. But the pipelines in Kanpur City corrode very fast. The reason is quite obvious. They remain empty for longer periods.
· Corrosion in RCC structures can occur, because of voids remained in the structure. Moisture will collect in these voids, air is also there, and the combination of two will lead to corrosion.
· In some cases like the pipes used in the shower pool in front of the PK Kelkar library, the metal is exposed to air in presence of water. Severe corrosion is observed in this case, even in the presence of regularly maintained protective layer of paint. In this case, there are also bio-organisms present on the surface of metal, which lead to crevice corrosion of the metal.
· In some cases, the underground pipelines corrode very fast and sever. A two or three weeks ago there was a maintenance work going on in VH. There one of the pipelines under the garden was severely corroded. It was no more than a paper sheet remained. The reason was not proper care for corrosion was taken at the time of installation and this region was very much prone to corrosion, due to very high moisture content. So the metal corroded severely in 5-7 years only.
· Galvanic corrosion:
Galvanic corrosion may be the problem in the pillars used for electric power supply, where two different metals come in contact. Here stray currents may also be the reason.
· Stress corrosion cracking:
SCC is mainly found in the CI pipelines, near the threads mainly.
5.Life of a material & Remedies provided:
The most practical means of controlling corrosion of steel is complete removal of corrosion products by mechanical means and by maintaining the protective coating system (usually a plating, often combined with a paint system). The steel is provided a protective layer of synthetic enamel paint, which works as barrier between the metal and atmosphere (electrolyte) and thus prevents corrosion. This paint is applied once in two years. This much prevention is enough for steel bodies exposed to atmosphere, having a life of more than 35-40 years. The steel bodies not being painted regularly corrode fast. Its life is decreased to less than half of that of the painted.
- The RCC pillars after having been identified corroding are given epoxy treatment and thus preventing any further corrosion. Generally RCC pillars have long lives. But defective pillars may have problems due to corrosion in 10-15 years, and must be given epoxy treatment.
- The underground pipes, which are being corroded in the soil environment, are firstly provided a protective layer of Anticorrosive Ditumatic paint, and then they are surrounded by a 6 inches layer of sand. So that water does not stay long near the pipe, and any moisture present does not come in contact with metal. Generally pipelines given this type of protection have a life of 35-40 years. Otherwise they might have corroded in 5-6 years.
- Except these all steel and iron based alloy bodies being exposed to atmosphere are provided a protective layer of primer, zinc chromate at the time of installation.
- The pipelines at laboratories corrode very fast if made of some metal, because of presence of acids, salts and alchohals. So these pipelines are made up of PVC.
- Electric power supply pillars must be made of same metal or metal/alloy not too far in the galvanic series. Insulation must be provided at the points of contact of two different metals/alloys.
- Stainless steel:
The corrosion resistance of these steels is due to their ability to form a protective oxide film on the surface. This “passive” film can be reinforced by treatment in certain chemical solutions. However, such steels will pit when exposed to harsh corrosive environments such as airborne salts and industrial pollutants. Particularly susceptible are crevices and other areas in which foreign materials collect. Corrosion can be prevented by keeping stainless steel clean.
· The synthetic enamel painted on the atmosphere exposed metals costs 14 Rs per square meter.
· The epoxy treatment provided to the RCC pillars is very expensive. It is 500-800 Rs per square meter.
The atmosphere of IITKanpur is quite clean and free of pollutants. But the RH is very high which lead to the corrosion problems. So prevention must be provided at all the corrosion prone sites. All the metal bodies exposed to air must be painted at least once in two years. The pipelines must be made up of CI, coated with protective layer and surrounded by sand. Except this the pipelines in the laboratories must be made up of PVC, as concentration of acids t, salts etc may be high there. And insulator must be applied in electric power supply pillars to prevent any stray currents and also to prevent galvanic corrosion at the point of contact of two different metals.