Page 177 - CW E-Magazine (2-7-2024)

Special Report Special Report

invested in corrosion monitoring, control Table 1: Causes for failure of engi- fi ed as ‘wet’ or ‘dry’. A liquid or of corrosion. Further distinction bet- sion resistance, fabricability, aesthetic plants for determining the corrosion
and management will save Rs. 7 worth neering structures moisture is necessary for the for- ween macroscopically localized cor- appearance, ease of availability, and allowances to be provided so that the
of corrosion losses. Cause Share mer, and dry corrosion usually in- rosion and microscopic local attack can costs. plants can be operated and maintained

High temperature corrosion 7% volves reaction with high tempera- be made as shown in Figure-3. Macro- optimally throughout their economic
Indirect losses occur due to the ture gases. scopic forms of corrosion affect greater Alteration of environment lifetime. Corrosion tests are also needed
following reasons: Stress corrosion cracking (SCC) 6%  Mechanism of corrosion: This in- areas of corroded metal and are gene- Several alterations can be made in the to troubleshoot corrosion problems
 Loss in revenue due to downtime. Other forms of corrosion 29% volves either electrochemical or rally observable with the naked eye or medium for controlling corrosion: during normal operation of the plant in

 Loss in product through leakage. Fatigue 25% direct chemical reactions. can be viewed with the aid of a low  Lowering the temperature; order to increase operational reliability

 Loss in effi ciency. Brittle fracture 16%  Appearance of the corroded metal: power magnifi cation. In microscopic  Reducing the velocity of the medium of the assets.
 Contamination of product(s). It is either uniform (entire surface attack, the amount of metal dissolved is and removing solid particles;
 Loss incurred due to over-design of Overload 11% is attacked uniformly) or localised minute, and considerable damage can  Removing oxygen or oxidisers; Well planned and executed tests

assets (huge corrosion allowances Creep 3% (small area is affected). occur before the problem becomes  Changing the concentration; and usually results in reproducibility and

and selection of costly corrosion Wear/abrasion/erosion 3% visible to the naked eye.  Dozing corrosion inhibitors. reliability. It is very important for the
resistant materials). Classifi cation by appearance, which tests to duplicate the actual plant ser-
leads to partial or complete damage of is particularly useful in failure analy- The factors infl uencing corrosion in Other strategies include: vice conditions as closely as possible.
Another important indirect cost of assets, incurring huge economic losses sis, is based on identifying forms of any asset can be summarized as: stress  Selecting adequate design of the The greater the deviation from plant

corrosion is safety and environmental and creating safety hazards for the plant corrosion by visual observation. The factors, material factors, and environ- equipment and selecting adequate conditions the less reliable the tests.
hazards. Lots of accidents take place people and also people at large living in morphology of attack is the basis for mental factors. Corrosion occurring due wall thickness; Corrosion testing include laboratory
due to failure of assets due to corro- the society. classifi cation. Figure-2, illustrates to the interaction of the above factors is  Applying cathodic and anodic pro- tests including acceptance or qualifying

sion, particularly when handling hazar- schematically the most common forms depicted schematically in Figure-4. tection for protecting critical assets; tests; pilot-plant tests; plant or actual
dous chemicals. For example, in the Table 1 clearly shows that corrosion and service tests; and fi eld tests.
Bhopal gas accident, corroded methyl problems cause majority of failures in Asset integrity management by  Applying protective coatings on the
isocyanate (MIC) storage tanks and assets. However, in chemical industry corrosion control assets. Laboratory tests are classifi ed by
valves allowed water ingress leading the majority of failures affecting asset small specimens and small volumes
to a fi ve-fold increase in pressure in an integrity are due to corrosion of static The following methods are gene- Corrosion testing for asset integrity of solutions, and actual conditions are
hour. In addition, the fl are system could equipment subjected to aggressive rally applied for controlling corrosion management simulated in sofar as conveniently pos-
not be used due to a corroded pipeline. environments. in assets: Corrosion tests are necessary to sible. They serve as screening tests to
The disintegrated (ruptured) storage select materials of construction for determine which materials warrant
tanks (assets) led to immediate death Mechanism and classifi cation of Proper material selection equipment used in the process industry. further investigation. Figure-5 shows
of 2,259 people and caused exposure of corrosion The criteria for proper material The test results (corrosion rate, etc.) are a laboratory setup where samples are
MIC vapour to about 5,00,000 people It is convenient to classify corrosion selection are mechanical strength, corro- used at the design stage of the process subjected to boiling solution.
in December 1984. by the forms in which it manifests itself
in order to manage it. Classifi cation is
Figure-1 shows the schematic view usually based on one of three factors:
of the different kinds of losses encoun-  Nature of corrodent: It can be classi- Fig. 3: Broad Classifi cation of Corrosion
tered due to corrosion.

ECONOMIC CONSERVATION HUMAN SAFETY
INDIRECT LOSSES (3.5%) DIRECT LOSSES (4.2%)
LOSS IN REVENUE DUE TO DOWNTIME. Fig. 5: Laboratory tests in boiling solutions
LOSS IN PRODUCT THROUGH LEAKAGE.
LOSS IN EFFICIENCY Pilot plant tests are usually the best
CONTAMINATION OF PRODUCT and most desirable. Here the tests are
OVER-DESIGN made in a small-scale plant, which es-
sentially duplicates the intended large-
Fig. 1: Signifi cance of Corrosion Control &
Asset Integrity MGT scale operation. Actual raw materials,
concentrations, temperatures, veloci-
Failures of structures due to lack of ties, and volume of liquor to area of
asset integrity management metal exposed are involved. Pilot plants
Lack of asset integrity management Fig. 2: Common forms of corrosion Fig. 4: Factors infl uencing corrosion are usually run long enough to ensure

176 Chemical Weekly July 2, 2024 Chemical Weekly July 2, 2024 177

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