A sample of stainless steel AISI 316L
TREATMENT TYPE: ½ of the sample was treated by degreasing, pickling and passivation.
TEST: according to ASTM G48-03 Method A - sample immersed in a 6% solution of iron (III) chloride over a period of 72 hours - is applied to determine the general tendency of steel pitting corrosion, which is important for predicting the corrosion behavior of steel exposed the influence of sea water, and other chloride solutions.
CONCLUSION: On the half of the sample which was chemically treated, it is evident that there is no corrosion damage, and on the other half which was not chemically treated, there is visible corrosion damage in the form of pits - dimple corrosion.
WHY CORROSION OCCURS
It should be borne in mind that in practice corrosion on the surfaces of stainless steel is not unusual at all. Pipelines and construction made out of stainless steel in the food, pharmaceutical, water, oil and other industries are not immune to corrosion. In practice, corrosion occurs due to disruption of the passive layer of stainless steel, and which might occur due to improper handling of stainless steel, improper welding, unprofessional cleaning, aggressive environment, or even due to the application of particles from other systems that are not properly constructed and protected, and are in contact the with other systems.
CORROSION DEVELOPMENT EFFECT
Problems that arise due to the development of corrosion damage on the surface are liquid contamination with particles of metal oxides and growth of micro organisms on surfaces. In addition to these problems at an early stage of corrosion development, emergence of serious problems is possible in terms of pipeline ruptures, medium leakages, plants failures, plant shutdown, or shortly the occurrence of significant costs.
HOW TO PREVENT CORROSION
Pickling and passivation of new systems is one of the most important factors in the prevention of corrosion. High quality passivation method (method of immersion in bath) guarantees long lifetime of plants in the best possible way. For complete safety of the plant and eliminating the possibility of development of corrosion and consequent problems, it is necessary to predict a periodic re-cleaning procedure, respectively to remove possible corrosion and renew the passive layer.