Lesson 3 - Classification and Properties SAQ
This lesson allows you to test yourself on the material covered in the lesson on Classification and Properties and determine the level to which you have met the learning outcomes.
Suggested Response - Q5
**What steps do you need to take to prevent corrosion throughout the brewery?
Response:
The material selected must be resistant to the conditions in which it is expected to operate. If conditions require high corrosion resistance the material properties need to match this.
Precautions to prevent galvanic corrosion, or at the very least minimise the impact of galvanic corrosion, should be taken. Examples include:
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Where metals that could be in contact with each other are exposed to an electrolytic solution. Various solutions to this problem are possible such as:
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Use metals that have similar galvanic potential
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Insulate the different metals from each other
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Remove one of the metals from the solution by coating it or keeping it above the moisture line.
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If fasteners are used make sure the fasteners will act as the cathode and the bigger material volume will act as the anode. Thus the impact will be less as a relatively small proportion of the larger volume metal will corrode.
Any build-of dirt can cause an area to be exposed to different conditions than the main metal and thus result in galvanic corrosion. Dirt can also shield a metal from repassivating itself and accelerate corrosion. Therefore, equipment should be kept clean and dirt should not be allowed to accumulate anywhere. Crevices should be avoided as these can lead to crevice corrosion.
Welding should be carried out by a qualified welder to the correct specification for the intended purpose. Incorrect welding technique can result in welds being contaminated with other metals, too much or uncontrolled heating and other defects. These can all result in changes in the structure which can cause corrosion.
Inert gas shielding should be used to prevent oxides forming which can cause uneven distribution of chromium in the metal and lead to intergranular corrosion. Welds should be pickled and passivated to ensure that the weld areas uniformly passivated and corrosion due to uneven passivation is avoided.