Corrosion

Question 1

what is weld decay?

Answer 1

welds in stainless steel sometimes show severe corrosion attack along grain boundaries

Question 2

what happens in weld decay?

Answer 2

steel cools near a weld and the carbon in the stainless steel ‘soaks up’ the chromium to form precipitates of chromium carbide
so insufficient chromium in steel to form a chromium oxide cover
depleted regions are no longer protected so corrode badly

Question 3

when does galvanic corrosion happen?

Answer 3

two different metals in direct contact or connected through an electric current
metals are immersed in a common electrolyte solution

Question 4

what does galvanic corrosion form?

Answer 4

an anode and cathode (one metal forms anode, one forms cathode)

Question 5

what is galvanised steel?

Answer 5

steel is zinc plated
(zinc more reactive than steel, so zinc corrodes preferentially)

Question 6

how can we prevent corrosion?

Answer 6

galvanising
eliminate cause
correct choice of material for application
consideration of material surface condition
corrosion inhibitors
physical barriers

Question 7

what type of material is aluminium and why?

Answer 7

physical barrier
aluminium oxide coating is chemically inert, preventing further corrosion so aluminium doesn’t tarnish

Question 8

what are red metals?

Answer 8

copper and copper alloys

Question 9

what is copper like?

Answer 9

relatively inert and takes a long time to oxidise

Question 10

what is bronze like?

Answer 10

highly resistant to corrosion and oxidation

Question 11

how does brass often corrode?

Answer 11

dezincification

Question 12

what can often happen to bronze?

Answer 12

can experience bronze disease (form of corrosion)