Corrosion & Erosion

Question 1

Corrosion & Erosion: Types?

Answer 1

Question 2

Corrosion & Erosion: Chemical corrosion

Answer 2

Question 3

Corrosion & Erosion: Dry Corrosion 1

Answer 3

Question 4

Corrosion & Erosion: Dry corrosion 2

Answer 4

Question 5

Corrosion & Erosion: Galvanic corrosion

Answer 5

Question 6

Corrosion & Erosion: Wet corrosion, Anode & Cathode
must draw

Answer 6

Question 7

Corrosion & Erosion: Anode & Cathode & Greater Anode
must draw

Answer 7

Question 8

Wet Corrosion: Dissimilar Metals

Answer 8

Question 9

Wet Corrosion: Sacrifical Anode

Answer 9

Question 10

Wet Corrosion: Galvanic corrosion 2

Answer 10

Question 11

Wet Corrosion: Impressed current system

Answer 11

Question 12

Crevice Corrosion

Answer 12

Question 13

Crevice Corrosion 1

Answer 13

Question 14

Crevice Corrosion 2

Answer 14

Question 15

Fretting & Stress corrosion

Answer 15

Question 16

Cavitation

Answer 16

Question 17

Osmosis

Answer 17

Osmosis:
FRP construction can be damaged by Osmosis. This is seen by cracking or blistering of the
surface. Gel coat damage allows water to come into direct contact with the resins which
are porous and allow water to be ‘sucked’ in. If the resin is damaged, it must be replaced
before repairing the Gel coat. Cheaper FRPs use a polyester resin in the mix which absorbs
and produces water creating an acidic mixture. This may collect in small gaps in the layup
caused by bits of grit in the mix. This increases the pressure in these gaps forcing the
laminate apart and breaking up the FRP. High quality builds using non-polyester resins will
cure fully without absorbing more water.

Question 18

Impressed Current System

Answer 18

Impressed Current System:
If the Galvanic Current can be suppressed, the corrosion can be stopped. By measuring the
current flowing and creating a reverse current from the ship to a cathode (or, in fact, a
series of cathodes) on the outside of the hull. This is only effective if the current is
constantly monitored and adjusted so the system must be controlled by a computer.