CORROSION Flashcards
WHAT IS THE DEFINITION OF CORROSION?
THE DESTRUCTION OR DETERIATION OF A MATERIAL, OR ITS PROPERTIES, CAUSED BY REACTION WITH ITS ENVIRONMENT.
WHAT IS WET CORROSION
OCCURS WHEN A LIQUID IS PRESENT - ‘WET’ INCLUDES HUMIDITY IN THE AIR AND MOISTURE IN SOIL.
WHAT ARE SOME COSTS OF CORROSION?
- PLANT DOWNTIME
- LOSS OF PRODUCT
- LOSS OF EFFICIENCY
- contamination of product
WHAT ARE THE 4 COMPONENTS OF GALVANIC CORROSION?
- ANODE
- CATHODE
- ELECTROLYTE
- ELECTRICAL CONNECTION
WHAT IS AN ANODE?
THE METAL THAT IS CORRODING. ELECTRONS ARE PRODUCED HERE. OXIDATION IS THE LOSS OF ELECTRONS.
WHAT IS A CATHODE?
THIS IS THE METAL WHOSE SURFACE PROVIDES THE SITES FOR THE ENVIRONMENT TO REACT. ELECTRONS ARE CONSUMED HERE
WHAT IS AN ELECTROLYTE?
PROVIDES AQUEOUS ENVIRONMENT AND MUST BE IN CONTACT WITH BOTH THE ANODE AND THE CATHODE. IT PROVIDES A PATH FOR THE IONIC CONDUCTION.
WHAT IS THE ELECTRICAL CONNECTION FOR GALVANIC CORROSION?
THIS MUST BE PRESENT BETWEEN THE ANODE AND CATHODE TO ALLOW FOR THE FLOW OF ELECTRONS BETWEEN THEM. OFTEN THIS ELECTRICAL CONNECTION IS JUST THE CONTACT OF THE METALS.
WHICH WAY DO THE ELECTRONS FLOW FOR GALVANIC CORROSION?
THEY FLOW FROM THE ANODE (LESS NOBLE) TO CATHODE (MORE NOBLE).
WHAT FACTORS AFFECT CORROSION?
- METALLURGIC FACTORS
- ENVIRONMENT
- OPERATING CONDITIONS
WHAT ARE METALLURGICAL FACTORS?
- ALLOYS CAN BE HOMOGENOUS SOLID SOLUTIONS OR HETEROGENOUS MIXTURES
- DISCONTINUITIES
WHAT ARE THE 9 FORMS OF CORROSION?
- UNIFORM ATTACK
- GALVANIC OR TWO METAL CORROSION
- CREVICE CORROSION
- PITTING
- INTER-GRANULAR CORROSION
- SELECTIVE LEACHING
- EROSION CORROSION
- STRESS CORROSION CRACKING
- HYDROGEN DAMAGE
WHAT IS GROUP 1 OF CORROSION CALLED?
GENERAL CORROSION
WHAT IS GROUP 2 OF CORROSION CALLED?
LOCALIZED CORROSION
WHAT IS GROUP 3 OF CORROSION CALLED?
CORROSION CRACKING
BEFORE APPLYING A COATING WHAT MUST BE CONSIDERED?
- CHEMICAL RESISTANCE OF THE COATING
- PROPER ADHERENCE
- ABRASION RESISTANCE
- ABILITY TO EXPAND AND CONTRACT WITH THE METAL
- WATER RESISTANT
- AGING RESISTANT
- EASE OF APPLICATION
WHAT ARE THE 2 GENERAL CATEGORIES OF COATINGS?
- INERT
- ACTIVE
WHICH COATING IS CONSIDERED SUPERIOR?
ACTIVE
WHAT ARE THE 6 TYPES OF CORROSION PREVENTION TECHNIQUES?
- CORROSION ALLOWANCE
- SELECTION OF DIFFERENT MATERIAL THAT IS MORE RESISTANT
- ADD INHIBITORS
- CATHODIC PROTECTION
- APPLY COATING
- CHANGE ENVIRONMENT
WHAT ARE THE 2 WAYS METAL CAN BE CATHODICALLY PROTECTED?
- SACRIFICIAL ANODE
- IMPRESSED CURRENT
WHAT IS PITTING CORROSION VERY SIMILAR TO ?
CREVICE CORROSION
WHAT IS INTERGRANULAR CORROSION SIMILAR TO AND HOW DO YOU PREVENT IT.
SIMILAR TO CREEP AND TO PREVENT IT IS TO PROVIDE BIGGER GRAINS.
WHAT ARE 3 WAYS TO PREVENT IGC
- USE VERY LOW CARBON
- ADD OTHER ALLOYING ELEMENTSTHAT HAVE A HIGHER AFFINITY TO COMBINE WITH CARBON
- PERFORM A HEAT TREATMENT TO MAKE THE CHEMICAL COMPOSITION MORE UNIFORM
how to prevent IGC in aluminum alloys
- coating the material where possible
- selecting a more exfoliation-resistant aluminum alloy
- use a heat treatment after forming the part to control precipitate distribution.
what is selective leaching?
the removal of one element from a solid alloy
what are the 3 requirements for stress corrosion cracking?
- tensile stress
- susceptible material
- corrosive environment
what is hydrogen damage
refers to the deterioration of material caused by the presence of or interaction of a material with hydrogen.
what are 3 ways to prevent hydrogen damage?
use clean steels
use coatings
use inhibitors
