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senior Corrosion^ Technologist^ Exam
An __________ is established within the pit, and the surrounding surfaces act as cathodes. - CORRECT ANSWER-anode True or false? Pits develop at weak spots in the surface film and at sites where the film is damaged mechanically under conditions where self repair will not occur. - CORRECT ANSWER-True The importance of pitting depends on the thickness of the metal, thus on ____ sections pitting may be serious, while on _______ pitting is of less importance. - CORRECT ANSWER-thin, thick List the four stages of pitting. - CORRECT ANSWER-
- initiation
- propagation
- termination
- reinitiation True or false? Pits develop at weak spots in the surface film and at sites where self repair will occur. - CORRECT ANSWER-False: Pits develop at weak spots in the surface film and at sites where self repair will NOT occur. In general the rate of penetration ______________ if the number of pits increase. - CORRECT ANSWER-decreases List the four types of environmental cracking - CORRECT ANSWER-
- Stress corrosion cracking
- Hydrogen-induced cracking and sulfide stress cracking
- Liquid metal embrittlement
- Corrosion fatigue List the 3 types of flow-assisted corrosion - CORRECT ANSWER-
- Erosion-corrosion
- Impingement
- Cavitation
What combination will result in more than one form of corrosion within a system? - CORRECT ANSWER-Metals used in structures/equipment and a wide range of environments Even a single alloy exposed to different environments at different points within a system can undergo _______ - CORRECT ANSWER-More than one type of attack ________ is attack that proceeds more or less uniformly over the exposed surface with appreciable localization of attack - CORRECT ANSWER-General corrosion Two other names for general corrosion are _______________ - CORRECT ANSWER- General attack corrosion and uniform corrosion For round bars or wires, corrosion proceeds radially inward at essentially a uniform rate around the entire circumference. The result is ______________________ - CORRECT ANSWER-A bar or wire of progressively smaller diameter Pipe and tubing that suffer from general corrosion are - CORRECT ANSWER-Thinned from one side, or the other, or both General attack corrosion can be recognized by - CORRECT ANSWER-A roughening of the surface and by the presence of corrosion products Why may corrosion products not always be present with general corrosion? - CORRECT ANSWER-They can be soluble or can be removed by wind, rain, and other forces An electrochemical process taking place on the surface of the material - CORRECT ANSWER-general attack corrosion When corrosion rates are __________ or ___________, long-term projections of corrosion damage are possible. - CORRECT ANSWER-Linear, decrease with time When corrosion rates ______________, it is more difficult to predict long-term corrosion. - CORRECT ANSWER-Increasing with time General attack corrosion is usually measured in terms of - CORRECT ANSWER- Penetration rates per unit of time in millimeters per year or mils per year Experimental measurement of general attack corrosion is usually made by measuring ________________ and calculating ________________. - CORRECT ANSWER- Weight loss, the equivalent loss of metal thickness
__________________________ is a method which interferes with the flow of the current in the electrochemical cell - CORRECT ANSWER-cathodic protection ________________ can be used in underground or emersion situations. - CORRECT ANSWER-cathodic protection _________________________________ are low-alloy steels formulated specifically to form tightly adherent, dense corrosion products that inhibit corrosion in some atmospheric environments. - CORRECT ANSWER-weathering steels _______________________, unlike general corrosion, occurs at discrete sites on a metal surface. - CORRECT ANSWER-localized corrosion _____________________ is a deep, narrow corrosive attack which often cause rapid penetration of the substrate thickness. - CORRECT ANSWER-pitting _________________________ is characterized by corrosive attack in a localized region surrounded by corrosion free surfaces, or surfaces that are attacked to a much lesser extent. - CORRECT ANSWER-pitting corrosion Very often, a local cell is set up between the interior of the pit and the external surface. The interior contains ______________________ that are quite corrosive compared with the bulk of the solution. - CORRECT ANSWER-acidic, hydrolyzed salts Movement of the solution over the metal surface often ______________ and may even _______________ pitting that otherwise would occur if the liquid were stagnant (such as with austenitic stainless steels in seawater). - CORRECT ANSWER-reduces, prevent During the initiation step of pitting, where does pit initiation occur? - CORRECT ANSWER-at defects or imperfections in a protective or passive film Defects that cause pit initiation may be _____________________ or are caused by________________. - CORRECT ANSWER-randomly distributed, mechanial damage to the films Pitting may not initiate for long periods, but once it does it can - CORRECT ANSWER- propagate rapidly In the propagation step, corrosion is driven by - CORRECT ANSWER-the potential difference between the anodic area inside the pit and the surrounding cathodic area A pit may terminate because of.... - CORRECT ANSWER-increased internal resistance of the local cell caused by filling with corrosion products, filming of the cathode, etc.
Sometime pits are reinitiated when they are ___________ - CORRECT ANSWER- Rewetted due to re-establishment of the conditions or to the differential aeration between the solution in the main pit cavity and solutions in some of the cracks that emanate from deeper in the metal. True or False? In structural members where strength alone is a concern, pitting alone may not be as important as in a service of containing fluid. - CORRECT ANSWER-True What does PREN stand for? - CORRECT ANSWER-Pitting Resistance Equivalent Number _________________ removes material from the surface until no further pits are evident.
- CORRECT ANSWER-routing __________________ is the most accurate method for measuring pits. - CORRECT ANSWER-Routing What variation of the routing method can be used to measure the maximum pit depth on the outside of the pipe? - CORRECT ANSWER-Placing a sample length in a lathe and machine it until no further corrosion is evident What is pitting frequency? - CORRECT ANSWER-the number of pits per unit area Why is pitting corrosion more difficult to define than general corrosion? - CORRECT ANSWER-Because the exact location of the pits cannot be predicted. The introduction of small amount of ions, of metals such as _______________, _______________, and _______________ may cause severe corrosion of aluminum equipment. - CORRECT ANSWER-copper, lead, mercury Corrosion of upstream copper alloy can cause ... - CORRECT ANSWER-contamination of cooling water __________ _______________ has been used effectively to control pitting on body exposed surfaces. - CORRECT ANSWER-Cathodic Protection ___________ _______________ is not recommend where pitting may occur. - CORRECT ANSWER-Anodic Protection __________________ ___________ is a form of localized attack in which the size of the attack is an area where free access to the surrounding environment is restricted. - CORRECT ANSWER-Crevice corrosion What is caused by differences in concentrations of materials? - CORRECT ANSWER- crevice corrosion
_____________________ is a form of corrosion that occurs because of the potential differences between metals. - CORRECT ANSWER-Galvanic corrosion _____________________ occurs through the action through the electrochemical cell. - CORRECT ANSWER-Galvanic corrosion ____________________ is accelerated by the potential differences between different metals when they are in electrical contact and are exposed to an electrolyte. - CORRECT ANSWER-Galvanic corrosion _________________ can also occur between a metal and an electrically conductive non metal like graphite. - CORRECT ANSWER-Galvanic corrosion In ___________________ the rate of attack of one metal or alloy is usually accelerated, while the corrosion rate of the other is usually decrease. - CORRECT ANSWER- Galvanic corrosion _____________________ can be recognized by either increased corrosion of the anodic material, or decreased corrosion of the cathodic material. Is also often pronounced where the dissimilar materials are immediately adjacent to each other and at sharp edges or corners. - CORRECT ANSWER-Galvanic corrosion The mechanism of galvanic corrosion is the classical electrochemical cell. What are the four factors that must be present in the electrochemical cell? - CORRECT ANSWER-
- anode
- cathode
- metallic path
- electrolyte The __________ is the place where the metal is lost and electrons are. produced. - CORRECT ANSWER-anode The ______________ is the place where electrons produced at the anode are consumed. - CORRECT ANSWER-cathode The ______________ conducts electrons from the anodic sites to cathodic sites. - CORRECT ANSWER-metallic path The _________ provides reactants for the cathodic reaction and allows the flow of ions.
- CORRECT ANSWER-electrolytes A _______________ is a listing of metals in the order of their potential in a specific electrolyte. - CORRECT ANSWER-galvanic series
______________ ________________ are metals that are chemically vulnerable in both acidic and alkaline environments and can be affected at the cathode in a galvanic corrosion cell. - CORRECT ANSWER-amphoteric materials What factors affect the extent of accelerated corrosion resulting from galvanic coupling?
- potential difference between the metals or allows
- the specific nature of the environment
- polarization behavior of the coupled materials
- spatial effects, such as area, distance, and cell geometry
- resistivity of the electrolyte What causes current flow when dissimilar materials are coupled in a suitable electrolyte? - CORRECT ANSWER-potential difference What does the direction of current flow depend on? - CORRECT ANSWER-Which metal is more active The more active metal becomes the _____________, while the less active metal becomes the _____________. - CORRECT ANSWER-anode, cathode The galvanic series has been constructed from measurements ________________. - CORRECT ANSWER-seawater Electrode potentials are sensitive to what factors? - CORRECT ANSWER-
- electrode composition
- electrolyte composition
- temperature
- degree of agitation
- presence of depolarizers, inhibitors, or both
- surface conditions of electrodes
- metallurgical conditions of electrodes Galvanic corrosion can occur under ____________________ or _________________. - CORRECT ANSWER-immersion, atmospheric condition Under _____________ conditions, galvanic effects cover essentially the exposed surfaces of both the anode and cathode. - CORRECT ANSWER-immersion Galvanic effects are usually concentrated where the anode and cathode are _________________. - CORRECT ANSWER-closest together In _________________ , the resistance effects in the electrolyte limits the range of galvanic effects to the area where two electrodes are in contact and for a very short distance around the contact area. - CORRECT ANSWER-atmospheric exposures
- corrosion environment
- corrosion potentil
- temperature What are the types of environmental cracking? - CORRECT ANSWER-
- stress corrosion cracking (SCC)
- hydrogen induced cracking (HIC)
- liquid metal embrittlement (LME)
- corrosion fatigue (CF) ________________________ is a brittle failure in an otherwise ductile material, resulting from the combined action of tensile stress and specific corrosive environment.
- CORRECT ANSWER-stress corrosion cracking (SCC) What specific corrosive media promote stress corrosion cracking? - CORRECT ANSWER-
- caustic with carbon steel
- chlorides wit stainless steel
- ammonia with copper alloys Stress corrosion cracking is a(n) _________________ process, a fact which is verified by the applicability of ___________________ protection as an effective remedial measure. - CORRECT ANSWER-anodic, cathodic Usually with stress corrosion cracking there is a _____________________ where the crack begins at a microscopic level. - CORRECT ANSWER-incubation period If there is severe ________________ corrosion, usually stress corrosion cracking will not occur, however when products from this form of corrosion are trapped so as to cause stress in the structure, ________________ will occur. - CORRECT ANSWER- general Stress corrosion cracking of ______________________ stainless steels have been reported in hot concentrated caustic solutions and in some salt atmospheres. In these stainless steels the cracking was transgranular. - CORRECT ANSWER-martensitic __________________ grades of stainless steel tend to be resistant to chlorine stress corrosion cracking, although they will suffer environmental cracking in hot concentrated caustic. - CORRECT ANSWER-Ferritic Transcrystalline stress corrosion cracking is induced in __________________ grades of stainless steel and related alloys by chlorides especially, and by hot concentrated caustic. - CORRECT ANSWER-austenitic Depending on the heat treatment, ________________________________ of stainless steel may or may not be resistant to chloride stress corrosion cracking. In general the
heat treatment that gives alloys a very high strength cause a susceptibility to chloride stress corrosion cracking. - CORRECT ANSWER-precipitation hardened grades List the grades of stainless steel: - CORRECT ANSWER-
- martesitic
- ferretic
- austenitic
- precipitation hardened
- superaustenitic _______________________________ are subject to stress corrosion cracking in hot salt (sodium chloride above 275 degrees), 10 % hydrochloric acid at slightly above room temperature, and in nitrogen tetroxide or red fuming nitric acid. - CORRECT ANSWER- commercial titanium allows
