API 651 - 5 ( Determination of Need for Cathodic Protection) Flashcards
the decisions governing the need for cathodic protection should be based
on data from corrosion surveys , operating records; prior test results on similar tank systems; jurisdictional requirements and recommendations of API 651
corrosion control by cathodic protection for the new aboveground storage tanks should be evaluated
in the initial design of the tank
corrosion control by cathodic protection for new aboveground storage tanks should be maintained
during the service life of the tank
studies should be made within a suitable time frame in accordance with API Standard 653 concerning the possible need for cathodic protection. when these studies indicate that corrosion will affect the safe or economic operation of the system
adequate corrosion control measure should be used
studies should be made within a suitable time frame in accordance with API Standard 653 concerning the possible need for cathodic protection.When these studies indicate that corrosion will affect the________ or economic operation of the system, adequate corrosion control measure should be used
safe
pure hydrocarbon fluids are usually
not corrosive
what is generally used to reduce or eliminate corrosion on the internal surfaces of underground storage tanks
coatings
internal cathodic protection in conjunction with coatings has:
not gained wide spread use
cathodic protection is an effective means of corrosion control only if it is possible to pass electric current between the
anode and the cathode (tank bottom)
prior to determining the need for cathodic protection of an aboveground storage tank:
a full evaluation of tank history is advised
information about an aboveground storage tank such as foundation design,site plan, construction date, soil properties, location of water table, presence and types (s) of linings, previous repairs,whether it has a secondary bottom, maintenance history,etc. all make up:
the tank design and construction history
information about an aboveground storage tank such as the type of product stored, the producttemperature , the presence and depth of water bottoms, and the frequency of fill and discharge, all make up:
the type of service the tank is in
in certain cases, internal cathodic protection in conjunction with a ________may be applicable.
lining
if internal corrosion is known to be a problem with an aboveground storage tank:
use of an internal lining should be considered.
the _______ under the tank bottom has a significant effect on external corrosion of the tank bottom
cushion material
if large particle sizes are used in the cushion beneath a tank bottom,differentinal aeration _______ may result at points where the large particles or debris contact the bottom .
corrosion
Soil __________provides valuable information about the corrosivity of the material used under and around a tank bottom.
resistivity
Soils with a resistivity range,OHM-CM, of less than 500 indicates it is probably:
very corrosive
corrosive soil beneath a high resistivity foundation material may contaminate the foundation fill by:
capillary action
a properly designed concrete tank cushion constructed on a stable , properly prepared subsoil may be effective in eliminating:
intrusion of groundwater, soil- soil corrosion, and the need for cathodic protection
Unstable soil beneath a concrete tank cushion constructed on a stable, properly prepared subsoil may be effective in eliminating :
intrusion of ground water ,soil-side corrosion , and the need for cathodic protection
Unstable soil beneath a concrete tank cushion may induce cracks in the slab through which water and contaminants can permeate to steel tank bottom and provide a ____ environment
corrosive
corrosion from soil may be prevented by a:
concrete pad
if a tank is constructed on a concrete pad or foundation (or cushion) ,corrosion of the external tank bottom may occur from:
moisture accumulation because of condensation,flooding,blowing rain.etc.
where a non -continuous concrete pad is utilized oxygen entry is not restricted.In situations where water may condense on the tank bottom or water is retained above the concrete pad,_____ may occur
accelerated atmospheric corrosion
a cushion of new ____ may provide many of the same advantages as a concrete cushion for reducing corrosion and eliminating the need for cathodic protection
asphalt
Asphalt degrades with the time and can provide a path for water and dissolved chemicals to come into contact with the steel tank bottom,allowing _______ to occur
corrosion
a deteriorated asphalt cushion may allow corrosion of the tank bottom to occur . cathodic protection, if applied
may or may not stop corrosion occurring
a useful test of sand pad material for helping to determine whether potential corrosion activity will be high enough to make cathodic protection necessary is
an electrical resistivity test
measuring pH and soil resistivity are tests that are helpful in further corrosion analysis of the native soil cushion if a pH measured to be less than 5.0 this indicates that the soil cushion is
very corrosive
the presence of aggressive ions such as chlorides and sulfates in the native soil cushion are very helpful in corrosion analysis. if the chlorides are measured to be greater then 10 ppm, this indicates that the soil cushion could cause ________type corrosion to a carbon steel bottom .
pitting
the presence of aggressive ions such as chlorides and sulfates in the native soil cushion are very helpful in corrosion analysis. if the sulfates are measured to be greater than 200 ppm, this indicates that the soil cushion contains__________.
a high concentration of organic matter
when soil analysis data ( by resisivity testing) indicates that a sand pad cushion for a tank is corrosive , what measures should be considered ?
install cathodic protection or take other corrosion control measures
what is the most common material used as a cushion beneath storage tank bottoms ?
clean sand
if oil alone is added to the clean sand beneath a tank bottom, industry experience show that it:
does not eliminate the need for cathodic protection
Salt sprays ( especially in coastal areas) fertilizers or chemicals from spraying may:
get into the tank cushion and contaminate it where corrosion may take place.
if a tank with water bottoms leaks into the tank’ s cushion, the environment under the tank may become :
more corrosive
if product leaks from a tank into the tank’ s cushion, it could create corrosion cells that did not exist before or adversely affect the effectiveness of the :
cathodic protection
cathodic protection is. ___________in areas beneath a tank bottom where a leak has washed away part of the foundation material
not effective
the use of crushed limestone or calm shells as tank cushion makes the environment under tanks alkaline. this does what ?
it may reduce corrosion
Accelerated corrosion can occur on the external surface of the bottom of heated tanks due to elevated temperatures if the areas is :
wet
an impervious clay pad beneath the tank levees,a dual bottom tank bottom design, or an impervious non metallic membrane beneath the primary bottom of a tank are all examples of:
secondary containment
To reduce the environmental impact of a tank bottom leak
secondary containment may be used
most cathodic protection systems are rendered ineffective when:
an impervious membrane lining is a diked area prior to tank construction.
Thick -film,laminated,corrosion & chemical resistant linings are installed in tanks primarily to prevent:
internal corrosion
The use of a thick-film laminate or other type of internal lining can:
not be considered as sufficient justification to eliminate external cathodic protection
A thick - film,laminated ,internal tank bottom lining:
is not designed for structural strength.
