API 653 REVIEWED EXAM
QUESTIONS AND THEIR COMPLETE
CORRECT SOLUTIONS
External Inspection Interval
Lesser of 5 years or RCA/4xN (N being corrosion rate)
RCA
Remain Corrosion Allowance (current thickness - required
thickness)
Ultrasonic Inspection Interval
lesser of 15 yrs or RCA/2N (if corrosion rate is not known
then the max interval is 5 years)
Internal Inspection Intervals
Initial Internal Interval 10 years without Safeguards or 30
years with Safegaurds - Interval maximum of 20 years
without Release Prevention Barrier or 30 years with RPB
Table for Internal Interval Safeguards
Table 6.1 of API 653
Uniform Corrosion calculation
2.6 ( H - 1 ) DG / SE
Localized Thin Area Caculation
2.6HDG / SE
Shell Corrosion Averaging caculation
L = 3.7√Dt₂ (Critical Length across corroded area can't be
> 40 " )
Widely scattered pits can be ignored if :
no pit depth results in the remaining shell thickness being
less than 50 % of Tmin
,The sum of their dimensions along any vertical line does
not exceed 2 in . in an 8 - in . length
What is the longest initial internal inspection interval
allowed by API 653 ?
30 years ( 10 year base interval plus 10 years for RPB
plus 10 years for SS bottom)
What is the longest initial internal inspection interval
allowed by API 653 for an oil storage tank without
Safeguards ?
10 years
What is the maximum internal inspection interval , if
an RBI was not performed and no other special
condition is applicable ?
10 years
What is the longest subsequent internal inspection
interval allowed by API 653 for an oil storage tank
without RPBS and corrosion - rate is known ?
20 years
What type of records is the owner / operator required
to maintain ?
Construction , inspection and repair / alteration records
Who must write the external and internal reports ?
Authorized Inspector
How long must external and internal inspection
reports be kept ?
Life of the tank
What type of weld joint is required for new shell joints
in a reconstructed tank ?
Butt joints with complete penetration and complete fusion
, What is the thickness used in the design calculations
based upon for a reconstructed tank
Thickness measurements taken 180 days prior to
relocation
What code is used to determine the allowable stress
for a reconstructed tank ?
API 650
Liquid Heights Caculations
API 653 Table 4.1 and Table 4.2
Liquid Heights on the test
Hydro Test Will 99 % Be A Question On the Test Not
pocess liquid
What is the maximum length allowed for averaging a
corroded area
40"
Two basic types of foundations ;
1 ) Earth foundation without a ring wall 2 ) Earth
foundation with a concrete ring wall
Tanks foundation grade ;
1) Should be at least 1 ft above ground level
2) Normally the tank bottom will slop from OD toward
center of tank ( slope of 1" inch in 10ft ) .
3) As an alternative the tank bottom can slop toward the
sump .
4) Minimum of 3 " of clean , compacted sand directly
under tank bottom .
Annular Plate
Bottom plate that the shell rests on that has butt joints
Sketch Plate
Bottom plate that the shell rests on that has lap joints
Three plate lap joints
QUESTIONS AND THEIR COMPLETE
CORRECT SOLUTIONS
External Inspection Interval
Lesser of 5 years or RCA/4xN (N being corrosion rate)
RCA
Remain Corrosion Allowance (current thickness - required
thickness)
Ultrasonic Inspection Interval
lesser of 15 yrs or RCA/2N (if corrosion rate is not known
then the max interval is 5 years)
Internal Inspection Intervals
Initial Internal Interval 10 years without Safeguards or 30
years with Safegaurds - Interval maximum of 20 years
without Release Prevention Barrier or 30 years with RPB
Table for Internal Interval Safeguards
Table 6.1 of API 653
Uniform Corrosion calculation
2.6 ( H - 1 ) DG / SE
Localized Thin Area Caculation
2.6HDG / SE
Shell Corrosion Averaging caculation
L = 3.7√Dt₂ (Critical Length across corroded area can't be
> 40 " )
Widely scattered pits can be ignored if :
no pit depth results in the remaining shell thickness being
less than 50 % of Tmin
,The sum of their dimensions along any vertical line does
not exceed 2 in . in an 8 - in . length
What is the longest initial internal inspection interval
allowed by API 653 ?
30 years ( 10 year base interval plus 10 years for RPB
plus 10 years for SS bottom)
What is the longest initial internal inspection interval
allowed by API 653 for an oil storage tank without
Safeguards ?
10 years
What is the maximum internal inspection interval , if
an RBI was not performed and no other special
condition is applicable ?
10 years
What is the longest subsequent internal inspection
interval allowed by API 653 for an oil storage tank
without RPBS and corrosion - rate is known ?
20 years
What type of records is the owner / operator required
to maintain ?
Construction , inspection and repair / alteration records
Who must write the external and internal reports ?
Authorized Inspector
How long must external and internal inspection
reports be kept ?
Life of the tank
What type of weld joint is required for new shell joints
in a reconstructed tank ?
Butt joints with complete penetration and complete fusion
, What is the thickness used in the design calculations
based upon for a reconstructed tank
Thickness measurements taken 180 days prior to
relocation
What code is used to determine the allowable stress
for a reconstructed tank ?
API 650
Liquid Heights Caculations
API 653 Table 4.1 and Table 4.2
Liquid Heights on the test
Hydro Test Will 99 % Be A Question On the Test Not
pocess liquid
What is the maximum length allowed for averaging a
corroded area
40"
Two basic types of foundations ;
1 ) Earth foundation without a ring wall 2 ) Earth
foundation with a concrete ring wall
Tanks foundation grade ;
1) Should be at least 1 ft above ground level
2) Normally the tank bottom will slop from OD toward
center of tank ( slope of 1" inch in 10ft ) .
3) As an alternative the tank bottom can slop toward the
sump .
4) Minimum of 3 " of clean , compacted sand directly
under tank bottom .
Annular Plate
Bottom plate that the shell rests on that has butt joints
Sketch Plate
Bottom plate that the shell rests on that has lap joints
Three plate lap joints
