API 575 Section 7

Question 1

Which of the following should be immediately addressed by either the inspector or tank engineer?

A. Isolated pitting up to 0.050” deep on the plate-extension
B. Hole in a tank roof
C. Insulation on north side of tank with algae growing
D. Tight temperature crack in the concrete ring-wall

Answer 1

B. Hole in a tank roof (7.1.2.1)

Question 2

Which of the following should be checked after very high winds or heavy rain? This may have more than one correct answer, select all answers that apply.

A. External floating roof seals B. Foundation deterioration
C. Soundness of the floating roof legs
D. Water loads on external floating roof tanks

Answer 2

A. External floating roof seals, B. Foundation deterioration, D. Water loads on external floating roof tanks (7.1.2.2)

Question 3

Inspection intervals that are based on past and current performance are called:

A. Condition-Based intervals.
B. Fitness-for-Service intervals. C. RBI intervals.
D. Time-Based intervals

Answer 3

A. Condition-Based intervals. (7.2.1)

Question 4

Determine the corrosion rate occurring on a shell course based on this data.
tmin 10/2021 4/2017
0.525” 0.570” 0.588”

A. 3.6 mpy (mils per year)
B. 4.0 mpy
C. 4.5 mpy
D. 10 mpy

Answer 4

B. 4.0 mpy (7.2.2 – see calc pg 54)

Time Period=2021 10/12–2017 4/12 = 2021.83 – 2017.33 = 4.5 yrs
Corr Rate = Metal Lost / Time = (588 – 570) / 4.5 = 18 / 4.5 = 4 mpy (or 0.004 ipy)

Question 5

Determine the Remaining Life for a shell course based on the following data.
tmin 6/2008 6/2017 11/2021 0.344” 0.422” 0.395” 0.368”

A. 3 years
B. 4 years
C. 6 years
D. 9 years

Answer 5

B. 4 years (7.2.2 – see calc pg 54)

Calculate Long Term Corrosion Rate:
Time Period = 2021 11/12 – 2008 6/12 = 2021.92 – 2008.5 = 13.42 yrs
Corr Rate = Metal Lost / Time = (422 – 368) / 13.42 = 54 / 13.42 = 4 mpy (or 0.004 ipy)

Calculate Short Term Corrosion Rate:
Time Period = 2021-11/12 – 2017-6/12 = 2021.92 – 2017.5 = 4.42 yrs Corr Rate = Metal Lost / Time = (395 – 368) / 4.42 = 27 / 4.42 = 6.1 mpy (or 0.0061 ipy)

Select Controlling Corrosion Rate:
Larger of Long or Short = 6.1 mpy

Calculate Remaining Life: Life = Remain Corr Allowance / Rate = (368 – 344) / 6.1 = 3.94 yrs

Round up to 4 yrs

Question 6

In the tank construction code, API 650, the needed shell thickness are calculated. Which of the follow statements is correct?

A. Calculations are based on a 4-to-1 safety factor.
B. One calculation applies to all courses. (one tmin for the entire shell)
C. In most cases, the tmin calculate actually has some excess thickness.
D. The formula always used is called the Variable-Design-Point method.

Answer 6

C. In most cases, the tmin calculate actually has some excess thickness. (7.3.1.2)

Question 7

For new tanks built to API 650, the new thickness for the shell plates:

A. should never be less than ½”.
B. considers only the shell stresses resulting from the product.
C. considers only the shell stresses resulting from the hydrotest water.
D. considers both shell stresses resulting from the product & the hydro water.

Answer 7

D. considers both shell stresses resulting from the product & the hydro water. (7.3.1.3)

Question 8

While in operation, which tank component has a low membrane stress?

A. Bottom plates away from the critical zone and any annular plates
B. Annular plate
C. Bulged area on the shell
D. Nozzle-to-shell weld on a tank product nozzle
E. Shell vertical welds

Answer 8

A. Bottom plates away from the critical zone and any annular plates (7.3.1.3)

Question 9

The Variable-Design-Point method is always used to calculate the tmin of:

A. annular plates.
B. nozzles.
C. tank shells over 200’ in diameter.
D. all tank shells.

Answer 9

C. tank shells over 200’ in diameter. (7.3.1.3)

Question 10

If a tank is subject to external pressure (a vacuum), the shell tmin should be calculated using:

A. API 650’s 1-foot method.
B. API 650’s Variable-Design-Point method.
C. API 653’s Annex H.
D. API 650’s Annex V.

Answer 10

D. API 650’s Annex V. (7.3.1.3)

Question 11

A large area on a shell course is corroded below acceptable limits. Which of the following is not an acceptable option?

A. Change to a product with a lower specific gravity
B. Coat the corroded area with a lining
C. Lower the fill height
D. Replace the corroded area

Answer 11

B. Coat the corroded area with a lining (7.3.1.4)

Question 12

An isolated deep pit in the shell:

A. does not appreciably weaken the shell.
B. must always be repaired.
C. never needs to be repaired. D. should be evaluated per API 580.

Answer 12

A. does not appreciably weaken the shell. (7.3.2.1)

Question 13

Neither API 650 or API 653 have a method for determining the minimum required thickness of a tank’s:

A. annular plates.
B. floor plates.
C. nozzles.
D. shell plates.

Answer 13

C. nozzles. (7.3.2.2)

Question 14

Roof supports are normally:

A. designed per AISC’s Steel Construction Manual.
B. designed per API 650.
C. made from 3/16” steel.
D. made from pipe.

Answer 14

A. designed per AISC’s Steel Construction Manual. (7.3.2.3)

Question 15

The Internal Inspection interval in API 653 is normally controlled by the corrosion on the:

A. bottom.
B. nozzles.
C. shell.
D. thinnest component.

Answer 15

A. bottom. (7.4.1)

Question 16

What is an acceptable way of obtaining a suggested corrosion rate for tank components?

A. Take a wild guess and run with it!
B. Obtain corrosion rates from a Professional Engineer
C. Obtain corrosion rates from NACE publications
D. Use corrosion rates from tanks in Similar Service

Answer 16

D. Use corrosion rates from tanks in Similar Service (7.4.1)

Question 17

Similar Service corrosion rate data for soil-side corrosion:

A. should be from the same site as the Candidate Tank.
B. is always higher than top-side corrosion rate.
C. is relatively easy to determine.
D. is determined by finding the highest soil-side rate at a facility and multiplying it by 1.3

Answer 17

A. should be from the same site as the Candidate Tank. (7.4.3.2)

Question 18

The top-side corrosion rate is normally the result of:

A. the corrosion from hydrocarbons stored in the tank.
B. the corrosion from “water bottoms”.
C. galvanic corrosion.
D. reaction with air when the tank is out-of-service.

Answer 18

B. the corrosion from “water bottoms”. (7.4.3.3)

Question 19

When using Similar Service to establish corrosion rates, what makes it difficult to obtain a similar-service soil-side corrosion rate?

A. Difficult to find a tank with similar product
B. Don’t know if foundations/sand pads are actually the same
C. Don’t know if CP is being used on either tank
D. Inspections can’t contrast top-side vs soil-side corrosion rates

Answer 19

B. Don’t know if foundations/sand pads are actually the same (7.4.2)

Question 20

Which of the following is often in the “water bottoms” and accelerates top-side corrosion?

A. Bismuth
B. Hydrogen
C. Pepper
D. Salt
E. Sulfur

Answer 20

D. Salt (7.4.3.3)

Question 21

Similar Service data is going to be used to analyze a tank bottom. Which of the following is true about the tank that is providing the Corrosion Rate Data?

A. This tank must be at the same site as the Candidate Tank.
B. The tank must contain exactly the same process as the Candidate Tank.
C. One tank may provide soil-side corrosion rate data, and another tank. provides top-side corrosion rate data.
D. One tank can always be found to provide the both the top-side and soil-side corrosion rate data

Answer 21

C. One tank may provide soil-side corrosion rate data, and another tank. provides top-side corrosion rate data. (7.4.3.4)

Question 22

Which document can be used during fitness for service assessments?

A. API 579
B. API 580
C. API 581
D. API 2201

Answer 22

A. API 579 (7.5)