API 653 Exam Chapter 6

1.

Q1. API 653: isolated pitting
How many pits of less than half the minimum required wall thickness, each of 0.25 in diameter, are allowed in an 8 in vertical line of corrosion on a tank?

2.

Q2. API 653: joint efficiencies (unknown construction standard)
What is the weld joint efficiency factor for a tank built in 1950 with a single butt welded joint with a ‘back-up bar’? The construction standard is not known.

3.

Q3. API 653: allowable stress S
If the yield strength (Y) of a material of construction is 35 000 psi and the tensile strength (T) is 60 000 psi, what is the value of the maximum allowable stress for the bottom two courses of a tank made of this material?

4.

Q4. API 653: allowable stress for unspecified steel
What is the design strength of unspecified steel used in the top courses of a storage tank?

5.

Q5. API 653: calculation of the averaging length
The minimum shell thickness t2 (exclusive of isolated pits) in a tank of 100 ft diameter is measured at 0.375 in. What is the critical length over which the thickness readings should be averaged out?

6.

Q6. API 653: calculation of minimum acceptable shell thickness
A tank has the following dimensions:
Nominal tank diameter 150 ft
Total height of tank 30 ft
Maximum fill height 30 ft
Number of courses equally spaced 5
The specific gravity of contents 0.85
Construction code API 650 basic standard
5th edition
Material of construction A283 C
What is the minimum acceptable thickness tmin for the bottom
course? Use the ‘full course’ equation tmin = 2.6(H – 1)DG/SE

7.

Q7. API 653: hydro test height (entire course consideration)
An API 12C 15th edition tank of diameter 150 ft has a bottom course made of A285C. The measured minimum average thickness for the entire bottom course is 0.2 in. What is the maximum allowable fill height for hydro testing this tank?

8.

Q8. API 653: calculation of allowable t2 (including corrosion allowance)
A tank has an average minimum measured thickness (t1) of 0.5 in and has a design corrosion allowance of 0.125 in. What is the minimum allowable individual thickness (t2) of a corroded area anywhere, excluding any isolated pitting?

9.

Q9. API 653: bottom annular plate thickness
If the stress in the first course of a tank is 26 000 psi and the course is 1/2 in thick, what is the minimum thickness for the bottom annular plate?

10.

Q10. API 653: hydro test fill height for a complete tank
A tank is constructed to an unknown code but all the joints are butt welded. It is 120 ft in diameter and the material of construction is an unknown low carbon steel. There is localized corrosion on the bottom course and the minimum thickness is 0.25 in. What is the maximum fill height for hydro testing the complete tank?

11.

6.9 API 653 appendix B: tank bottom settlement: practice questions (set 2)

Q1. API 653: types of settlement
Shell settlement can be made up of three types. What are they?

12.

Q2. API 653: types of settlement
Which of these does not induce stresses in the tank structure (but may in the connections)?

13.

Q3. API 653: shell settlement
What shape does differential settlement follow?

14. Q4. API 653: maximum allowable deflection
Maximum allowable out-of-plane deflection S (ft) is given by the equation:
S< (L2 – Yx11) [2(ExH]
where
L = arc length (ft) between measurement points = 20 ft
Y = yield strength (psi) = 20 000 psi
E = Young’s modulus (psi) = 24×106 psi
H = tank height (ft) = 50 ft

What is the maximum allowable out-of-plane deflection S?

15.

Q5. API 653: shell settlement
In general, when is most settlement presumed to have occurred for (say) a 10-year-old tank that is showing settlement?

16.

Q6. API 653: edge settlement repairs
It is acceptable to repair the bottom-to-shell weld without further investigation by an experienced engineer as long as the actual settlement is not greater than:

17.

Q7. API 653: measured edge settlement
A tank which when new has the center of its bottom lower than its edges is called a:

18.

Q8. API 653: settlement
What are the ‘least squares fit’ method all about?

19.

Q9. API 653: settlement
What can be caused by rigid (planar) tilt?

20.

Q10. API 653: settlement
A lack of circularity at the top of a tank is typically a feature of: