Basic Piping Inspection Terminology: Top 17 Latest API RP 574 Practice Questions and Answers
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API currently lists API RP 574, 5th Edition, published in February 2024.
Q1. In the simplified Barlow formula used to determine pipe pressure-design thickness, what does the term S represent?
A. Internal design gauge pressure of the pipe, in psi
B. Pressure-design strength for internal pressure, in inches
C. Allowable unit stress at the design temperature, in psi
D. Maximum strain at the average operating temperature, in psi
Correct Answer: C. Allowable unit stress at the design temperature, in psi
Explanation:
The simplified Barlow thickness equation is:
In this equation, (S) is the allowable stress of the pipe material at the design temperature. The allowable stress generally changes with material specification and temperature.
Q2. At low pressures and temperatures, the thickness calculated using the Barlow formula may be so small that the pipe would have:
A. Ample structural strength
B. Insufficient structural strength
C. Adequate corrosion resistance
D. Excessive pressure strength
Correct Answer: B. Insufficient structural strength
Explanation:
The Barlow formula primarily calculates the thickness needed to resist internal pressure. At low pressure, the calculated thickness may not be sufficient to withstand mechanical loads, vibration, pipe-support loads, external forces or the pipe’s own weight. Structural minimum thickness must therefore also be considered.
Q3. A seamless NPS 12, ASTM A106 Grade A pipe operates at 300°F and 941 psi. The allowable stress is 16,000 psi. Using the simplified Barlow equation, what is the required pressure-design thickness?
A. 0.375 in.
B. 0.750 in.
C. 0.353 in.
D. 0.706 in.
Correct Answer: A. 0.375 in.
Explanation:
Rounded to three decimal places, the required thickness is 0.375 in. API piping inspectors are expected to calculate the minimum required thickness for internal pressure and apply applicable corrosion allowances.
Q4. A seamless NPS 6, ASTM A106 Grade A pipe operates at 300°F and 941 psi. The allowable stress is 16,000 psi. The owner-user requires a corrosion allowance of 0.100 in. What total thickness is required using the simplified Barlow equation?
A. 0.195 in.
B. 0.277 in.
C. 0.706 in.
D. 0.295 in.
Correct Answer: D. 0.295 in.
Explanation:
The outside diameter of NPS 6 pipe is 6.625 in.
Q5. A seamless NPS 8, ASTM A53 Grade B pipe operates at 700°F and 700 psi. The allowable stress is 16,500 psi. Its original measured thickness was 0.375 in., and its current thickness after six years is 0.300 in. Ignoring structural minimum thickness, what is its approximate remaining life?
A. 4.7 years
B. 9.4 years
C. 0 years
D. 10.4 years
Correct Answer: B. 9.4 years
Explanation:
Therefore, the calculated remaining life is approximately 9.4 years. The original 9.8-year answer does not precisely match the values stated in the question. API examination knowledge includes corrosion-rate and remaining-life calculations.
Q6. An inspector finds a locally thinned area in the body of an NPS 8, Class 600 gate valve. The valve body is ASTM A216 WCB material and operates at 700 psi and 750°F. Use an allowable stress of 12,700 psi, a casting factor of 1.0, a valve-body factor of 1.5, and a corrosion allowance of 0.125 in. What target thickness must be present?
A. 0.48 in.
B. 0.38 in.
C. 0.51 in.
D. 0.43 in.
Correct Answer: A. 0.48 in.
Explanation:
For valve Classes 150 through 2500, the simplified cylindrical thickness may be multiplied by 1.5 for evaluating the valve body.
Rounded to the nearest hundredth, the target thickness is 0.48 in. API RP 574 explains that valve-wall thickness is greater than simple-cylinder thickness because of valve geometry, mechanical loads, and stress concentrations.
Q7. When corrosion or erosion of a valve is anticipated, what should be done when the valve is installed?
A. Determine the valve’s severance thickness
B. Wait until retirement before taking measurements
C. Record reference thickness measurements
D. Perform measurements only after visible leakage occurs
Correct Answer: C. Record reference thickness measurements
Explanation:
Reference or baseline thickness readings should be taken at selected locations when the valve is installed. Future measurements can then be compared with the baseline readings to calculate metal loss, identify thinning trends, and estimate corrosion or erosion rates.
Q8. Which of the following would not normally be included in the inspection records for a piping system?
A. Original installation date and material specifications
B. Original and subsequent thickness measurements
C. Calculated retirement or minimum required thicknesses
D. Hydrostatic-test details for an unrelated pressure vessel
Correct Answer: D. Hydrostatic-test details for an unrelated pressure vessel
Explanation:
Piping records normally include piping identification, material information, installation data, thickness readings, inspection locations, repairs, alterations, and applicable minimum thickness calculations. Hydrostatic-test information for an unrelated pressure vessel belongs in that vessel’s records, not in the piping inspection file.
Q9. Accurate inspection records make it possible to evaluate the ________ of piping, valves and fittings.
A. Purchase cost
B. Service life
C. Manufacturer’s market share
D. Production capacity
Correct Answer: B. Service life
Explanation:
Historical thickness readings allow the inspector to determine corrosion rates and estimate remaining service life. Accurate records also support decisions regarding inspection intervals, repairs, replacements, and continued operation.
Q10. The initial record for an NPS 6 pipe shows a nominal thickness of 0.432 in. One year later, an ultrasonic reading is 0.378 in. A second ultrasonic reading taken another year later is also 0.378 in. The service is non-corrosive or only slightly corrosive. What is the most reasonable conclusion?
A. The original entry was nominal thickness, and the actual pipe wall was approximately 12.5% below nominal
B. The piping lost 0.054 in. during the first year and then stopped corroding
C. The ultrasonic instrument was necessarily defective
D. The installer necessarily used the wrong pipe schedule
Correct Answer: A. The original entry was nominal thickness, and the actual pipe wall was approximately 12.5% below nominal
Explanation:
The original value was marked as nominal rather than measured. Applying a 12.5% manufacturing under-tolerance:
0.432×0.875=0.378 in.
Because both subsequent UT readings were 0.378 in., the most reasonable conclusion is that the actual installed thickness was approximately 0.378 in. and little or no corrosion occurred.
Q11. While reviewing a piping thickness table, an inspector finds the letter “C” in the column headed “Method.” What does “C” normally indicate in this terminology system?
A. The pipe was inspected while cold
B. The reading was confirmed by another inspector
C. The thickness was measured using calipers
D. The inspection was performed at a corrosion-monitoring location
Correct Answer: C. The thickness was measured using calipers
Explanation:
The method column identifies the equipment or technique used for the thickness measurement. In this terminology system, “C” identifies a measurement taken using calipers. Other method abbreviations may be used for ultrasonic, radiographic, or other examination techniques.
Q12. Which of the following is not an important function of an accurate piping inspection sketch?
A. Identifying examination locations that may require future attention
B. Identifying systems and circuits by location, size, and material
C. Serving as a field data sheet for recording inspection information
D. None of the above
Correct Answer: D. None of the above
Explanation:
All three listed functions are important. An accurate sketch helps inspectors relocate examination points, understand piping-system configuration, and consistently record inspection findings during future inspections.
Q13. As soon as practicable after completing an inspection, the inspector should:
A. Review the inspection records and determine or schedule the next inspection
B. Require a hydrostatic test in every case
C. Sign every radiographic examination record
D. Replace every component showing measurable wall loss
Correct Answer: A. Review the inspection records and determine or schedule the next inspection
Explanation:
Inspection findings should be reviewed promptly so that corrosion rates, remaining life, repairs, and future inspection requirements can be evaluated. A hydrostatic test or component replacement is not automatically required after every inspection.
Q14. The Wenner four-pin method, soil bar, and soil box are soil-resistivity testing methods. They are not direct methods for determining which of the following?
A. Coating holidays only
B. All of the above
C. Pipe-to-soil potential only
D. Cathodic-protection acceptability only
Correct Answer: B. All of the above
Explanation:
These three methods measure soil resistivity. They do not directly locate coating holidays, measure pipe-to-soil potential, or independently establish whether a cathodic-protection system meets acceptance criteria. Separate survey instruments and evaluation criteria are required for those purposes.
Q15.A Wenner four-pin test uses pins spaced 2 ft apart and produces an (R) value of 6 ohms. Using the formula (\rho=191.5dR), what is the soil resistivity?
A. 3,500 Ω·cm
B. 6,000 Ω·cm
C. 2,298 Ω·cm
D. 8,000 Ω·cm
Correct Answer: C. 2,298 Ω·cm
Explanation:
The correct unit is ohm-centimetres, written as Ω·cm, not ohms per centimetre.
Q16.Which of the following is not a recommended consideration when using a soil bar?
A. Using a standard prod bar to form the initial hole
B. Avoiding the addition of water to the hole
C. Applying pressure to the soil bar after insertion
D. None of the above
Correct Answer: D. None of the above
Explanation:
All three practices are considerations when using a soil bar. A standard prod bar can form the opening; adding water should be avoided because it can alter the measured resistivity, and proper pressure helps establish good contact between the soil bar and surrounding soil.
Q17. Which of the following is an important consideration when collecting and testing a soil sample in a soil box?
A. Avoid contamination of the sample during handling and storage
B. Allow the soil sample to dry completely before testing
C. Add water until the lowest possible resistance is obtained
D. Treat the test as a direct measurement of pipe-to-soil potential
Correct Answer: A. Avoid contamination of the sample during handling and storage
Explanation:
The sample should remain representative of the soil at the inspection location. Contamination, moisture loss, or the addition of foreign material can change its electrical resistance and produce an inaccurate soil-resistivity result. A soil box measures the resistivity of the collected sample, not pipe-to-soil potential.