API 510 Practice Questions, With Answers and Explanations

Answer: D, Both b and c. External-pressure design (UG-28) is a stability/buckling calculation based on Do/t, L/Do and the material's external pressure chart, which is entered at the design metal temperature because the modulus of elasticity falls as temperature rises. Corrosion allowance matters because the calculation must use the corroded (remaining) thickness, and a thinner shell buckles at lower pressure. Weld joint efficiency plays no part, since the shell is in compression and seam quality is not credited. (ASME VIII, UW, II (c))

Answer: C, Charpy V-notch only is acceptable. Section VIII, Div. 1 toughness rules (UG-84) accept only the Charpy V-notch impact test, run on specified specimen sets at the designated test temperature and judged against absorbed-energy and/or lateral-expansion acceptance criteria. The code specifies this one test so that results are directly comparable to its toughness curves and exemption rules. No other impact geometry is permitted as a substitute. (ASME VIII, UG - 84)

Answer: A, Ensure that welds around nozzles were inspected by PT or MT prior to commencement of test. UW-50 requires that, before a pneumatic test, all welds around openings and attachment welds of chambers and appurtenances that were not previously hydrostatically tested be examined by MT or PT. The reason is stored energy: a gas-filled vessel that fails releases far more energy than a water-filled one, so surface-breaking flaws must be ruled out before pressurization. Verifying that this surface NDE is complete is therefore a pre-test prerequisite the inspector checks before any gas is introduced. (ASME VIII, UG - 100)

Answer: B, 208.66 psi. Static head adds to the vessel pressure with depth: for a liquid of specific gravity 1.0, the head is 0.433 psi per foot. Twenty feet below the top gives 20 x 0.433 = 8.66 psi, so total pressure there is 200 + 8.66 = 208.66 psi. Inspectors must add liquid head to the design or test pressure when checking the lowest point of a vessel. (Body of Knowledge, 3 (d), page 2)

Answer: D, Permitted only if design or operating conditions do not permit use of water as test medium.. Section VIII, UG-100(a) allows a pneumatic test in place of hydrostatic only for vessels that are not designed or supported to be filled with water, or that cannot be dried and would be damaged by traces of the test liquid. The restriction exists because compressed gas stores far more energy than water, making brittle failure during test far more hazardous. It is a design/service-based permission, not a convenience choice. (ASME VIII, UG, 100 (a))

Answer: C, 200 psi. For a pneumatic test, Section VIII (UG-100) requires the pressure to be raised to the full test pressure, then reduced to the test pressure divided by 1.1 and held while the vessel is visually examined for leaks. With a test pressure of 220 psig, the inspection pressure is 220 / 1.1 = 200 psi. Examining at the reduced pressure limits the hazard to personnel standing near a gas-pressurized vessel. (ASME VIII, UG, 100 (d))

Answer: D, E is modulus of elasticity and does not depend on radiography. In UG-28 the symbol E is the modulus of elasticity of the material at design temperature, taken from the external-pressure charts in Section II, Part D; external-pressure thickness is governed by elastic/plastic buckling stability, not by weld quality. Joint efficiency (the E of UG-27) does not enter external-pressure calculations at all, because a shell collapsing inward is not controlled by the longitudinal weld's examination level. (ASME VIII, UG, 28, Step 7)

Answer: A, Shell outside diameter, thickness and unstiffened length. In UG-28 the factor A is the strain factor read from the geometry chart using only the ratios L/Do and Do/t, so it depends on outside diameter, thickness, and the unstiffened length between lines of support. Material and temperature enter the calculation only afterward, when A is carried into the applicable material chart to obtain factor B. Those external-pressure charts are published in ASME Section II, Part D, Subpart 3. (ASME VIII, UG, 28, Steps 2 and 3)

Answer: C, 7 mm. For an equal-leg fillet weld the stated size is the leg length, and the theoretical throat is the perpendicular distance from the root to the hypotenuse of that triangle, equal to 0.707 times the leg. For a 10 mm fillet this gives 0.707 x 10 = 7.07 mm, approximately 7 mm. The theoretical throat is the dimension used in fillet weld strength calculations. (Body of Knowledge)

Answer: C, Both (a) and (b). UW-16 and Fig. UW-16.1 illustrate acceptable nozzle attachment details, including nozzles inserted through the shell opening (set-in) and nozzles abutting the outside surface (set-on), with minimum weld sizes and throat dimensions given for each. Both constructions are acceptable provided the weld details, sizes, and required reinforcement comply with UW-16 and UG-37. (ASME VIII, UW, 16, Fig. UW 16.1)

Answer: A, 1% for shell I.D.. UG-80(a) limits out-of-roundness of a cylindrical shell under internal pressure: the difference between the maximum and minimum inside diameters at any cross section shall not exceed 1% of the nominal inside diameter. The check is made on diameters, and the reference dimension is the inside diameter. (ASME VIII, UG, 80 (a))

Answer: D, toughness. A notched-bar impact test (Charpy V-notch) deliberately introduces a stress concentration and loads it dynamically to characterize the material's resistance to crack initiation and propagation, i.e. its notch toughness. The absorbed energy, lateral expansion, or fracture appearance are simply the measured indicators of that toughness property. (General Knowledge)

Answer: B, 8.0 sq. inches. For a radial opening in a shell under internal pressure, the required reinforcement area is A = d × tr × F, where d is the finished diameter of the opening, tr the required shell thickness, and F = 1.0 for a radial nozzle. Here A = 8 in × 1.0 in × 1.0 = 8.0 sq in, which must be supplied by excess shell metal, excess nozzle metal, and weld metal within the reinforcement limits. Note the rule credits only metal inside those limits, and F can be reduced below 1.0 only for non-radial (hillside/lateral) openings in cylinders. (ASME VIII, UG - 37)

Answer: A, Due to process requirement. When the code (thickness, P-number, and service rules of UCS-56 and UW-40) does not mandate PWHT, any heat treatment performed is applied for reasons outside the construction code, typically a process or service requirement such as reducing residual stress and hardness to resist environmental cracking in wet H2S, amine, or caustic service. User's Design Specification or owner-user process requirements therefore drive such optional PWHT. (General Knowledge)

Answer: B, Till the MDR is signed. UW-51(c) requires the Manufacturer to retain the radiographs and the radiographic examination records, making them available to the Inspector, until the Manufacturer's Data Report has been signed by the Inspector. The retention obligation is tied to completion and certification of the vessel, not to a calendar period. (ASME VIII, UW, 51 c (1))

Answer: B, 330 psig, 6 steps. A pneumatic test is performed at a minimum of 1.1 times MAWP corrected by the stress ratio; with design and test temperature equal the ratio is 1.0, giving 1.1 × 300 = 330 psig. The pressure is then raised to one-half the test pressure (165 psig) as the first step, and increased in increments of one-tenth the test pressure (33 psig) until the full test pressure is reached: 165 psig plus five 33 psig increments. That is one first step plus five increments, so six steps, with the stepwise approach and intermediate holds required because stored energy in a gas test makes a sudden failure far more hazardous than in a hydrotest. (ASME VIII, UG, 100 (d))

Answer: B, Fatigue. Vibration imposes cyclic stress, and cyclic stress is what initiates and propagates fatigue cracks, typically at stress concentrations such as nozzle welds, attachment welds, small-bore connections and supports. Failure can occur well below the material's yield strength once enough cycles accumulate, so inspection focuses on crack detection at discontinuities using surface methods (MT/PT) rather than general thickness loss. (API 571, 3.43.1)

Answer: A, Accepted. Out-of-roundness of a cylindrical shell under internal pressure is limited so that the difference between maximum and minimum inside diameters at any cross section does not exceed 1% of the nominal inside diameter. Here the limit is 1% × 2200 = 22 mm, while the measured difference is 2215 − 2195 = 20 mm, so the shell is within tolerance and is accepted. The tolerance exists because excessive ovality creates bending stresses that the thin-shell membrane formulas do not account for. (ASME VIII-1, UG-80(a)(1))

Answer: D, All of the above. API 510 lets widely scattered pitting be disregarded provided all three limits hold together: remaining thickness at the bottom of the deepest pit is at least one-half the required wall, total pit area stays within 7 sq in inside any 8 in diameter circle, and the sum of pit dimensions along any straight line in that circle does not exceed 2 in. The three criteria work as a set, controlling depth, total metal loss and the risk that aligned pits link into a continuous groove. If any one limit is exceeded, the pitted area must be evaluated as a thickness-loss region rather than ignored. (API 510, 7.4.3)

Answer: B, 140 inches. A 2:1 ellipsoidal head has an inside depth of dish equal to one quarter of the vessel diameter, so each head adds 40/4 = 10 in. beyond the tangent line. Overall length = tangent-to-tangent length plus two head depths = 120 + 10 + 10 = 140 in. (straight flange is contained within the tangent-to-tangent dimension). (ASME VIII-1, UG-32(c))