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The U4 exam has 50 questions and runs 1 hours.
These 10 free U4 questions are organized by exam domain, so you can see how each part of the UST Cathodic Protection - U4 blueprint is tested. Reveal the answer and explanation under each question.
A steel UST with impressed-current protection is taken out of service for six weeks. Contents are removed using commonly employed practices, leaving 0.5 inch of residue. Under federal temporary-closure requirements, which statement about ongoing operation is correct?
Correct answer: C - Cathodic protection must continue, but release detection may be suspended while the tank is empty.
Two surveys appear to show improved protection: last year's ON potential was −0.91 V CSE at a marked location over the tank; today's is −1.14 V CSE near an anode. Rectifier output is unchanged, and the meter and reference electrode are verified. What must be corrected before interpreting this as a historical trend?
Correct answer: C - Repeat the ON measurement at the original marked location under comparable conditions.
A Wenner survey uses four equally spaced pins in a straight line, with penetration small relative to spacing. The measured result is 4,800 Ω·cm at a site with layered soil. In the anode-bed planning notes, that value represents:
Correct answer: B - The apparent resistivity of the ground sampled by the test geometry.
A steel tank's test procedure accepts at least 100 mV of polarization decay. All influencing CP sources are interrupted together, switching transients are excluded, and the CSE measurements are valid: ON −1,135 mV, instant-off −805 mV, and later −690 mV. A reviewer calls for increased output solely because instant-off is less negative than −850 mV. Which finding resolves that recommendation?
Correct answer: B - The 115 mV decay meets the applicable criterion; that increase is not justified.
Without disturbing the tank contact or CSE position, a tester alternates between two calibrated DC voltmeters while CP operation remains steady. Each exchange reproduces the same ON potentials: −640 mV with the 10 kΩ input meter and −910 mV with the 10 MΩ input meter. Both use the same verified lead polarity. Which mechanism explains the repeatable difference?
Correct answer: D - The lower input resistance loads the structure-to-reference measuring circuit.
The field sheet for a galvanic UST test reads: "Dedicated tank test lead severed; separate anode-to-tank connections intact; no alternative tank contact verified." The previous scheduled test passed. The next entry should call for:
Correct answer: D - Restoring a verified electrical contact to the tank, then measuring its protection.
A supplier proposes replacing specified magnesium anodes with the same total mass of zinc. For the initial comparison, assume the same steel operating potential and total circuit resistance. How should the claim of equivalent protective-current output be assessed?
Correct answer: B - Magnesium has greater driving voltage; equal mass does not establish equal current output.
An anode-life worksheet specifies 10 kg of metal, effective capacity of 1,100 Ah/kg, utilization of 0.80, and average current of 0.10 A. Effective capacity already includes current efficiency. A reviewer applies another 0.80 efficiency factor, obtains about eight years, and requests a larger anode for a nine-year charge-life requirement. Using 8,760 hours per year, identify the sound review finding.
Correct answer: A - About 10.0 years: remove duplicate efficiency; the charge-life requirement is met, but current output still needs verification.
For months, a rectifier has operated at 12 V and 2.2 A. Immediately after excavation crosses its field-cable route, output stabilizes at 12 V and 0 A. Independent instruments confirm both readings. The evidence most strongly points to:
Correct answer: A - An open anode or structure-return connection along the disturbed cable route.
During an authorized tank entry governed by OSHA's general-industry permit-space rule, the entrant's monitor rises from 3% to 12% LFL. The permit prohibits hazardous flammable atmospheres. Oxygen remains 20.9%, and the toxic-gas channels show no alarm. The attendant can increase ventilation from outside. What response is required now?
Correct answer: D - Order exit; allow reentry only after correction and renewed entry authorization.
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