Liquid and Vapor Piping Systems
What this domain covers
Piping is the most frequent release point on a UST system, so this domain tests materials, layout, containment, and the testing that proves the line is tight.
Core rules and concepts
- Common materials: flexible (often double-wall), fiberglass-reinforced plastic, and coated or galvanically protected steel. New and replaced piping must be secondarily contained and interstitial-monitored where the federal rule applies.
- Suction lines slope back to the tank so product drains and air cannot be trapped. Pressurized lines require a line leak detector and an annual operability check at the 3.0 gph test rate.
- A shear (impact) valve at the dispenser base and an emergency shutoff valve protect the line if a dispenser is struck.
- Sumps at the tank top, at transition points, and under dispensers must stay liquid-tight and clean.
- Vapor lines (Stage I balance or dual-point, Stage II where required) carry vapor, not product; they are not given product release detection but must be tight, sloped, and free of liquid traps.
- Steel components need dielectric isolation and cathodic protection testing.
Worked example
A pressurized line fails an annual 0.1 gph line tightness test. Before calling it a leak, the technician isolates the line at the shear valve and tank, confirms the line has been at rest long enough for thermal stabilization, and repeats the test with a calibrated device. A second failure is a suspected release: stop dispensing, investigate, and follow the reporting procedure rather than simply retesting until it passes.
Traps that cost marks
- Testing while product is moving or before temperatures equalize.
- Skipping the annual 3.0 gph line leak detector check because the ATG "already monitors" the line.
- Expecting vapor lines to have product release detection.
- Ignoring transition sumps that hide a failed entry boot.