PHMSA patrol intervals under 49 CFR 195.412: what the rule requires
If you operate a hazardous liquid line, the patrol interval you're working against is spelled out in 49 CFR 195.412(a). It's a specific number, and it's worth knowing exactly what it says before you build a patrol schedule around it.
What 195.412 actually says
The rule requires that each operator inspect the surface conditions on and immediately adjacent to the right-of-way at intervals not exceeding three weeks, with a minimum of 26 patrols per calendar year. Do the math on that and you land close to biweekly. The regulation sets a ceiling of three weeks and a floor of 26 patrols a year, and operators have some flexibility in how they space those 26 patrols across the calendar, as long as no gap runs past three weeks.
Patrols can be done on foot, by vehicle, by boat, or by aircraft. PHMSA doesn't mandate the method, just the coverage and the interval. What the inspector is looking for is also spelled out: indications of leaks, construction activity on or near the right-of-way, encroachments, and any other factors affecting safety and operation.
That last clause, encroachments, is where most right-of-way managers spend their attention, because it's the fastest-moving risk category on the list. A leak indication from last month is usually still there next month. A contractor's excavator six feet off your centerline is a problem that can appear and disappear inside a three-week window.
Where the regulatory floor stops being enough
The three-week ceiling tells you how often you're required to patrol. It doesn't tell you whether that's often enough for a given stretch of line. PHMSA builds in an escalation clause: 195.412(a) also requires more frequent patrols of areas with a history of encroachment, populated areas, or construction activity. Run your corridor through a growth corridor, a development zone, or anywhere you've had third-party contacts before, and the rule expects a tighter interval than the base one, measured against what's actually changing on the ground there.
This is the gap most right-of-way programs live in. A foot or aerial patrol every three weeks satisfies the letter of 195.412. But a new foundation pour, a drainage ditch dug across the ROW, or a utility crossing installed without a locate request can all happen and get backfilled inside that window. By the time the next scheduled patrol rolls through, the encroachment is either already built or already buried, and what should have been a stop-work call becomes a damage claim.
The honest answer to "how often should a right-of-way be patrolled" has two parts. Twenty-six times a year, at minimum, to stay compliant. Tighter than that, in practice, for any stretch where land use is changing. Most integrity teams already know which miles those are. The hard part is closing the gap between patrols without adding headcount or waiting for the next scheduled flyover.
Documentation that holds up
195.412 also expects records: what was patrolled, when, and what was found. An encroachment log that ties findings to milepost, with a date stamp, gives you something defensible if PHMSA asks to see your patrol history or if a third-party strike ends up in a post-incident review. A patrol report that says "right-of-way clear" with no supporting detail doesn't do much for you after the fact.
If your team is stretched between scheduled patrol windows and wants a way to catch what's changing on the ground in between them, Pipeline Encroachment reviews VHR imagery along your corridor every two weeks and produces a mileage-indexed log of new structures, excavations, and crossings inside the right-of-way, built to route straight to a patrol crew or landowner outreach.
Worth a look if your next encroachment is more likely to show up between patrols than during one.