Camera inspection of a pipe under pressure without draining

A 700 mm gate valve will not seat, the main holds 4.5 barg, the water is still, and draining the system is off the table. That rules out pulling the valve and leaves one practical route: bring the camera to the valve through a valved opening in the live pipe. This guide walks the decisions in the order you meet them. The way in, the pressure ratings to demand, the thrust the seal must take, the pixels you need on the seat face, the lighting that survives a wet bore, and the point where flushing beats imaging. The arithmetic uses this line's numbers, so you can substitute your own pressure and bore and re-run it.

Can you inspect a pipe under pressure without draining it?

Yes: with zero flow, a pressure-rated push or pan-and-tilt camera inserted through a valved branch inspects the line live. The 4.5 barg of static water exerts no flow force on the camera, so the only design duty is the seal's pressure rating.

Static water is the enabler. Drag on a submerged body rises with the square of velocity, so at zero flow the head sees only hydrostatic pressure. That pressure squeezes it equally from every side. A flooded, pressure-balanced body carries no net load from the squeeze. What remains is external pressure on the housings and thrust across the insertion seal, both plain rating problems. Soft water is a benign medium for seals and optics. Freezing and line stops stay as last resorts for cutting into the line; for looking, a valved entry is reversible — close the branch valve and the main is exactly as it was.

How do you get a camera into a live main?

Enter through an existing valved tapping point or order a hot tap. The contractor welds a branch and valve onto the live main and cuts the hole under pressure, which leaves you a gated doorway the camera passes through without draining anything.

Walk the line first: an existing tapping point, air valve or valved branch near the gate saves the entire tapping operation. If there is none, the technique is called hot tapping — a new branch connection made while the line stays in service. Your tapping contractor supplies the procedure, fittings and weld qualification; ask them for their references. The sequence in practice:

1. The tapping crew welds a reinforcing branch fitting and valve onto the live main and drills the hole under pressure, through the closed valve.
2. With the cutter retracted and the branch valve shut, the drilling machine comes off and a guide nozzle sized to the camera head goes on.
3. The camera enters through the open branch valve. Retrieval is the same path in reverse, with the branch closed before the head leaves the nozzle.

What pressure rating does the camera head need?

Every wetted part must carry a printed rating above the line pressure. For a 4.5 barg main, demand a camera head, cable, gland and insertion seal whose data sheets each read higher than 4.5 barg at water temperature — not a generic claim of suitability for water mains.

Ask for four barg figures separately: the camera head, the push cable or tether, the cable entry on the head, and the insertion seal or nozzle at the branch. Camera heads are rated for external pressure — water squeezing in — which is the direction that matters here. Ratings fall as temperature rises, so quote the water temperature with the pressure. The branch fitting, valve and tapping machine are the contractor's rated hardware; your camera only has to live downstream of their valve.

How much force does still water put on the seal?

The flooded camera body feels no net force at all. The only thrust is pressure acting across the seal face, and for an illustrative 60 mm diameter head that is about 1.3 kN — roughly 130 kgf — of axial blow-out load the gland has to hold.

Worked example, illustrative 60 mm head: p = 4.5 barg = 450,000 Pa; A = π × 0.060² / 4 = 0.00283 m²; F = 450,000 Pa × 0.00283 m² ≈ 1,270 N. The load scales with diameter squared: an 85 mm head sees π × 0.085² / 4 × 450,000 ≈ 2,550 N. That is why serious insertion seals are roller or capstan types. They carry the thrust on the branch hardware rather than the tether, and the crew never loads the push rod against a partly open branch valve.

What can the camera actually see in a 700 mm main?

From 150 mm away, a 6 mm lens on a 2/3-inch, 3 MP sensor covers about 220 mm of seat face at 0.11 mm per pixel. A 0.5 mm scoring mark then spans roughly five pixels — enough to judge seat condition and spot debris.

The seat ring sits near the pipe wall, but the operator controls standoff, and a push head can be worked in to roughly 150 mm off the seat face. Use that number in the optics math. Take an illustrative 2/3-inch sensor, 8.8 mm wide, at the 3 MP class: 2048 pixels across, so 8.8 / 2048 = 4.3 µm per pixel.

At f = 6 mm and WD = 150 mm: FOV = 8.8 × 150 / 6 = 220 mm; pixel footprint = 220 / 2048 = 0.107 mm; a 0.5 mm mark spans 0.5 / 0.107 ≈ 5 pixels. From the pipe axis at 350 mm the same 6 mm setting gives 8.8 × 350 / 6 = 513 mm, and the mark spans only about 2 pixels. So either walk the head in or zoom: at the 15 mm end, FOV = 8.8 × 350 / 15 ≈ 205 mm and the mark spans about 5 pixels again. Compact CCTV varifocal lenses cover both ends of that range on one head.

A 2/3-inch varifocal spanning 6–15 mm covers both standoffs from one head:

A 360-degree lens solves a different shot. It unwraps a ring of wall inside its printed working distance — 65 to 110 mm on the LS-TCL-0054 — so it suits a carrier that rides near the wall, not a view across the bore from the axis. It belongs to the fixed station below, not the seat verdict.

How do you light a wet bore for a usable image?

The camera head's own ring of LEDs lights the near wall. The far side of a 700 mm main needs the pan-tilt head aimed at the surface at an angle, because light from the nose returns as glare while diffuse reflections from the wall carry the detail.

Three habits decide the image. Keep the standoff short, since light crosses the water twice and turbidity eats contrast on both passes. Angle the illumination 30–45 degrees off the optical axis so the wet seat's specular reflection misses the lens — the same geometry set out in controlling glare during pipe internal surface inspection and the cylindrical bore inspection lighting and camera layout guide. If fine silt still washes out a white LED, IR often buys a little contrast back because scattering falls at longer wavelengths. Any close-range IR source should then meet the IEC 62471 exposure limits described in IR LED eye safety at close range.

A fixed station does better still with sequencing: light each zone for its own frame and the neighbours never wash the exposure. The special lights range — AOI, strobe, structured and custom-built — holds the odd shapes; the LS-SPC-0086 sequences 8 zones on a 150 mm ring from a 24 V supply.

When is a fixed inspection station the better answer?

Once the valved branch exists, a vented or zero-flow section can carry a permanent station built from machine-vision parts. That beats re-hiring a push camera every time the gate needs checking; a 360-degree lens on a retractable carrier does the routine wall survey.

If the gate must be watched every shutdown, build on the doorway the tap created. A carrier through the branch holds a 360-degree lens against the wall for the survey and a short varifocal for the seat; when the branch can be isolated and vented, no optic needs a pressure housing. Nothing in the catalog prints a pressure rating. Treat shop lenses and lights as components for the vented side of the valve or behind a rated window, and keep live under-pressure runs with the contractor's head.

The primer on inner wall, outer wall and bore imaging with a 360 degree inspection lens explains the unwrap geometry, and 360° inspection lenses for inside-bore defect checks covers the defect side. The 360-degree inspection lenses split the standoff bands:

The LS-PCL-0042 covers 12.5 to 50 mm on a 1/3-inch sensor; the LS-TCL-0054 spans 65 to 110 mm on 2/3-inch, so the carrier position picks the lens.

Can you jet the debris out while the camera is in there?

No: withdrawing the camera comes first. Throttling the valve to raise seat velocity turns still water into a jet and moves the problem from a seal calculation to erosion and vibration you cannot watch. Flush with the bore empty of tools, then re-inspect.

The flush that clears a seat is hydraulic, not optical. Throttle a healthy upstream valve until velocity through the leaking seat carries the debris off, run it a fixed time, restore normal flow, then re-image from the branch. Expect the debris downstream, and keep the throttle pass short — sustained high velocity through a partly closed seat erodes it. Treat it as a separate operation with its own sign-off, because none of the ratings and thrust numbers above describe a tool in a moving stream.

What do you check before booking the tap and the camera?

Before anyone welds, confirm the line pressure and medium in writing, pick a tapping point within reel reach of the valve, match the branch bore to the camera head diameter with clearance, and get the head's printed barg rating plus its cable entry detail.

• Line pressure, medium and temperature in writing — every rating and thrust number here hangs off the 4.5 barg figure.
• Pipe material, outside diameter and wall thickness — the tapping contractor sizes the branch fitting and valve from these.
• Branch-to-valve distance plus several metres for steering — the reel must cover it; long runs or tight bends call for a winched carrier instead of a push rod.
• Printed barg ratings for head, tether and cable entry separately — one blended number hides the weakest part.
• Branch bore versus head diameter — clearance for the guide nozzle, so the head never loads the branch valve.
• Bench image check at the planned standoff — a 0.5 mm line target should read about five pixels across; keep the frame as the reference for the seat verdict.

The decisions, per case. A one-off look at a stuck gate on a 4.5 barg main: an existing valved point or a hot tap, plus a contractor's pressure-rated pan-and-tilt push camera rated above line pressure. A gate that needs watching every shutdown: keep the valved branch and put a fixed, vented station behind it. Debris confirmed on the images: withdraw the tools, flush by throttling, re-image. To size the fixed-station optics, start in the lens finder, configure a lens against your standoff, and send unusual bore geometry through the contact page.