A ditch magnet sees the fluid once. The coarse swarf sticks and the fines carry on. A high-gradient unit runs as a continuous recirculating slip-stream: modest capture per pass, compounded over hundreds of passes a shift, on a system that is already circulating anyway.
No single pass through any device is 100% efficient. What matters is how many passes you get. A ditch magnet gets one. A kidney loop on a live active system gets one every time the tank turns over, automatically, while the well is drilling.
Run the shift and watch the two bars separate. The left column is a ditch magnet: it does its work in the first few seconds and then nothing changes, because the fluid never comes back. The right column keeps grinding down.
At a modest 20% capture per pass, five passes reaches 67%, ten reaches 89%, twenty reaches 99%. That is not a claim about a better magnet. It is what happens to any repeated process with a fixed success rate.
A ditch magnet lives permanently in the "1 pass" column. That single structural fact is the entire difference between the two technologies.
The number in market is 97%: the share of ferrous wear debris captured from the fluid that passes through the unit, on a single pass, ferrous and entrained non-ferrous alike, down to and below half a micron.
Do not restate that as "97% of contamination removed from the mud system." That is a different quantity, it depends on how much of the system passes through the loop, and an engineer will take it apart in front of you. How fast the whole tank comes clean is the separate curve shown in panel 1, and it is always labelled as inventory cleared.
A magnetised particle in a field gradient experiences a body force proportional to its volume, its magnetisation, and the steepness of the field.
Balance that against Stokes drag and you get a migration velocity — how fast the particle crosses the fluid toward the element. Compare it to what gravity manages on the same particle and the gap is not close.
Magnetic force scales with particle volume, so it falls away as d³ for the very finest debris. Drag only falls as d. The ratio gets harder, not easier, as particles shrink.
That is precisely why high gradient and many passes both matter. Field strength alone is not the answer: you need an enormous ∇B right at the element surface, and you need the particle to come back and try again.
Anyone claiming a single-pass device that strips sub-micron ferrous from a full flow stream is describing something that does not balance.
Everything below stays inside the envelope of the approved comparison. The day-rate slider is clamped to the published range for the class you select and cannot be driven outside it.
The NPT figure is a contributor to the benefit range, not an addition to it. The comparison document is explicit: the indicative per-rig total already contains the NPT, consumable, fluid and asset-life lines. Adding them together is the easiest way to get caught overstating, and it is the first thing a CFO will test.
Benefit scales linearly with rig count here, which is a simplification. A fleet rollout carries shared costs and learning effects the comparison document does not model, so a large-fleet number will read high. Use the per-rig range in anything public.
Removes roughly 48 manual interventions per day at the flowline, about 17,500 a year. Each one is a hands-on handling of ferrous debris near rotating and flowing equipment, with the usual lifting, pinch-point, slip and sharp-edge exposure.
Fully automatic operation means no operator contact with the captured contamination at all. Fewer manual tasks means fewer chances for a recordable incident, and a single recordable commonly runs into tens of thousands in direct cost and several times that once indirect costs are counted.
Cleaner fluid needs less dilution. Vendor field data shows 40% to 60% less mud dilution, which means proportionally less waste fluid generated, hauled and disposed of.
Fewer waste-haul trips and offshore supply runs lowers fuel use and associated CO₂. The magnetic elements are reusable, so there is no spent filter-media waste stream as there is with consumable mechanical filtration.
Public assets show the range. The single-point number belongs in a conversation where the assumptions can be stated out loud.
A different quantity to capture per pass. This is how fast the active system comes clean on a conservative 15% slip-stream at 2.14 turnovers an hour.
Element efficiency against particle size. Capture falls with size, which is the honest limit of the technology.