Writing and Qualifying a UT Procedure for Fixed Plant and Conveyors on Remote Sites

The essential variable list is the procedure

Everything else in a UT procedure is narrative; the essential variable list is the contract. Under ASME Section V Article 4 the table of essential and nonessential variables defines which changes require the procedure to be requalified and which merely require a revision. Weld and material configuration, thickness range, search unit type, frequency and angle, wedge, couplant, surface condition, calibration block, technique, reference level, scanning technique, and where encoded equipment is used the software and its version — these are the things a procedure genuinely fixes.

Writers get this backwards in one predictable way: they write generously to avoid being constrained. A thickness range of three to two hundred millimetres, any couplant, any surface condition, angles from forty-five to seventy degrees. That reads like flexibility and functions as a trap, because the qualification demonstration behind it covered one thickness, one couplant and one geometry, and the procedure now claims an envelope it never proved. An auditor who asks what evidence supports the upper end of that range gets silence.

The disciplined alternative is a narrow envelope with a stated extension path. Qualify what the plant actually has: the pulley shell thickness range that exists on site, the two couplants the stores will actually carry, the temperature band the site really works in, the surface condition achievable with the blasting equipment available. Then say in the procedure how the envelope gets extended when new plant arrives. A narrow, honest procedure is defensible; a wide, unproven one is a finding with a signature on it.

Finding the referencing document in an industry that often has none

Refinery and power UT procedures inherit a referencing code almost automatically. Mining does not. A conveyor gantry truss, a stacker boom, a mill shell, an apron feeder frame and a shovel dipper are structures, not pressure equipment, and outside the acid plant, autoclave or pressure oxidation circuit there may be no code that governs them at all. The examination gets bought anyway, because the failure consequence is a plant stoppage measured in days.

That creates a decision the procedure must make explicitly. Either the owner adopts a named code's criteria as a contractual basis — AWS D1.1 for structural welds is the usual and reasonable answer, with D1.5 where a client imposes bridge-quality criteria on a heavily loaded structure — or the criteria are derived from the component's actual stress state as engineering-critical acceptance limits. Both are legitimate. What is not legitimate is a procedure that describes a technique in detail and then reports indications against no stated acceptance basis, leaving the site to argue with itself about whether a recorded indication matters.

Where pressure equipment is in scope, the picture inverts and gets stricter. An autoclave in a pressure oxidation or high-pressure acid leach circuit, or a vessel in the acid plant, is registered pressure equipment. In the United States that pulls Section V and Section VIII into the procedure; in Canada it pulls in a provincial safety authority with its own registration and personnel expectations. A single site can therefore need two procedure families with genuinely different rules, and writing one document that pretends to cover both is where audits start.

Damage mechanisms drive the technique, not the other way round

The technique choice should fall out of the mechanism, and in mining the mechanisms are mechanical far more often than they are corrosive. High-cycle fatigue dominates: weld toe cracking on conveyor truss chords and diagonals, cracking at the end disc to shaft weld on pulleys, transverse fatigue at fillets and keyway run-outs on drive and gearbox shafts, cracking around mill shell bolt holes and at the shell-to-head junction, and fatigue in screen deck frames that live their whole life in resonance.

Wear and erosion produce a different examination entirely. Slurry lines, tailings pipelines, cyclone feed and mill discharge chutes lose wall from the inside, preferentially at bends, tees and any change of direction, and the resulting profile is nothing like general corrosion. A grid of spot thickness readings on a slurry bend will miss the eroded groove between the grid points. That scope wants corrosion mapping or at minimum a scan-based technique with a defined pitch justified against the expected wear geometry, and the procedure has to say so.

Then there is the repair history problem. Mine plant is repair-welded, often by site maintenance under production pressure, frequently on high-carbon or manganese-bearing material with limited preheat control. The resulting defects — root cracks, lack of side wall fusion in a narrow prepared groove, hydrogen cracking in the heat affected zone — are planar and unfavourably oriented for a casual angle beam scan. A procedure written for volumetric slag and porosity will pass welds it should not. Naming the expected defect types and orientations in the procedure, and choosing angles and scan directions to suit them, is the difference between an examination and a formality.

Reference reflectors, DAC, DGS and the argument for a mock-up

A distance amplitude correction curve built on side-drilled holes in a basic calibration block is the right tool for a butt weld in plate or pipe of comparable geometry and material. It is the wrong tool for a corner-trapped fatigue crack at a shaft fillet, where the reflector is planar, the geometry concentrates and redirects the beam, and the sound path runs through a changing section. The amplitude relationship between a broadside hole and that crack has no physical basis, and sizing derived from it is invented.

Distance gain size carries its own failure. DGS curves are tied to a specific probe's beam parameters, so a worn wedge, a rebuilt probe or a nominally equivalent unit from another supplier invalidates the setup without any visible symptom. DGS also assumes a reference — often a back wall — that must be genuinely available and genuinely representative. On a mill shell with heavy internal wear and liner bolt penetrations, the back wall is not a clean reference, and a DGS setup taken from a workshop block does not transfer.

The honest answer for critical mining geometries is a mock-up. Take a decommissioned pulley end, a section of shaft, a cut piece of trunnion or a representative truss node; introduce EDM notches at the depths and orientations the real cracks take; and qualify the technique on that. It costs one component and a workshop day, and it converts a procedure from a plausible document into a demonstrated capability. It also gives you a practical specimen for technician qualification, which is otherwise the hardest thing on a mine site to obtain.

Temperature, couplant and the physics of a remote site

North American mining spans a brutal environmental range. A conveyor gallery in northern Ontario or the Labrador Trough works at minus thirty-five in February; an open pit in Arizona or Nevada puts steel surfaces well past fifty degrees in July. Both extremes attack the procedure at the same point: the wedge and the couplant. Cross-linked polystyrene wedge material slows as it heats, and because the refracted angle follows from the wedge velocity, a nominal forty-five degree probe verified in a workshop refracts appreciably steeper on a hot surface. Plotted depth and surface distance move with it, and an indication gets placed in the wrong region of the weld.

Cold does the reverse and adds mechanical problems. Couplants thicken or freeze, cable insulation stiffens and cracks, battery capacity collapses, and the instrument's own temperature compensation may be outside its rated range. Technicians solve all of this informally — warming couplant in a pocket, working from a heated hut, switching to whatever gel remained liquid — and every one of those solutions is an undocumented departure from a qualified essential variable.

The remedy is to write the environment into the procedure rather than pretend it away. State the surface temperature band the technique was verified across and require exit point and angle verification at working temperature when the band is exceeded. Name more than one approved couplant and qualify each. Specify the surface preparation standard achievable with equipment the site actually owns. Require a calibration block on site rather than four hours away, and say what happens when the block is unavailable — because the real answer today is that the examination proceeds anyway.

What the qualification demonstration must prove

Qualification is not a signature ceremony. It is a recorded event in which the procedure, run by a technician of the level the procedure names, using the specified equipment and setup, is shown to detect the targets it claims on a specimen representative of the component. The specimen matters most. A demonstration on a flat plate coupon proves nothing about a procedure written for a curved shell with a weld cap left proud and a hundred and fifty millimetres of access on one side only.

The record has to include the uncomfortable parts. Which targets were found, at what amplitude, at what plotted position against their true position, and which were missed or mislocated. A demonstration report that lists only successes has quietly become a marketing document. Sizing error against the known reflector dimensions is equally important, because sizing is what the maintenance planner will act on when deciding whether the pulley runs to the next shutdown.

Witnessing and traceability finish the job. The demonstration should be witnessed and signed, the instrument and probe serial numbers recorded, the specimen retained and identified, and the resulting technique sheet issued as a controlled document tied to the procedure revision it qualifies. Retain the raw data. Two years later, when a crack is found in service in a location the procedure covered, the only way to answer whether the technique was capable is to go back to the demonstration file. If that file is a single page with a signature, the answer will be assumed against you.

Scan plans, coverage and encoded data on structures

A scan plan is the part of the procedure that converts intention into geometry. It states the beam angles, the scan surfaces, the index and scan directions, the required overlap, the standoff limits imposed by the actual component, and the volume each pass covers. On mine structures the constraint is almost always access: a truss node with a gusset in the way, a pulley end disc reachable only from inside the drum, a trunnion with a bearing housing occupying the ideal scan surface. Coverage that is theoretically available is not coverage that exists.

This is where honest procedures earn their keep. If the geometry allows examination of seventy percent of the weld volume, the scan plan should say seventy percent and identify which thirty percent is not examined. That statement is useful to the asset owner, who can then decide whether to accept the gap, cut access, or change the inspection strategy. A procedure that implies full coverage the geometry cannot deliver produces reports that quietly overstate what is known about the structure, and that overstatement is what gets relied on when a component is left in service.

Encoded phased array changes the record but not the discipline. Encoded data on a conveyor pulley weld or a mill shell seam gives you a permanent, reviewable dataset — genuinely valuable on a remote site where re-examination means mobilising a crew again. But the procedure must then address encoder calibration and verification, data quality criteria such as coupling loss limits, the file naming and archiving scheme, and the software version as an essential variable. Encoded data with no retained raw files is worse than manual data, because everyone believes it exists.

The findings that recur when a mining UT procedure is audited

First and most common: no transfer correction, on a procedure that requires it. Second: the calibration block does not represent the part in material, product form, heat treatment, thickness or curvature, and nobody has written down why the substitution is acceptable. Third: the procedure cites a code edition that is not the edition in the contract, usually because the document was written years earlier and the revision block was never touched.

Fourth, and specific to this industry: the acceptance criteria are absent or borrowed. A procedure written against ASME Section V technique is used to examine a structural weld whose contract calls for AWS criteria, or vice versa, and the report cites neither cleanly. Fifth: the technique sheet exists but the essential variable fields are blank or carry the words "as required", which converts a controlled document into a suggestion.

Sixth: personnel. The technician holds a valid UT Level II certificate but has no record of being qualified against this specific procedure or demonstrated on this specific technique. Method certification and procedure qualification are different things, and in mining — where a single technician might cover thickness surveys, structural welds, shafts and an autoclave in one rotation — the gap is wide. A procedure should state the level required, the technique-specific demonstration required, and the interval at which that demonstration is repeated. Closing these six items is usually two weeks of documentary work and one workshop day, and it removes most of what a client audit will find.

Bringing procedure and people together

A qualified procedure and a certified technician are two halves of the same claim. The written practice controls certification; the procedure controls execution; the link between them is the demonstration that this person can run this technique on this geometry. On mine sites that link is the piece most often missing, because certification is bought from a contractor and procedures are written by someone who never meets the crew.

Practically, that means procedure development should produce three artefacts, not one: the procedure itself, a technique sheet per component family that a technician can work from without interpretation, and a practical specimen with a known answer that can be used for both qualification and periodic reverification. The third artefact is what keeps the programme alive after the consultant leaves.

Atlantis develops and qualifies ultrasonic procedures for mining fixed plant and materials handling, prepares the mock-ups and technique sheets that go with them, and provides Level III approval and audit representation on technical questions. Engagements are scoped to the plant list rather than sold by the document. For a consultation on your conveyor, mill or shaft examination scope, or a quote covering procedure development and qualification, contact info@atlantisndt.com.

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