Why one interval does not fit all

There is no single number for wire rope inspection intervals. The same rope on a crane making dozens of lifts a day and on a gate opened occasionally can degrade several times faster in one case than the other. The interval follows the duty, not the rope specification.

The factors include load size and variation, number of bends, sheave and drum diameter, corrosive environment, working temperature and shock. Where any one of these is severe, shorten the interval. They act together rather than adding up, and the severest factor usually sets the interval.

Where legislation or an industry standard sets a requirement for a particular machine, follow the stricter rule. The plant's own inspection history should also inform adjustments. Write down the reason for each change, so the next revision has something to go on.

What the pre-shift check covers

The pre-shift check is done by the operator and concentrates on conditions that affect safety during that shift. Look at how the rope lies on the drum: even, without jumping the groove, overlapping or slack turns. Poor spooling can develop into a jammed or tangled rope during the shift.

Look along the visible length for broken wires, loose strands, flattening, kinks and obvious corrosion, and at the terminations for looseness, cracks and deformation. Hooks, shackles and other fittings are part of the check. Mark a few fixed points on the rope so later checks compare like with like.

Run the machine empty once and listen for unusual friction; watch whether the rope runs smoothly over the sheaves and drum. If anything is wrong, stop and report it rather than working on. Note any judder or unusual noise as a lead for the periodic inspection.

Periodic inspection by duty class

Periodic inspection is done by a competent person, at an interval set by duty. The bands below are a common approach; the actual figures should follow the machine type, legislation and service history. Grading is not a guess: load, frequency, environment and the importance of the machine are weighed together.

Equipment that is heavy-duty, frequent, dusty or in wet corrosive conditions is typically inspected monthly; medium duty in normal conditions quarterly; light duty, dry and infrequent, every six to twelve months. Seasonal change counts too: a wet or cold season can justify a shorter interval.

Man-riding equipment, lifting slings and critical process equipment should be inspected more often than that, and at least as often as local regulations require.

• Heavy, frequent, harsh: typically monthly.
• Medium load, normal conditions: typically quarterly.
• Light, dry, infrequent: typically six to twelve months.
• Where regulations set a limit, follow the stricter one.

What to inspect

Broken wires: count them over one lay length and record the location and pattern. Broken wires concentrated in one strand or one section are more serious than an even spread. A rounded wire end means the break is old; a bright, fresh break may be recent.

Diameter: measure with a caliper in several directions and compare with nominal and with the previous record. A clear reduction may mean wear, corrosion or core damage. Measure at fixed points, usually sections clear of the ends and of the spots where the rope rests on sheaves.

Corrosion and deformation: look for rust spots, pitting, flattening, kinks, waviness and strand extrusion. At the terminations, check closely for cracks, slip and corrosion. A kink is permanent deformation; once it appears, assess the rope for discard rather than trying to straighten it and carry on.

Lubrication: check whether oil is present on the surface and in the strand gaps, and whether it has dried, emulsified or picked up dirt. Poor lubrication accelerates internal wear and corrosion. Clean the surface before adding oil, so the oil enters the gaps instead of sitting on top.

Records and trends

Every inspection should be recorded: date, inspector, machine number, rope specification and installation date, items checked and results. A record that says only 'normal' tells nothing about the trend. A photo or a sketch is sometimes clearer than words, especially for the position of broken wires and rust.

The value of records is in the trend. A broken-wire count rising month by month, a diameter falling at each measurement, a rust patch spreading: these say more about condition than any single reading. A trend needs enough history; on a new rope, wait for several inspections before reading much into it.

Keep the records in the machine file for shift handover, maintenance and replacement decisions. When the rope is replaced, the old records are a reference for what to expect from the new one. After a replacement, check the new rope more often for its first few inspections.

When non-destructive testing is needed

Visual inspection sees only the surface. Internal broken wires, deep corrosion and core damage need a non-destructive method, electromagnetic testing being the common one. Visual and NDT are complementary; neither replaces the other.

NDT is usually considered when visual inspection finds something whose extent cannot be judged; when the rope is close to discard criteria; at defined inspection points on critical or man-riding equipment; and after an overload, shock or incident. The test should cover the full length, with more closely spaced points in critical sections.

Non-destructive testing should be done by qualified personnel with proper equipment, and the results judged together with visual findings and history, not as the sole basis. The report should state method, points, results and conclusion, and be compared with the previous one.

• Visual findings whose extent is unclear.
• The rope is close to discard criteria.
• Critical equipment reaches a defined point.
• The rope has seen overload, shock or an incident.

Discard decisions and the data behind them

Discard decisions follow the standard and the service conditions. Broken wire count, loss of diameter, corrosion, deformation and termination damage each have limits, and reaching any one of them calls for retirement. Limits for the same item can differ between standards; apply the one that governs the machine.

Breaking strength is the base data. Design starts from minimum breaking strength and a safety factor; in service, degradation is assessed against the measured condition. If the actual breaking strength is below the nominal figure, the safety margin falls with it. The base figures are in the wire rope breaking strength data

If it is unclear whether a rope can stay in service, recalculate the safety factor. If the result is far from the original design, shorten the inspection interval or replace the rope early. To put the actual load and rope condition into the calculation, use the wire rope selector tool

Construction and technical figures should be checked item by item and used as the basis of the decision. Check nominal diameter, construction and surface condition together, so the right figures are used. The full tables are in the steel wire rope data tables

One-line rule

Check condition before each shift, watch trends at periodic inspections, use NDT at the key points; set the interval by duty, read the records for trend and apply the standard when judging.

Inspection is not about filling in a form; it is about finding the rope before it fails. A sensible interval and clear records give the replacement decision a basis. Treat inspection as part of routine maintenance, not a burden imposed by auditors.