Accepting a Mixed Delivery of Tubes and Couplers
A supplier delivers 240 used galvanised steel scaffold tubes, 48.3 mm outside diameter and 3.2 mm nominal wall, plus 150 right-angle couplers, to a school refurbishment site. You are asked to accept or reject the lot before unloading is completed. Your inspection finds 18 tubes with dents up to 8 mm deep, 12 tubes with pitting about 1.5 mm deep near the ends, and 6 tubes bent about 20 mm over a 3 m length. Of the couplers, 9 have flattened or crossed threads, several bolts turn by hand only, and the only torque wrench on site has a calibration sticker dated 14 months ago with no calibration register. The storekeeper says rejecting the lot will delay the job by a week and asks you to 'accept with a note'.
1. State your acceptance criteria for the tubes and couplers and give a disposition for each defect group.
Read the worked answer
Acceptance is against the tube/coupler standard and the supplier's certificate, not against how much the site needs the material.
- Dents up to 8 mm: reject. A dent of that depth on a 48.3 × 3.2 mm tube is a large local deformation and a buckling initiator. Cut out the damaged section only if a competent person authorises it and the remaining length is still fit for purpose; otherwise tag and remove from site.
- Pitting about 1.5 mm deep: reject. That is roughly half the nominal wall thickness, so the effective section is no longer the one the design assumed. Surface rust that brushes off is different from pitting; pitting is a wall-loss defect.
- Bend of 20 mm over 3 m (about 1 in 150): reject. Straightness limits are much tighter than this; a bent tube will not align couplers and will induce eccentric load.
- Flattened or crossed threads on 9 couplers: reject those couplers. A coupler that cannot be tightened to the specified torque cannot develop its slip capacity.
- Hand-tight bolts: not a defect by themselves; they must be tightened to the specified torque during erection.
Record the counts, tag the rejected items separately, and issue a non-conformance to the supplier.
2. Explain how you would verify coupler tightening on site, given that the torque wrench is overdue for calibration.
Read the worked answer
An out-of-calibration torque wrench cannot be used as evidence. The sequence is:
- Quarantine the wrench and send it for calibration; obtain a certificate and record the due date in a register.
- Until it returns, use a calibrated spare or have the supplier's calibrated wrench on loan. Do not 'estimate by feel' and do not accept a wrench that has been dropped without checking.
- Set the wrench to the torque specified by the coupler manufacturer, commonly around 40 Nm for right-angle and swivel couplers; confirm the figure from the manufacturer's data rather than from memory.
- Check a sample across the scaffold: right-angle couplers at ledger-to-standard connections, swivel couplers at bracing, and joint pins/sleeves. Mark each checked coupler with paint or a tag so it is not re-checked or missed.
- Record the wrench serial number, setting, date, checker and result on the inspection form.
If any coupler slips or the bolt continues to turn without reaching torque, replace it rather than over-tightening.
3. Set out the storage and maintenance rules you would enforce so that this delivery does not degrade further on site.
Read the worked answer
The defects arrived partly because the material was stored badly before delivery, so storage is part of the technical answer.
- Lay tubes on timber bearers clear of the ground, with drainage, and keep them under cover or sheeted so water does not sit inside them. Open tube ends trap water and rust from the inside.
- Sort by condition and length; do not mix rejected tubes with accepted stock. Tag reject bins clearly.
- Store couplers in crates or bins, not in a heap on the ground; keep bolts lightly oiled and threads protected. Do not store couplers in contact with wet cement or acid.
- Inspect on receipt and before each issue; remove bent, dented, cracked or heavily pitted tubes from the rack immediately.
- Keep a materials register: quantity received, quantity rejected, certificate numbers, and calibration dates for torque wrenches.
- Return rejected items with a non-conformance report and do not sign the delivery note as fully accepted.