Galvanized Coil Acceptance: The 6 Defects to Inspect Before You Pay

Once galvanized coil lands at your plant, disputes get expensive: freight is sunk, your press line is waiting, and the mill is 8,000 km away. The time to inspect is before payment release — at loading port or with a pre-shipment inspection company. Here are the six defects that account for most galvanized coil claims, and how to judge them.

1. Dross ridges / zinc protuberances

Raised lines or dots of zinc-iron dross from the pot bottom or sink rolls. Under EN 10162 surface classes, localized protuberances are permitted to a depth limit, but continuous ridge lines across a wrap band are rejectable for visible-part buyers. Photograph the coil edge-to-edge with a raking light — a torch laid along the surface at 15 degrees reveals every ridge.

2. Zinc pops / pick-up

Small bright spatter dots. A few scattered pops are normal in commercial surface class; dense pop fields indicate pot chemistry or wipe problems and will telegraph through paint on visible panels.

3. Wipe streaks and drag lines

Longitudinal thin-coating lines where air wiper nozzles contacted the strip, or roll drag marks. Streaks with coating below 60 percent of nominal are a coating-mass issue, not cosmetic — check with an XRF spot test, not by eye.

4. Roll marks (impressions)

Periodic impressions from sink or feed rolls, repeating every roll circumference. Cosmetic for hidden brackets, rejectable for exposed panels — measure the repeat pitch (it identifies which roll) in your claim.

5. Coating peeling / adhesion failure

Zinc flaking at bend radii. Test on a sample: form a 180-degree bend over a radius equal to one coil thickness; adhesion failure at this severity means a defective inhibition layer — reject the wrap, do not rework.

6. Shape: coil set, waviness, buckles

Center buckle and wavy edges come from tension or roll-force control in cold rolling, and stay after galvanizing. For blanking lines, request flatness spec (max waviness amplitude over 2 m) in your PO; for laser-welded tailor parts, coil set can exceed downstream flattener capability.

Documentation discipline

A claim that gets paid looks like: numbered photos plus location (wrap / coil head / metre mark) plus measurement (XRF coating values, depth gauge) plus the applicable surface class clause plus the MTC for that heat. Build the inspection certificate template into your PO before the first shipment — that single page is worth more than any post-facto argument.