A ground-mount solar array asks its steel to do two opposite things at once: behave like a structure, holding torque, panel weight and wind load, and behave like a coating product, surviving 25 years of soil contact and weather without maintenance. The catalogue covers both halves, but they are bought in different forms - pipe for posts, beams for rafters and trackers, slit strip for rails, plate for brackets - and the coating decision differs for each layer. Setting the stack out in order prevents the commonest mistake, which is buying structure-quality steel with a coating meant for indoor appliances.

The stack, and the form each layer wants

A fixed-tilt structure divides into four layers. Posts or ground screws take the vertical load and the overturning moment; rafters or torque tubes span between posts; rails or purlins carry the modules; clamps and brackets connect everything. Each layer maps to a product form: pipe or H-section for posts, welded H-section steel for the larger spans, roll-formed strip for rails, and punched plate or deep-drawing coil for brackets. Buying all four layers from one coated-coil and section programme keeps the galvanizing system consistent across the array, which matters because a mixed coating scheme corrodes at its weakest member first.

Posts: pipe, galvanized or black

Driven and concreted posts come from the pipe family. The ASTM A53 structural pipe is specified from 1/2 to 36 inch nominal bore in SCH 40, 80 and 160, seamless or ERW, black or hot-dip galvanized, in lengths of 3 to 18 m. Grade A carries a minimum of 48,000 psi tensile and 30,000 psi yield; Grade B raises that to 60,000 psi and 35,000 psi, which is the usual post grade where wind loads are calculated rather than guessed. The specification is written for coiling, bending and flanging - the operations a post line actually performs - and mill test certificates issue to EN 10204 3.1B, which is the document a structural reviewer will ask for. The shorter A53 pipe listing covers the same specification for buyers ordering by size rather than schedule.

Beams and tracker structures

Larger arrays and tracker torque structures move up to sections. The ASTM A36 and A992 H-shaped steel comes welded in Q235B and Q345B with flanges 50 to 400 mm wide and webs 100 to 900 mm deep in 6 to 12 m lengths. The hot-rolled 50x150 H-beam - 50 mm flange, 150 mm deep - is the light purlin-and-rafter size, and the Q235 IPE 450 page explains the European equivalent: an IPE 450 is a parallel-leg I-beam about 450 mm deep, roughly Q235B in Chinese grade terms, with material options through S355JR. Where the soil or the site demands it, the hot-dip 300 galvanized H-beam ships pre-dipped in sections from 100x100 to 900x300 mm with webs of 4.5 to 21 mm and flanges to 35 mm - the 300 g/m² figure being the zinc mass the section carries into the ground line.

Rails: roll-formed from slit strip

Rails and C-purlins are roll-formed, and roll forming starts from strip. The DX51D+Z galvanized strip is specified at Z40 to Z275 with 200 to 550 N/mm² tensile and 16 to 30% elongation, on 3 to 10 t coils at 508 or 610 mm ID - the elongation band is what lets a rail line bend a lip without cracking the coating. For higher-strength rails, structural grades in the Q345 hot-rolled coil, 3 to 18 t coils in the usual 1000, 1250 and 1500 mm widths, form the heavier sections. Where reflectivity under the array matters, the cold-rolled aluzinc coil runs 30 to 1500 mm wide at a ±0.01 mm thickness tolerance with T-bend formability of 3T top and 4T back, and the AZ150 galvalume coil carries the 55% aluminium coating whose corrosion life the product pages rate at three times pure galvanizing, stable above 300 °C.

The coating arithmetic: pre-galvanized coil or hot-dip after fabrication

This is the decision that decides the maintenance bill. Pre-galvanized coil arrives coated at the mill: on the gsm explanation page, a coating mass converts at roughly 0.14 µm of zinc per g/m², so a Z275 order is about 38 µm of zinc across two faces, and the ASTM A653 structural coils can be ordered up to 600 g/m² for severe sites, with the SPGC Z350 coil programme carrying grades through DX56D+Z and S550GD. The weakness is the cut edge: every punched hole and saw cut in a roll-formed rail is bare steel until touched up. Hot-dip galvanizing after fabrication reverses the logic - the hot-dip galvanized coil specification describes the zinc-iron alloy layer that bonds metallurgically, and a post-dip covers inside and outside of a hollow post plus every cut edge. The rule of thumb that holds up in practice: roll-formed rails from pre-galv coil with Z275 or better, and anything that goes into the ground or gets welded, hot-dipped after fabrication.

Clamps, brackets and the stainless margin

Mid-clamps and end-clamps are stamped, not formed, which puts them on deep-drawing stock: the DX54D+Z coil is the drawing-quality end of the galvanized range, 0.12 to 6.0 mm thick, while the general galvanized steel plate covers 0.19 to 2 mm sheet up to 2500 mm wide for brackets and backers. On coastal and floating sites, hardware migrates to stainless: 304 and 304L pipe from 3 mm to 2200 mm outer diameter, square 304 tube from 10x10 mm upward, and the 304 stainless grade page, all starting from 1 t - a practical minimum for the fastener-adjacent parts of an otherwise carbon-steel array.

Fabrication, minimums and the order

The processing pages turn the material into parts before it ships: cutting and punching for the hole patterns that make rails and brackets site-fast, bending with its 180° and double-layer work for brackets and flashings, welding for post caps and torque-tube ends, all orderable through the galvanized processing product menu. Minimums and lead times differ by layer: galvanized coil from 5 t in 7 to 14 days, welded H-sections from 1 t inside 7 days, hot-rolled beams in 8 to 14 days, IPE sections at a 25 t minimum in 22 to 30 days, DX54D+Z at 25 t in about 30. State the coating mass by zone, the grade by calculated load, and which parts are to be hot-dipped after fabrication - those three lines on the enquiry are the difference between a mounting structure specified once and one revisited at year five.