Introduction
An RFQ that says GI coil, 0.45 x 1000, Z80 or Z140 OK does not freeze a coating. One mill quotes EN 10346 Z140. Another fills Z80 at the same FOB number and writes “equivalent zinc.” A third prints G90 on the proforma and Z140 on the EN 10204 3.1 MTC. Thickness can match. Spangle can match. The zinc on the strip will not.
This is a specification tear-down for importers who buy DX51D galvanized coil for roofing, cladding, ducts, and export stock. It is procurement guidance, not a substitute for the ordered edition of EN 10346, ASTM A653/A653M, JIS G 3302, EN 10143, or ISO 9223. Forming grade still lives on a separate line: G550 galvanized coil is a yield class, not a zinc class. Come back here when the mill changes the coating mass under those fields.
The Coating Line That Makes Three Quotes Incomparable
Quick Technical Summary (Featured Snippet Direct Answer): Z80, Z140, and Z275 name minimum zinc mass, total both sides, not microns on a PO and not 100% equivalent mill stock. Freeze the standard (EN 10346, ASTM A653, or JIS G 3302), the coating designation, and the test method (triple-spot versus single-spot) before comparing FOB prices.
The bid fails when the coating line is a nickname. Z275 is a mass. G90 is a mass in ounces. 20 um is a guidance thickness, not a weigh-strip-weigh result. If the RFQ leaves any of those three languages open, the least-defined compliant-looking offer can appear competitive without being comparable.
| Missing RFQ field | What the mill will fill | Why the three quotes cannot be ranked |
|---|---|---|
| Standard omitted (“GI / HDG coil”) | EN 10346, ASTM A653, or a mill card | Z140 and G60 are not the same test gate |
| Designation omitted (“heavy zinc”) | Z80, Z140, or leftover Z100 | Outdoor duty and indoor ducting share one price |
| Test method omitted | Triple-spot average, single-spot, or a handheld gauge | A passing micron photo can fail ASTM A653 Table 1 |
| Which surfaces | Total both sides vs one-side minimum | Differential coating hides a thin exposed face |
| ISO 9223 site class | Whatever zinc the mill already has | C2 indoor stock is sold into a C4 coastal PO |
Write the coating as a copy block, not as a conversation. The rest of this article is the field list that belongs on that block.
What Z80, Z140, And Z275 Actually Freeze
Coating designations on continuously galvanized sheet are minimum coating mass, total both sides, usually proved by a triple-spot test. They are not a promise that each face carries half the zinc, and they are not 100% equivalent across EN, ASTM, and JIS.
| Designation | System buyers actually write | Minimum total both sides (triple-spot) | Typical guidance thickness per side | Do not treat as |
|---|---|---|---|---|
| Z80 | Commercial offer; often JIS-style Z08 | 80 g/m2 if the mill accepts that code | About 5-6 um guidance only | An EN 10346:2015 listed zinc class |
| Z140 | EN 10346 Z140 | 140 g/m2 | About 10 um | ASTM A653M Z120 or Z180 |
| Z275 | EN 10346 Z275 / ASTM A653M Z275 | 275 g/m2 | About 20 um | A batch-galvanized ISO 1461 micron call-out |
| G60 | ASTM A653 G60 | 0.60 oz/ft2 (about 183 g/m2) | Guidance only | Z140 |
| G90 | ASTM A653 G90 | 0.90 oz/ft2 (about 275 g/m2) | About 20-21 um if the split is even | A free upgrade from Z140 |
SSAB and other mill product cards for EN 10346:2015 list zinc from Z100 to Z600, with Z140 at 140 g/m2 and Z275 at 275 g/m2, both as minimum total mass on both surfaces in the triple-spot test. Guidance thickness is just that: guidance. The purchase order should freeze grams per square metre (or oz/ft2), not a warehouse micron gun.
ASTM A653 Table 1 is stricter about how that mass is proved. For G90, the triple-spot average must reach 0.90 oz/ft2 total both sides, the single-spot total must reach 0.80 oz/ft2, and any one side is normally not less than 0.32 oz/ft2 (about 40% of the single-spot total). GalvInfo converts 1.00 oz/ft2 = 305 g/m2, so G90 sits next to Z275. Sitting next to is not identity. A mill that dual-stamps Z275 / G90 still has to pass the test method named on your PO.
Z80 is the field that leaks. Construction catalogs that publish EN 10346 zinc tables mark Z80 as not included in the standard and keep Z100 as the first listed class. Export offers still print Z80 because it is cheap, formable, and close to JIS Z08. If your drawing cites EN 10346, make the mill name Z100, Z140, or Z275. Do not let Z80 inherit the EN number.
Do not convert Z140 to G60 in a spreadsheet and call it closed. G60 is about 183 g/m2. Z140 is 140 g/m2. The ASTM family nearest Z140 on a mill card is often Z120 or G40, not G60. Confirm the ordered edition; do not invent a one-line equivalent.
ISO 9223 Corrosivity Belongs On The RFQ, Not As A Mill Nickname
Zinc life tracks thickness in a given atmosphere. That does not turn Z275 into a coastal warranty, and it does not turn ISO 9223 C5 into a coating code the mill can roll.
| ISO 9223 class buyers name | Typical atmosphere language | What a GI coil RFQ should freeze instead of a year-life slogan |
|---|---|---|
| C1-C2 | Heated indoor / rural inland | Z80 or Z100 only if the drawing is indoor and cut edges stay dry |
| C3 | Urban / light industrial / low-salinity coast | Z140 or Z275 as the project names; not “Z80 heavy zinc” |
| C4-C5 | Industrial wet / moderate-to-high chloride | Z275 is often still a light coil coating; ask whether AZ, ZM, or batch HDG is the specified system |
| CX | Offshore / extreme | Continuously galvanized DX51D coil is rarely the specified system |
Mill product literature that maps EN 10346 zinc to corrosivity is conservative compared with trade-floor slogans. One producer mapping hot-dip zinc to EN 55634-1 places Z275 (about 20 um per side) around C3 duty, not C5. Treat that as mill guidance, confirm the project specification, and do not buy a 25-year coastal story on a Z140 PI.
If the site is chloride-heavy, the next question is coating chemistry, not only mass. Zinc (GI), 55% aluminium-zinc, and zinc-aluminium-magnesium are different systems. This article freezes Z mass on galvanized coil. It does not convert Z275 into a Galvalume or ZAM substitute.
Paint does not rewrite the zinc line. A PPGI coil still needs the metallic coating named on the substrate (DX51D+Z140, DX51D+Z275, or the ordered class). RAL 9002 is a color target. It is not a coating mass.
Substrate Chemistry, Forming Grade, And Thickness Still Sit On The Same Coil
Coating mass sits on a steel substrate. A Z275 stamp does not freeze DX51D, and a DX51D stamp does not freeze Z275. Put both on the same RFQ line.
| Substrate family | Standard language | C % max (typical table) | Mn % max | P % max | S % max |
|---|---|---|---|---|---|
| DX51D | EN 10346 DX51D+Z | 0.18 | 1.20 | 0.12 | 0.045 |
| S550GD | EN 10346 S550GD+Z | 0.20 | 1.70 | 0.10 | 0.045 |
| SGCC | JIS G 3302 SGCC | Confirm ordered edition | Confirm | Confirm | Confirm |
| CS Type B | ASTM A653 CS Type B | Confirm ordered edition | Confirm | Confirm | Confirm |
Use the table as a reminder that chemistry belongs on the PO. Confirm the ordered edition of EN 10346; do not treat DX51D, SGCC, and CS Type B as 100% equivalent.
| Family | Yield / tensile direction (confirm ordered edition) | Elongation / forming | Coating note |
|---|---|---|---|
| DX51D+Z | Tensile often discussed as 270-500 MPa; no 550 MPa min | Elongation is the acceptance field for profiling and bending | Z80 to Z275 can all sit on this grade |
| SGCC | Commercial GI; not a 550 MPa class | Same job family as DX51D on many export offers | JIS coating codes (Z08, Z12, Z27) are not EN nicknames |
| S550GD+Z / mill G550 | Yield min 550 MPa class | Low leftover stretch; high-rib roofing | Zinc class is still a separate field |
| SGCH full hard | Full-hard GI, not DX51D | Poor lock-seam stretch | SGCH carbon steel coil is a hardness family, not a zinc family |
| Coil field | What to freeze on the PO | Typical export range (confirm mill card) | Bid failure if omitted |
|---|---|---|---|
| Thickness basis | Base metal or total coated product | 0.30-1.50 mm common for GI coil | 0.45 mm G550 rib vs 0.45 mm DX51D base metal |
| Thickness tolerance class | EN 10143 / ASTM A924 class as ordered | Special vs normal class | Mill ships the looser class at the same price |
| Width / edge | Mill edge or slit edge; width +0/-0 or named | 600-1250 mm common | Slit-edge camber on a lock-seam line |
| Coil ID / OD / mass | ID 508 mm or 610 mm; max OD; kg per coil | 3-8 MT on thin GI; 20GP payload 25-28 MT | Eye-to-wall coils that will not fit the cradle |
A first-hand pattern from Shandong export coils: the PI says DX51D+Z, Z80/Z140, 0.40 x 1000. The mill loads Z80 because the slash looked like a buyer option. The MTC coating column prints a total mass under 100 g/m2. The fabricator in a C3 industrial estate then argues white rust, because white rust is visible and zinc mass is not. Hold the coil at the mill if the PO named Z140 and the certificate cannot show it.
Surface, Packing, And MTC Fields That Must Name The Coating
Surface language is how a light coating hides. Zero spangle and regular spangle do not change Z140 into Z275. Passivation and oiling change white-rust risk in a 20GP; they do not add grams of zinc.
| Surface / coating field | Options to freeze | Why it belongs next to Z80 / Z140 / Z275 |
|---|---|---|
| Spangle | Zero / minimized / regular | Appearance only; not a mass upgrade |
| Surface quality | As-coated A / improved B (EN language) | Skin-pass for painting is not extra zinc |
| Passivation | Cr-free / chromated / none | Unpassivated Z275 still white-rusts in a hot container |
| Oiling | Dry / light oil | Dry coil + long sea transit is a packing claim waiting to happen |
| Differential coating | Equal both sides vs named g/m2 per face | A thin exposed face fails first |
| Packing field | Seaworthy default to name | Hold point |
|---|---|---|
| Wrap | VCI paper + plastic + outer steel sheet | Bare OD wrap on a rainy yard |
| Edge | Inner and outer metal edge protectors | Cut OD that starts white rust in week one |
| Straps | At least 3 circumferential + 4 radial steel straps | Collapsed eye after stuffing |
| Desiccant | Named silica-gel mass per coil | ”Anti-rust packing” with no packet count |
| Stowage | Eye-to-sky or eye-to-wall; wooden cradle; 1x20GP 25-28 MT | Mixed stowage that rubs the zinc off the OD |
| MTC 3.1 field | Must print | Reject / hold if |
|---|---|---|
| Standard + coating designation | EN 10346 Z140, ASTM A653 G90, or the PO string | ”GI” or “Z80/Z140” as a range |
| Coating mass | Total both sides, unit g/m2 or oz/ft2 | Micron-only remark with no mass |
| Test method | Triple-spot and/or single-spot as ordered | Warehouse gauge photo only |
| Heat / coil identity | Heat number matching stencil and packing list | Heat on MTC, different heat on tag |
| Substrate grade + mechanicals | DX51D / SGCC / CS plus tensile / elongation as ordered | Coating matches, grade swapped |
| Inspection representative | EN 10204 3.1 issuer independent of production | Unsigned mill list |
Third-party inspection belongs on the same hold. SGS, BV, or TUV can cut coupons for weigh-strip-weigh to ASTM A90/A90M and check that the average is the ordered class. A shiny OD is not that test. EN 10204 3.1 mill documentation practice is the paper trail; PSI is the coil-side check.
Copy Block For The Coating-Mass Purchase Order
Paste this block into the RFQ. Delete the options you do not want. Do not leave a slash between Z80 and Z275.
- Product: continuously hot-dip galvanized steel coil, not batch HDG after fabrication.
- Standard / grade: EN 10346 DX51D+Z (or ASTM A653 CS Type B / JIS G 3302 SGCC as the drawing names). Not dual-stamped against S550GD or mill G550 unless accepted.
- Coating designation: Z140 or Z275 or G90 — one code only. Z80 only if the drawing is indoor and the standard is not EN 10346.
- Coating test: minimum total both sides by triple-spot; single-spot gate as in the ordered ASTM A653 / EN 10346 table. Weigh-strip-weigh referee (ASTM A90/A90M or the EN method named).
- Split: equal both sides unless a differential coating is named per face.
- Surface: zero or regular spangle; Cr-free passivation; oiled or dry as named.
- Size: thickness (state base metal or total coated) x width x coil ID 508/610 mm; EN 10143 / ASTM A924 tolerance class.
- ISO 9223 site class on the RFQ header (C2 / C3 / C4), not as a mill zinc nickname.
- Documents: EN 10204 3.1 MTC with heat number, coating mass, test method, and substrate mechanicals. TPI coupons allowed.
- Packing / lot: VCI + edge guards + named strap count; 1 x 20GP (25-28 MT); dispatch 7-15 days for standard sizes.
If the mill answers with “Z80 equivalent to Z140” or “G90 / Z140 same,” the quote is not comparable. Send the block back with one coating code before anyone prices the coil family.
Conclusion
Z80, Z140, and Z275 are zinc-mass designations on continuously galvanized coil. They are not mill nicknames, not indoor/outdoor slogans, and not 100% equivalent across EN 10346, ASTM A653, and JIS G 3302. Freeze one designation, one test method, one substrate grade, and one ISO 9223 site class. Then read those four fields on the EN 10204 3.1 MTC before the coil is stuffed.
Planning an Order or Need a Technical Verification?
If you are sourcing galvanized steel coil (Z80 / Z140 / Z275 or G90) or you need the mill to confirm coating mass against a project atmosphere:
- Fast Technical Quote: Standard trial orders supported from 1 x 20GP container (25-28 MT) with 7-15 days dispatch for standard sizes. Submit grade, coating designation, thickness x width, and quantity via our Online RFQ Form.
- Quality Assurance: Every order is backed by genuine EN 10204 3.1 Mill Test Certificates with full heat-lot traceability. Third-party inspections (SGS, BV, TUV) are welcomed.
- Urgent Inquiries: Contact our Shandong export desk directly on WhatsApp at +86 151 5311 2221 for instant specification confirmation.
