Corrosion Resistance 2026: EN 1670 Grades 0–5, Salt Spray Hours, and What the Test Does Not Tell You

Corrosion is the only hardware failure that happens on a schedule. A lock either works or it does not; a finish degrades predictably, visibly, and in front of the person who signed the order.

It is also the property most often specified by material name rather than by grade — "stainless", as though that settled it — which is why a coastal project can be built entirely from stainless hardware and still be streaked with rust in eighteen months.

THE EN 1670 GRADES

EN 1670 classifies corrosion resistance in six grades, and each is defined by a duration in a neutral salt spray cabinet.

Grade 0 is not a failure. It is a declaration that the property was not claimed, and on an internal door in a dry building it is the honest and correct grade.

The grade appears as one digit inside the longer classification codes on EN-tested products — it is the corrosion digit in an EN 1935 hinge classification, in an EN 1906 handle classification, and in the classifications of most other EN hardware standards. A specification that quotes only the load grade or the durability grade has left the corrosion digit unspecified.

WHAT THE HOURS ACTUALLY MEAN

A neutral salt spray test puts the sample in a sealed cabinet at a controlled temperature and sprays it continuously with a salt solution. After the stated hours, the sample is examined for defined defects.

This is a comparative test, not a predictive one. 480 hours in a cabinet does not correspond to any particular number of years on a building, and nobody in the industry claims it does. What it gives you is a reliable ranking: a grade 5 product will outlast a grade 3 product in the same environment, by a margin the test does not quantify.

That limitation is worth stating plainly because the alternative — quoting salt spray hours as though they were a service life — is a claim that cannot be supported and that a knowledgeable buyer will discount.

THE NORTH AMERICAN SIDE

ASTM B117 is the standard practice for salt spray apparatus, and it is the method underneath most North American corrosion claims. ANSI/BHMA A156.18 covers materials and finishes and sets out the tests a finish has to pass, salt spray among them.

The two systems are testing the same physical phenomenon with closely related methods, but they package the result differently: EN gives you a single grade digit, A156.18 gives you a finish that has passed the requirements for its category.

For a cross-market specification, the workable approach is the same one that works for closers and hinges: state the environment rather than the grade. A supplier in either market can map "external, coastal, within 1km of open salt water" onto their own classification. Neither can reliably map the other's grade number.

THE THREE ENVIRONMENTS THAT DEFEAT A HABITUAL CHOICE

Coastal. Airborne chloride does not require immersion or even rain; it deposits on surfaces and concentrates as water evaporates. Hardware on a sheltered balcony facing the sea can corrode faster than hardware that gets rinsed by rain, because rinsing removes chloride and shelter concentrates it.

Swimming pools and their plant rooms. Chlorinated and especially brominated atmospheres attack some stainless grades in ways that ordinary marine exposure does not, and the failure mode — stress corrosion cracking in the fixings, not surface rust on the visible part — gives very little warning. Hardware in a pool hall is a specialist selection, not a coastal selection with extra hours.

Industrial and urban atmospheres carrying sulphur compounds. These attack copper alloys and some plated finishes disproportionately, which is why a brass finish that performs well on a rural building can look poor on an arterial road in a city.

In all three, the mistake is the same: treating corrosion as a single axis where more hours is always the answer. It is a set of different chemical attacks, and a grade is a general ranking rather than a guarantee against a specific one.

WHERE CORROSION ACTUALLY STARTS

Not usually on the face of the product. It starts at the places the finish is thinnest or absent.

Cut edges and machined faces, where a coating applied before machining has been cut through. Fixing holes and countersinks. The screws themselves, which are frequently specified to a lower grade than the product they hold — a stainless lever on a coastal door held by plated steel screws will bleed rust from the screw heads long before the lever shows anything.

Contact between dissimilar metals in the presence of moisture, which drives galvanic corrosion at the junction. A stainless plate fixed to an aluminium frame with the wrong fixings is a battery.

The practical rule that follows: specify the fixings to the same corrosion grade as the product. It is the cheapest line on the order and the most common place the specification silently drops a grade.

MAINTENANCE IS PART OF THE SPECIFICATION

Stainless steel is not inert; it is self-repairing, and it repairs itself using oxygen. A surface kept clean re-passivates. A surface under a film of salt, dust or building residue does not, which is why stainless hardware in a sheltered external position often does worse than the same hardware fully exposed.

Where a building owner will not or cannot rinse external hardware, that has to be part of the material decision at specification stage rather than a complaint at handover. A higher grade partially compensates for no maintenance. It does not replace it.

WHAT WE PUBLISH, AND WHAT WE DO NOT

Our product pages state material and finish as we supply them. Where a model has been tested to an EN 1670 grade or to a A156.18 finish requirement, the result is stated with the standard it was tested to.

Where a model has not been tested, no grade appears and no salt spray figure appears. A corrosion grade is a laboratory result on a specific sample of a specific finish, and quoting a number for an untested finish — even a conservative one, even one we believe — would be inventing a test result. Our position on invented specification numbers is the same here as it is on dimensions: an absent row is a question a buyer can ask, and a plausible row is a decision a buyer makes wrongly.