--- title: "weathering steel: Definition and Meaning | NPSA" description: "Weathering steel is a group of steel alloys that form a stable outer layer of rust, which removes the need for painting. U.S." url: https://npsa.preview.multisites.ai/glossary/weathering-steel publisher: National Portable Storage Association (NPSA) phone: "(816) 960-6552" email: info@npsa.org --- Materials and construction # weathering steel Weathering steel is a group of steel alloys that form a stable outer layer of rust, which removes the need for painting. U.S. Steel introduced it in 1933 under the COR-TEN name. It is widely used in intermodal containers, bridges and outdoor structures. ## Why it matters The name describes how the steel behaves: weather helps it build its own protective layer. The layer forms through repeated wetting and drying. It does not form well where the steel stays wet or in heavy sea salt air, so conditions matter. For container operators, this explains why a rusty-looking container can still be sound, while deep pitting or holes mean a problem. A common mistake is to confuse the surface look with the steel condition. Check for thin spots, cracks and seams. Weathering steel can also stain nearby concrete or siding with rust runoff. Put a pad or barrier under a container that sits on a finished surface. [Read: Container modifications for rental: Doors, windows, lock boxes and HVAC](https://npsa.preview.multisites.ai/guides/container-modifications) Definition source: [en.wikipedia.org](https://en.wikipedia.org/wiki/Weathering_steel) ## Related terms [### corten steel Corten steel is a weathering steel alloy used for the walls and roof of most standard shipping containers. It contains copper and chromium. When it is exposed to weather, it forms a stable, rust-like surface layer that protects the metal below. COR-TEN began as a trademarked name.](https://npsa.preview.multisites.ai/glossary/corten-steel)[### corrugated steel Corrugated steel is sheet steel pressed into a pattern of ridges and valleys. Shipping containers use it for the walls and roof. The ridges add stiffness, so a thin panel resists bending and racking forces during ocean transport, lifting and everyday handling.](https://npsa.preview.multisites.ai/glossary/corrugated-steel)[### 14 gauge steel 14 gauge steel is steel sheet about 0.0747 inch (1.9 mm) thick on the standard steel gauge scale. Many sources name 14 gauge corrugated corten steel for the walls and roof of a standard shipping container. Actual builds can vary by maker.](https://npsa.preview.multisites.ai/glossary/14-gauge-steel)[### container inspection A container inspection is a check of a container's outside, inside, doors, floor and roof for damage, leaks and wear. Buyers do it before purchase. Operators do it when units go out and come back. It can be a quick look or a formal review to a standard.](https://npsa.preview.multisites.ai/glossary/container-inspection)[### site preparation Site preparation is the work done on a spot before a container arrives. It includes clearing the access path, checking overhead room, making the ground firm and fairly level, and sometimes adding a gravel or stone base. The goal is a safe drop and a unit that sits flat.](https://npsa.preview.multisites.ai/glossary/site-preparation)[### gravel pad A gravel pad is a prepared base of crushed stone or gravel placed on the ground for a container to sit on. Conexwest calls a compacted gravel pad one of the most practical base options for many storage containers because it improves drainage and is generally easier to install than concrete.](https://npsa.preview.multisites.ai/glossary/gravel-pad) [All 220 terms](https://npsa.preview.multisites.ai/glossary) For the industry ## Grow your portable storage business with NPSA Members get event rates, the Community Forum, the directory listing and leads from this website. [Join NPSA](https://npsa.preview.multisites.ai/join-us)[See member benefits](https://npsa.preview.multisites.ai/member-benefits) Need storage? ## Get quotes from NPSA member companies Tell us what you need and where. A member company that serves your area will contact you. [Request a quote](https://npsa.preview.multisites.ai/request-a-quote)[Which unit do I need?](https://npsa.preview.multisites.ai/find-storage)