Why the G101 reference matters
ASTM lists G101-04(2025) as an active guide for estimating the atmospheric corrosion resistance of low-alloy weathering steels. Its public summary describes estimation from short-term exposure data and relative resistance inferred from composition. That is useful background when assessing a material, but it does not convert a grade name into a guaranteed service life at every site.
The guide also warns that corrosion rates can rise when steel stays wet for long periods or is exposed to substantial salt and other corrosive contamination. An unpainted design therefore needs site-specific review as well as a material specification.
Turn the exposure question into a usable brief
| Site detail | What the buyer should show |
|---|---|
| Wet and dry cycling | Where surfaces can dry, and where water, dirt or leaves may remain. |
| Salt exposure | Distance from sea spray, deicing operations or process contaminants. |
| Drainage and runoff | Horizontal ledges, joints, contact with other materials and staining-sensitive areas. |
| Access for inspection | Which faces or crevices can be checked and maintained after installation. |
These fields help a supplier and the project team discuss the intended material and finish on the same basis. They do not replace engineering assessment or a corrosion prediction for the actual location.
Separate material identity from expected appearance
A rust-coloured photograph cannot verify the steel grade or prove that the protective layer will perform at a particular site. The purchase order should state the actual standard and grade, while the design documents address drainage, visible-face expectations and any coating decision. Ask for mill identification and inspection documents against the accepted material.
For additional background, read the patina guide, the coastal exposure guide and our A606 type-selection update. These are complementary checks: grade, delivered form and site conditions all matter.
Before accepting an unpainted proposal
- Send the project location and exposure description with the RFQ.
- Show joints, drainage paths and areas where moisture could collect.
- Confirm grade, standard edition, surface condition and inspection records.
- Agree who evaluates corrosion performance and maintenance expectations.
ASTM G101-04(2025) public guide summary
Reviewed 9 October 2026. This buyer note summarizes public guide information and is not a project-specific corrosion forecast.