Short answer
Stainless steel is a family of materials; 304, 316 and other grades do not behave the same in every environment. Fluid, chlorides, temperature, stress and connection geometry are evaluated together; the word 'stainless' is not a guarantee against corrosion.
Technical explanation
The protective surface layer is important to how stainless steel behaves; in certain environments, pitting, crevice or stress-related corrosion mechanisms can occur. The material grade and actual chemical composition should be taken from the product documentation. Confirming the grade number with a magnet test alone is not a suitable documentation method. The internal fluid and the external atmosphere can create different exposures. A material certificate also does not, on its own, confirm the full performance of the finished assembly.
Topic-specific checkpoints
| Item | Description |
|---|---|
| Grade | Actual material code and documentation |
| Environment | Internal fluid and external atmosphere |
| Mechanism | General, pitting or crevice corrosion |
| Assembly | Stress, surface and connection design |
How to evaluate it in practice
For a fitting in an outdoor area, add salty humidity and cleaning chemicals to the technical form, not just the fluid. When a grade change is proposed, ask in writing which damage mechanism it is intended to address. Record whether the corrosion is only on the outer surface, under the seal or in the flow path. On the documentation, verify the link between the material and batch information and the part delivered. Do not turn a general material advantage into unlimited field life. Do not give acceptance based on the word 'stainless' alone without knowing the stainless grade, the manufacturing form and the fluid/environmental conditions.
Original editorial recommendation; not a clause of a standard.
Frequently asked questions
Does a '316' marking mean the part is suitable for every chemical?
No. Suitability for the chemical's composition and the operating conditions must be evaluated separately.
Source coverage
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S086
Material Selection Guide and Additional Resources Swagelok · accessed 2026-10-19 Public sections: material selection, pitting, crevice and galvanic corrosion; product-specific alloy claims not generalized
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S098
Materials of Construction Swagelok · accessed 2026-10-19 Descriptions of corrosion mechanisms and material selection; quantitative limit tables not imported