This guide supports procurement discussion and does not replace the approved design code, materials-engineering review or project specification. Verify the current edition of every referenced standard.
Chemical name alone is not enough
Corrosion behaviour can change with concentration, temperature, impurities, aeration, velocity, deposits and shutdown conditions. A generic statement such as ‘acid service’ is not sufficient for material selection.
Stainless steel relies on a passive surface. Localised corrosion, general corrosion, stress-corrosion cracking and intergranular effects need different controls and may lead to different materials.
- Document normal, start-up, cleaning and upset conditions.
- Review both process-side and external exposure.
- Consider crevices, dead legs and heat-transfer surfaces.
- Approve material through the responsible process/materials authority.
Procurement must preserve the design intent
Once a material is selected, the purchase documents should control grade, product standard, heat treatment, dimensions, finish, testing and traceability. Fabrication should use approved procedures and avoid contamination.
For higher-alloy packages, confirm compatible fittings, flanges, filler metals and fasteners rather than treating the pipe as an isolated item.
Service review questions
| Area | Questions | Procurement output |
|---|---|---|
| Chemistry | Concentration, contaminants, pH, oxidising/reducing nature | Approved grade/UNS |
| Temperature | Normal, design and cleaning temperatures | Condition and material limits |
| Geometry | Crevices, deposits, stagnant zones | Design/material review |
| Fabrication | Welding, forming, heat treatment, cleaning | Procedure and finish requirements |
| Verification | Corrosion tests, PMI, MTC, inspection | Defined acceptance scope |
Common buyer questions.
Is 316L suitable for hydrochloric acid?+
Do not assume so. Suitability depends strongly on concentration, temperature, contaminants and equipment conditions and needs specialist review.
Why specify pickling or passivation?+
Controlled post-fabrication treatment can remove heat tint or contamination and support a clean passive surface; the exact requirement belongs in the fabrication specification.
When are nickel alloys considered?+
They may be evaluated for conditions beyond the useful range of common stainless grades, subject to chemistry-specific engineering assessment.
Standards and technical sources.
Links are provided for source context. Always use the edition required by the contract and approved project documents.
Nickel Institute — nickel in process engineeringworldstainless — corrosion properties of stainless steel