Article
Chemical and petrochemical plants handle acids, alkalis, solvents, chlorides and hydrocarbons, often at high temperature. A single plant may use half a dozen stainless grades, each chosen for a particular stream.
Selection factors
- Chemical composition of the fluid, including trace contaminants like chlorides
- Temperature and pressure
- Concentration – many acids are far more aggressive at certain concentrations
- Velocity and erosion
- Shutdown conditions – moisture and polythionic acid can attack sensitised steel
Typical grade choices
| Service | Common grades |
|---|---|
| Mild chemicals, alkalis, solvents | 304L |
| Chlorides, organic acids, general process | 316L |
| Stronger acids, higher chlorides | 317L, 904L |
| Chlorides with high strength need | Duplex 2205, super duplex 2507 |
| High temperature (425–815 °C) | 321, 347, 321H, 347H |
| Very high temperature, oxidising | 309S, 310S |
| Nitric acid service | 304L with Huey test (ASTM A262 Practice C) |
Testing often requested
- Intergranular corrosion test (ASTM A262 Practice E or C)
- PMI for every alloy item
- Ferrite measurement for duplex and welds
- Radiography of welded fittings (WX class)
Information a supplier needs
Besides size, schedule and grade, share the project specification, required supplementary tests and certificate type at enquiry stage. It lets the supplier confirm availability and avoid substitutions later.
Frequently asked questions
Which stainless grade is most used in chemical plants?
316L is the most widely used, with 304L, 317L, 904L and duplex used for specific services.
Why is the Huey test used for nitric acid service?
ASTM A262 Practice C (boiling nitric acid) directly evaluates resistance to nitric acid attack.
Why are stabilised grades used in petrochemical units?
Grades like 321 and 347 resist sensitisation at high temperature and polythionic acid cracking during shutdowns.
Key takeaways
- Fluid, temperature, concentration and shutdown conditions drive selection.
- 316L is the workhorse; 317L, 904L and duplex handle tougher streams.
- Share project specs and test requirements at enquiry stage.
Need these products?
Sawariya Metal Industries supplies stainless steel pipes, flanges and buttweld pipe fittings from Mumbai to buyers in India and overseas. Send your size, grade, standard and quantity through our enquiry form and we will reply with a clear quotation and the test documents you need. You can also browse our stainless steel pipes, flanges and buttweld fittings.