Petrochemical

Eighty percent of plant failures are corrosion, and corrosion is decided by the medium rather than the temperature. We size the grade on chloride content, pH and whether crevices exist, and put inspection and solution annealing into the certificate.

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Typical parts and material selection

Part	Grade	Surface / size	Watch out for
Atmospheric storage tank	304 / 316L	Plate 6–30 mm	Weld quality, bottom corrosion
Heat exchanger tube / tubesheet	316L / 2205	Plate 10–60 mm, tube Φ19–25	PREN, stress corrosion
Column internals / packing support	316L / 2205	3–12 mm	Crevice corrosion, stiffness
Process piping	316L / 904L	Seamless / welded tube	Intergranular corrosion, UT/RT
High-chloride service	2205 / 904L	Full range	PREN ≥ 34

These are the usual configurations. Actual selection depends on medium, temperature and welding method — the same part may move from 304 to 316L or 2205. Describing the service conditions is more useful than naming a grade.

Three real constraints in this industry

Calculate PREN before naming a grade

PREN = Cr + 3.3Mo + 16N. 316L is roughly 24–26, 2205 roughly 34–36. Above 200 ppm chloride and 60 °C, 316L stress-corrosion risk rises sharply and duplex becomes the safe choice.

Delivery condition fails more often than chemistry

Chemical plate must be solution annealed (1050–1100 °C, rapid quench) and pickled. Buying "as-rolled" and treating it yourself usually fails the intergranular test, and cannot be fixed on site.

Put the inspection standard in the contract

Tanks and exchangers normally require UT (EN 10160 S1/E1 or equivalent) plus RT. If it is not in the contract, demanding a re-test after delivery is extremely expensive.