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Stainless steel tanks — grades, surface finish, sanitary vs industrial, and procurement

Stainless steel tanks are specified wherever hygiene, corrosion resistance, or product purity is critical. Understanding the material grades, surface finish requirements, and application-specific standards is essential for effective procurement. Grade selection: - AISI 304 / EN 1.4301 (18-8 stainless): The most widely used grade. Excellent corrosion resistance for water, dairy, food, beverages, organic chemicals, and mild acids. Standard choice for food-grade water storage, brewing tanks, edible oil tanks, and pharmaceutical tanks where chloride exposure is minimal. - AISI 316L / EN 1.4404 (18-10-2 Mo, low carbon): Higher corrosion resistance than 304, particularly against chloride, salt water, acetic acid, and halide-containing process fluids. Specified for marine environments, coastal water tanks, chlorinated potable water systems, pharmaceutical API production, and aggressive chemical storage. The 'L' (low carbon) grade avoids sensitisation during welding and is mandatory for welded process vessels in pharmaceutical and high-purity applications. - AISI 316Ti / EN 1.4571 (Ti stabilised): Preferred in some European chemical and pharmaceutical specifications as a welded equivalent to 316L — used where elevated temperature service is required. Surface finish: - 2B (mill finish, cold rolled): Standard finish for industrial applications not requiring hygienic grade. Ra 0.4–0.8 μm. - BA (bright annealed): Mirror-like finish for aesthetic or low-adhesion applications. - No. 4 (brushed / satin): Common interior finish for food-grade tanks — easy to clean, Ra 0.6–0.8 μm. - Ra 0.4 μm (electropolished): Required for pharmaceutical, biotech, and high-purity sanitary applications. Minimises bacterial adhesion and supports CIP (clean-in-place) and SIP (sterilise-in-place) protocols. - Ra 0.2 μm electropolished: For parenteral pharmaceutical, semiconductor chemical, and ultra-pure water applications. Sanitary vs industrial tanks: Sanitary (hygienic) tanks comply with 3-A, EHEDG, FDA, or ASME BPE standards. Features include: crevice-free welded internal joints, full drain capability, spray ball or spray nozzle CIP provision, sanitary clamp connections (Tri-Clamp / DIN 11851), no internal pits or ledges where product can accumulate. Industrial grade tanks use standard flanged or threaded connections and do not require hygienic weld standards. Key standards: 3-A Sanitary Standards (dairy and food, US); EHEDG (European Hygienic Engineering and Design Group guidelines); ASME BPE (Bioprocessing Equipment, pharmaceutical USA); FDA 21 CFR (materials of construction for food contact); PED 2014/68/EU (pressure equipment, EU); ASME Section VIII Div 1 (pressure vessels, US). Procurement specifications: Grade (304/316L), capacity, configuration (vertical/horizontal/conical-bottom/jacketed), surface finish (Ra value), connection schedule (Tri-Clamp, DIN 11851, ASME BPE, or flanged), manhole type, insulation (if required), agitator provision, legs/skid, pressure rating, CIP/SIP provision, applicable standard (3-A, EHEDG, ASME BPE, PED).