AS1528.1 Stainless Steel Sanitary Tubes

Manufacturing Process              The manufacturing process of ASTM A270 sanitary tubing, commonly used in hygienic applications like food, beverage, pharmaceutical, and dairy industries, involves several key steps to ensure high cleanliness, corrosion resistance, and smooth internal surfaces.  Here’s a detailed breakdown:  1. Material Selection – Grades: ASTM A270 covers austenitic stainless steels (e.g., 304/304L, 316/316L) and ferritic steels (e.g., 444). – Form: Starts with high-quality stainless steel coils or hollow billets. 2. Tube Formation 2.1 Welded Tubes (Most Common for Sanitary Applications) – Cold Rolling/Strip Preparation: Stainless steel strips are precision-rolled to required thickness.  – Forming: The strip is fed into a tube mill and gradually shaped into a cylindrical form via rollers. – Welding:   – TIG (Tungsten Inert Gas) Welding: Used for high-purity applications;  ensures a smooth, contamination-free weld.   – Laser Welding: For ultra-precise, minimal-heat-affected zones.   – Weld Seam Annealing & Polishing: The weld is annealed (heat-treated) to restore corrosion resistance and polished to match the parent material.  2.2 Seamless Tubes (Less Common, Higher Pressure Applications)  – Extrusion/Piercing: A billet is heated and pierced to form a hollow shell.  – Cold Drawing: The tube is drawn through dies to achieve precise dimensions and smooth surfaces. 3. Heat Treatment (Annealing)  – Tubes are annealed at 1900–2050°F (1040–1120°C) to relieve stresses and restore corrosion resistance.  – Rapid cooling (quenching) prevents carbide precipitation (critical for 316L/304L grades).   4. Finishing & Surface Treatment  – Pickling & Passivation: Acid bath (nitric/hydrofluoric) removes oxide layers and enhances chromium oxide passive layer.    – Electropolishing (Optional): Electrochemical process removes surface imperfections, improving cleanliness and corrosion resistance.  5. Internal Polishing  – Mechanical Polishing: Abrasive belts/buffing for Ra ≤ 15 µin (0.38 µm) or smoother (common for 3A sanitary standards).   – Electropolishing (Optional): Achieves Ra ≤ 5 µin (0.13 µm) for ultra-hygienic applications.    6. Cutting & End Finishing   – Precision-cut to length with square-cut ends or beveled edges for orbital welding.   – Sanitary Fittings: Ends may be expanded or swaged for tri-clamp, butt weld, or sanitary flanges.    7. Cleaning & Inspection     – Ultrasonic Cleaning: Removes residual contaminants.   – Non-Destructive Testing (NDT):    – Eddy Current/Ultrasonic Testing for defects.    – Hydrostatic/Pneumatic Testing for leaks.    – Dimensional Checks: OD, ID, wall thickness, and straightness per ASTM A270.   8. Certification & Packaging     – Mill Test Reports (MTRs) verify compliance with ASTM A270 (chemical composition, mechanical properties).     – Sterile Packaging: Tubes are sealed in plastic or protective caps to prevent contamination.