How to Weld Stainless Steel Sanitary Tubing and Fittings

Understanding Sanitary Stainless Steel Tubing

Sanitary stainless steel tubing refers to pipes, tubes, and fittings made from stainless steel alloys. They are designed for use in sanitary applications where cleanliness and corrosion resistance are essential, such as in the food, beverage, pharmaceutical, biotech, and cosmetic industries.

The most common alloys used are 316L and 316Ti stainless steels due to their high corrosion resistance and excellent weldability. The 'L' denotes the low carbon content which minimizes carbide precipitation during welding. 316Ti contains titanium which stabilizes carbon and minimizes chromium carbide precipitation.

Properties of Sanitary Stainless Steel

Sanitary stainless tubing offers the following properties:

• High corrosion resistance
• Excellent formability and weldability
• Smooth interior surface with high polish
• Non-toxic and non-reactive surface
• High temperature resistance
• Durability and long service life

These properties allow them to be thoroughly cleaned and sterilized while limiting bacterial adhesion, minimizing fluid turbulence, and preventing cross contamination - critical factors for sanitary process systems.

Common Types of Welded Sanitary Fittings

Sanitary tubing systems utilize a range of specially fabricated welded fittings including:

• Elbows
• Tees
• Crosses
• Reducers
• Traps
• Couplings

Fittings must meet dimensional and finish requirements per ASME standards for sanitary applications. Each fitting component is normally welded with a continuous interior weld seam to create a smooth, crevice-free flow path.

How to Weld Stainless Sanitary Tubes and Fittings

Welding is the most common and reliable method for joining stainless steel sanitary tubing systems. The most suitable welding processes are:

TIG Welding

Tungsten inert gas (TIG) welding uses a non-consumable tungsten electrode and inert shielding gas to produce high quality welds. It allows precision control over heat input and can create smooth, clean full penetration welds for stainless tube/fitting joints. Key tips for TIG welding sanitary tubes include:

• Select an appropriate filler metal like ER316L wire to match the tubing base material
• Use 100% argon shielding gas for stainless
• Machine or manually clean surfaces prior to welding
• Use 1% thoriated tungsten electrodes, sharpened to a taper
• Use pulsed current for gap bridging capability
• Adjust parameters to achieve adequate penetration and fusion

Orbital TIG Welding

Orbital TIG systems like welding heads on carriages that rotate around tubing produce accurate, repeatable stainless pipe welds with excellent coverage and quality control. It helps achieve the difficult inside weld requirements of sanitary process systems. Some guidelines include:

• Secure tubes in proper misalignment fixtures
• Select optimal head/carriage size configurations
• Adjust torch angles and electrode setback distances
• Set welding parameters for full penetration
• Use purge dams or chambers for internal argon shielding

Autogenous Laser Beam Welding

Laser beam welding fuses metals using the concentrated heat energy of a focused laser beam. It has become a popular specialist technique for welding smaller diameter thin wall sanitary tubes down to 0.5mm thickness while avoiding distortion and discoloration.

The precise nature of laser welding produces smooth, internal capillary-free welds ideal for sanitary specifications. It can help maximize sterile process system efficiency and cleanability.

Post-Weld Inspection and Finishing

Following tube/fitting welding, proper inspection and finishing procedures must be conducted before installation to preserve sanitary integrity including steps like:

• Visually check internal/external weld appearance for flaws or contamination
• Perform dye penetrant, x-ray or pressure testing for leaks/defects
• Utilize mechanical abrasion and electropolishing for internal weld blending and surface smoothing
• Remove heat tinted areas near welds via passivation processes
• Conduct cleaning procedures like CIP (Clean-in-Place) as necessary

Careful post-weld processing ensures the stainless steel tubing network conforms to the stringent requirements and standards for hygienic process systems.

Conclusion

The manufacture of consistently cleanable and sterilizable stainless steel sanitary piping relies heavily on expertise in specialized welding methods like TIG, orbital TIG and laser techniques. Strict control over weld quality and finishing steps allows precision-made sanitary tube fittings and process systems to prevent contamination and support superior hygiene.

FAQs

What are common issues when welding stainless steel sanitary tubing?

Common welding issues include inadequate penetration, poor fusion, cracks, overlapping, inclusions, pitting corrosion, distortion and discolored heat tinted zones.

What causes cracks when welding thin-wall sanitary tubing?

Cracking often results from high heat input, fast cooling rates or contamination. Proper purging, filler selection, heat control and cleaning helps avoid cracking.

Why is surface finish important for sanitary fittings and welds?

Smooth surface finishes with minimal imperfections and blended weld seams are vital to prevent bacterial adhesion and ensure proper cleanability and sterilization.

What post-weld inspection methods check sanitary weld quality?

Common inspection methods are visual examination, dye penetrant testing to reveal cracks, pressure tests to identify leaks and x-ray radiography to detect internal defects.