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Welding is one of the most critical operations in sanitary piping system fabrication. A properly executed weld maintains the hygienic integrity of the system, while a poor weld creates crevices, rough surfaces, and potential contamination points. This guide covers orbital welding, manual TIG welding, weld inspection standards, and common defects.
Orbital Welding: An automated welding process where the welding head rotates 360° around the tube while the tube remains stationary. The weld parameters (current, travel speed, gas flow) are pre-programmed and controlled by a microprocessor. Provides consistent, repeatable weld quality.
Manual TIG (GTAW) Welding: A skilled welder controls the torch and filler rod manually. While experienced welders can produce excellent results, manual welding introduces variability in weld penetration, heat input, and travel speed.
Recommendation: For sanitary and high-purity applications, orbital welding is strongly preferred. Manual TIG welding may be acceptable for non-sanitary sections or when orbital equipment is not available.
| Standard | Application | Key Requirements |
|---|---|---|
| ASME BPE | Bio-processing, pharmaceutical | Internal weld bead Ra ≤ 0.8 μm, 100% borescope inspection, weld log required |
| 3-A | Dairy, food processing | Smooth internal surface, no crevices, drainable |
| ISO 5817 | General welding quality | Defect limits for various quality levels (B, C, D) |
Borescope Inspection: Visual inspection of the internal weld bead using a fiber-optic borescope. Required for ASME BPE compliance. The internal weld surface must be smooth, fully penetrated, and free of discoloration, pits, or cracks.
Surface Finish (Ra) Measurement: The internal weld bead surface finish must match the parent tube finish — typically Ra ≤ 0.8 μm for sanitary applications. Measured using a profilometer.
Hydrostatic Testing: Completed welds should be pressure tested at 1.5× rated pressure. For sanitary systems, hydrostatic testing is typically performed on completed sub-assemblies before installation.
Sugaring (Oxidation): Internal oxidation of the weld caused by inadequate inert gas purging. Results in rough, dark internal surface. Prevention: use high-purity argon purge gas at correct flow rate.
Lack of Penetration: Insufficient weld penetration leaves a crevice at the root. Creates a contamination trap. Prevention: set correct weld parameters (amperage, travel speed, gap).
Weld Bead Drop-through: Excessive penetration creates a protruding internal weld bead. Restricts flow and creates cleaning difficulty. Prevention: reduce amperage or increase travel speed.
Discoloration (Heat Tint): Blue or straw-colored oxidation adjacent to the weld. Indicates inadequate gas shielding. Prevention: ensure proper gas flow and torch setup.
Our factory is equipped with 3 automatic welding machines capable of orbital welding from 1/2" to 6" tube sizes. We perform 100% borescope inspection on all sanitary welds. Surface finish of internal weld beads is verified to meet Ra ≤ 0.8 μm (or better upon request) before product release.
Yes. Properly executed orbital welds with full penetration and smooth internal bead are considered the most hygienic connection method — even more hygienic than tri-clamp because there is no gasket or crevice. The internal weld bead must be smooth and free of defects to achieve this level of hygiene.
High-purity argon (99.99% or better) is standard. For the internal purge, an argon flow rate of 10-20 CFH (cubic feet per hour) is typical, depending on tube diameter. Some specifications require a trailing gas shield for the external weld zone on larger diameter tubes (>4").
Standard sanitary weld inspection includes: (1) Visual inspection of the external weld bead for uniformity, (2) Borescope inspection of the internal weld bead for smoothness and full penetration, (3) Surface finish (Ra) measurement of the internal weld area, (4) Hydrostatic or pneumatic pressure testing. For ASME BPE compliance, a complete weld log must be maintained.
For standard food and dairy applications, mechanical polishing of the weld area to Ra ≤ 0.8 μm is sufficient. For pharmaceutical and biotech applications, electropolishing after welding is recommended to restore the passive layer and achieve Ra ≤ 0.4 μm. ONEMO offers post-weld electropolishing services.
ASME BPE-2022 — Welding requirements for bio-processing equipment
ISO 5817 — Fusion-weld imperfections quality levels
3-A Sanitary Standards — Weld finish requirements
Contact: Pershing
Phone: +8615858821847
E-mail: info@onemoss.com
Whatsapp:+8615858821847
Add: 71 Liuzhai Section, Luodongnan, Yongzhong Street, Longwan District, Wenzhou City
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