In industries where precision, hygiene, and durability are essential—such as pharmaceuticals, biotechnology, and food and beverage production—orbital welding has become the gold standard for joining stainless steel tubing and piping. This automated welding process ensures consistent, high-quality welds that meet stringent industry regulations.
However, not all orbital welds are created equal. To maintain product purity, prevent contamination, and ensure structural integrity, welds must meet strict acceptance criteria. In this blog, we will explore what makes an orbital weld acceptable, the key factors influencing weld quality, and the consequences of subpar welds.
What is Orbital Welding?
Orbital welding is an automated GTAW (Gas Tungsten Arc Welding) process that rotates the electrode around a fixed workpiece, producing a uniform weld without manual intervention. This method is widely used in high-purity piping systems due to its ability to create consistent, repeatable, and contamination-free welds.
Industries that rely on orbital welding include:
- Pharmaceuticals and Biotechnology (for sterile process piping)
- Food and Beverage (for sanitary stainless steel piping)
- Semiconductor Manufacturing (for ultra-pure gas delivery systems)
To ensure high-quality welds, industry standards such as ASME BPE (BioProcessing Equipment) and AWS D18.1 (Hygienic Tubing Welding) outline strict guidelines for acceptable orbital welds.
Characteristics of an Acceptable Orbital Weld
An acceptable orbital weld must meet several critical criteria related to appearance, structural integrity, and hygiene. Below are the key factors that define an ideal weld:
1. Proper Weld Profile
The weld should have a smooth, uniform bead with no excessive reinforcement or undercut.
Excessive convexity, undercutting, or an uneven bead can create dead legs, where bacteria and contaminants can accumulate.
2. Minimal Weld Bead Discoloration (Heat Tint)
Heat tint is caused by oxidation during welding. In high-purity industries, discoloration must be minimized because excessive oxidation can lead to:
- Increased surface roughness, which promotes bacterial growth
- Reduced corrosion resistance, compromising material integrity
- Lack of passive layer, reducing its corrosion resistance
Acceptable discoloration levels are typically defined by industry standards:
- Light straw or gold tint: Acceptable
- Blue, purple, or black tint: Unacceptable and requires rework (usually through mechanical polishing or electropolishing)
Proper purging with high-purity argon gas is essential to prevent oxidation and maintain the integrity of the weld.
3. Smooth Internal Weld Bead (ID – Inside Diameter)
The internal weld bead must be smooth and free of defects to ensure sanitary flow and prevent contamination buildup. Common defects to avoid include:
- Excessive root penetration, which can cause flow restrictions
- Lack of penetration, leading to weak joints and potential leaks
- Inclusions or porosity, which can harbor bacteria and compromise sterility
A properly executed orbital weld will have a consistent bead with minimal internal protrusion.
4. No Visible Defects (Cracks, Porosity, or Lack of Fusion)
A high-quality orbital weld should be free from visible defects such as:
- Cracks: Can compromise weld strength and cause leaks
- Porosity: Tiny gas pockets that weaken the weld and create contamination risks
- Lack of fusion: Incomplete bonding between the base metals, reducing structural integrity.
To detect defects, welds should undergo visual inspection, borescope examination, and non-destructive testing (NDT) as needed.
5. Controlled Surface Roughness (Ra Value)
In sanitary and high-purity applications, surface roughness (Ra) plays a crucial role in preventing microbial growth. Orbital welds should match the specified Ra value of the tubing, typically:
- ≤ 20 µin (0.5 µm) Ra for biotech and pharmaceutical applications.
- ≤ 30 µin (0.8 µm) Ra for food and beverage applications.
If needed, welds may be mechanically polished, electropolished, or passivated to meet surface finish requirements.
Consequences of Unacceptable Welds
Failing to meet orbital weld acceptance criteria can have serious consequences, including:
- Product Contamination: Poor weld quality can lead to bacterial growth, endangering product safety.
- Regulatory Non-Compliance: Failure to meet ASME BPE, FDA, or USDA standards can result in fines, recalls, or production shutdowns.
- Process Failures: Leaking or weak welds can cause costly downtime and equipment failures.
To prevent these issues, welds should be inspected using borescopes, X-ray analysis, or dye penetrant testing, depending on industry requirements.
Best Practices for Achieving Acceptable Orbital Welds
Ensuring high-quality orbital welds requires careful planning and execution. Here are some best practices to follow:
- Use High-Purity Argon for Purging: Prevents oxidation and discoloration inside the pipe.
- Optimize Weld Parameters: Adjust voltage, current, and travel speed to achieve proper penetration and bead profile.
- Perform Regular Equipment Maintenance: Ensure orbital weld heads and power supplies are in optimal condition.
- Follow Industry Standards: Adhere to ASME BPE, AWS D18.1, and ASTM specifications for weld quality.
- Conduct Thorough Inspections: Use borescopes, visual inspection, and NDT methods to verify weld quality.
Conclusion
In high-purity industries, the quality of orbital welds directly impacts product safety, process efficiency, and regulatory compliance. An acceptable orbital weld must have a smooth profile, minimal discoloration, no defects, and controlled surface roughness to ensure long-term performance and hygiene.
By following best practices and adhering to industry standards, manufacturers can achieve consistent, repeatable, and contamination-free welds, ensuring the integrity of their processing systems.
