In ASME B31.3, the number of welds that require visual inspection depends entirely on the Fluid Service Category designated for the piping system. Because visual inspection is the primary quality control method, the requirements are strict.
For the vast majority of process piping (Normal Fluid Service), 100% of the completed welds must be visually inspected.
| Fluid Service Category | Visual Inspection Requirement |
|---|---|
| Normal Fluid Service | 100% of all completed welds. |
| Category D (Low Risk) | Randomly selected (typically at least 5% or as specified). |
| Category M (Lethal/Toxic) | 100% of all fabrication. |
| Severe Cyclic Conditions | 100% of all fabrication. |
| High Pressure Service | High-Pressure Service |
Under Paragraph 341.4.1 for Normal Fluid Service, the inspector isn’t just looking at the finished bead. The code requires:
- 100% Visual Examination: Every completed weld must be checked for surface cracks, undercut, porosity, and proper reinforcement.
- In-Process Examination: A “sufficient number” of welds must be inspected during the process (randomly) to ensure the joint preparation, alignment, and welding procedures (WPS) are being followed.
While visual inspection is usually 100%, other types of NDE (Non-Destructive Examination) like Radiography (RT) often only require a 5% random sample.
However, if a defect is found in that 5%, ASME B31.3 triggers Progressive Sampling:
- Level 1: If 1 weld fails, you must inspect 2 additional welds of the same kind by the same welder.
- Level 2: If either of those fail, you must inspect 2 more welds.
- Level 3: If any of those fail, the entire lot (100% of the welds in that group) must be inspected, repaired, or replaced.