1. Visual Inspection (Immediate Post-Cooling)
Check Double Bead Formation
- Acceptable: Uniform molten ring at pipe/fitting junction (minimum 1mm height)
- Reject: Irregular bead, incomplete bead formation (indicates cold joint)
Examine Color & Texture
- Normal: Smooth surface, consistent light brown color
- Reject:
- Pale yellow (underheated)
- Dark brown/black (overheated)
- Bubbles/cracks (contamination)
Verify Insertion Depth
- Measure with calipers against marked line
- Allowable tolerance: 0.5mm deviation
2. Tactile & Dimensional Verification
Joint Uniformity Test
| Tool | Method | Pass Standard |
|---|---|---|
| Contour gauge | Profile junction contour | Seamless transition |
| Calipers | Measure bead circumference | Diameter variation ≤5% |
Internal Deformation Check
- Manual inspection (finger sweep for DN≥25)
- Bore scope inspection for DN≤20
- Reject if:
- Internal bead reduces flow >10%
- Oval deformation exceeds 3%
3. Pressure Testing (Mandatory Validation)
Stage 1: Preliminary Air Test
- Apply 0.5 bar air pressure
- Coat joints with soap solution
- Pass: No bubbles after 10 minutes
Stage 2: Hydrostatic Pressure Test
| Tham số | Requirement |
|---|---|
| Test medium | Clean water at 20±5°C |
| Test pressure | 1.5 × system operating pressure |
| Duration | Minimum 1 hour (critical systems: 24h) |
| Acceptance | Pressure drop ≤0.2 bar |
Note: In freezing conditions, use glycol-based test fluids
4. Defect Analysis & Correction
| Lỗi | Nguyên nhân | Hành động khắc phục |
|---|---|---|
| Irregular bead profile | Uneven heating | Replace joint; recalibrate dies |
| Bead micro-bubbles | Moisture contamination | Dry components; re-clean with alcohol |
| Excessive pressure drop | Voids/cold joint | Cut out and replace section |
| Stress whitening | Premature handling | Add supports; retest |
5. Documentation Requirements
Maintain records of:
- Welder calibration certificates
- Material batch numbers (pipes + fittings)
- Time-temperature logs per joint
- Pressure test results with timestamps
- Inspector verification reports
Joints passing all checks meet industry standards for permanent installations.
Technical Principle: A properly fused PPR joint fails within the pipe material, never at the welded interface.
