JIELIQuality is the backbone of any piping system. At JIELI, every malleable iron fitting undergoes rigorous inspection before leaving our factory. This article outlines the key inspection methods and quality control procedures that ensure our fittings meet international standards.
1. Visual Inspection (外观检查)
The first step in quality control is a thorough visual examination. Each fitting is checked for:
- Surface defects: Cracks, sand holes, porosity, cold shuts, and surface slag
- Finish quality: Uniformity of black coating or hot-dip galvanized layer
- Thread condition: Clean, well-formed threads without burrs or damage
- Marking accuracy: Correct size, standard, and manufacturer markings
2. Dimensional Inspection (尺寸检测)
All fittings must conform to the dimensional requirements of the applicable standard (BS EN 10242, ASME B16.3, ISO 49, etc.). Key measurements include:
| Dimension | Instrument | Tolerance |
|---|---|---|
| Center-to-face (elbow/tee) | Vernier caliper / CMM | ±0.5 mm |
| Thread pitch diameter | Thread plug gauge (GO/NO-GO) | Per standard class |
| Overall length | Digital caliper | ±1.0 mm |
| Wall thickness | Ultrasonic thickness gauge | ≥ min. specified |
| Hexagon/ Square dimensions | Gauge / Caliper | ±0.3 mm |
3. Thread Gauge Inspection (螺纹规检验)
Thread quality is critical for leak-free connections. Every fitting is tested with:
- GO gauge: Must screw on freely for the full length of the thread
- NO-GO gauge: Must not screw on more than 2-3 turns
- Thread taper: Checked with ring gauges for NPT/BSPT taper threads
4. Mechanical Property Testing (机械性能测试)
Malleable iron fittings must demonstrate adequate strength and ductility:
| Test | Method | Standard Requirement |
|---|---|---|
| Tensile strength | Tensile testing machine | ≥ 300 MPa (min) |
| Elongation | Tensile testing | ≥ 6% (K330 / EN 10242) |
| Hardness | Brinell (HB) or Rockwell (HRB) | ≤ 150 HB |
| Burst pressure | Hydrostatic pressure test | ≥ 4× rated pressure |
5. Pressure Testing (压力测试)
For fittings used in high-pressure applications, hydrostatic pressure tests are conducted:
- Fittings are sealed and filled with water at 1.5× the rated working pressure
- Pressure is held for a minimum of 30 seconds
- No leakage, sweating, or deformation is permitted
- Typical test pressure: 450 PSI for 300 PSI rated fittings
6. Coating & Galvanizing Inspection (镀层检验)
Galvanized fittings are tested to ensure corrosion resistance:
- Coating thickness: Measured with magnetic thickness gauge — min 45 µm for hot-dip galvanized
- Uniformity: Visual check for bare spots, drips, or excess zinc
- Adhesion: Hammer test — coating must not flake or peel
- Salt spray test: 72-hour accelerated corrosion test for marine/coastal applications
7. Sampling & AQL Standards (抽样标准)
Our QC team follows ANSI/ASQ Z1.4 (AQL) sampling plans:
| Lot Size | Sample Size | Accept (Major Defects) | Reject |
|---|---|---|---|
| Up to 500 pcs | 20 pcs | 0 | 1 |
| 501 – 10,000 pcs | 80 pcs | 1 | 2 |
| 10,001+ pcs | 125 pcs | 2 | 3 |
Critical defects (cracks, leaks, wrong thread) have zero tolerance — any single defect results in full lot rejection.
8. Certificate of Compliance
Each shipment at JIELI is accompanied by a Certificate of Conformance (COC) that documents:
- Standard & specification applied
- Mechanical test results (tensile, elongation, hardness)
- Pressure test results
- Dimensional inspection records
- Heat/lot number traceability
By following these rigorous inspection procedures, we ensure that every JIELI fitting delivers reliable performance, safety, and longevity in the field.
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