Testing of reducers shall cover four core aspects: dimensional accuracy, material compliance, structural integrity, and pressure resistance performance. Different test items correspond to different methods, and testing priorities shall be adjusted according to material (metal/plastic) and pressure class (high pressure/low pressure).
I. Material Testing: Ensuring Material Compliance
1. Chemical Composition Testing
- Test methods: spectrometer (portable/benchtop), X-ray fluorescence spectrometer (XRF)
- Test content: Verify the content of elements such as carbon (C), chromium (Cr), nickel (Ni), molybdenum (Mo) to meet material grade requirements (e.g. 20# steel, 304 stainless steel, PE100).
- Application: Random inspection of raw materials per batch to prevent material mixing (e.g. carbon steel used in place of stainless steel).
2. Mechanical Property Testing (for Metal Reducers)
- Test methods: tensile test, hardness test
- Test content:
- Tensile test: Sampling to determine tensile strength and yield strength (e.g. tensile strength of 20# steel ≥ 415 MPa).
- Hardness test: Measured with a Brinell hardness tester (HB); carbon steel ≤ 180 HB, stainless steel ≤ 200 HB.
- Application: One sample per batch for high-pressure reducers (PN ≥ 10 MPa).
II. Pressure Resistance Testing: Verifying Operational Safety
1. Hydrostatic Test (Core Test Item)
- Test equipment: hydrostatic testing machine, pressure gauge (accuracy ≥ Class 0.4)
- Test procedure:
- Plug both ends of the reducer, fill with water and completely vent air.
- Pressurize slowly to the test pressure (1.5 times the design pressure) and hold for 30 minutes.
- Inspect for no leakage and no deformation (no obvious plastic deformation for metal reducers, no rupture for plastic reducers).
- Acceptance criteria: No pressure drop, no leakage, and no visible deformation during pressure holding.
2. Pneumatic Tightness Test (for Reducers in Gas / Vacuum Pipelines)
- Test equipment: pneumatic tightness tester, soap solution
- Test procedure:
- Charge compressed air (or nitrogen) to the test pressure (1.15 times the design pressure).
- Hold pressure for 24 hours and apply soap solution to inspect joints/welds.
- Acceptance criteria: Pressure drop ≤ 1% and no bubble formation.
3. Burst Test (Type Test)
- Test method: Increase pressure gradually until the reducer ruptures, and record the burst pressure.
- Acceptance criteria: Burst pressure ≥ 2.5 times the design pressure.
- Application: Product qualification and batch sampling (1 piece per 1000 pieces).
III. Special Testing: Meeting Application Requirements
1. Wear Resistance Testing (for Reducers in Slurry / Particle-Containing Fluid Service)
- Test method: wear test bench (simulating particle erosion)
- Test content: Measure wear rate and verify adhesion of wear-resistant layers (e.g. ceramic lining).
- Acceptance criteria: Wear rate ≤ 0.1 mm per 1000 hours.
2. Aging Testing (for Plastic Reducers)
- Test methods: thermal aging test (100℃, 168 h), ultraviolet aging test
- Test content: Determine retention of tensile strength and elongation at break after aging.
- Acceptance criteria: Property retention rate ≥ 80%.
3. Soil Corrosion Testing (for Buried Reducers)
- Test method: soil corrosion test (simulating buried service environment)
- Test content: Measure corrosion rate and verify adhesion of anti-corrosion coatings (e.g. PE coating).
- Acceptance criteria: Corrosion rate ≤ 0.01 mm per year.
IV. Testing Procedure and Sampling Rules
Sampling Rules
- Mass production: 5% random sampling per batch (minimum 3 pieces), 100% inspection of critical dimensions.
- High-pressure reducers: 100% hydrostatic test + 20% non-destructive testing.
- Plastic reducers: 10 pieces sampled per batch for pressure resistance testing.
Acceptance Judgment
- A batch is accepted if all sampled items meet requirements.
- If one piece fails, double sampling shall be conducted for re-inspection. The batch shall be rejected if failures persist.
V. Common Testing Misconceptions
- Only appearance inspection is performed while wall thickness and material testing are neglected → resulting in insufficient pressure resistance of thin-walled reducers.
- Failure to completely vent air during hydrostatic testing → false high pressure leading to incorrect acceptance.
- No intergranular corrosion testing for stainless steel reducers → prone to corrosion failure in chemical media.
