As a widely used plastic pipe material, the strength characteristics of polyvinyl chloride (PVC) pipes are the key basis for engineering design and selection. The strength of PVC pipes is mainly measured by the following indicators:
1. Tensile Strength
Standard value: 50-60 MPa (tested according to ASTM D638 standard)
Test method: Stretch the specimen at a rate of 50 mm/min until it breaks at 23°C
Influencing factors: Resin molecular weight, additive formula, processing technology
2. Compressive Strength
Short-term compressive strength: 55-90 MPa
Long-term compressive strength: about 25-40 MPa (considering creep effect)
Test standard: ASTM D695
3. Ring Stiffness
Common grades:
SN2: 2 kN/m² (light)
SN4: 4 kN/m² (medium)
SN8: 8 kN/m² (heavy)
Test method: parallel plate loading test specified in ISO 9969
1. PVC-U pipe (unplasticized polyvinyl chloride pipe)
Typical wall thickness: 1.5-20mm (depending on the diameter)
Working pressure:
PN6: 0.6MPa
PN10: 1.0MPa
PN16: 1.6MPa
Burst pressure: usually 3-4 times the working pressure
2. PVC-O pipe (biaxially oriented polyvinyl chloride pipe)
Strength advantage:
Tensile strength increased to 80-100MPa
Impact strength 2-3 times higher than PVC-U
Weight reduction of 20-40% while maintaining the same strength
Production process: enhanced by molecular orientation technology
3. PVC-C pipe (chlorinated polyvinyl chloride pipe)
High temperature strength:
Still maintains a strength of more than 20MPa at 60°C
The maximum operating temperature can reach 93°C (short term)
Chemical stability: better than ordinary PVC-U
1. Material formula
Resin K value: The selection of K57-K67 resin directly affects the basic strength
Stabilizer system: Different stabilizers such as lead and calcium-zinc affect the long-term strength retention rate
Modifier addition: CPE, MBS and other impact modifiers can improve toughness
2. Processing technology
Extrusion parameters:
Melt temperature: 190-210℃ is the best range
Screw speed and cooling rate affect crystallinity
Mold design: The effect of die expansion ratio and stretch ratio on molecular orientation
3. Environmental conditions
Temperature effect:
For every 10℃ increase, the strength decreases by about 10-15%
Low-temperature brittle point: -10℃ to -20℃ (unmodified)
UV exposure:
UV absorbers such as TiO2 need to be added for outdoor use
Unprotected PVC can lose up to 30% of its strength in one year
1. Application of safety factor
General water supply pipe: use a safety factor of 2.5-4.0
Pressure pipe: minimum safety factor is not less than 2.0
Long-term strength calculation: consider the strength attenuation of 50-year service life
2. Wall thickness calculation basis
ISO 4065 formula:
e = (P×D)/(2S+P)
Where e is the minimum wall thickness, P is the working pressure, D is the outer diameter, and S is the allowable stress
3. Dynamic load considerations
Water hammer effect: instantaneous pressure can reach 4-6 times the working pressure
Traffic load:
Burial depth requirements under AASHTO HS20 standard
Minimum cover thickness under general roads is 0.9-1.2m
|
Performance Indicator |
PVC-U Pipe |
HDPE Pipe |
Cast Iron Pipe |
Steel Pipe |
|
Tensile Strength (MPa) |
50-60 |
20-30 |
140-420 |
300-500 |
|
Elastic Modulus (MPa) |
2,800-3,500 |
800-1,000 |
80-140 |
200,000 |
|
Density (g/cm³) |
1.38-1.45 |
0.94-0.96 |
7.1-7.2 |
7.85 |
|
Coefficient of Thermal Expansion |
6×10⁻⁵/°C |
20×10⁻⁵/°C |
1.1×10⁻⁵/°C |
1.2×10⁻⁵/°C |
1. Factory test
Hydraulic test: 1.5 times the working pressure is maintained for 1 hour without leakage
Flat test: Pressed to 50% diameter without cracking
Drop hammer impact: 4kg hammer 1m height impact at 23℃ without cracking
2. On-site inspection
Acoustic detection: percussion method to determine hidden damage
Endoscopic inspection: observe the structural integrity of the inner wall
Pressure decay test: monitor the pressure holding capacity of the system
3. Accelerated aging test
Thermal oxygen aging: test the strength retention rate at 80℃
UV accelerated aging: QUV tester simulates outdoor exposure
Stress cracking test: environmental stress cracking test specified by ASTM D5397
The strength characteristics of PVC pipe enable it to maintain a competitive advantage in many application scenarios. Its performance spectrum of typical tensile strength of 50-60MPa and ring stiffness of 2-8kN/m², combined with excellent chemical corrosion resistance and moderate installation cost, constitutes a complete engineering solution.
