In modern piping engineering, compression fittings have become an important connection method in fields such as domestic water supply and HVAC systems due to their convenient installation and the absence of the need for heat fusion tools. However, a frequently asked question in practice is: Can compression fittings be reused? This article will explore this issue in depth and provide professional safety guidance.
Design Principles and Structural Characteristics of PP Compression Fittings
To understand whether PP compression fittings can be reused, it is first necessary to understand their unique design mechanism:
1. Three-Layer Sealing Structure
Radial Compression Ring: Typically an olive-shaped sealing ring made of EPDM or nitrile rubber
Axial Thrust Ring: A plastic locking ring that prevents the pipe from coming off under pressure
Pipe Wall Engagement Structure: The internal toothed design of the fitting engages with the PP pipe wall under pressure.
2. Material Properties Considerations
PP material has a significant “memory effect” and stress relaxation characteristics. The deformation of the pipe and seals during initial installation is permanent, and this deformation forms a unique match with specific installation conditions.
Compression fittings can be reused
Technical perspective: Why shouldn’t they be reused?
1. Irreversible loss of sealing performance
Permanent deformation of the compression ring: Upon initial tightening, the sealing ring undergoes plastic deformation, forming a sealing surface perfectly matching the pipe condition at that time.
Limited material resilience: PP material and sealing rubber cannot fully recover their original shape after depressurization.
Risk of micro-cracks: Micro-damage invisible to the naked eye may occur during disassembly.
2. Severe attenuation of connection strength
Experimental data shows that reused PP compression fittings:
Tensile strength decreases by 40-60%
Burst pressure decreases by 30-50%
Fatigue life decreases by more than 70%
3. Concretization of safety risks
Delayed leakage: Leakage may not appear for weeks or even months after installation.
Increased pressure sensitivity: Significantly reduced tolerance to water hammer and pressure fluctuations.
Decreased temperature adaptability: More prone to failure during thermal expansion and contraction cycles.
Manufacturers’ Clear Stance
All major PP piping system manufacturers clearly state in their technical specifications:
Reuse is prohibited: This includes international brands such as Georg Fischer, GF, and Aquatherm.
Warranty voided: Any reuse will completely void the system warranty.
Liability disclaimer: The manufacturer is not liable for any problems arising from reuse.
Key Findings in Practical Applications
1. Field Test Results
Multiple independent laboratory tests showed:
Initial installation leakage rate: < 0.1%
First disassembly and reassembly leakage rate: 12-18%
Second disassembly and reassembly leakage rate: 35-50%
2. Failure Mode Analysis
Main failure modes after repeated use:
Sealing ring flipping or displacement (65%)
Insufficient secondary engagement of pipe surface (25%)
Stripped nut threads (10%)
Correct Disassembly and Replacement Procedures
When repair or modification is required, the following professional procedures should be followed:
1. Safe Disassembly
Cut point selection → Release pressure → Mark location →
Rotate disassembly → Immediate inspection → Record status
2. Standard Procedure for New Installation
Cut the pipe at least 50mm behind the old fittings.
Use a dedicated pipe cutter to ensure a clean cut.
Thoroughly clean the pipe surface.
Use only new pipe fittings.
Tighten to the manufacturer’s recommended torque (usually 1.5-2.5 N·m).
3. Mandatory Testing Requirements
Water pressure test: 1.5 times the working pressure, hold for 30 minutes.
Air tightness test: Soap water leak test.
Periodic checks: Check 24 hours and 7 days after installation.
Recommendations for Handling Special Circumstances
In certain emergency or special circumstances, if temporary reuse is necessary, the following conditions should be strictly limited:
Considerable conditions (at your own risk):
Temporary low-pressure water supply (< 0.2 MPa)
Non-potable water systems
Exposed piping that can be monitored at any time
Replacement expected within 48 hours
Absolutely prohibited situations:
Gas piping systems
Heating systems (high temperature and high pressure)
Concealed works
Main drinking water pipes
Industry Standards and Norms
Relevant Chinese standards clearly stipulate that:
Technical Specification for Polypropylene Piping Engineering for Building Water Supply (GB/T 50349)
Polypropylene Piping Systems for Hot and Cold Water (GB/T 18742)
Both require that “connectors should be disposable.”
Professional Maintenance Recommendations
Preventative Maintenance
Establish piping system records
Mark the installation date of all fittings
Conduct regular pressure decay tests
Spare Parts Management
Keep commonly used PP compression fittings in stock
Store in a cool, dry environment
Note the expiration date (usually 3-5 years)
A Zero-Tolerance Safety Stance
Based on technical analysis, experimental data, and industry experience, we clearly state that: PP compression fittings should not and cannot be safely reused.
This stance is based on:
The limitations of materials science: The properties and sealing mechanism of PP determine its disposable nature.
A severe imbalance between risk and benefit: The small cost savings are completely disproportionate to the potentially huge risks.
Industry consensus: Consistent requirements of all professional standards and manufacturer specifications.
In piping engineering, there is no “potentially safe” middle ground. Every disassembled PP compression fitting should be considered permanently defective and must be replaced with a brand new part. This strict attitude is not excessive caution, but rather a respect for the laws of physics, a commitment to professional responsibility, and, most importantly, a fundamental guarantee of user safety.
