Copper Pipe

Copper pipe and tube represent the predominant material choice for potable water distribution, hydronic heating systems, chilled water piping, and refrigerant lines in HVAC applications. The material’s exceptional thermal conductivity, inherent antimicrobial properties, corrosion resistance, and long service life make it the industry standard for pressure piping systems operating across a wide temperature range.

Material Properties

Thermal Properties

The thermal characteristics of copper directly influence heat transfer calculations and system performance.

Physical Properties

Electrical Properties

Copper’s high electrical conductivity requires consideration in systems with electrical grounding requirements or electromagnetic compatibility concerns.

Copper Tube Types

ASTM B88 defines standard copper tube types based on wall thickness. The designation system progresses from Type K (heaviest) through Type L (medium) to Type M (lightest) for pressure applications.

Type K Copper Tube

Type K represents the heaviest wall thickness designation, specified for underground service, high-pressure applications, and aggressive soil conditions.

Applications:

• Underground water service lines
• Fire protection systems
• High-pressure hydronic systems
• Medical gas systems
• Compressed air distribution

Dimensional Data (Selected Sizes):

Pressure Ratings (Type K):

Working pressure decreases with temperature according to ASME B31.9 derating factors.

Type L Copper Tube

Type L offers medium wall thickness and serves as the standard for above-ground plumbing and HVAC applications in commercial and residential construction.

Applications:

• Potable water distribution systems
• Chilled water piping
• Hot water heating systems
• Solar thermal systems
• Fuel oil lines

Dimensional Data (Selected Sizes):

Pressure Ratings (Type L):

Type M Copper Tube

Type M provides the thinnest wall thickness allowed for pressure applications, typically used in residential and light commercial heating systems where lower pressures prevail.

Applications:

• Residential potable water systems
• Low-pressure hydronic heating
• Snow melting systems
• Radiant floor heating
• Domestic hot water distribution

Dimensional Data (Selected Sizes):

Pressure Ratings (Type M):

Type DWV Copper Tube

Drainage, waste, and vent (DWV) copper tube operates under atmospheric or minimal pressure conditions. Wall thickness falls below Type M specifications.

Applications:

• Sanitary drainage systems
• Waste lines
• Vent stacks
• Condensate drain lines
• Gravity flow systems

Pressure Rating: Maximum 15 psig at 100°F

Dimensional Data (Selected Sizes):

ACR Copper Tube

Air Conditioning and Refrigeration (ACR) tube conforms to ASTM B280 rather than B88. Manufacturing includes dehydration, nitrogen charging, and sealed ends to maintain internal cleanliness for refrigerant systems.

Applications:

• Refrigerant suction lines
• Refrigerant liquid lines
• Refrigerant hot gas lines
• Heat pump reversing valve piping
• Condensate lines (soft temper)

Key Differences from ASTM B88:

• Sized by actual OD (not nominal)
• Factory cleaned and dehydrated
• Sealed with nitrogen charge
• Available in both hard drawn and annealed (soft) temper
• Wall thickness optimized for refrigerant pressures

ACR Tube Sizes (Common):

Pressure-Temperature Limits (ACR):

ACR tube must accommodate both operating pressures and vacuum conditions during evacuation. Design pressures vary by refrigerant type and system configuration.

Temper Designations

Copper tube manufacturing produces two distinct temper conditions affecting mechanical properties and installation methods.

Hard Drawn (H)

Manufactured in straight lengths (typically 20 feet) without post-draw annealing. The work hardening during drawing increases tensile strength and reduces ductility.

Properties:

• Higher tensile strength
• Lower ductility
• Cannot be bent significantly without special equipment
• Maintains dimensional stability
• Joined by brazing, soldering, or mechanical fittings

Applications:

• Underground installations requiring rigidity
• Vertical risers
• Exposed piping requiring straight runs
• High-pressure applications

Annealed (Soft) (O)

Thermal treatment after drawing restores ductility, allowing field bending without specialized equipment. Available in coils up to 100 feet or straight lengths.

Properties:

• Lower tensile strength
• High ductility
• Can be bent by hand or with simple tools
• Conforms to irregular paths
• Joined by brazing, soldering, or flare/compression fittings

Applications:

• Underground water service (coiled)
• Refrigerant piping with multiple direction changes
• Retrofit installations in congested spaces
• Radiant floor heating tubing
• Tight radius connections

Joining Methods

Soldered Joints

Capillary action draws molten solder into the fitting-tube annular space, creating a leak-tight joint. ASTM B828 specifies lead-free solder for potable water applications.

Solder Types:

Temperature Limits: 250°F maximum for water systems, 350°F for hydronic systems

Brazed Joints

Higher temperature joining process using copper-phosphorus or silver-bearing filler metals. Creates joints stronger than the base metal.

Brazing Filler Metals (AWS A5.8):

Temperature Limits: 400°F continuous, 450°F intermittent

Mechanical Joints

Press fittings, compression fittings, and flare fittings provide demountable connections without heat application.

Advantages:

• No hot work permits required
• Faster installation in occupied buildings
• No flame ignition risk
• Immediate system pressurization

Temperature Limits:

• Press: 250°F water, 300°F hydronic
• Compression: 200°F
• Flare: 150°F

Corrosion Resistance

Copper forms a protective oxide layer (patina) that inhibits further corrosion in most water chemistry conditions. However, specific water characteristics can cause accelerated corrosion.

Corrosion Modes

Pitting Corrosion: Localized attack creating small cavities, typically caused by chlorides, low pH, or high flow velocities.

Erosion Corrosion: Mechanical removal of protective oxide combined with corrosive attack, occurring at flow velocities exceeding 8 ft/s in cold water or 5 ft/s in hot water.

Galvanic Corrosion: Dissimilar metal contact in electrolyte creates electrical potential driving corrosion of the anodic material. Copper serves as cathode when coupled with steel or aluminum.

Dezincification: Selective leaching of zinc from brass fittings in aggressive water, leaving porous copper structure.

Water Chemistry Considerations

Design Considerations

Thermal Expansion

Copper’s thermal expansion coefficient requires accommodation in long runs experiencing temperature changes. Unrestrained expansion prevents stress-induced failures.

Linear Expansion:

ΔL = α × L × ΔT

Where:

• ΔL = change in length (in)
• α = 9.2 × 10⁻⁶ per °C (16.6 × 10⁻⁶ per °F)
• L = original length (in)
• ΔT = temperature change (°C or °F)

Example: 100 ft of Type L copper experiencing 100°F temperature change:

ΔL = 16.6 × 10⁻⁶ × (100 × 12) × 100 = 1.99 inches

Expansion Compensation Methods:

• Expansion loops (offset or offset U-configuration)
• Expansion joints (bellows or packed gland)
• Direction changes utilizing natural system geometry
• Building expansion joints aligned with piping expansion joints

Flow Velocity Limits

Excessive velocity causes erosion corrosion, noise, and water hammer susceptibility.

Insulation Requirements

Copper’s high thermal conductivity necessitates adequate insulation for energy efficiency and condensation prevention.

Chilled Water Systems:

• Minimum 1 inch closed-cell elastomeric insulation
• Vapor retarder jacket with sealed joints
• All-service jacket in outdoor applications

Hot Water Systems:

• Insulation thickness per ASHRAE 90.1 or local energy code
• Typically 1-2 inches for piping ≤ 4 inches
• Higher R-value for temperatures > 200°F

Support Spacing

Proper support prevents sagging and stress concentration at joints.

Vertical risers require support at each floor, maximum 10 feet.

Applicable Standards

Manufacturing Standards

• ASTM B88: Standard Specification for Seamless Copper Water Tube
• ASTM B280: Standard Specification for Seamless Copper Tube for Air Conditioning and Refrigeration Field Service
• ASTM B75: Standard Specification for Seamless Copper Tube
• ASTM B251: Standard Specification for General Requirements for Wrought Seamless Copper and Copper-Alloy Tube

Installation Standards

• ASME B31.9: Building Services Piping
• ASME B31.5: Refrigeration Piping and Heat Transfer Components
• IPC: International Plumbing Code
• UMC: Uniform Mechanical Code
• IMC: International Mechanical Code

Joining Standards

• ASTM B828: Standard Practice for Making Capillary Joints by Soldering of Copper and Copper Alloy Tube and Fittings
• AWS A5.8: Specification for Filler Metals for Brazing and Braze Welding
• ASTM B32: Standard Specification for Solder Metal

Testing Standards

• ASTM B819: Standard Specification for Seamless Copper Tube for Medical Gas Systems
• ASTM E213: Standard Practice for Ultrasonic Testing of Metal Pipe and Tubing

Advantages of Copper Piping

1. Antimicrobial Properties: Copper ions inhibit bacterial growth including Legionella
2. Corrosion Resistance: Self-passivating oxide layer protects against most water chemistries
3. Temperature Range: Operates from cryogenic to 400°F in pressure applications
4. Thermal Conductivity: Excellent heat transfer for hydronic and refrigerant systems
5. Durability: Service life exceeding 50 years in typical applications
6. Recyclability: 100% recyclable without property degradation
7. Fire Resistance: Non-combustible, does not produce toxic fumes
8. Proven Track Record: Decades of reliable performance data

Limitations

1. Cost: Higher material cost compared to plastic alternatives
2. Theft Risk: Scrap value makes copper attractive for theft in accessible locations
3. Water Chemistry Sensitivity: Aggressive water requires treatment or alternative materials
4. Thermal Losses: High conductivity increases heat loss/gain without proper insulation
5. Skilled Labor: Brazing and soldering require trained technicians
6. Electrolysis: Requires dielectric isolation from dissimilar metals

Selection Criteria

Type K Selection Factors:

• Underground installation
• High-pressure applications (> 300 psi)
• Aggressive soil conditions
• Critical systems (medical gas, fire protection)
• Long service life requirement

Type L Selection Factors:

• Standard above-ground plumbing
• Commercial HVAC systems
• Code requirement in specific jurisdictions
• Balance of cost and performance

Type M Selection Factors:

• Residential applications
• Low-pressure hydronic systems (< 150 psi)
• Cost-sensitive projects where code permits
• Protected indoor installations

ACR Selection Factors:

• All refrigerant piping applications
• Requires factory cleanliness
• Vacuum-tight system requirement