Piping Materials

Detailed material selection for compressed air systems.

Metallic

Black Steel (Carbon Steel)

Specification: ASTM A53/A106, Schedule 40 or 80

Property	Value
Working pressure	Up to 300+ PSI
Maximum temperature	400°F (204°C)
Connections	Threaded, welded, flanged
Availability	Very high

Typical chemical composition:

• Carbon: 0.25-0.30%
• Manganese: 0.95%
• Phosphorus: 0.05% max
• Sulfur: 0.06% max

Advantages:

• Lowest cost
• High mechanical strength
• Easy to weld
• Wide availability
• Withstands high temperatures

Disadvantages:

• Internal corrosion generates scale
• Scale contaminates air
• Rough surface increases pressure drop
• Requires exterior protection
• Limited service life (15-20 years typical)

Recommended treatment:

• Interior: Residual compressor oil provides some protection
• Exterior: Paint or hot-dip galvanizing

Galvanized Steel

Specification: ASTM A53 with zinc coating

Property	Value
Working pressure	Up to 300+ PSI
Maximum temperature	400°F (204°C)
Zinc thickness	1.8-2.0 oz/ft²
Coating life	20-40 years

Advantages:

• Better corrosion resistance than black steel
• Sacrificial zinc protection
• No exterior paint required

Disadvantages:

• Zinc degrades with acidic condensate
• Zinc flakes contaminate air
• Cannot weld (destroys galvanizing)
• More expensive than black steel

Galvanized and Welding

Never weld galvanized pipe. Vaporized zinc is toxic and destroys protection. Use only threaded or mechanical connections.

Copper Type L

Specification: ASTM B88

Type	Wall Thickness	Pressure @ 100°F
K (heavy)	0.049" (1/2")	1,000+ PSI
L (standard)	0.040" (1/2")	850 PSI
M (light)	0.028" (1/2")	600 PSI

Use Type L minimum for compressed air.

Property	Value
Working pressure	Up to 250 PSI (Type L)
Maximum temperature	400°F (204°C)
Connections	Brazed, compression
Thermal conductivity	223 BTU/(hr·ft·°F)

Advantages:

• Excellent corrosion resistance
• Very smooth interior (low pressure drop)
• Decades of proven history
• No particle generation
• Recyclable

Disadvantages:

• High material cost
• Installation requires torch brazing
• Longer installation time
• Susceptible to theft

Stainless Steel

Common specifications:

• 304/304L: General use
• 316/316L: Corrosive environments

Property	304 SS	316 SS
Working pressure	300+ PSI	300+ PSI
Maximum temperature	800°F	800°F
Corrosion resistance	High	Very high
Relative cost	$$$$$	$$$$$$

Advantages:

• Maximum corrosion resistance
• Withstands high temperatures
• Smooth interior
• Long service life (50+ years)
• Sanitary grade available

Disadvantages:

• Very expensive
• Requires special welding techniques (TIG)
• Limited availability in some sizes

Applications:

• Pharmaceutical industry
• Food and beverage
• Semiconductors
• Corrosive environments

Extruded Aluminum

Commercial systems: Parker Transair, Atlas Copco AIRnet, Ingersoll Rand SimplAir

Property	Value
Typical alloy	6063-T6
Working pressure	188-232 PSI (per manufacturer)
Maximum temperature	150°F (65°C)
Connections	Push-to-connect, mechanical

Advantages:

• Zero corrosion
• Very lightweight (easy installation)
• Quick tool-free connections
• Modular (easy to modify)
• Perfectly smooth interior
• Aesthetic
• 10+ year warranties

Disadvantages:

• High initial cost
• Limited temperature
• Requires same-manufacturer components
• Not compatible with some synthetic oils

Cost-benefit: Although material costs more, quick installation can reduce total project cost by 30-50%.

Non-Metallic

Systems Approved for Compressed Air

Some manufacturers offer plastic systems specifically designed and certified for compressed air:

System	Material	Max Pressure	Max Temp
Prevost PPS	Reinforced polymer	232 PSI	140°F
Infinity by AIRpipe	Multilayer polymer	188 PSI	140°F

Required characteristics:

• Certification for compressed air (not water or gas)
• Resistance to cyclic pressure fatigue
• Compatibility with compressor oils
• UV resistance if exposed to sun

PVC/CPVC - PROHIBITED

Do Not Use PVC/CPVC

PVC (Polyvinyl chloride) and CPVC must never be used for compressed air.

Reasons:

1. Catastrophic failure: Shatters into sharp fragments
2. Fatigue: Cannot withstand pressure cycles
3. Oil: Degrades with compressor oils
4. UV: Becomes brittle with sun exposure
5. Impact: A blow can cause rupture

Violations:

• OSHA 29 CFR 1910.242(b)
• ASME B31.1
• Local plumbing codes

Legal consequences:

• OSHA fines
• Insurance invalidation
• Civil liability for injuries

Comparison Table

Criterion	Black Steel	Galvanized	Copper L	304 SS	Aluminum
Material cost	1x	1.3x	3x	6x	4x
Installation cost	High	High	High	Very high	Low
Corrosion resistance	Low	Medium	High	Very high	High
Max temperature	400°F	400°F	400°F	800°F	150°F
Max pressure	300+ PSI	300+ PSI	250 PSI	300+ PSI	200 PSI
Typical service life	15-20 years	20-30 years	40+ years	50+ years	30+ years
Air contamination	High	Medium	None	None	None
Modifications	Difficult	Difficult	Difficult	Very difficult	Easy

Selection by Application

Application	Recommended Material	Alternative
New plant, high budget	Aluminum	Copper
New plant, limited budget	Black steel	Galvanized
Instrument air	Copper	304 SS
Pharmaceutical/Food	316 SS	304 SS
Frequent modifications	Aluminum	-
Corrosive environment	316 SS	Aluminum
Outdoor exposed	Aluminum	304 SS
High temperature (post-compressor)	Black steel	304 SS

Connections and Fittings

Connection Types by Material

Material	Recommended Connections
Black steel	Welded, threaded (NPT), flanged
Galvanized	Threaded (NPT), Victaulic
Copper	Brazed, compression
Stainless	TIG welded, compression, Swagelok
Aluminum	Proprietary push-to-connect

Thread Sealants

Product	Application	Max Pressure
Teflon (PTFE tape)	General use	500+ PSI
Paste with PTFE	Difficult connections	10,000 PSI
Anaerobic sealant	Permanent	10,000 PSI

Do not use:

• Compounds with solvents that damage O-rings
• Sealants that harden and fragment