P1 Piping Systems

Non-critical piping systems that are low-pressure and low temperature.

Typical Characteristics:

• Operating pressure is usually less than 150 psi

• Operating temperature is below 200°F

• Failure would not endanger the ship or crew

Examples:

• Drain systems

• Vent lines

• Potable water

• Sanitary waste lines

Testing Requirements:

• Generally visual inspection and/or operational test (flow check)

• No hydrostatic or high-pressure test required

P1 = Low-risk, low-pressure (simple test/inspection)

P2 Piping Systems

Moderate- to high-criticality systems that are higher pressure, higher temperature, or more vital to ship operations.

Typical Characteristics:

• Operating pressure 150–1000 psi

• Operating temperature up to 650°F (varies by material and system)

• Failure could impair operations or present a hazard

Examples:

• Firemain systems

• Fuel oil service and transfer

• Hydraulic systems

• Lube oil systems

• Steam systems (in some applications)

Testing Requirements:

• Hydrostatic testing or air test at prescribed pressures (per system specs)

• Visual weld inspections and often NDT (Non-Destructive Testing) such as radiography or dye penetrant

P2 = Higher-risk, higher-pressure (requires hydro or NDT testing)

Materials for Piping Systems

1. Stainless Steel (CRES)

Characteristics:

Corrosion-resistant, durable, strong at high pressures/temperatures.

Common Grades in Ship Work:

304L, 316L, and higher alloys depending on service.

Typical Applications:

• High-pressure air systems

• Potable water systems (due to corrosion resistance and cleanliness)

• Hydraulic lines

• Fuel and lube oil piping in certain environments

Why Used:

Long service life, resistance to seawater and chemicals, maintains strength in harsh environments.

2. Carbon Steel

Characteristics:

Strong, cost-effective, widely available. Susceptible to corrosion if unprotected.

Common Forms:

Seamless and welded pipe.

Typical Applications:

• Low-pressure steam systems

• Firemain systems (when internally coated)

• Machinery systems not exposed to seawater

• Structural supports, foundations, and ship framing

Why Used:

High strength-to-cost ratio, easy to fabricate and weld. Must be properly coated/preserved.

3. Copper-Nickel (CuNi)

Types Used in Shipbuilding:

70/30 (70% Cu, 30% Ni) and 90/10 (90% Cu, 10% Ni).

Characteristics:

Excellent corrosion resistance, especially in seawater. Good biofouling resistance.

Typical Applications:

• Seawater cooling systems

• Firemain (Navy often requires 90/10 or 70/30 CuNi)

• Ballast systems

• Desalination and heat exchanger tubing

Why Used:

Superior resistance to saltwater corrosion, long-term reliability, required by NAVSEA for critical seawater systems.

4. Aluminum

Characteristics:

Lightweight, corrosion-resistant, non-magnetic, but not as strong as steel.

Typical Applications:

• Superstructures (to reduce top weight on ships)

• Small boat hulls and decks

• HVAC ducts and light piping systems

• Electrical cable trays and supports

Why Used:

Reduces weight, improves fuel efficiency, and is easier to handle. Requires special welding procedures (MIG/TIG).

✅ Quick Reference:

• Stainless Steel = Corrosion resistance, clean systems, high strength

• Carbon Steel = Strong, cost-effective, needs coating

• Copper-Nickel = Best for seawater systems, anti-corrosion

• Aluminum = Lightweight, corrosion-resistant, used in structures & light-duty piping