Main Materials for Marine Valves

In the marine industry, the quality of marine valves is directly related to the safety and performance of the vessel. Choosing the right valve material not only improves equipment durability but also effectively reduces maintenance costs, ensuring reliable operation in a variety of harsh environments. Understanding the main materials and advantages of marine valves will help you make informed purchasing decisions.

Overview

The following are the main materials and characteristics of marine valves:

Copper Alloy

Properties: Excellent corrosion resistance, wear resistance, and machinability, as well as good casting properties, high casting density, and good airtightness.

Common grades:

Tin bronze (ZCuSn10Zn2): used for valve bodies, bonnets, and valve cores; aluminum bronze (QA19-2): used for valve stems and high-wear components (such as nuts). Aluminum Bronze (C95800): Used for valve bodies, bonnets, and valve cores.

Applications: Fire protection systems, seawater valves, seawater pumps and valves, cooling systems (such as GB/T 2030 seawater valves), and suitable for low-pressure valves.

Carbon Steel

Characteristics: Low cost and high strength, but poor corrosion resistance, requiring coating protection.

Common Grades:

ZG230-450 Cast Steel: Tensile Strength σb ≥ 450 MPa, Yield Strength σs ≥ 230 MPa

WCB Carbon Steel: Composition: Carbon content 0.2%-0.3%, with trace amounts of manganese and silicon, low cost and excellent processability.

Performance Advantages: Tensile strength ≥ 485 MPa, operating temperature range -29°C to 425°C, suitable for media such as water, steam, and oil.

Stainless Steel

Characteristics: Seawater corrosion resistance, oxidation resistance, high strength, suitable for high-pressure and high-temperature environments. Commonly used grades:

304/316 austenitic stainless steel (such as CF8 and CF8M): Used in seawater cooling systems and fuel pipes.

Duplex stainless steel (such as 2205/2507): Resistant to chloride ion corrosion, suitable for seawater piping. (Duplex stainless steel 2205 is recommended for valves in seawater systems, such as ball valves and butterfly valves, due to its excellent corrosion resistance.)

Ductile Iron

Properties: Ductile iron offers high strength, excellent wear resistance, and corrosion resistance.

Commonly used grades:

QT450 Ductile Iron: Primarily used for marine butterfly valve bodies (GB/T3037-2017). Ductile iron butterfly valves are widely used on ships due to their compact structure, light weight, and low cost. Ductile iron also offers strength similar to that of cast steel and better corrosion resistance than ordinary cast iron.

Cast Iron

Characteristics: Low price; HT200 tensile strength and elongation are significantly lower than those of ductile iron and cast steel; in seawater, humid salt spray environments, or corrosive media (such as sewage and certain chemicals), gray cast iron's corrosion resistance is far inferior to that of ductile iron (especially coated ductile iron), bronze, or stainless steel. It is highly susceptible to rust and pitting, leading to valve failure or leakage.

Common grades:

HT200 gray cast iron

Material Type	Cost	Resistance to corrosion	Strength	Temperature resistance	Applicable pressure	System of application	Note	Reference Picture
Bronze	Highest	Excellent (small valve)	Low	-40~250℃	PN≤2.5MPa	Seawater cooling system; Sea valve	Dezincification prevention
Carbon Steel	Medium	Medium (requires coating protection)	High	-29~425℃	PN≤32MPa	Drainage system; Low temperature oil circuit	Need for corrosion protection
Stainless Steel	Higher	Best	High	-196~650℃	PN≤32MPa	Fuel oil system; High temperature steam line	High temperature chloride ion protection
Ductile Iron	Medium	Better than cast iron	Medium	-30~350℃	PN≤4.0MPa	Seawater system; Ballast water treatment system‌	Not recommended for strong alkali and hydrochloric acid media
Cast Iron	Lowest	poor	Low (crisp)	-15~250℃	PN≤1.6MPa	Low pressure, low temperature, non-corrosive fluid	Do not use in combustible media