Blog

The Complete Guide to Iron & SS Bulkhead Fittings and Bulkhead Unions

25 11 月, 2025

The Complete Guide to Iron & SS Bulkhead Fittings and Bulkhead Unions

Bulkhead fittings may look like simple mechanical components, but they play a critical role in fluid handling, tank construction, industrial piping, and system safety. Whether you are building a chemical tank, designing a water filtration system, or assembling agricultural machinery, choosing the right bulkhead fitting can determine whether the entire system stays leak-free—or fails unexpectedly.

As a professional manufacturer of iron (carbon steel) and stainless steel (SS304/SS316) bulkhead fittings, we understand how important material, design, and proper installation are. In this in-depth guide, we explain what a bulkhead fitting is, how it works, why it’s called a “bulkhead fitting,” and where it is used. We will also explore the benefits of metal bulkhead fittings versus plastic versions and provide practical selection tips.

1. What Is a Bulkhead Fitting?

A bulkhead fitting is a specialized connector designed to create a secure, leak-proof passage for liquids or gases through the wall of a tank, container, or panel. Unlike standard pipe fittings that connect pipes to pipes, bulkhead fittings connect a pipe through a barrier.

A typical bulkhead fitting includes:

A main body (male or female threaded)
A locknut that tightens from the opposite side of the wall
Sealing gaskets or O-rings
Threads such as NPT, BSP, or straight thread

When installed properly, bulkhead fittings offer a reliable connection that withstands pressure, temperature changes, vibration, and corrosion.

2. What Is the Purpose of a Bulkhead?

The primary purpose of a bulkhead fitting is simple:

To provide a sealed, stable passageway through a tank or panel wall.

More specifically, bulkhead fittings are used to:

Prevent leaks between connected pipelines and the tank interior
Create a clean and safe outlet point
Transfer liquids or gases between compartments
Withstand pressure and fluid force
Maintain tank integrity and durability
Connect hoses, pipes, valves, sprayers, pumps, and filters

Metal bulkhead fittings—especially iron and stainless steel—are often chosen for applications involving:

High-pressure systems
Fuel, oil, or industrial chemicals
High temperatures
Mechanical stress, vibration, or impact
Harsh or corrosive environments

In short, bulkhead fittings ensure that tanks and piping systems operate safely and efficiently, even under demanding conditions.

3. Why Is It Called a “Bulkhead Fitting”?

The name “bulkhead” originally comes from the shipbuilding industry, where a “bulkhead” is a structural wall or divider inside a ship.

Since these fittings are installed through the wall of a tank or container—much like how pipes would pass through the wall of a ship—they became known as bulkhead fittings.

Today, the term is widely used across industries, from agriculture and water treatment to fuel systems and chemical processing.

4. What Is Another Name for a Bulkhead Fitting?

Depending on the industry, bulkhead fittings may also be called:

Tank fittings
Through-wall fittings
Wall-pass fittings
Tank connectors
Bulkhead union fittings
Threaded tank adapters

While names vary, the function remains the same: enabling a liquid-tight or gas-tight connection through a barrier.

5. Bulkhead Fitting vs. Bulkhead Union — What’s the Difference?

Both terms often appear together, so it’s important to clarify:

Bulkhead Fitting

A generic term for any tank-through connector that seals against a wall.

Bulkhead Union

A specific two-sided connector designed to join two pipes or tubes through a wall while allowing flow in both directions.

Bulkhead unions are commonly used in:

Hydraulic systems
Fuel systems
Chemical distribution pipelines
High-pressure industrial lines

If your application requires connecting two pipe sections directly through a wall—rather than creating just an outlet—then a bulkhead union is the correct choice.

6. Why Choose Metal Bulkhead Fittings? (Iron vs. Stainless Steel)

Metal bulkhead fittings offer major advantages over PVC, PP, and nylon fittings. For industrial users, metal is often the only reliable long-term choice.

6.1 Iron (Carbon Steel) Bulkhead Fittings

Iron bulkhead fittings are:

Strong and impact-resistant
More affordable than stainless steel
Suitable for oil, fuel, hydraulic fluid, and mechanical systems
Ideal for agricultural machinery, construction equipment, automotive use, and pump systems
Capable of handling higher pressures

Surface treatments such as zinc plating, black oxide, electrophoresis, heat treatment, or chemical nickel plating can significantly enhance corrosion resistance—processes your factory already specializes in.

6.2 Stainless Steel Bulkhead Fittings (SS304 / SS316)

Stainless steel bulkhead fittings deliver top-tier performance:

Excellent corrosion resistance
Suitable for chemical processing and aggressive liquids
Hygienic—safe for drinking water and food systems
Withstand high temperatures and fluid pressure
Long lifespan with minimal maintenance

SS316 offers even stronger resistance to saltwater and chlorides, making it suitable for marine, offshore, pharma, and semiconductor environments.

7. How Bulkhead Fittings Work (Structure & Sealing Principle)

A bulkhead fitting works by clamping tightly against both sides of a tank wall. When the locknut is tightened, the gasket compresses and forms a watertight or airtight seal.

Key design features:

External threads for the locknut
Internal threads for pipe connection
Dual-sided sealing to prevent leaks
Flat-face or tapered seals depending on the application
Optional O-ring grooves for enhanced sealing

Metal bulkhead fittings can also withstand:

Pulsation
High torque
Water hammer
Vibration from pumps or motors
Long-term chemical exposure

8. Common Applications of Bulkhead Fittings & Bulkhead Unions

Because bulkhead fittings serve as secure pass-through connectors, they appear in almost every industry that handles liquids or gases.

Industrial Applications

Chemical tanks and reactors
Electroplating and surface treatment tanks
Wastewater treatment systems
Fuel storage tanks
Hydraulic equipment
Air compressor tanks
Oil and gas pipeline systems

Agriculture & Irrigation

Sprayers
Fertilizer tanks
Water storage reservoirs
Irrigation control systems

Marine & Offshore

Saltwater tanks
Engine room piping
Bilge water systems

Commercial & Residential

Rainwater harvesting systems
Aquariums
Water pumps

Metal bulkhead fittings—especially stainless steel—are often chosen for their durability and resistance to environmental conditions.

9. How to Install a Bulkhead Fitting Correctly

Proper installation is essential for ensuring the lifespan and sealing performance of bulkhead fittings.

Step-by-step guidelines:

Drill or cut the hole cleanly—ensure the wall surface is flat and free from burrs.
Place the gasket on the flange side, not on the nut side.
Insert the fitting into the tank wall.
Tighten the locknut by hand, then with tools gently.
Do not overtighten—overpressure can deform the gasket.
Apply PTFE tape or sealant if the threads require it.
Pressure-test the connection before putting it into service.

For metal bulkhead fittings, proper torque is critical to prevent galling or cracking.

10. How to Choose the Right Bulkhead Fitting

When selecting a bulkhead fitting or bulkhead union, consider:

Material Selection

Iron (carbon steel): Strong, economical, good for oil/fuel/hydraulics
Stainless steel: Best for corrosion, chemical resistance, food-grade & marine use

Thread Type

NPT (tapered)
BSP (parallel or tapered)
Straight thread
Metric options for OEM projects

Size

Common sizes: 1/4″, 3/8″, 1/2″, 3/4″, 1″, 1-1/2″, 2″

Pressure & Temperature

Higher pressure applications always require metal bulkhead fittings.

Wall Thickness Compatibility

Ensure thread length suits your tank thickness.

Chemical Compatibility

Stainless steel is preferred for chemical tanks, plating lines, purification systems, and seawater.

11. About Us – Professional Manufacturer of Iron & Stainless Steel Bulkhead Fittings

We are a dedicated manufacturer specializing in:

Iron (carbon steel) bulkhead fittings
Stainless steel bulkhead fittings (304/316)
Bulkhead unions for hydraulic, fuel, and chemical systems

Our capabilities include:

Precision CNC turning and milling
Custom NPT and BSP thread solutions
Surface treatments: polishing, galvanizing, electroplating, chemical nickel, blackening, electrophoresis, anodizing, chrome plating, gold plating, and sandblasting
Small-batch prototyping and mass production
OEM & ODM services for global brands

Our fittings are exported to Europe, the U.S., the Middle East, and Asia, serving industries such as chemical processing, agriculture, fuel systems, water treatment, machinery, and manufacturing.

12. Conclusion

Bulkhead fittings and bulkhead unions may seem like simple components, but they are essential for the safe transfer of liquids and gases through tank and panel walls. Metal bulkhead fittings—especially iron and stainless steel—offer unmatched durability, sealing performance, and pressure resistance.

Whether you’re building a fuel tank, designing a chemical line, or engineering industrial equipment, choosing the right bulkhead fitting is crucial for long-term performance.

As a professional manufacturer of metal bulkhead fittings, we supply high-quality, reliable, and customizable solutions to help customers worldwide build stronger and safer systems.