304H, 316L, or Super Duplex? Choosing the Right Grade for Heat Exchanger Fittings

Published on 27 August, 2025

Heat exchangers remain the backbone of countless process industries. From power stations and petrochemical plants to desalination facilities, they continuously move heat, balance energy, and keep complex systems running. While the overall design of a heat exchanger is impressive, the true secret behind long-term performance is the choice of fittings and material grade.

 

As we move deeper into 2025, engineers are focusing on three leading contenders for heat exchanger fittings: 304H stainless steel, 316L stainless steel, and Super Duplex stainless steel. Each has its own set of strengths, and selecting the correct one depends on temperature range, corrosion exposure, and lifecycle costs.

 

Let us dive into the material science that makes each grade valuable.

 

304H: Reliable Strength at Elevated Temperatures

 

304H is a high-carbon variation of the standard 304 stainless steel. The “H” designation highlights its reliability for high-temperature service, due to its higher carbon content. This modification enhances its creep resistance and stability when exposed to prolonged heat above 500°C.

 

Why do engineers select 304H fittings?

a. Solid performance in power and steam service
b. More economical compared to higher alloys
c. Strong mechanical stability and easy weldability

 

304H is often found in boiler tubing, power generation exchangers, and superheater components, where durability at sustained high temperatures is critical.

 

316L: Corrosion Resistance with Smooth Surfaces

 

316L is the low-carbon grade of 316 stainless steel. The presence of molybdenum sets it apart from the 304 family, providing strong resistance against chloride corrosion and pitting. The “L” indicates low carbon, which prevents carbide precipitation during welding and maintains clean internal surfaces.

 

Why 316L remains popular?

a. Excellent resistance to chlorides and acidic conditions
b. Ideal for welded joints without intergranular corrosion
c. Long service life in food, chemical, and seawater environments

 

316L fittings are widely used in pharmaceutical production, desalination cooling systems, and chemical plants, where cleanability and corrosion resistance outweigh initial cost.

 

Super Duplex: Strength and Corrosion Resistance Together

 

Super Duplex stainless steels, such as UNS S32750, combine austenitic and ferritic structures. This dual-phase composition offers double the strength of austenitic grades and unmatched resistance to chloride stress corrosion cracking. Higher chromium, nitrogen, and molybdenum content ensures performance in extreme environments.

 

Why is Super Duplex chosen?

a. Incredible strength-to-weight ratio, allowing thinner sections
b. Outstanding resistance to seawater corrosion and erosion
c. Extended lifespan in offshore and high-pressure facilities

 

Although more expensive and requiring precise welding expertise, Super Duplex fittings offer the best return in marine, oil, and gas projects where conditions are the harshest.

 

Quick Comparison Table

Which One Should You Choose?

 

There is no universal material that fits every project. The right grade depends on operating temperature, fluid chemistry, and design life.

 

Choose 304H when the system faces high temperatures with low chloride exposure.

Choose 316L when the environment involves chlorides, mild acids, or hygienic requirements.

Choose Super Duplex when the conditions demand maximum strength and resistance in seawater or aggressive chlorides.

 

Increasingly, engineers in 2025 are requesting customised fittings in these grades to match wall thickness, pressure ratings, and international standards such as ASME, ASTM, and ISO. Heat exchangers leave no margin for error. A poor choice of material can quickly lead to leaks, corrosion, and expensive downtime. That is why industries around the world rely on 304H, 316L, and Super Duplex stainless steel fittings to handle heat, pressure, and corrosive environments with reliability.

 

At Online Fittings, we manufacture and supply fittings in all three grades — customised to exact specifications, fully tested, certified, and shipped globally.

 

When durability matters, the grade makes the difference.