Differences Between ASTM A358 304H and 304L: Comparison of High-Temperature and Corrosion Resistance

In petrochemical plants, power station boilers, heat exchangers, and high-temperature piping systems, many engineers face a typical question when selecting ASTM A358 austenitic stainless steel welded pipes:

What exactly is the difference between ASTM A358 304H and 304L? Should 304H be chosen for high-temperature environments, or is 304L more suitable for corrosive environments?

Although both belong to the 304 series austenitic stainless steel, they differ significantly in high-temperature strength, weldability, and corrosion resistance due to variations in carbon content and design purpose.

This article provides a comprehensive analysis from the perspectives of chemical composition, mechanical properties, inspection requirements, actual working conditions, and procurement risks, combined with YOUFASS’s nearly 10 years of manufacturing experience, to help you make a more scientific material selection decision.

What Are ASTM A358 304H and 304L?

ASTM A358 is the standard for electric fusion welded (EFW) austenitic stainless steel pipes, widely used in high-temperature and corrosive service conditions.

• ASTM A358 304H: High-carbon type 304 stainless steel, emphasizing high-temperature strength
• ASTM A358 304L: Low-carbon type 304 stainless steel, emphasizing weldability and intergranular corrosion resistance

Chemical Composition Comparison of 304H and 304L

Chemical composition determines material performance, especially carbon content (C).

1.ASTM A358 Chemical Composition (wt%)

Element	304H	304L
C (Carbon)	0.04–0.10	≤0.03
Cr (Chromium)	18.0–20.0	18.0–20.0
Ni (Nickel)	8.0–11.0	8.0–12.0
Mn (Manganese)	≤2.0	≤2.0
Si (Silicon)	≤1.0	≤1.0

2.Why Is Carbon Content Critical?

• 304H (High Carbon)
  • Improves high-temperature creep strength
  • Enhances high-temperature load-bearing capacity
  • More suitable for long-term high-temperature service
• 304L (Low Carbon)
  • Reduces carbide precipitation after welding
  • Lowers the risk of intergranular corrosion
  • More suitable for welded structures

Conclusion:

• Prioritize 304H for high-temperature service
• Prioritize 304L for welding and corrosion resistance

High-Temperature Performance Comparison (304H Has Obvious Advantages)

Creep strength and oxidation resistance are critical in high-temperature environments.

Item	304H	304L
Recommended long-term service temperature	≤800℃	≤450℃
High-temperature creep performance	Excellent	Fair
High-temperature strength	Higher	Lower
Oxidation resistance	Excellent	Good

Typical Applications of 304H

• Power station boilers
• Superheater pipes
• Heat exchangers
• High-temperature steam systems

 Corrosion Resistance and Weldability Comparison (304L Is Superior)

Although 304H has stronger high-temperature performance, 304L is more popular in welded structures.

Why Does 304L Have Better Corrosion Resistance?

The low-carbon design reduces carbide precipitation in the weld heat-affected zone (HAZ), thereby lowering the risk of intergranular corrosion.

Item	304H	304L
Weldability	Good	Excellent
Intergranular corrosion risk	Relatively high	Very low
Adaptability to acidic environments	Fair	Better

Typical Applications of 304L

• Chemical pipelines
• Pharmaceutical equipment
• Food processing systems
• Water treatment projects

Especially suitable for ASTM A358 stainless steel pipes with extensive welding.

Inspection Requirements in the ASTM A358 Standard

In the ASTM A358 specification, materials must not only meet chemical composition requirements but also pass strict inspections.

1.Chemical Composition Analysis

• Standard: ASTM A751
• Purpose: Verify carbon content differences between 304H and 304L
• Method: Optical Emission Spectrometry (OES)

2.Tensile Test

• Standard: ASTM A370
• Test items:
  • Tensile strength
  • Yield strength
  • Elongation

3.Non-Destructive Testing (NDT)

Requirements vary by class:

Class	RT Requirement
ASTM A358 Class 1	Not mandatory
ASTM A358 Class 2	100% RT
ASTM A358 Class 3	Stricter RT

ASTM A358 vs. A312: How to Choose 304H/304L?

Many buyers also compare ASTM A358 vs. A312.

Item	ASTM A358	ASTM A312
Manufacturing process	Electric fusion welded (EFW)	Seamless / welded
Advantage for large diameters	Obvious	Moderate
Cost	More economical	Higher

Large-diameter high-temperature projects usually prefer ASTM A358.

Common Risks in Procurement

In actual procurement, 304H and 304L are often confused.

Common Issues

• Using 304 to counterfeit 304L
• Excessive carbon content
• Non-standard heat treatment
• Falsified inspection reports

Engineer’s Suggestions for Key Verification

• Material Test Certificate (MTC)
• Actual carbon content data
• Compliance with the ASTM A358 specification
• Post-weld heat treatment records

How Does YOUFASS Ensure the Quality of 304H and 304L?

As a stainless steel pipe manufacturer with nearly 10 years of experience, YOUFASS has established a complete quality system for ASTM A358 pipes.

1.In-House Laboratory (Core Advantage)

YOUFASS is equipped with:

• Spectrometer (for chemical composition testing)
• Tensile testing equipment
• RT / UT / PT inspection systems

All data are authentic and traceable to avoid “paper-qualified” products.

2.Strict Compliance with ASTM Standards

• Conforms to the latest ASTM A358 standard
• Supports:
  • ASTM A358 304H
  • ASTM A358 304L
  • ASTM A358 TP304 CL1

3.Engineering Customization Capability

• Large-diameter heavy-wall pipe production
• Special size and tolerance control
• Technical selection support

Conclusion: 304H or 304L? Depends on Service Conditions

If you are still unsure, remember one rule:

Choose 304H for high temperature; choose 304L for welding and corrosion resistance.

• Long-term high-temperature service → 304H
• Complex welding & corrosive environment → 304L

Professional material selection depends not only on price but also on whether the material truly fits the working conditions.

Contact YOUFASS now to get:

• Latest ASTM A358 PDF free download
• Sample material inspection reports
• ASTM A358 selection advice and quotation

Let genuine testing, professional manufacturing, and stable delivery safeguard your project.