What are the differences between 347H stainless steel pipe and 316L stainless steel pipe

The 347H stainless steel pipe and the 316L stainless steel pipe have significant differences in composition design, performance, and application scenarios. The following presents a comparative analysis from six dimensions: 

1. Differences in core alloy elements 

Picture (Picture One) 

II. Key Performance Comparison

1. High Temperature Mechanical Properties 347H

Tensile strength ≥ 515 MPa (ASTM A213), the service stress remains above 100 MPa at 600℃. The maximum oxidation resistance temperature is 850℃ (for non-pressure-bearing components). It is suitable for the high-temperature superheater of supercritical power station boilers (such as the Φ51×8mm steel pipe of Huaneng Jinggangshan Power Plant). 316L

Tensile strength ≥ 520 MPa (ASTM A312), but the high-temperature strength decreases rapidly. The maximum operating temperature is approximately 590℃. It is mainly used for corrosion-resistant structures at normal or medium temperatures.

2. Corrosion Resistance

Intergranular corrosion

347H can pass the intergranular corrosion test (such as T method, L method) after stabilization treatment with niobium and welding without needing solution treatment; 316L relies on ultra-low carbon (C ≤ 0.03%) to avoid sensitization, but requires controlling the heat input after welding to prevent carbide precipitation.

Pitting and crevice corrosion

The molybdenum content (2-3%) of 316L enables it to have a corrosion resistance equivalent (PREN) of 26, significantly higher than 18 of 347H, making it more suitable for marine engineering (such as seawater desalination equipment) and chemical environments containing Cl⁻.

Sodium salt corrosion

347H performs well in 450-565℃ sodium salt solutions and has been applied in the storage tanks of the Yumen solar thermal power station; 316L has insufficient corrosion resistance due to the easy reaction of molybdenum with sodium salts.

3. Processing and Welding Characteristics

Cold processing

The cold work hardening effect of 347H is significant, and intermediate annealing (850-900℃) is required; 316L has better processing performance and is suitable for complex shapes (such as corrugated tubes).

Welding process 347H

It is recommended to use niobium-containing welding wire (such as ER347). When using TIG welding, the heat input should be controlled at ≤ 1.5 kJ/mm, and the interlayer temperature should be ≤ 150℃. Avoiding the precipitation of NbC which leads to embrittlement. 316L

Use a molybdenum-containing welding wire (such as ER316L), which has good weldability. The use of a non-argon-filled flux-cored welding wire (such as TGF-316L) can enhance on-site efficiency without the need for strict preheating. 

III. Typical Application Scenarios 

Picture (Figure 2) 

IV. Processing Techniques and Costs

1. Manufacturing Process 347H

The hot rolling temperature (1150 - 1200℃) and the solution treatment (1020 - 1100℃ water cooling) must be strictly controlled to ensure that the niobium carbides are fully dissolved. 316L

The cold drawing and cold rolling processes are well-established, and the cost of surface treatment (such as mirror polishing) is relatively low.

2. Market price 347H

In 2025, the price of Φ51×8mm seamless pipe is approximately 28,000 - 32,000 yuan per ton, which is 10 - 15% higher than that of 316L. 316L

The price for the same specification is approximately 25,000 - 28,000 yuan per ton, with a significant advantage in terms of cost-effectiveness. 

V. Standards and Execution Specifications

Picture (Figure 3) 

VI. Recommendation for Selection

Scenarios where 347H should be chosen as the primary option: 

High-temperature environment (>550℃): such as power station boilers, concentrated solar power plants.

Components that cannot undergo heat treatment after welding: rely on niobium stabilization to prevent intergranular corrosion.

Sulfide corrosion resistance: such as in hydrogenation units of oil refineries.

Scenarios where 316L is preferred: 

Chloride environment: such as marine engineering, chemical equipment.

Requires frequent welding and no post-processing conditions: Ultra-low carbon characteristics reduce the risk of sensitization.

Cost-sensitive general corrosion-resistant structures: such as food machinery, medical equipment. 

VII. Typical Cases 347H

Jiu'an provided Φ108×12mm type of pipes for the 50MW solar thermal project in Qinghai. The cumulative welding length reached over 10 kilometers, and these pipes can withstand the corrosion of 565℃ high-temperature molten salt. 316L

The desalination plant in Saudi Arabia uses Φ600×10mm pipes, which can withstand a Cl⁻ concentration of up to 50,000 ppm and has a service life of over 20 years. 

Summary: The main difference between 347H and 316L lies in their alloying designs with niobium and molybdenum. The former is known for its high-temperature strength and intergranular corrosion resistance, while the latter is advantageous in terms of resistance to chloride corrosion and processing economy. The actual selection should be based on comprehensive considerations of operating temperature, corrosive nature of the medium, processing costs, and maintenance conditions.