ASTM A387 Alloy Steel, Grade 5, Class 1

ASTM A387 Grade 5 Class 1 (often abbreviated as SA 387 Gr 5 Cl 1) is a high-quality chromium-molybdenum alloy steel plate. It is primarily used in the fabrication of weldable boilers and pressure vessels designed for elevated temperature service, such as those found in the oil, gas, and petrochemical industries.

Processing Techniques 

Heat Treatment:

The heat treatment process is carefully controlled to optimize the material's microstructure. It primarily involves Normalizing at a temperature range of 900°C to 950°C, which refines grain size, eliminates internal defects and homogenizes the structure. This step is followed by Tempering at above 675°C, a critical operation to relieve residual stresses from normalization, improve ductility and toughness, and stabilize the mechanical properties required for Class 1 applications, ensuring the material can withstand harsh working conditions.

Welding Protocol:

Welding of this chromium-molybdenum alloy demands strict adherence to pre-weld and filler metal requirements. Preheating between 150°C and 250°C is mandatory to reduce the temperature gradient across the weld zone, minimizing the risk of cold cracking caused by rapid cooling. Meanwhile, low-hydrogen filler metals (e.g., E8018-B6) are exclusively used to lower hydrogen content in the weld, further preventing hydrogen-induced cracking and ensuring weld joint strength matches the base material.

Post-Weld Heat Treatment (PWHT):

Stress-relieving PWHT is essential after welding, conducted at 700°C to 760°C. This process effectively reduces residual welding stresses, softens the hardened Heat Affected Zone (HAZ), and improves the weld joint's toughness and corrosion resistance, avoiding premature failure under high pressure and temperature.

Edge Conditioning:

Thermal cutting inevitably forms a hardened layer on edges, which impairs weld quality and mechanical performance. Thus, all thermal cut edges must be thoroughly ground to remove this hardened layer, ensuring clean, uniform edge surfaces before welding and guaranteeing sound fusion between the base material and filler metal.

Applications

Industry Standard for Heat‑Intensive Service

This material is widely regarded as the industry benchmark for equipment operating in high‑temperature environments where structural integrity, thermal stability, and resistance to creep, oxidation, and corrosion are essential. Its ability to retain strength and toughness at elevated temperatures, combined with good weldability and fabricability, makes it a preferred choice for critical components across multiple sectors.

Petrochemical & Refining Applications

In petrochemical and refining facilities, it is extensively used in pressure vessels, heat exchangers, and reactor vessels that process sour crude oil, high‑pressure hydrogen, and other aggressive hydrocarbons. These applications demand resistance to hydrogen attack, sulfide stress cracking, and thermal cycling, as well as compliance with stringent safety and pressure vessel codes. The material's robust performance helps minimize downtime, enhance operational reliability, and support the efficient conversion of crude oil into valuable products.

Power Generation Applications

Within power generation, the material is a staple for industrial boilers, steam piping, and high‑temperature ducting systems. It provides excellent creep strength and fatigue resistance under prolonged exposure to high temperatures and pressures, ensuring the safe and continuous production of steam for electricity generation and industrial processes. Its durability also contributes to lower maintenance costs and longer service life for power plant infrastructure.

Chemical Processing Applications

In chemical processing plants, it is employed in vessels and storage systems handling hot acidic media, corrosive chemicals, and reactive process streams. The material's resistance to oxidation, scaling, and chemical attack helps maintain vessel integrity, prevent leaks, and ensure compliance with strict environmental and safety regulations. Its versatility allows it to be used in a wide range of chemical processes, from acid production to specialty chemical manufacturing.

Oil & Gas Applications

For the oil and gas industry, the material is used in gas separators, offshore processing modules, and other equipment operating in harsh offshore and onshore environments. It must withstand high temperatures, corrosive fluids, and mechanical stresses, while also meeting the industry's rigorous requirements for reliability and safety. Its combination of heat resistance and corrosion resistance makes it well‑suited for critical applications in upstream and midstream operations.

Advantages 

Creep Resistance:

Molybdenum ensures the steel does not permanently deform under long-term stress at high temperatures.

Oxidation Resistance:

5% Chromium provides a robust barrier against scaling in hot environments.

HTHA Protection:

Specifically resistant to High-Temperature Hydrogen Attack, a critical safety feature for refineries.

Superior Ductility:

Compared to Class 2, Class 1 offers better impact toughness and is easier to cold-form (roll or bend).

Cost-Effective Durability:

Provides high-tier performance at a significantly lower price point than stainless steel or nickel-based alloys.

Contact now

Full specification and details are available on request. The above information is provided for guidance purposes only. For specific design requirements please contact our technical sales staff.

What's the difference in chemical composition between A387 Grade 5 Class 1 and A387 Grade 11 Class 1?

Grade 11 Class 1 has 1.00-1.50% chromium, while Grade 5 Class 1 has 4.00-6.00% chromium, enhancing the latter's high-temp performance.

What's the difference in chemical composition between A387 Grade 5 Class 1 and A387 Grade 11 Class 1?

Grade 11 Class 1 has 1.00-1.50% chromium, while Grade 5 Class 1 has 4.00-6.00% chromium, enhancing the latter's high-temp performance.

How does the ductility of A387 Grade 5 Class 1 differ from A516 Grade 70?

A516 Grade 70 has higher ductility (elongation ≥21%) than A387 Grade 5 Class 1 (≥18%), but the latter is more heat-resistant.

What distinguishes the application scope of A387 Grade 5 Class 1 from A242 Type 1?

Grade 5 Class 1 is for high-pressure boilers and vessels, while A242 Type 1 is for structural use, differing in pressure and temp resistance.

How is the heat treatment process of A387 Grade 5 Class 1 different from A387 Grade 7 Class 1?

oth need normalizing and tempering, but Grade 5 Class 1's tempering temp is 620-705°C, 20-30°C lower than Grade 7 Class 1, adapting to its alloy ratio.

How does the ductility of A387 Grade 5 Class 1 differ from A516 Grade 70?

A516 Grade 70 has higher ductility (elongation ≥21%) than A387 Grade 5 Class 1 (≥18%), but the latter is more heat-resistant.

What distinguishes the application scope of A387 Grade 5 Class 1 from A242 Type 1?

Grade 5 Class 1 is for high-pressure boilers and vessels, while A242 Type 1 is for structural use, differing in pressure and temp resistance.

How is the heat treatment process of A387 Grade 5 Class 1 different from A387 Grade 7 Class 1?

Both need normalizing and tempering, but Grade 5 Class 1's tempering temp is 620-705°C, 20-30°C lower than Grade 7 Class 1, adapting to its alloy ratio.