Low-Alloy Weathering Steel Tubes for High-Temperature Flue Gas Environments
Introduction
APH Pipes are specialised Air Pre-Heater tubes used in boilers, thermal power plants, recovery boilers, furnaces, and industrial heating systems. These pipes operate in high-temperature, corrosive flue gas environments where conventional carbon steel tubes fail rapidly.
At Sharoff Steel Suppliers, we supply ASTM A423 low-alloy weathering steel APH pipes, engineered specifically to resist sulphur attack, acid condensation, soot corrosion, and cyclic heating.
ASTM A242 is a high-strength, corrosion-resistant steel used for structural and architectural applications. It provides improved atmospheric resistance and forms a protective rust layer, minimizing the need for paint and maintenance in harsh environments.
APH pipes are heat-transfer tubes installed inside air pre-heaters, where hot flue gases transfer residual heat to incoming combustion air.
They are exposed to:
• High temperatures
• Sulphur-bearing flue gases
• Moisture & acid condensation
• Soot and ash deposition
• Repeated heating and cooling cycles
Because of this duty, APH pipes require special low-alloy corrosion-resistant steel, not ordinary structural or ducting pipes.
ASTM A423 is a dedicated specification for low-alloy steel tubes with atmospheric and high-temperature corrosion resistance.
Key advantages:
• Improved resistance to sulphur corrosion
• Better performance under acid dew-point conditions
• Enhanced durability during thermal cycling
• Proven service record in boiler air pre-heater zones
This is why ASTM A423 is widely used in power plant APH systems.
Sharoff Steel supplies APH pipes in ASTM A423 grades including:
• Grade 1
• Grade 3
(Grade selection depends on operating temperature, flue gas chemistry, and design life.)
Apart from these, APH Pipes are available via our sister concern in the below grades:
• BS 6323 Part V (Now BS EN 10305-5)
• BS 3059 Part 1 (Now BS EN 10217-1)
• JIS G3461
• ASTM A214
| Annealing and Surface Treatment | Straightening and Eddy Current Testing | Hydro Testing |
|---|---|---|
 |
 |
 |
| Element | Typical Role |
|---|---|
| Copper (Cu) | Atmospheric & sulphur corrosion resistance |
| Chromium (Cr) | Oxidation & scale resistance |
| Nickel (Ni) | Improves toughness & corrosion behaviour |
| Carbon (C) | Controlled for weldability |
Exact limits vary by grade. Always refer to MTC for project approval.
• Designed for elevated temperature operation
• Stable performance under cyclic heating & cooling
• Compatible with boiler fabrication and welding practices
• Optimised for long service life in APH zones
APH pipes are functional heat-exchange components, not just structural pipes.
Sharoff Steel Suppliers supplies ASTM A423 APH pipes in:
• 1.6mm to 6mm thickness
• 25mm to 120mm OD
Power & Energy
• Thermal power plants
• Captive power plants
Boiler Systems
• Air pre-heaters
• Recuperators
Industrial Heating
• Recovery boilers
• Furnaces and kilns
• Thermal oil heaters
| Aspect | APH Pipes (ASTM A423) | Corten Pipes |
|---|---|---|
| Primary role | Heat transfer | Ducting / piping |
| Operating temperature | High | Ambient–moderate |
| Corrosion type | Sulphur + acid | Atmospheric |
| Specification | ASTM A423 | ASTM A588 / EN / JIS |
| Application | Boilers & APH | Industrial piping |
👉Do not substitute Corten Pipes for APH duty without engineering approval.
◊ Experience supplying power & boiler segment
◊ Correct grade selection for APH duty
◊ Shutdown-critical supply understanding
◊ Clear differentiation between:
♦ APH Pipes
♦ Corten Pipes
♦ Structural WR steels
We support customers where tube failure equals downtime.
Why are APH pipes different from normal steel pipes?
They operate in hot, corrosive flue gas environments and require low-alloy steel designed for sulphur and acid resistance.
Can Corten pipes be used instead of ASTM A423 for APH?
No. Corten pipes are designed for atmospheric corrosion, not high-temperature and pressure sensitive flue gas duty.
What causes failure of conventional APH tubes?
Sulphur attack, acid dew-point corrosion, soot deposition, and thermal cycling.
Are APH pipes used only in power plants?
No. They are also used in recovery boilers, furnaces, kilns, and industrial heating systems.
Do APH pipes require special welding practices?
Yes. Welding consumables and procedures must match ASTM A423 chemistry.
APH Pipes (ASTM A423) are critical components in boiler and power plant efficiency. Using the correct low-alloy steel directly impacts plant reliability, efficiency, and shutdown frequency.
At Sharoff Steel Suppliers, APH pipes are supplied with application clarity, grade correctness, and power-segment experience.