ASTM A335 P5 Studded Fin Tube With Carbon Steel Stud Fins For Boiler Economizers
ASTM A335 P5 Studded Fin Tube is a chromium-molybdenum alloy steel designed to offer a balance of good high-temperature strength, oxidation resistance, and cost-effectiveness. It serves as a middle-ground material between carbon steel and higher-grade stainless steels (like the 321H discussed previously) in demanding thermal applications like the studded fin tube. This is a heavy-duty heat exchanger tube designed for high-temperature service, where the primary goal is to maximize heat transfer in environments with low gas heat transfer coefficients. It consists of a chrome-moly alloy steel base tube (P5) with short, robust studs made of carbon steel welded onto its surface.
Here are some detailed breakdowns:
1. Base Tube: ASTM A335 P5 seamless pipes
(1). Chemical Composition (Weight %)
The composition is specified in the ASTM A335/A335M standard.
| Element | Composition (%) | Notes |
| Carbon (C) | 0.15 max | |
| Manganese (Mn) | 0.30 - 0.60 | |
| Phosphorus (P) | 0.025 max | |
| Sulfur (S) | 0.025 max | |
| Silicon (Si) | 0.50 max | |
| Chromium (Cr) | 4.00 - 6.00 | Primary alloying element. Provides oxidation and corrosion resistance. |
| Molybdenum (Mo) | 0.45 - 0.65 | Key alloying element. Provides high-temperature strength and stability. |
| Other Elements | - | The standard may have limits on other residual elements. |
(2). Mechanical Properties
The mechanical properties are specified for the material in the annealed or normalized and tempered heat-treated condition.
| Property | Requirement | Notes |
| Tensile Strength, min | 415 MPa (60 ksi) | |
| Yield Strength (0.2% Offset), min | 205 MPa (30 ksi) | |
| Elongation in 2 in. (50 mm), min | 30% | The minimum elongation requirement varies with wall thickness; this is a typical value. |
(3). Additional Requirements for A335 P5
- Heat Treatment: P5 pipe must be annealed or normalized and tempered to achieve the specified microstructure and mechanical properties. This is crucial for its high-temperature performance.
- Hardness (Typical): A typical maximum is 250 HBW (Brinell).
(4). Key Properties:
- Excellent High-Temperature Strength: Good resistance to creep and thermal stress.
- Good Oxidation Resistance: The 5% Chromium content provides much better resistance to scaling (oxidation) in steam and flue gas environments than carbon steel, but less than the higher-chromium (e.g., 9Cr, 12Cr) or stainless grades.
- Sulfidation Resistance: Offers reasonable resistance to sulfur attacks found in flue gases, making it a cost-effective choice for many applications.
2. Fin Type: Studded Fin
- Studded Fins: Instead of a continuous, wrapped fin, this tube has discrete, short, cylindrical pins or studs welded in a staggered pattern over the outer surface of the tube.
Key Advantage of Studs:
- Robustness: Studs are much less prone to damage and bending than thin, continuous fins, making them ideal for environments with high ash-laden gases, potential for soot blowing, or mechanical abuse.
- Enhanced Turbulence: The pattern of studs disrupts gas flow more effectively than continuous fins, creating turbulence that improves the heat transfer coefficient on the gas side.
3. Fins’ Material: Carbon Steel
Why use Carbon Steel material for Studs?
- Weldability: Carbon steel is very easy to weld to the P5 base tube, creating a strong, reliable bond.
- Cost-Effectiveness: It is the most economical material for the fins.
- Sufficient Performance: In many applications, the gas temperature, while hot, is not high enough to cause rapid oxidation of carbon steel fins. The primary function of the fins is to extend the surface area, and carbon steel accomplishes this at the lowest cost. The base tube (P5) remains the critical component for pressure containment and temperature resistance.
Core Application: High-Temperature Heat Recovery in Aggressive Environments
This tube is engineered for situations where the primary challenges are:
- High Temperature: Sustained operation at metal temperatures typically in the range of 800°F to 1100°F (425°C to 595°C), where carbon steel would weaken rapidly.
- Abrasion & Erosion: Gas streams that carry hard, abrasive particulate matter like fly ash.
- Moderately Corrosive Atmospheres: Flue gases that contain sulfur compounds (sulfidation) and are oxidizing, but not highly chloridic.
- High Internal Pressure: The base tube must contain a process fluid (water, steam, or process gas) under significant pressure.
Specific Industries and Equipment
You will find this studded fin tube in the convection sections and heat recovery areas of the following equipment:
1. Coal-Fired Power Plant Boilers
Application: In the Economizer and sometimes the Air Heater.
2. Waste-to-Energy & Biomass Boilers
Application: Heat transfer surfaces in the boiler convection pass.
3. Refinery and Petrochemical Fired Heaters
Application: Convection section tubes where heat is recovered from combustion flue gases to preheat process fluid or generate steam.
4. Cement Plant Waste Heat Boilers
Application: Recovering heat from extremely abrasive kiln exhaust gases.
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ASTM A335 P5 Studded Fin Tube With Carbon Steel Stud Fins For Boiler Economizers Images
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