The ASTM A335 P22 studded fin tube is specified for heat transfer surfaces that operate in the convection section of fired heaters, waste heat recovery boilers, and process gas coolers within shell and tube heat exchangers, where the gas-side heat transfer coefficient is low and the flue gas carries ash, soot, or catalyst fines. In refinery fired heaters and petrochemical furnaces, the studded surface recovers heat from dirty combustion gases without the fin blockage that degrades continuous-fin tubes. In waste heat recovery boilers and HRSG units, the tubes withstand thermal cycling and aggressive cleaning while maintaining a stable heat transfer area. When assembled into a finned tube bundle and rolled or welded into a heat exchanger tubesheet, the studded tubes provide a pressure boundary between the process fluid and the hot gas stream.
The base tube is manufactured to ASTM A335 / ASME SA335 Grade P22, the standard specification for seamless ferritic alloy-steel pipe for high-temperature service. Stud welding is performed under qualified welding procedures per ASME Section IX, and the finished tubes are inspected in accordance with ASME Section I and Section VIII Division 1 requirements for pressure parts. Certification is available per EN 10204 Type 3.1, with PED compliance and third-party inspection available upon request.
Continuous-fin tubes lose effective heat transfer area in dirty gas service because ash and particulate matter bridge between adjacent fins, blocking the gas passages. Studded tubes address this by using individual, widely spaced cylindrical studs that leave open channels between projections. The studs increase the external surface area to approximately 2–3 times that of a bare tube while maintaining an open geometry that resists fouling and allows aggressive cleaning without fin damage. The P22 base material also solves the high-temperature strength problem: the 2.25Cr-1Mo composition provides creep and rupture resistance up to approximately 565°C (1050°F), where carbon steel and low-chrome grades would suffer excessive deformation.
Material Specification – ASTM A335 P22ASTM A335 P22 is a seamless ferritic alloy steel with nominally 2.25% chromium and 1% molybdenum. The chromium content provides oxidation and sulfidation resistance, while molybdenum contributes creep strength and hardenability. The grade is specified for high-temperature service in power plants, refineries, and petrochemical facilities.
Chemical Composition (per ASTM A335 / ASME SA335 P22)| Element | Composition (%) |
|---|---|
| Carbon (C) | 0.05 – 0.15 |
| Manganese (Mn) | 0.30 – 0.60 |
| Phosphorus (P) | 0.025 max |
| Sulfur (S) | 0.025 max |
| Silicon (Si) | 0.50 max |
| Chromium (Cr) | 1.90 – 2.60 |
| Molybdenum (Mo) | 0.87 – 1.13 |
| Property | Requirement (min) |
|---|---|
| Tensile Strength | 415 MPa (60 ksi) |
| Yield Strength (0.2% offset) | 205 MPa (30 ksi) |
| Hardness (HBW) | 163 max |
The studded tube consists of an ASTM A335 P22 seamless base tube and solid cylindrical studs resistance-welded to the outside surface. Stud material is selected to be compatible with the P22 base tube, typically a matching low-alloy steel. Stud diameter, height, and pitch are specified in the purchase order and approved drawing. The resistance welding process produces a metallurgical bond between each stud and the tube without filler metal addition. Welding parameters are controlled to limit the heat-affected zone and preserve the base tube properties.
Manufacturing ProcessThe manufacturing sequence includes raw material inspection, tube cutting and end preparation, automatic resistance stud welding, weld integrity verification, straightness inspection, dimensional measurement, heat treatment when specified, surface cleaning, final inspection, and protective packaging. Studs are welded uniformly around the tube circumference using automated equipment, and the finished tube is checked for stud alignment, weld soundness, and overall straightness.
Size RangeStudded pipe size and material
| Tube O.D.: | 25~355.6 (mm) | 1"~14"(NPS) |
| Tube Wall Thk.: | 3.5~28.6 (mm) | 0.14"~1.1" |
| Tube Length: | ≤25,000 (mm) | ≤82 ft |
| Stud Dia.: | 6~25.4 (mm) | 0.23"~1" |
| Stud Height: | 10~50.8 (mm) | 0.4"~2" |
| Stud Pitch: | 8~30 (mm) | 0.3"~1.2" |
| Stud Shape: | Cylindrical, Elliptical, Round, Lens type | |
| Stud to tube surface angle: | Vertical, angular, staggered rows | |
| Stud Material: | C.S. (most common grade is Q235B) | |
| Tube Material: | C.S. (most common grade is A106 Gr.B) | |
| * This table is used as a general guide to our capabilities, please call us for any other customized cases. | ||
Each lot of studded tube is subjected to chemical composition verification, tensile testing, hardness testing, and dimensional inspection. Stud weld integrity is examined by visual inspection and, where specified, by bend testing or macro-examination of weld cross-sections. The base tube is hydrostatically or non-destructively tested in accordance with the applicable ASTM A335 requirements. Positive Material Identification (PMI) is performed to confirm alloy grade, and full material traceability is maintained to mill certificates.
DocumentationEach shipment is supplied with Mill Test Certificates (EN 10204 Type 3.1) covering the base tube and stud material, heat treatment records, dimensional inspection reports, stud weld inspection reports, and NDE reports when applicable. Welding procedure specifications (WPS) and procedure qualification records (PQR) are available for review.
For a rapid quotation on ASTM A335 P22 Studded Fin Tubes, please provide the following information:
Quantity (number of pieces or total meters)
Base tube outside diameter and wall thickness
Stud diameter, height, and pitch/spacing
Tube length (straight or U-bend)
Finned length and bare end length
Heat treatment requirement (normalize and temper)
Design pressure and temperature
Delivery period required
