ASME A335 P22 Studded Finned Tube 4 Inch Sch80 SMLS 13Cr Studs 12.7mm x 25.4mm 4604mm for Radiant Coil

ASME A335 P22 Studded Finned Tube — 4 inch Sch80 SMLS with 13Cr Studs for High Heat Flux Radiant Coils

This studded finned tube is a composite heat transfer element built on a seamless ASME SA335 / ASTM A335 Grade P22 (2.25Cr-1Mo) alloy steel pipe of 4 inch (114.3 mm) OD and Sch80 wall. Solid 13Cr (SS410 / 1.4006 type) studs of 12.7 mm diameter and 25.4 mm height are welded onto the outer surface at a density of 63 studs per meter, and the assembly is supplied in 4604 mm lengths.

It is specified for the radiant and convection coil sections of fired heaters, process heaters, reformer furnaces and waste heat recovery boilers, where the gas-side heat flux is too high and too dirty for plain tube or spiral fin tube. The product solves the three failures that limit plain P22 tubing in these zones: insufficient gas-side surface area that forces an oversized furnace; tube-wall overheating and coking caused by local hot spots; and rapid oxidation and sulfidation of the extended surface in 450–650 °C flue gas.

Its difference from a conventional finned tube is the studded geometry itself. Discrete studs stay rigid under thermal cycling, cannot unwind or de-bond along a continuous fin root, keep a fully drainable and soot-blowable surface, and hold their heat-transfer area in ash-laden and fouling service where continuous fins flatten, corrode through or blind over.

The dimensions quoted on this page are the actual production set for this item: base pipe 4 inch Sch80 SMLS, stud 12.7 mm × 25.4 mm at 63 studs per meter, tube length 4604 mm, eddy-current tested, and hydrostatically tested at 2800 Psi.

ASME SA335 P22 seamless pipe, 2.25Cr-1Mo low alloy steel, 4 inch OD × Sch80 (8.56 mm nominal wall). P22 is suitable for metal temperatures up to approximately 565 °C. Above that level its creep rupture strength falls away quickly and the 9Cr / Grade 91 family becomes the economically justified choice; below 565 °C, P22 delivers the required creep strength and structural stability at a lower cost and with far better weldability and availability than 9Cr material. The heavy Sch80 wall provides corrosion allowance and stiffness for long unsupported coil runs.

13Cr martensitic stainless studs, 12.7 mm diameter × 25.4 mm height, supplied in the hardened and tempered condition and welded by high-frequency resistance welding with full fusion at the collar. 13Cr is used instead of carbon steel studs because in sulfur-bearing and vanadium-bearing flue gas carbon steel studs scale at roughly 1 mm per year above 500 °C, while 13Cr builds a thin protective chromium oxide layer and keeps its section. Stud height of 25.4 mm is sized to reach past the laminar gas film.

63 studs per meter corresponds to a pitch of about 15.9 mm and a clear gap of about 3 mm between studs at 12.7 mm diameter. This is a high-density layout specified for radiant duty where the gas-side heat flux exceeds 30 kW/m²; it is not a general-purpose density, and lower densities are used for convection and economizer sections.

The studded pattern provides approximately 2.5 to 3.0 times the bare-tube gas-side area, and the discrete stud geometry additionally disrupts the gas boundary layer at every stud, together delivering the equivalent of 2 to 3 times bare-tube heat transfer capacity in fouling service. Area ratio alone is not the whole story: the turbulating effect of the stud field is what keeps the gain in place once the surface starts to foul.

Tensile strength 415 MPa min, yield strength 205 MPa min, elongation 30% min. Values are stated per ASTM A335 and are confirmed on the mill certificate supplied with each heat.

In the hardened and tempered condition the studs develop a typical tensile strength of 650–850 MPa and a 0.2% yield strength of 550 MPa minimum, well above the base-tube values quoted above. Hardness is controlled within an agreed range, typically 20–28 HRC (approx. 217–269 HB), so that the stud stays hard enough to resist soot-blower erosion while remaining tough enough for welding and for thermal cycling without cracking at the collar.

A refinery fired heater firing fuel gas with sulfur in the flue gas, radiant coil duty met by burners aimed directly at the tubes, gas-side heat flux above 30 kW/m² on the projected surface, and soot blowers running on a shift cycle. The process fluid inside the tube is vacuum residue or coking feed that begins to crack and coke as soon as the tube-wall temperature drifts above its limit.

The 63 studs per meter of 12.7 mm × 25.4 mm 13Cr studs take the burner radiation and hand it to the gas film over roughly three times the bare-tube area, then conduct it through short, thick, fully fused stud bodies into the Sch80 P22 wall. Because the extended surface is chopped into discrete studs rather than a continuous helical fin, the gas reaches the whole surface, the boundary layer restarts at every stud, and the surface stays cleanable. The P22 wall then spreads the absorbed flux circumferentially so that the crest-to-crest tube temperature stays even instead of peaking on the fire side.

• Coking and hot-spot burnout on the fire-side crest — the flux is spread over the stud area and the wall temperature drops back inside the coking threshold, which is what extends run length between decokes.
• Oxidation and sulfidation of the extended surface — hardened and tempered 13Cr studs survive the sulfur-bearing flue gas that consumes carbon steel studs within one or two campaigns.
• Loss of duty after fouling — a studded surface keeps its area under ash and can be cleaned by soot blowing, where a spiral finned tube blinds over and then runs hot.
• Furnace debottlenecking — the higher area per meter of tube lets an existing radiant box pick up more duty, or lets a new box be built shorter, without raising the tube-metal temperature.

The same construction is used in ethylene cracking furnace convection banks, reformer outlet sections, sulfur recovery unit waste heat boilers and HRSG evaporators, where the same combination of high gas temperature, corrosive flue gas and fouling applies.

1 piece for this size, and 1 × 20GP container for mixed sizes, mixed stud patterns and mixed grades in one shipment. Trial orders of a single coil length are accepted so the studded configuration can be verified on site before a full coil is released.

FOB Shanghai, FOB Qingdao or FOB Tianjin, at buyer option; CFR and CIF quotations are also issued when the buyer prefers the freight to be booked by us. Price basis is per piece or per ton, confirmed against the final tube length, stud density and stud material.

7–15 days for standard P22 studded finned tube held in stock or cut from stock pipe; 20–30 days for a full coil set produced to drawing, counted from receipt of the down payment and confirmation of the drawing. Lead time for third-party inspection (ABS, BV, DNV, CCS, LR, SGS) is confirmed at order stage and runs in parallel with production.

T/T with 30% down payment and the balance against copy of B/L, or irrevocable L/C at sight. Shipping documents include invoice, packing list, B/L, mill certificates to EN 10204 3.1 and, where required, the inspection release note.

Plywood cases or iron cases, plastic end caps on both tube ends, studded zone protected against handling damage, bundles braced inside the container. Tube ends can be supplied plain or beveled, and the length can be cut to the coil drawing so that no field trimming is needed.