1. What "Pressure Tube" Actually Means in a Modern Plant

"Pressure tube" is a term of art, not a generic synonym for pipe. In boiler and heat-exchanger practice it refers to the small-diameter, thin-wall, seamless tubes that carry steam, water or process fluid on the fired or hot side of a system. They are sized by outside diameter in millimetres or inches, have wall thicknesses typically between 2.0 mm and 12 mm, and are produced to tighter dimensional and testing tolerances than line pipe.

The three service families where pressure tubes dominate are:

• Utility and industrial boilers — waterwalls, economizers, superheaters, reheaters, downcomers, and steam headers.
• Shell-and-tube heat exchangers — condensers, feedwater heaters, oil coolers, and process gas coolers on the tube side.
• Fired heaters in refineries and petrochemical plants — radiant and convection sections of hydrocracker, FCC, ethylene cracking, reformer and reboiler furnaces.

Because the same tube is doing three jobs at once — containing pressure, conducting heat, and resisting corrosion — the consequences of mis-specification show up fast: tube rupture, weld cracking, external wastage, or creep rupture after only a few years of service.

2. The Three Standard Families: A192/A210, A213, A335

Almost every pressure tube you will ever quote falls under one of three ASTM specifications. They are not interchangeable.

A useful rule of thumb: if it bends back on itself inside a furnace, it is a tube and is covered by A192, A210 or A213. If it runs straight along a header or across a piperack, it is a pipe and is covered by A106, A335 or A312.

3. Carbon vs Alloy vs Stainless: A Side-by-Side View

The reference article circulating in the industry right now ("What Materials are Used to Make Boiler Tubes?") gives a useful but broad-brush comparison. The view below is what an actual mill specification sheet looks like.

The first three rows of the table are the ones a buyer's engineer should defend in front of a metallurgist. The last three rows belong to the procurement side of the project — and they only matter once the technical case has already been made.

4. Reading the Standard for What Matters: Chemistry, Strength, Testing

A copy of ASTM A213 on the desk is not the same as understanding what it actually constrains. Four clauses do almost all of the work:

• Heat analysis and product analysis — the chemistry band is the contract. C, Mn, Si, Cr, Mo, V, Nb, N, and residuals such as S, P, and As are not negotiable without a formal deviation.
• Tensile, yield, elongation and hardness — what the tube must deliver at room temperature. Hardness limits are often the simplest way to reject mis-heat-treated material on receipt.
• Flattening, flaring, and bend tests — proves ductility and weldability of the actual lot, not just the heat.
• Hydrostatic or NDT (eddy current / ultrasonic) — every tube is pressure-tested or NDT-tested at the mill. The certificate should show the test method, the test pressure or sensitivity, and the acceptance criteria.

For alloy grades, also request the grain-size number, the heat-treatment condition (normalized, normalized-and-tempered, quenched-and-tempered), and the actual Brinell or Vickers hardness per lot. T91 and T92 in particular are notoriously easy to under-temper at small mills, and the failure shows up only after 30 000 hours of creep exposure.

5. Boiler-Side Selection: Waterwall, Economizer, Superheater, Reheater

Boiler design is a temperature-graded system. The right tube grade moves up the temperature ladder as you move from the economizer inlet to the final superheater outlet.

• Waterwall and economizer: A192 or A210 A-1 carbon steel is still the default for sub-critical units. For supercritical and USC units moving to higher heat flux, T12 or T23 alloy economizer tubing is increasingly common.
• Primary superheater (up to ~540 °C): T12, T22, P22 — well-understood Cr-Mo grades, straightforward welding, predictable creep life.
• Final superheater and reheater (560 °C to 625 °C): T91, T92, or TP304H/TP347H depending on the firing duty. T92 is the workhorse of the 600 °C USC class; TP347H dominates once cyclic duty and corrosion start to dominate the failure mode.
• Main steam and hot reheat piping: this is where carbon steel pipe and A335 P11 / P22 / P91 picks up — the same grade families, but in pipe dimensions.

For a 600 MW supercritical unit the gradient is typically: waterwall A192 → economizer T12 → primary SH T22 → platen SH T91 → final SH TP347H → main steam P92. Every step is a different specification, and almost every step is sourced from a different lot of steel.

6. Refinery and Petrochemical Selection: Fired Heaters and Hydrocracker Service

Refinery and petrochemical process heaters are the second home of A213 tubes, and they impose a different set of constraints than utility boilers. Temperatures are usually lower, but the process gas chemistry is far more aggressive: hydrogen, hydrogen sulfide, naphthenic acid, and molten salt carryover all show up in different services.

• Hydrocracker and hydrotreater reactor charge heaters: 1.25Cr-0.5Mo (T11/P11) and 2.25Cr-1Mo (T22/P22) are still the workhorses for the radiant section. For high-pressure units, T/P91 increasingly replaces T/P22 for the highest-flux tubes.
• Catalytic reformer and CCR units: TP304H and TP347H for the radiant coils where decoking cycles push metal temperature through oxidation-driven cycling.
• Ethylene cracking furnaces: centrifugally cast HP/HP-Nb and 35Cr-45Ni-Nb tubes dominate the radiant section. For the convection bank, A213 T22 in welded panels is still common.
• Process-side condensers and overhead coolers: stainless steel pipe and tube in TP304L / TP316L is the workhorse for amine, sour-water and overhead systems where carbon steel would fail by chloride or sour-service cracking.

For offshore and marine service — LNG carriers, FPSOs, and seawater cooling trains — the alloy conversation shifts again, and copper nickel alloy 90/10 and 70/30, plus titanium and super-duplex stainless, ｒｅｐｌａｃｅ the Cr-Mo family for seawater-side tubing.

7. Common Buyer Mistakes and How to Avoid Them

Most pressure-tube problems in service are not mysteries. They trace back to one of six well-known buyer errors:

• Buying to A192 when A179 was the actual spec. A179 is the heat-exchanger / condenser tube; A192 is the high-pressure boiler tube. The two are routinely confused in PO templates.
• Quoting "T11" without checking the heat-treatment condition. An A213 T11 tube can be supplied as-rolled, normalized, or normalized-and-tempered. Only N&T is acceptable for high-temperature service.
• Ignoring the "S" in SA-213. ASME Section I uses SA-213, not A-213. For pressure-boundary work covered by the ASME Boiler Code, the SA-prefixed edition is what the inspector will look for.
• Accepting EN 10216-2 without checking the impact-test temperature. EN 10216-2 has a "-CC" suffix for low-temperature impact; without it the tube is only qualified to 0 °C, which can disqualify it for outdoor or arctic service.
• Letting the gasket and bolt package be specified separately from the tube. A correct tube grade with the wrong gasket, stud bolt and nut still leaks. The bolting grade has to match the design temperature and the gasket facing.
• Sourcing in too many small lots. Every extra mill heat is an extra set of traceability documents and an extra set of field welds with different weld-procedure qualifications. For 500 t of T22, one or two mill heats is far safer than ten.

8. Sourcing Pressure Tubes as Part of a Bundled Project Package

The most expensive part of a pressure-tube order is rarely the tube itself. It is the engineering time, the MTC review, the third-party inspection, the freight for 20-tonne bundles of small-diameter tubes, and the field-side rework when something does not match. The fastest way to compress all of that is to source pressure tubes, industrial valves, and the bolting and gasket package from a single supplier that holds the full documentation chain.

At EZ Steel Industrial we have supplied pressure-tube packages to utility, refinery, petrochemical and marine EPCs since 1994. A typical bundled package from our mill covers:

• ASTM A192 / A210 / A213 / A335 tubes in carbon, Cr-Mo alloy and austenitic stainless, with full MTC per EN 10204 3.1 or 3.2 as required.
• Matching steel flanges in ASTM A105, A182 F11/F22/F91/F304/F316 grades to ASME B16.5 / B16.47.
• Butt-weld, socket-weld and threaded fittings to ASME B16.9 / B16.11 in the same material families.
• Gaskets, stud bolts and nuts in the matching ASME / ASTM grade for the design temperature.
• Pre-coordinated industrial valves — gate, globe, check and ball — flanged and BW-ended to match the line class.

Single-source documentation, single MTC numbering system, and a single point of accountability for non-conformance. For a 200 MW boiler, a hydrocracker revamp, or a marine LNG fuel-gas system, that is what actually shortens the project schedule.

9. Closing Notes

Pressure tubes are not interchangeable with line pipe, and A192, A210, A213 and A335 are not interchangeable with each other. The right spec, the right heat-treatment condition, and the right test certificate are what separate a 30-year run from a five-year forced outage. Once the tube spec is correct, the right flanges, fittings, gaskets, bolts and valves need to be specified in the same material and pressure class — which is exactly what a project-bundled mill supply is set up to deliver.