1. Why "a pressure tube" is never just one product

Walk a refinery boiler, a utility coal-fired unit, an ethylene cracking furnace, and a combined-cycle HRSG side by side, and the component that looks most interchangeable — a 50 mm OD steel tube carrying water or steam — is in fact six different product families governed by six different ASTM/ASME standards. The reason is metallurgical: each zone on a fired unit operates at a different combination of internal pressure, metal temperature, and external corrosion, and the tube grade that survives 600°C in a superheater is not the grade that survives 250°C in an economizer.

For a procurement engineer or EPC piping lead, the question is therefore not "what is a pressure tube." It is "for this specific zone of this specific unit, with this design pressure, this design temperature, and this fuel or process gas on the outside, which combination of standard, grade, manufacturing route, and inspection plan is fit for the duty." The reference is the ASME BPVC Section II and the family of ASTM product specifications (A192, A178, A179, A210, A213, A334, A450, A530) that ASME adopts as SA-versions.

This guide walks through those families, the standards that govern them, and the procurement logic that lets you pull the whole pressure tube package — plus the matching heat exchanger tubes, the carbon steel pipe that ties the boiler into the rest of the unit, the pipe fittings, the pipe flanges, the gaskets, and the stud bolts — from one mill-direct supplier rather than five different trading desks.

2. The four application zones on a typical utility or process unit

Before any standard is named, the application zone has to be locked. ASME practice groups fired-unit tubing into four broad zones. Each zone has a different dominant failure mechanism, which drives the grade selection.

• Water-wall and economizer (low-to-medium temperature, water side). The tube sees saturated water or low-quality two-phase flow, with the metal temperature controlled by internal nucleate boiling. The dominant failure mode is external gas-side corrosion from the fuel chemistry. The standard family is ASTM A192, A210, and A178.
• Primary superheater and reheater (high temperature, steam side). The tube carries superheated or reheated steam at metal temperatures from 450°C up to 625°C. The dominant failure mode is long-term creep and external oxidation. The standard family is ASME SA213 with grades T2 through T92 (ferritic alloy) and TP304H / TP347H (austenitic).
• Heat-recovery steam generator (HRSG) hot end (cyclic, oxidation-prone). The tube sees daily start-stop cycling, fuel-side corrosion from the gas turbine exhaust, and metal temperatures crossing the 565°C creep range on a regular basis. The dominant failure mode is thermal-fatigue cracking combined with external oxidation. The standard family is SA213 TP304H, TP347H, and on supercritical / ultra-supercritical HRSG, T91 and T92.
• Heat-exchanger and condenser service (low-to-medium temperature, no flame). The tube carries a process fluid on one side and a heating/cooling medium on the other, with no external flame. The dominant failure mode is internal corrosion or external fouling, not creep. The standard family is ASTM A179 (low-temperature seamless) and SA213 TP304 / TP316 / TP321 (stainless).

3. Carbon-steel boiler tubes — ASTM A192, A210, A178, A179

Carbon-steel boiler tubes cover the water-wall, the economizer, and the lower-temperature superheater / reheater sections of every coal-fired, oil-fired, and many gas-fired units. The four standards below account for the majority of utility and industrial boiler tube purchases.

ASTM A192 / ASME SA192 — seamless carbon-steel boiler tube

A192 is the workhorse specification for seamless carbon-steel boiler tubes on low-to-medium-pressure service. Typical size range is OD 12.7–127 mm (1/2–5 in) with minimum wall thickness 2.0 mm. Minimum tensile strength is 325 MPa (47 ksi) and minimum yield is 180 MPa (26 ksi). A192 is the standard default for water-wall panels on smaller industrial boilers and for the economizer inlet section on utility units where the metal temperature is below 450°C.

ASTM A210 / ASME SA210 — seamless medium-carbon steel boiler and superheater tube

A210 is the higher-strength cousin of A192. Three grades are defined: A1 (min tensile 415 MPa / 60 ksi, min yield 255 MPa / 37 ksi), A2 (most common, min tensile 415 MPa, min yield 260 MPa), and C (min tensile 485 MPa, min yield 275 MPa). A210 is widely used for water-wall panels, economizer bends, and the lower-temperature superheater / reheater sections where the higher yield allows a thinner wall for the same pressure rating. Manufacturing route is hot-finished seamless (piercer + mandrel mill) for OD above 50 mm, and cold-drawn seamless for tighter OD / wall tolerances on heat-exchanger duty.

ASTM A178 / ASME SA178 — ERW carbon and carbon-manganese boiler and superheater tube

A178 is the electric-resistance-welded specification for carbon and carbon-manganese steel boiler tubes, in grades A (carbon), C (carbon), and D (carbon-manganese). Because of the longitudinal weld, A178 is limited to lower-pressure service (typically economizer coils and air-preheater tubes), and the weld is required to pass a 100% flattening test per ASTM A530. A178 is the standard choice when the size required exceeds what is practical in seamless (above OD 100 mm at thinner walls) and the duty is non-cyclic.

ASTM A179 / ASME SA179 — seamless cold-drawn low-carbon heat-exchanger and condenser tube

A179 is the cold-drawn seamless specification for low-carbon steel heat-exchanger and condenser tubes, with a minimum tensile of 325 MPa and a smooth, precision OD / wall surface. A179 is the default for the cold-end of an economizer, for closed-feedwater heater tubing, and for low-pressure air-cooled condenser service. Cold drawing gives tighter tolerances (typically ±0.05 mm on OD) than hot-finished, which makes A179 the right choice when the tube is rolled into a tubesheet.

4. Alloy-steel superheater and reheater tubes — ASME SA213 T2 through T92

As metal temperature climbs above 450°C, plain carbon steel runs out of creep strength and the grade has to move into the low-alloy Cr-Mo family. ASME SA213 is the umbrella specification for seamless ferritic and austenitic alloy-steel boiler, superheater, and heat-exchanger tubes, and the grade list below is the one a buyer will see on almost every utility RFQ.

T2, T11, T12 — the original 1%Cr / 1.25%Cr / 1%Cr-0.5%Mo family

T2 (0.5% Cr, 0.5% Mo), T11 (1.25% Cr, 0.5% Mo), and T12 (1% Cr, 0.5% Mo) are the workhorse low-alloy grades for superheater and reheater sections of subcritical and older sub-critical units. Maximum metal temperature is roughly 540°C for sustained service. T11 and T12 are still specified on refinery process heaters, ethylene cracking furnace transfer-line exchangers (TLE), and on many industrial boiler superheaters.

T22, T23, T24 — the 2.25%Cr family upgraded for higher temperature

T22 (2.25% Cr, 1% Mo) is the standard for utility boiler superheater and reheater tubes on subcritical units up to about 565°C. T23 is a modified 2.25%Cr grade with W, Nb, V, and B microalloying, giving roughly 100°C of additional creep strength compared to T22 at the same wall thickness. T24 is the analogous upgrade for the water-wall side. T23 / T24 are the typical grades for 600°C-class once-through boilers and for the hot reheat sections of 600°C-class ultrasupercritical units.

T91 and T92 — the 9%Cr martensitic family

T91 (9% Cr, 1% Mo, V, Nb, N) was developed in the late 1970s for fast-reactor and fusion-reactor steam generators, and is now the workhorse grade for 600°C-class supercritical and ultra-supercritical boiler headers, superheater, and reheater tubing. T92 is the tungsten-modified 9%Cr grade, with about 30°C additional creep strength compared to T91, used in 620°C-class and 650°C-class units. Both grades require strict preheat and PWHT control on welding, and the MTC must include the heat-treatment condition (normalized and tempered).

5. Stainless and duplex tubes for the hot-end of an HRSG

For metal temperatures above about 600°C, or for HRSG hot-end service where cyclic oxidation dominates, the grade list moves out of the ferritic alloy family and into the austenitic stainless and duplex families. The same SA213 specification covers these grades.

TP304H, TP321H, TP347H — the austenitic superheater family

TP304H is the 18%Cr / 8%Ni grade with controlled carbon (0.04–0.10%) for high-temperature strength. TP321H adds titanium stabilization for resistance to intergranular corrosion after long-term high-temperature exposure. TP347H adds niobium stabilization and is the standard for the hot-end superheater and reheater tubes of combined-cycle HRSGs at metal temperatures up to about 700°C. Above 700°C, the grade moves to advanced austenitic alloys (Super 304H, HR3C, NF709) or nickel alloys (Alloy 617, 740H) for 700°C-class A-USC units.

TP316 / TP316L and duplex for corrosion-side service

On the cold-end of an HRSG, where the gas-side temperature is below the dew point of the flue gas, the tubes are at risk of external aqueous corrosion and chloride-induced stress-corrosion cracking. The grade choice is usually TP316L (low-carbon 18%Cr / 12%Ni / 2.5%Mo) or a duplex grade such as 2205 (S31803 / S32205) for chloride-containing environments. For seawater-cooled HRSGs and for offshore platform waste-heat recovery, the grade list moves into super-austenitic (254 SMO, AL-6XN) or nickel-copper alloy 400 (Monel).

Copper-nickel for seawater and fire-fighting

On offshore platforms, in ship engine rooms, and in coastal refineries, the seawater cooling and fire-fighting lines are almost universally copper nickel alloy (90-10 / C70600 or 70-30 / C71500) because of the alloy's resistance to biofouling and chloride pitting. The matching flanges are copper nickel flanges per ASME B16.5, and the standards that cover the tube are ASTM B111, B466, and B467. A bundled RFQ for a marine HRSG that includes the boiler tubes plus the seawater-side copper-nickel system has to specify all four at once (tube + flange + fitting + gasket) on the same PO.

6. The seven selection factors that decide between two otherwise identical tubes

Once the zone and the standard are fixed, the following factors decide between two tubes that look the same on paper. They map directly to what an inspector checks during an RFQ review.

• Design metal temperature and pressure. Match the ASME BPVC allowable stress table for the chosen grade at the design temperature; confirm the calculated wall thickness includes the corrosion allowance and the mill negative tolerance.
• Fluid service and water chemistry. Internal scale, dissolved oxygen, and pH drive the choice between carbon steel, low alloy, and stainless. External fuel chemistry drives the gas-side corrosion allowance.
• Manufacturing route. Hot-finished seamless, cold-drawn seamless, or ERW. Cold-drawn gives tighter tolerances for heat-exchanger service; hot-finished is preferred for thicker walls; ERW is acceptable for lower-pressure economizer and air-preheater service.
• Heat-treatment condition on the MTC. T91 and T92 must be in the normalized-and-tempered condition; T23, T24, and 321H / 347H have specific solution-anneal and stabilization requirements.
• Dimensional tolerance and surface finish. Cold-drawn tubes for tubesheet rolling have OD tolerance typically ±0.05 mm and surface roughness below 0.8 µm Ra; hot-finished tubes are usually ±0.40 mm OD with rougher surface.
• Inspection and test plan. Hydrostatic test, eddy-current, ultrasonic, flaring, flattening, hardness. ASME SA213 requires 100% eddy-current or ultrasonic; A192 / A210 allow the buyer to choose.
• Delivery form and packaging. Straight lengths (typically 6–12 m), U-bends (for headers and economizer inlet), finned tubes (G-type embedded, H-type welded, KL/KLM tension-wound). Confirm the U-bend bend radius and the post-bend heat-treatment requirement up front.

7. How to read a pressure-tube datasheet and MTC

A typical pressure-tube datasheet should carry the following ten data points. If any one of them is missing, the supplier's offer is incomplete and the receiving inspector will reject on first sight.

• Standard and grade, with edition year. "ASME SA213 T91, latest edition" is the right form. "T91" alone is not.
• OD, wall, and length, with tolerance class. Specify OD, minimum wall, and length, and the tolerance per ASTM A450 / A530.
• Heat-treatment condition. Normalized and tempered, solution annealed, stress-relieved, or as-rolled, with the actual temperature range.
• Chemistry range (heat analysis and product analysis). Carbon, manganese, sulfur, phosphorus, chromium, molybdenum, nickel, vanadium, niobium, nitrogen as required for the grade.
• Mechanical properties (room temperature). Tensile strength, yield strength, elongation, hardness (HB or HV), impact (if specified).
• Hydrostatic test pressure or NDE alternative. Per ASTM A450 / A530, or 100% eddy-current per ASTM E213, or 100% ultrasonic per ASTM E213.
• Flattening / flaring / reverse-bend test results. For A192, A210, and SA213 ferritic grades, the flattening test is mandatory.
• Surface condition and end finish. As-pickled, as-polished, as-drawn; ends plain-end, beveled to ASME B16.25, or rolled-and-expanded for tubesheet service.
• Marking and traceability. Each tube marked with standard, grade, OD x wall, heat number, and manufacturer mark per ASTM A450 / A530.
• MTC type. EN 10204 3.1 (mill-issued, independent of the commercial department) is the default; 3.2 (independent third-party witnessed) is required for some refinery and offshore projects.

8. Bundled sourcing: tubing + heat-exchanger tube + pipe + fittings + flanges from one mill

For a typical project RFQ, the pressure tube is only one of six items on the same boiler or HRSG. The pressure tubes are welded into headers by butt weld fittings, the headers tie into the steam piping in carbon steel pipe per ASTM A106 Grade B, the steam line is bolted between two pipe flanges with a gasket and a set of stud bolts, and the HRSG economizer downstream uses heat exchanger tubes rolled into a tubesheet. Each of those six items has its own MTC, its own delivery date, and its own rejection rate.

Sourcing them from six different suppliers adds three structural problems. First, the six MTCs do not always match on heat number, lot, or even material grade, which holds up the receiving inspector. Second, partial deliveries on a long line force the site team to choose between storing half a system or installing mismatched components. Third, when a flange and a pipe arrive with different facing finishes (RF vs FF), or a stud bolt does not match the flange class, the fix is at site, not in the warehouse.

A mill-direct supplier that produces the pressure tubes, the heat-exchanger tubes, the carbon steel pipe, the butt-weld fittings, the steel flanges, the gaskets, and the stud bolts on the same production schedule can deliver a matched package with one set of mill test certificates, one delivery window, and one point of contact for any non-conformance. For a utility boiler outage with a hard start date, that consolidation is often worth more than any individual price concession.

9. Six pre-PO checks that catch 90% of field problems

Before signing the purchase order, run these six checks against the supplier's datasheet and quality plan. Items that fail here will not be fixable in the field without a return-to-vendor cost.

• Standard, grade, and edition year are all named. "SA213 T91" is not enough; the edition year, the supplementary requirements (NACE, impact, hot tensile), and the MTC type (3.1 vs 3.2) must be explicit.
• Heat-treatment condition is named and matches the grade. T91 / T92 must be normalized-and-tempered; 321H / 347H must be solution-annealed and stabilization-treated. A tube that arrives in the wrong condition cannot be re-heat-treated in the field.
• Inspection and test plan is named. Hydrostatic test pressure (or NDE alternative), flattening / flaring test, hardness, eddy-current or ultrasonic, surface finish, and dimensional tolerances all need a yes/no on the PO.
• End finish and delivery form are specified. Plain-end, beveled to ASME B16.25, or pre-rolled for tubesheet; straight length, U-bend with bend radius, or finned. The U-bend post-bend heat-treatment requirement (typically stress-relief at 620–680°C for carbon and low-alloy grades) must be on the PO.
• Packaging, marking, and shipping protection are specified. Each tube end capped, each tube individually marked, bundle wrapped in waterproof textile, bundles on wooden or steel skids. For T91 and T92, the packaging should prevent rain ingress because surface rust on these grades triggers a costly pickling pass at site.
• Documentation pack is complete and on the PO. MTC per EN 10204 3.1, dimensional and visual report, hydrostatic test report or NDE report, flattening / flaring report, heat-treatment chart, PMI (positive material identification) report for stainless and alloy grades, shipping list with heat-number-level traceability.