What are the heat treatment and cold-drawing requirements for A192 A192M steel tube?

ASTM A192/A192M is the canonical specification for seamless carbon-steel boiler tubes used in high-pressure service. It defines the minimum-wall-thickness tubes that go into the boiler, superheater and heat-recovery sections of power and process plants. Two of the manufacturing details engineers get wrong most often are heat treatment and cold drawing, and these are precisely the points that determine whether an A192 tube is fit for service. This guide walks through what the standard actually requires, why the two conditions exist, and how the requirements are translated into production practice.

If you are sourcing ASTM A192/A192M steel tube for a new boiler build or a replacement order, the information below will help you read the certificate, validate the delivery condition, and avoid the rework that comes from misreading the standard.

Where A192/A192M Fits in the Boiler Tube Family

A192 lives next to A179, A210 and the higher-temperature alloy grades such as A335 alloy steel pipes. Its job is to cover the lower-temperature, high-pressure side of the boiler envelope: water walls, economiser inlets, and the cooler legs of the superheater circuit. The standard covers tubes from 1/2 in. (12.7 mm) to 7 in. (177.8 mm) outside diameter with a minimum wall thickness between 0.085 in. (2.2 mm) and 1.000 in. (25.4 mm). It is a carbon-manganese steel, not an alloy, so the way it is finished at the mill matters more than its chemistry.

Because A192 sits between the cold-side ASTM A179/A179M heat-exchanger tubes and the hot-side alloy grades, the standard intentionally keeps the chemistry simple and pushes the performance guarantees into forming and heat treatment.

Manufacturing Methods Allowed by the Standard

Clause 5 of A192/A192M states that the tubes shall be made by a seamless process and that the tube can be either hot finished or cold drawn, according to what the purchaser specifies. In practice this means the order needs to ｄｅｃｌａｒｅ one of the two delivery conditions. Mixing them on the same purchase order without a defined split usually leads to dimensional inconsistencies on the shop floor and confusion in inspection.

Hot-finished tubes are produced by hot piercing and hot rolling. The as-hot-rolled microstructure is the delivery condition. The standard does not require any additional heat treatment for hot-finished product.
Cold-drawn tubes are produced by further reducing the hot-finished tube through one or more cold-drawing passes with a die and plug or a floating plug. The cold work changes the dimensions, surface finish, and mechanical properties, and the standard therefore mandates a final heat treatment.

In day-to-day boiler fabrication, hot-finished A192 is used when wall thickness and OD tolerances from the hot mill are acceptable. Cold-drawn A192 is chosen when the boiler designer needs tighter OD and wall control, a smoother ID surface for better heat transfer, or a narrower hardness window for tube-bending operations.

Heat Treatment Requirements of A192/A192M

Clause 6 is short but decisive. It reads:

"Hot-finished tubes need not be heat treated. Cold-finished tubes shall be heat treated after the final cold-finishing at a temperature of 1200 °F [650 °C] or higher."

There are two practical points hidden in that sentence.

Hot-finished tubes are exempt. No mandatory soak, no mandatory cool-down profile. The as-rolled microstructure is acceptable.
Cold-finished tubes must be treated at a minimum of 650 °C (1200 °F). The standard does not prescribe a soak time or a cooling rate, but the temperature is the floor. A sub-critical stress relief below 650 °C is not a substitute.

The metallurgical purpose of the 650 °C minimum is to take the work-hardened ferrite plus deformed pearlite produced by cold drawing back to a softened, recrystallised condition with uniform ferrite and spheroidised or finely divided pearlite. This restores ductility, brings hardness back under the 137 HB / 77 HRB ceiling required in Clause 9, and stabilises the tube for the bending, swaging and welding operations it will see during boiler assembly.

For most producers the heat treatment is performed as a full anneal or a sub-critical anneal at 650–700 °C, followed by controlled cooling. Continuous furnaces are common for large lots; batch furnaces are used when the tubes need to be straightened, cut or U-bent afterwards. In both cases the certificate must show the actual furnace temperature and the position of the recorder thermocouple, not just the nominal setpoint.

Why Cold Drawing Is Treated Differently

Cold drawing is what gives the tube its tighter dimensions and its surface finish, but it is also what raises the hardness above the A192 ceiling. A typical cold reduction of 20–35 % can push the hardness of a low-carbon steel well over 90 HRB and the tensile strength above 450 MPa, both of which would fail the mechanical property table in Clause 9. Without the mandatory post-draw heat treatment, the tube would also be unsuitable for the flaring, flattening and bending operations required later in fabrication.

The cold-drawing process itself needs to be controlled as well. The standard relies on A450/A450M for the general requirements, but in practice the items most often checked are:

Drawing lubricant residue. Residual oil or soap on the OD and ID will burn into the surface during the 650 °C anneal and leave scale pits. A proper pre-anneal wash or a reducing-atmosphere furnace prevents this.
Cold-work uniformity. Excessive reduction in a single pass can cause surface checks and eccentric wall. Most producers cap single-pass reduction at around 25–30 % and use multiple passes with intermediate annealing when the total reduction is large.
Straightness. Cold drawing tends to bend the tube, so a post-anneal straightening pass is normal. Over-straightening can reintroduce local work hardening and is one of the most common reasons a tube fails a later hardness survey.

Dimensional Tolerances Tied to the Delivery Condition

Because heat treatment and cold drawing are linked, the tolerances in A192/A450 are also split by condition. The figures most often referenced in procurement are summarised below.

Parameter	Hot-finished	Cold-drawn
OD, 12.7–25.4 mm (1/2–1 in.)	+0.40 / −0.80 mm	±0.10 mm
OD, 25.4–38.1 mm (1–1.5 in.)	+0.40 / −0.80 mm	±0.15 mm
OD, 38.1–50.8 mm (1.5–2 in.)	+0.40 / −0.80 mm	±0.20 mm
OD, 50.8–63.5 mm (2–2.5 in.)	+0.40 / −0.80 mm	±0.25 mm
OD, 63.5–76.2 mm (2.5–3 in.)	+0.40 / −0.80 mm	±0.30 mm
OD, 76.2–101.6 mm (3–4 in.)	+0.40 / −0.80 mm	±0.38 mm
OD, 101.6–177.8 mm (4–7 in.)	+0.40 / −1.20 mm	+0.38 / −0.64 mm
Wall, OD ≤ 101.6 mm, WT ≤ 2.4 mm	+40 % / 0	+20 % / 0
Wall, OD ≤ 101.6 mm, 2.4 < WT ≤ 3.8 mm	+35 % / 0	+20 % / 0
Wall, OD ≤ 101.6 mm, 3.8 < WT ≤ 4.6 mm	+33 % / 0	+22 % / 0
Wall, OD ≤ 101.6 mm, WT > 4.6 mm	+28 % / 0	+22 % / 0

The table makes the practical link between process and tolerance obvious: if the project needs the tighter OD band, the order has to be placed as cold-drawn A192, which in turn means the mill is committed to the post-draw anneal. Asking for hot-finished tolerances on a cold-drawn tube is not a valid substitution; it is just a different delivery condition with different cost and lead time.

Mechanical Properties and How the Heat Treatment Holds Them

Clause 9 of A192/A192M sets the mechanical targets that the heat treatment is designed to deliver:

Tensile strength ≥ 325 MPa (47 ksi)
Yield strength ≥ 180 MPa (26 ksi)
Elongation in 2 in. or 50 mm ≥ 35 %
Brinell hardness ≤ 137 HBW (wall ≥ 5.1 mm) or Rockwell hardness ≤ 77 HRB (wall < 5.1 mm)

A correctly performed 650 °C anneal brings the hardness of a cold-drawn tube back into the 60–75 HRB range, comfortably under the ceiling and with enough margin for the local work-hardening that the swaging and bending tools introduce. A sub-critical stress relief that runs too cool, or that uses too short a soak, will leave the tube just above 77 HRB and will show up as flaring-test failures or as split ends during tube-end expansion.

Required Tests for Each Delivery Condition

The standard ties the test set to the heat-treated lot. The mandatory mechanical tests, per Clause 10, are:

Flattening test – two tubes per lot, one sample per end.
Flaring test – two tubes per lot, different tubes from the flattening sample, one sample per end. A typical acceptance is an expansion of at least 15 % without cracking.
Hardness test – two tubes per lot, Brinell for wall ≥ 5.1 mm or Rockwell for thinner wall.
Hydrostatic test – every tube, or an equivalent non-destructive test when the purchaser agrees.

A batch in this context is the tubes of the same heat, the same nominal size, and the same wall thickness, processed in the same furnace charge. For a continuous furnace the batch is defined by the same dimensions, the same heat number, and the same time-temperature profile in the same furnace run. That is why the certificate must carry the heat number, the furnace identifier and the recorder chart, not just the tube dimensions.

Marking and Traceability

Clause 12 requires that, in addition to the standard A450/A450M marking, the tube must be marked to indicate whether it is hot finished or cold finished. For cold-drawn A192 that is the moment the inspector can confirm, on the tube itself, that the mandatory 650 °C anneal has been performed. A heat-numbered, condition-stamped tube is also the only way to trace the material back to the correct batch for any later non-conformance review.

Practical Checklist When Ordering A192/A192M Tubes

Specify the delivery condition explicitly: hot-finished or cold-drawn. Do not leave it open.
For cold-drawn orders, require a mill certificate that records the actual heat-treatment temperature (≥ 650 °C), the soak time, and the cooling method.
Match the dimensional tolerances to the delivery condition. Cold-drawn A192 is the only way to reach the tighter OD bands.
If the tubes will be U-bent for a heat-exchanger application, state the bend radius and any post-bend stress-relief requirement; the standard's 650 °C anneal is not a substitute for a post-bend treatment.
For high-temperature sections above ~480 °C, move to ASTM A335 alloy steel pipes rather than asking A192 to do alloy work.
Keep the certificate, the recorder chart and the marking photos together for traceability under the boiler's quality plan.

FAQ

Does A192/A192M require a heat treatment for hot-finished tubes?

No. Clause 6.1 explicitly states that hot-finished tubes need not be heat treated. The hot-rolling exit temperature is sufficient to put the tube in its delivery condition.

What is the minimum heat-treatment temperature for cold-drawn A192?

Clause 6.1 sets the floor at 1200 °F (650 °C). The treatment must be performed after the final cold-drawing pass. A sub-critical stress relief below 650 °C does not satisfy the standard.

Can a cold-drawn tube be supplied without the post-draw anneal?

No. Any tube sold as cold-finished A192 must be heat treated at 650 °C or higher. Supplying as-drawn material labelled A192 is a non-conformance and will fail the hardness and flaring tests.

Why does cold-drawn A192 have tighter OD tolerances than hot-finished A192?

The cold-drawing die and plug set the OD directly, and the post-draw anneal stabilises that dimension. Hot rolling is a free-forming process, so the as-rolled OD band is wider.

Is A192 suitable for superheater service?

A192 is used in the cooler sections of the superheater circuit and in water walls. For sections where the metal temperature routinely exceeds about 480 °C, the project should step up to an alloy grade such as A335 P11/P22 or GB/T 5310 alloy tubes.

What information should the mill certificate carry for cold-drawn A192?

Heat number, delivery condition (cold-drawn), actual heat-treatment temperature and soak time, the furnace identifier, the chemical analysis, the mechanical test results, and the hydrostatic or NDT report. Without the heat-treatment record, the certificate is incomplete for cold-drawn product.

Closing Note

A192/A192M is a short, focused standard, and that is its strength. Two clauses, 5 and 6, capture almost everything that matters in production: how the tube is made, and what condition it must be in when it leaves the mill. A correct ASTM A192/A192M steel tube order is one that names the delivery condition, accepts the tolerances that go with it, and verifies the heat-treatment record on the certificate. With those three things in place, the rest of the boiler fabrication — bending, welding, hydrotest, commissioning — follows the standard's expectations rather than fighting them.