Boiler

Boiler Steel Tube

Boiler tube selection is a code decision before it is a purchasing decision. Each circuit in a unit operates at its own metal temperature and in its own environment, and the approved grade schedule for that circuit governs what can be supplied.

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Boiler circuits

Six circuits, six different selection bases

A boiler is not one temperature. What changes between these circuits is the operating envelope, and that envelope is what the grade schedule answers to.

Boiler circuits: what the duty involves and what to state before enquiring
Circuit	What the duty involves	Before you enquire
Waterwall and furnace-wall tubes	Exposed to radiant heat and to the furnace atmosphere, so both the temperature and the environment act on the tube.	State the design code, the grade schedule and the required surface condition.
Superheater and reheater tubes	The highest metal temperatures in the unit, and the duty where grade selection is most tightly specified.	Provide the code-approved grade and the outlet temperature basis.
Economiser tubes	Lower-temperature heat recovery, where the feedwater condition affects the corrosion requirement.	State the feedwater condition and the applicable grade.
Heat-exchanger and condenser tubes	Tube-to-tubesheet joints and the cooling medium both influence the material requirement.	State the medium, the joint method and the required grade.
Steam and feedwater connection tubing	Small-bore runs where the termination and the pressure basis govern.	Provide the fitting or termination detail and the design basis.
Replacement and outage programmes	The replacement tube has to match the unit as built, including any permitted change already approved.	Supply the as-built schedule and the approval history for the unit.

The design code

Four things the design code owns

These belong to the equipment design and the responsible engineering authority. A tube supplier can quote against them; it cannot set or waive them.

The approved grade schedule

Which grades are permitted for each circuit, and at which metal temperatures. The schedule is code-driven, not catalogue-driven.

The allowable stress basis

Allowable stress at temperature follows from the code and the grade — it is not a tube property that can be read off a mill certificate.

The required heat treatment

The condition the tube must be in at delivery, and any treatment after forming or welding.

The test and inspection plan

Which tests are required, at which stage, and who witnesses or certifies them.

Approval warning. No grade, temperature limit, stress value or test requirement is published on this page, and no tube or circuit is approved for boiler service here. Those determinations rest with the design code and the responsible engineering authority for the unit.

Supply decisions

What to fix before the order is placed

Once the code-approved schedule is settled, six supply decisions remain — and each one is a field on the enquiry.

State the unit, the circuit and the equipment tag or line number the tube is for.
State the exact grade and the code-approved schedule identifier.
State the required heat-treatment condition at delivery.
State dimensions, the controlling dimension and the applicable tolerance basis.
State the test and inspection plan, including who witnesses it.
State how grade identity is preserved through cutting, bending and bundling.

Alloy steel tube

The Alloy Steel Tube page covers the material family across mechanical and thermal duties, and provides the specification builder and RFQ handoff.

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Continue from the application to the specification

The circuit and the code come first. The standard, grade and treatment follow them.