Boiler Tubes are metal tubes located inside of boilers that heat water in order to produce steam. There are two major types of tube boilers: water-tube boilers and fire-tube boilers. In water-tube boilers, water circulates inside the tubes and is heated externally by hot gases generated by the furnace.

What are the tubes in a boiler called?

Boiler tubes can either be medium-pressure boiler pipe or high-pressure boiler pipe.

How Are Boiler Tubes Made?

Both medium-pressure and high-pressure boiler tubes undergo the same initial process of manufacturing, which includes fine drawing, surface bright, hot rolling, cold drawn and heat expansion. However, the following steps are undertaken to make high-pressure pipes stronger and more resistant.

Heat treatment includes heating and cooling of the high-pressure boiler pipes which increases toughness, hardness and wear resistance. The different steps that come under heat treatment include quenching, tempering and annealing.

Quenching is done to increase the hardness of the high-pressure boiler tube. The pipe is heated evenly to an appropriate temperature and then quickly immersed into water or oil for instant cooling. This is followed by cooling in air or in the freezing zone.

Tempering is used to remove brittleness from the pipe. Quenching can cause the pipe to become tapped or broken.

Annealing can remove the internal stress in the pipe. In this process, the seamless tube is heated to the critical temperature and then left for slow cooling in ash or lime.

Rust Removal of the Boiler Tube

There are several methods for removing rust from the boiler tube, the simplest being cleaning using a solvent and emulsion. However, this can remove only dust, oil, etc. but will not rid the pipe completely off organic remnants.

The second method is rust removal using manual or power tools. Tool cleaning can get rid of oxide coatings, welding slag and rust.

The most common method is through chemical and electrolytic methods, also known as acid cleaning.

Spray rust removal is the most ideal method for cleaning of the boiler tube as it can remove dirt, oxide and rust to a greater level. Furthermore, it can increase the roughness of the pipe.

How to Choose Good Quality Boiler Tubes?

While choosing boiler tubes, look for the following to pick out the right and good quality tubes:

Look at the cross-section of the tube. A good quality seamless tube will have a smooth cross-section and will be devoid of bumps and irregularities.
Check the density of the pipe to understand the percentage of impurities in the pipe. If the pipe shows low density, steer clear!
Make sure you check the trademark. Reputed manufacturers always put their trademark on their seamless tubes.
Check the surface of the boiler tube. A good quality boiler tube will have a smooth surface. If you find the surface to be rough and uneven, you can be sure that the quality is not up to the mark.

Where are boiler tubes used?

Boiler tubing is used in these industries:

Steam Boilers.
Fossil Fuel Plants.
Heat Exchangers.
Electric Power Plants.
Cogeneration Facilities.
Air Preheater Unit.
Waste Heat Plants.
Power Generation.

What is the Material of Boiler Tubes?

There are two significant types of boiler tubes: water-tube tubes and fire-tube tubes.

Water-tube Boiler tubes

A boiler with a high-pressure water tube has become a boiler in which water flows in tubes externally heated by gases. Within the furnace, fuel is burned, producing hot gas that heats water in the pipes to produce steam. In smaller Boiler tubes, the furnace is isolated by external heating tubing. In contrast, larger service Boilers depend on the water-filled tubing that makes up the furnace walls to produce steam.

Fire-tube Boiler tubes

A fire tube boiler is a boiler whereby heated gasses flow from a flame through one or more tubes, flowing through a sealed water tube. The heat of the gasses is transmitted through thermal conduction through the tube walls, heating up the water and eventually producing steam. This boiler was used in the horizontal locomotive configuration on nearly all steam locomotives. This has a tubular container that holds the fire tubes and an extension to fit the one-end firebox. This firebox has an open foundation to have a wide area of the grate, stretching to create a rectangular or tapered structure outside the cylindrical container.

Materials used for Manufacturing Boiler Tubes

A boiler tube is typically constructed of steel (or alloy) or traditionally wrought iron. Due to corrosion and stress corrosion cracking, Stainless steel, particularly of the austenitic forms, is not used in wetted sections of Boiler tubes. Ferritic stainless steel is, however, frequently found in overheated areas that are not subject to boiling water, and electrically heated stainless steel shell Boiler tubes are allowed for steam processing for sterilizers and disinfectors under the European “Pressure Device Guideline.”

Copper or brass is also used in live steam versions since it is cheaper to produce in smaller Boiler tubes. Traditionally, copper is most often used in fireboxes because of its better formability and higher thermal conductivity; however, in recent years, copper prices have rendered this an economical option and then use affordable alternatives (such as steel).

The only commodity used in boiler construction during most of the Victorian “era of steam” was the lowest quality wrought iron, with mounting by riveting. This iron was primarily sourced from specialist ironworks, such as those in the Celator Moor region (UK), known for the high nature of their rolled steel, which was ideal for use in essential applications such as increased-pressure Boiler tubes. Technology innovation in the 20th century shifted towards steel usage of welded production, which is safer and more straightforward, which can be made quicker and with less labour. Wrought iron Boiler tubes corrode even more gradually than their counterparts in conventional steel and are less prone to irregular pitting and stress corrosion. The longevity of older wrought-iron Boiler tubes is far superior to that of welded steel Boiler tubes.

Boiler Tube Standard Specifications

Carbon steel

GB
Chinese National standards

GB 3087: Seamless steel tubes for low and medium pressure boiler
GB 5310: Seamless steel tube for high pressure boiler
GB 13296: Seamless steel tubes for boilers and heat exchangers
GB 6479: Seamless steel tubes for high-pressure chemical fertilizer equipment
GB 9948: Seamless steel tubes for petroleum cracking

ASME
American society of mechanical engineers

ASME SA-106: Standard Specification for Seamless Carbon Steel Pipe for High-Temperature Service
ASME SA-192M: Seamless Carbon Steel Boiler Tubes for High Pressure
ASME SA-209M: Seamless carbon-Molybdenum Alloy-Steel Boiler and Superheater Tubes
ASME SA-210M: Seamless Medium-carbon Steel Boiler and Superheater Tubes
ASME SA-213M: Seamless ferritic and austenitic alloy steel boiler, superheater and heat exchanger tubes
ASME SA178: Electric-Resistance-Welded Carbon Steel and Carbon-Manganese Steel Boiler and Superheater

ASTM
American Society of Testing Materials standards

ASTM A213: Seamless ferritic and austenitic alloy steel boiler, superheater and heat exchanger tubes
SA213-T2: ASME SA213 T2 has allowable stresses listed up to 1000F in the ASME Boiler Code.
SA213-T9
SA213-T12: Seamless Ferritic and Austenitic Alloy-Steel Boiler, Superheater, Heat-Exchanger Tubes.
SA213-T11: The tubes are used in heat exchangers, super heaters and in boilers.
SA213-T22: ASM T22 Boiler Tube is a high temperature tolerance tube that is used in acidic and corrosive environments such as the hydrochloric processing and in aluminum chloride catalyst involving applications.
ASTM A 106M: Seamless Carbon Steel Pipe for High-Temperature Service
ASTM A192M: Seamless Carbon Steel Boiler Tubes for High Pressure
ASTM A210M: Seamless Medium-carbon Steel Boiler and Superheater Tubes
ASTM A 335M: Seamless ferritic alloy-steel pipe for high-temperature service

EN
European standards

EN 10216-2 : Seamless steel tubes for pressure purposes

DIN
German standards

DIN 17175:Seamless Tubes of Heat-resistant Steels – Technical Conditions of Delivery

JIS
Japanese industrial standards

JIS G3461: Carbon steel boiler and heat exchanger tubes
JIS G3462: Alloy steel boiler and heat exchanger tubes
JIS G3463: Stainless Steel for Boiler and Heat Exchanger Tubes

Stainless steel

SA213-T304:

– The SA 213 Tp 304 Material consists of 18% chromium and carbon, manganese, phosphorus, sulfur, silicon and nickel in the composition.

SA213 TP304 is a range of minimum wall thickness pipe series. We supply the SA 213 TP 304 Pipes in different types, shapes and sizes. The SA 213 Tp 304 Material consists of 18% chromium and carbon, manganese, phosphorus, sulfur, silicon and nickel in the composition. There is also the molybdenum, nitrogen, niobium and titanium addition in trace quantities. The SA 213 Tp 304 Density is lower than the ordinary 304 material. It is 7.8 grams per cubic centimeter. We offer ASTM A213 TP 304 for high temperature services. Our 304 Stainless Steel Tube components are of less absolute roughness which means they could be used in high precision equipment and applications.

Austenitic stainless steels are presented in the ASME Boiler and Pressure Vessel Code with two sets of allowable stresses. The reason for this is their relatively low yield strength. The higher allowable stress values were determined at temperatures where the usage would be restricted by the short-time tensile properties.

The higher stresses exceed 62-1/2%, but do not exceed 90% of the yield strength. At these stresses, small amounts of plastic deformation can be expected. These higher stress values are usually used for super-heater and reheater tubing.

The Boiler Code lists maximum allowable stresses for varying temperatures depending on the individual austenitic stainless grade.

Variations of this 18 chromium, 8 nickel grade include 304L, 304LN, 304H and 304N. Each of these offers excellent corrosion and oxidation resistance along with high strength.

High strengths are maintained in the low carbon grades by controlling the nitrogen content.

T304 has higher carbon and a minimum solution annealing temperature to assure good long-time elevated temperature strengths. T304 grades are limited to 1650F under oxidizing conditions. Section I of the ASME Boiler Code lists allowable stresses up to 1500F.

SA213-T316:

– SA213 TP316 Tube is a material standard for heat exchanger tubes that are made from 316 austenitic stainless steel.

The chromium nickel alloy also has molybdenum in its composition which makes it more corrosion resistant and heat resistant than the 304 material. ASME SA213 TP316 is the second most used pipe material in the world next to the 304 material. ASTM A213 TP316 Tube is an austenitic stainless steel but the 213 standard covers both the austenitic and ferritic steels.

SA213-TP321 & 347:

– SA213 TP321 is a specification of heat exchanger tubes that are made from the 321 austenitic stainless steel.

SA213 TP321 is a specification of heat exchanger tubes that are made from the 321 austenitic stainless steel. The SA 213 specifies pipe products for heat exchangers in different material grades, both the ferritic and austenitic steels.

Bestar Steel is a supplier of all kinds of stainless steel pipes. The SA213 Tp321 Material is special in that the composition includes titanium which reduces the density of the ASME SA213 Tp321 and therefore making it lightweight.

T321 and 347 are variations of T304 and have comparable minimum tensile properties. These two grades are stabilized with additions of titanium and columbian respectively, along with proper heat treatment.

To insure good long-time strength at elevated temperatures, T321H and 347H-like 304H-were developed with higher carbon contents and specified minimum solution annealing temperatures.

Of all the stainless steels, T309 (25 chromium, 13 nickel) and T310 (25 chromium, 20 nickel) offer the maximum resistance to oxidation and corrosion. They also offer good high-temperature properties. Since these steels contain ferrite, however, they are more susceptible to sigma phase.