What are Boiler Pipes?
Boiler pipes are piping made from chromium molybdenum alloys for high-temperature applications. They can be seamless or ERW, but the former is more popular due to its higher pressure/temperature resistance. According to these requirements, boiler tubes can be divided into two types;
- General use/ medium-pressure boiler pipes
- High-pressure boiler pipes
Types of Boiler Pipes
General use/ medium-pressure boiler pipes are used in environments up to 842 degrees Fahrenheit. These pipes are typically made via the hot rolling and cold drawing process. These pipes have applications such as boiling water pipes, locomotive boilers, arch brick pies, superheated steam pipes, smoke pipes, and more.
On the other hand, high-pressure boiler piping has higher corrosion resistance and durability than general-use boiler pipes. They are used for high-temperature and high-pressure applications where the pipes risk oxidation on exposure to corrosive steam and fluid. Due to their structural stability, high-pressure boiler tubes are used in high and ultra-high-pressure applications, including
- Air ducts in petrochemical industries
- Reheater tubes
- Main steam tubes,
- Superheater pipes
Manufacturing Process for Boiler Pipes
The manufacturing for both general-use boiler pipes and high-pressure boiler tubes is the same initially. Both types of boiler tubing follow the crucial steps of
- Fine Drawing
- Surface Brightening
- Hot Rolling
- Cold Drawing
- Heat Expansion
However, high-pressure boiler pipes are processed further to improve their corrosion resistance, toughness, and hardness. These pipes go through the following extra process compared to general boiler pipes and medium-pressure boiler pipes.
- Quenching- This process refers to instant cooling, where heated pipes are dipped into water and oil for cooling. Quenching improves steel hardness as the pipes must adjust to the quick changes in surface temperature.
- Tempering is done to rid the pipe of the brittleness caused by quenching.
- In annealing, the steel is heated to a specific temperature and left to cool slowly in lime. This process helps get rid of the pipe’s internal stress.
Dehydrogenation of Boiler Pipes: How Does it Work?
In pipe manufacturing, it is crucial for steel plates/billets to pass through multiple chemical and electrochemical processes. This includes surface rolling, head extension, annealing, and more for boiler pipes. However, during this process, it is common for hydrogen to be absorbed into the steel, resulting in a degradation of the mechanical properties of the boiler pipes.
Exposure to various elements during manufacturing causes hydrogen atoms to diffuse and dissolve into steel n a phenomenon known as hydrogen embrittlement. Dehydrogenation is a post-welding treatment that allows this hydrogen to escape from the heat-affected zones on the pipe. The general requirements for this process are as follows:
- The heat must be between 482 to 572 Degrees Fahrenheit
- Process time should be between 2 hours to 6 hours.
Compared to other post-weld treatments, dehydrogenation requires a lower temperature range. However, this is a crucial step as it allows the diffused hydrogen in the steel to escape, reducing product brittleness.
Characteristic Features of Boiler Pipes
- Owing to the high-pressure application, only seamless pipes and ERW are used as boiler products.
- Boiler pipes are available in carbon steel, alloy, and stainless steel options.
- The Outer Diameter of boiler pipes varies from 6 mm to 1250 mm.
- Boiler pipes have a low thickness ranging from 1 mm to 50 mm.
Boiler Pipe Applications
Boiler pipes have applications in
- Energy Generation
- Electric Power Plants
- Steam Boilers
- Petrochemical Industry
Boiler Pipe Specifications
Some important specifications for boiler pipes include ASTM A178, ASTM A192, ASTM 210. ASTM 209. These classifications are used to standardise boiler pipes according to their
- Size
- Shape
- Marking
- Tensile Properties
- Hardness and Softness Index
- Weight Deviations
- Quality Testing and Inspections
ASTM A192 Specifications for Boiler Pipes
This standard covers minimal wall thickness, seamless carbon steel boiler tubes for high-pressure application. Pipes made under ASTM A192 specifications in high-pressure boilers whose working pressure does not exceed 9.8 MPa. These pipes also possess the following characteristics
- These pipes have an average thickness of 3 mm to 12 mm.
- ASTM A192 pipes are either cold rolled or cold drawn.
- This standard covers schedules 40, 80, 160, XS, XXS.
- ASTM A192 boiler pipes are available in straight tube and U-bend tube.
- These pipes have an Outside Diameter of ½ inch to 7 inches.
- The length of the boiler piping varies from 19 feet to 104 feet.
Tensile Properties for ASTM A192
| Properties | ASTM A192 |
| Hardness(maximum) | 77 HRB |
| Tensile Strength | 325 MPa |
| Yield Strength | 180 MPa |
| Elongation(Minimum %) | 35 % |
Chemical Properties for ASTM A192 Boiler Pipes
| Elements | ASTM A192 |
| Silicon | 0.25% (max %) |
| Sulfur | 0.035% (max %) |
| Carbon | 0.06% to 0.18 % |
| Manganese | 0.27 % to 0.63 % |
| Phosphorous | 0.035% (max %) |
ASTM A178 Specification for Boiler Pipes
This specification covers ERW carbon steel and carbon manganese pipes for application in superheaters and boilers. Under AST A178, pipes fall under the following range;
- ASTM Grade A- For steel with low carbon content
- ASTM Grade C- For steel with medium carbon content
- ASTM Grade D- For carbon-manganese steel
Chemical Properties of ASTM A178 Pipes
| Elements | ASTM A178 Grade A | ASTM A178 Grade C | ASTM A178 Grade D |
| Silicon | 0.10% (min %) | ||
| Sulfur | 0.035% (max %) | 0.035% (max %) | 0.015% (max %) |
| Carbon | 0.06% to 0.18 % | 0.035% (max %) | 0.25 % (max %) |
| Manganese | 0.27 % to 0.63 % | 0.80 % (max %) | 1.0% to 1.50% |
| Phosphorous | 0.035% (max %) | 0.035% (max %) | 0.30% (max %) |
Tensile Properties of ASTM A178 Pipes
| Properties | ASTM A178 Grade A | ASTM A178 Grade C | ASTM A178 Grade D |
| Hardness(maximum) | 77 HRB | 79 HRB | 77 HRB |
| Tensile Strength | 325 MPa | 415 MPa | 485 MPa |
| Yield Strength | 180 MPa | 425 MPa | 275 MPa |
ASTM 210 Specifications for Boiler Pipes
This specification covers the standards for seamless medium carbon steel boiler and superheater tubing. Some of the chief characteristics of ASTM 210 pipes include;\
- Two ASTM Grades A1 and C cover the standard for carbon steel boiler pipes.
- The Outer Diameter of these pipes ranges from 12.7 mm to 114.3 mm
- The average wall thickness of ASTM 210 ppes ranges from 0.8 mm to 15 mm
Tensile Properties for ASTM 210
| Properties | ASTM A210 Grade A1 | ASTM A210 Grade C |
| Elongation (%) | >30 | >30 |
| Tensile Strength | >415 MPa | >485 MPa |
| Yield Strength | >255 MPa | >275 MPa |
Chemical Properties for ASTM 210
| Elements | ASTM 210 Grade A1 | ASTM 210 Grade C |
| Silicon | 0.035 (max) | 0.035 (max) |
| Sulfur | 0.035 (max) | 0.035 (max) |
| Carbon | 0.27 (max) | 0.35 (max) |
| Manganese | 0.93 (max) | 0.29 to 1.06 |
| Phosphorous | 0.035 (max) | 0.035 (max) |
ASTM A335 P91 Specification for Boiler Pipes
ASTM A335 is the specification covering minimal and nominal wall requirements for seamless ferritic alloy-steel pipe for use in high-temperature service. Piping under this specification contains more alloying elements like Chromium, Nickel and Molybdenum than carbon steel pipes. The presence of these substances makes A335 pipes apt for projects that require tolerance to extremely high or low temperatures (cryogenic).
ASTM A335 pipes are also called low-alloy pipes because the amount of alloying elements in these piping is typically below 5%. These elements improve the properties of the steel piping in the following ways.
These pipes also exhibit high tensile strength and corrosion resistance, making them withstand high pressure, making P91s well-suited for several forming and fusion welding operations, including flanging and bending.
These pipes have a general NPS of ¼ to 24 and cover schedules 40 through 160, XXH, XH, and STD. ASTM A335 P91 Pipes are used in power plants, downstream oil and gas:l
Chemical Properties of ASTM A335 P91 Pipes
| Element | P91 Type 1 | P91 Type 2 |
| Molybdenum | 0.85 to 1.05 | 0.003 (max) |
| Chromium | 8.0 to 9.50 | 8.0 to 9.50 |
| Sulfur (Max %) | 0.010 | 0.005 |
| Phosphorous (Max %) | 0.020 | 0.020 |
| Manganese | 0.30 to 0.60 | 0.30 to 0.50 |
| Carbon | 0.08 to 0.12 | 0.08 to 0.12 |
| Silicon | 0.20 to 0.50 | 0.20 to 0.40 |
| Nitrogen | 0030 to 0.070 | 0.035 to 0.070 |
- In addition, ASTM A335 P91 Type Pipes also contain Tin (0.010 max) and Antimony (0.005 max).
Tensile Properties of ASTM A335 P91 Pipes
| Tensile Strength (Minimum) | Yield Strength (Minimum) | |
| P91 | 585 MPa | 415 Mpa |
Other Specifications for Stainless Steel Boiler Pipes
- ASTM A213
- ASTM A210M: Specification for seamless medium-carbon steel boiler and superheater tube
- ASTM A213: Specification used for making seamless ferritic/austenitic alloy steel super heater, steel boiler, and heat exchanger tubes
- SA213-T2: ASME SA213 T2 SA213-T9
- SA213-T12: Specification for seamless ferritic and austenitic alloy boiler, superheater, and heat-exchanger.
- SA213-T11: The tubes made using this specification are used in heat exchangers, superheaters, and boilers.
- SA213-T22: ASM T22 Boiler Tube: used in acidic and corrosive applications such as hydrochloric processing that require hydrochloric acid and aluminium chloride catalyst.