Editing Boiler (section)

==Materials==
The [[pressure vessel]] of a boiler is usually made of [[mild steel|steel]] (or [[alloy steel]]), or historically of [[wrought iron]]. [[Stainless steel]], especially of the [[Austenitic stainless steel|austenitic]] types, is not used in wetted parts of boilers due to corrosion and [[stress corrosion cracking]].<ref>{{cite book| title=ASME Boiler and Pressure Vessel Code, Section I, PG-5.5| publisher=[[American Society of Mechanical Engineers]]| year=2010}}</ref>{{page needed|date=February 2021}} However, ferritic stainless steel is often used in superheater sections that will not be exposed to boiling water, and electrically heated stainless steel shell boilers are allowed under the European "Pressure Equipment Directive" for production of steam for sterilizers and disinfectors.<ref>BS EN 14222: "Stainless steel shell boilers"{{full citation needed|date=February 2021}}</ref>

In [[live steam]] [[Scale model|models]], copper or brass is often used because it is more easily fabricated in smaller size boilers. Historically, copper was often used for [[Firebox (locomotive)|firebox]]es (particularly for [[steam locomotive]]s), because of its better formability and higher thermal conductivity; however, in more recent times, the high price of copper often makes this an uneconomic choice and cheaper substitutes (such as steel) are used instead.{{citation needed|date=November 2023}}

For much of the Victorian "age of steam", the only material used for boilermaking was the highest grade of [[wrought iron]], with assembly by [[rivet]]ing. This iron was often obtained from specialist [[ironworks]], such as those in the [[Cleator Moor]] (UK) area, noted for the high quality of their [[Rolling (metalworking)|rolled]] [[Structural steel|plate]], which was especially suitable for use in critical applications such as high-pressure boilers. In the 20th century, design practice moved towards the use of steel, with [[Welding|welded]] construction, which is stronger and cheaper, and can be fabricated more quickly and with less labour. Wrought iron boilers corrode far more slowly than their modern-day steel counterparts, and are less susceptible to localized pitting and stress-corrosion. That makes the longevity of older wrought-iron boilers far superior to that of welded steel boilers.{{Citation needed|date=August 2018}}

[[Cast iron]] may be used for the heating vessel of domestic water heaters. Although such heaters are usually termed "boilers" in some countries, their purpose is usually to produce hot water, not steam, and so they run at low pressure and try to avoid boiling. The brittleness of cast iron makes it impractical for high-pressure steam boilers.