Materials of Construction
Material properties are of great importance in all aspects of pressure
equipment design and manufacture. It is essential to check the up-to-date
version of the relevant British Standards, or equivalent, when choosing or
assessing a material. The most common steels used for pressure equipment
are divided into the generic categories of carbon, alloy, stainless steel, and
8.1 Plain carbon steels – basic data
Typical properties of plain carbon steels are shown in Table 8.1
Table 8.1 Plain carbon steel: properties
Low C steel
General structural steel
8.2 Alloy steels
Alloy steels have various amounts of Ni, Cr, Mn, or Mo added to improve
properties. Typical properties are shown in Table 8.2.
Engineers’ Guide to Pressure Equipment
Table 8.2 Alloy steels: properties
8.3 Stainless steels – basic data
Stainless steel is a generic term used to describe a family of steel alloys
containing more than about 11 per cent chromium. The family consists of
four main classes, subdivided into approximately 100 grades and variants.
The main classes are austenitic and duplex; the other two classes, ferritic
and martensitic, tend to have more specialized application and so are not as
commonly found in general pressure equipment use. The basic
characteristics of each class are given below.
• Austenitic The most commonly used basic grades of stainless steel are
usually austenitic. They have 17–25% Cr, combined with 8–20% Ni, Mn,
and other trace alloying elements that encourage the formation of
austenite. They have low carbon content, which makes them weldable.
They have the highest general corrosion resistance of the family of
• Ferritic Ferritic stainless steels have high chrom