3.1.1 Pressure piping systems are divided into three classes for the purpose of
assigning appropriate testing requirements, types of joints to be adopted, heat
treatment and weld procedure.
3.1.2 Dependent on the service for which they are intended, Class II and III pipes are not to
be used for design pressure or temperature conditions in excess of those shown in Table 1.3.1 Maximum pressure and temperature
conditions for Class II and III piping systems.
Where either the maximum design pressure or temperature exceeds that applicable to Class
II pipes, Class I pipes are to be used. To illustrate this, see
Figure 1.3.1 Classes of piping system.
Figure 1.3.1 Classes of piping system
Table 1.3.1 Maximum pressure and temperature
conditions for Class II and III piping systems
| Piping system
|
Class II
|
Class III
|
| P2
|
T
2
|
P1
|
T
1
|
|
|
bar
|
oC
|
bar
|
oC
|
| Steam
|
16,0
|
300
|
7,0
|
170
|
| Thermal
oil
|
16,0
|
300
|
7,0
|
150
|
Flammable
liquids,
see Note 1
|
16,0
|
150
|
7,0
|
60
|
| Other media,
see Note 2
|
40,0
|
300
|
16,0
|
200
|
|
Note 1. Flammable liquids
include: fuel oil, lubricating oil and flammable hydraulic oil.
Note 2. Including water, air, gases, non-flammable hydraulic oil.
|
3.1.4 Class II and III pipes are not to be used for toxic media.
3.1.5 Class I pipes are generally required for corrosive media. Class II pipes may be used for
corrosive media where special safeguards for reducing the potential for leakage and
limiting its consequences are provided, e.g. the use of pipe ducts, shielding,
screening, etc. in such a way that a leakage will not cause a potential hazard or damage
to surrounding areas. Class III pipes are not to be used for corrosive media. Materials
used for piping for corrosive media are to be specially considered.