Page 43 - Pressure Vessel Design Manual

General Design 29

stress value at each temperature would be used. When more e MAP, new and cold, PM
than one set of conditions is specified for a given vessel, the Shell:
vessel designer and user should decide which set of condi-
tions will govern for the setting of the relief valve.
Maximum Allowable Pressure (MAP): The term MAP PM = SaEtsn or SaEtsn
is often used. It refers to the maximum permissible pressure Rn + 0.6tsn R, - 0.4tsn
based on the weakest part in the new (uncorroded) and cold
condition, and all other loadings are not taken into consid- 2:l S.E. Head:
eration.
Design Pressure: The pressure used in the design of a
vessel component for the most severe condition of coinci-
dent pressure and temperature expected in normal opera-
tion. For this condition, and test condition, the maximum
difference in pressure between the inside and outside of a e Shop test pressure, Ps.
vessel, or between any two chambers of a combination unit,
shall be considered. Any thichess required for static head or P, = 1.3P~ or 1.3P~ -
other loadings shall be additional to that required for the
design pressure.
Design Temperature: For most vessels, it is the tem- e Field test pressure, PF.
perature that corresponds to the design pressure.
However, there is a maximum design temperature and a PF = 1.3P
minimum design temperature for any given vessel. The mini-
mum design temperature would be the MDMT (see e For clad vessels where credit is taken for the clad material,
Procedure 2-17). The MDMT shall be the lowest tempera- the following thicknesses may be substituted into the equa-
ture expected in service or the lowest allowable temperature tions for MAP and MAWP:
as calculated for the individual parts. Design temperature for
vessels under external pressure shall not exceed the maxi-
mum temperatures given on the external pressure charts.
Operating Pressure: The pressure at the top of the
vessel at which it normally operates. It shall be lower than
the MAWP, design pressure, or the set pressure of any pres-
sure relieving device.
Operating Temperature: The temperature that will be
maintained in the metal of the part of the vessel being con-
sidered for the specified operation of the vessel.
Notes

Calculations 1. Also check the pressure-temperature rating of the
flanges for MAWP and MAP.
e MAWP, corroded at Design Temperature P,. 2. All nozzles should be reinforced for MAWP.
3. The MAP and MAWP for other components, i.e.,
Shell: cones, flat heads, hemi-heads, torispherical heads,
etc., may be checked in the same manner by using
the formula for pressure found in Procedure 2-1 and
substituting the appropriate terms into the equations.
4. It is not necessary to take credit for the cladding thick-
2:l S.E. Head: ness. If it is elected not to take credit for the cladding
thickness, then base all calculations on the full base
metal thickness. This assumes the cladding is equiva-
lent to a corrosion allowance, and no credit is taken for
the strength of the cladding.