Section
1 General requirements
1.1 Application
1.1.1 The requirements of this Chapter are applicable to fusion welded pressure
vessels, including process pressure vessels, and heat exchangers, intended for marine
purposes but not included in Pt 5, Ch 10 Steam Raising Plant and Associated Pressure Vessels. The equations in this Chapter may be used for determining
the thickness of seamless pressure vessels using a joint factor of 1,0. Seamless
pressure vessels are to be manufactured and tested in accordance with the requirements
of Ch 5 Steel Forgings of the Rules for the Manufacture, Testing and Certification of Materials, July 2022. For
the construction and design of pressure vessels and plate heat exchangers for liquefied
gas or chemical cargo applications, see the
Rules and Regulations for the Construction and Classification of Ships for the Carriage of Liquefied Gases in Bulk, July 2022
or the
Rules and Regulations for the Construction and Classification of Ships for the Carriage of Liquid Chemicals in Bulk, July
2022
or the Rules and Regulations for the Classification of Ships using Gases or other Low-flashpoint Fuels, July 2022 as applicable.
1.2 Definition of symbols
1.2.1 The
symbols used in the various formulae in Pt 5, Ch 11, 2 Cylindrical shells and drums subject to internal pressure to Pt 5, Ch 11, 7 Standpipes and branches inclusive, unless
otherwise stated, are defined as follows, and are applicable to the
specific part of the pressure vessel under consideration:
d
|
= |
diameter
of hole, or opening, in mm |
r
i
|
= |
inside knuckle radius, in mm |
r
o
|
= |
outside knuckle radius, in mm |
t
|
= |
minimum
thickness, in mm |
c |
= |
corrosion allowance in mm for design and operating condition taking
into account the intended life cycle; a minimum corrosion allowance of 0,75 mm is
to be used, any deviation is to be agreed with LR taking into consideration the
material type, service fluid, design and operating conditions. The corrosion
allowance is to be added to the calculated Rule thickness as well as to the
minimum thickness specified by the Rules. |
D
i
|
= |
inside diameter, in mm |
D
o
|
= |
outside diameter, in mm |
R
i
|
= |
inside radius, in mm |
R
o
|
= |
outside radius, in mm |
T
|
= |
design
temperature, in °C |
1.2.2 Where reference is made to calculated or actual plate thickness for the
derivation of other values, these thicknesses are to be minus the corrosion allowance of
(c).
1.3 Design pressure
1.3.1 The
design pressure is the maximum permissible working pressure, and is
to be not less than the highest set pressure of any relief valve.
1.3.2 Calculations
made to determine the scantlings of the pressure parts are to be based
on the design pressure, adjusted where necessary to take account of
pressure variations corresponding to the most severe operational conditions.
1.3.3 It
is desirable that there should be a margin between the normal pressure
at which the pressure vessel operates and the lowest pressure at which
any relief valve is set to lift, to prevent unnecessary lifting of
the relief valve.
1.4 Metal temperature
1.4.1 The
metal temperature, T, used to evaluate the allowable
stress, σ, is to be taken as the actual metal temperature expected
under operating conditions for the pressure part concerned, and is
to be stated by the manufacturer when plans of the pressure parts
are submitted for consideration.
1.4.2 The
design temperature, T, for calculation purposes is to
be not less than 50°C.
1.5 Classification of fusion welded pressure vessels
1.5.1 For
Rule purposes, pressure vessels are graded as Class 1 where the shell
thickness exceeds 38 mm.
1.5.2 For
Rule purposes, pressure vessels are graded as Class 2/1 and Class
2/2 if they comply with the following conditions:
-
where the design pressure exceeds 1,72 MPa, or
-
where the metal
temperature exceeds 150°C, or
-
where the design pressure, in MPa, multiplied by the actual thickness
of the shell, in mm, exceeds 15,7, or
-
where the shell
thickness does not exceed 38 mm.
1.5.3 For
Rule purposes, Class 3 pressure vessels are to have a maximum shell
thickness of 16 mm, and are pressure vessels not included in Classes
1, 2/1 or 2/2.
1.5.4 Pressure
vessels which are constructed in accordance with Classes 2/1, 2/2
or 3 standards (as indicated above) will, if manufactured in accordance
with the requirements of superior Class, be approved with the scantlings
appropriate to that Class.
1.5.6 In
special circumstances relating to service conditions, materials, operating
temperature, the carriage of dangerous gases and liquids, etc. it
may be required that certain pressure vessels be manufactured in accordance
with the requirements of a superior Class.
1.5.8 Hydraulic
testing is required for all Classes of pressure vessels.
1.6 Plans
1.6.1 Plans
of pressure vessels are to be submitted in triplicate for consideration
where all the conditions in Pt 5, Ch 11, 1.6 Plans 1.6.1 or Pt 5, Ch 11, 1.6 Plans 1.6.1.(b) are satisfied:
-
The vessel contains
vapours or gases, e.g. air receivers, hydrophore or similar vessels
and gaseous CO2 vessels for fire-fighting, and
V
|
= |
volume
(litres) of gas or vapour space |
-
The vessel contains
liquefied gases, or flammable liquids
1.6.2 Plans
of full constructional features of the vessel and dimensional details
of the weld preparations for longitudinal and circumferential seams
and attachments, together with particulars of the welding consumables
and of the mechanical properties of the materials, are to be submitted
before construction is commenced.
1.7 Materials
1.7.1 Materials
used in the construction of Class 1, 2/1 and 2/2 pressure vessels
are to be manufactured, tested and certified in accordance with the
requirements of the Rules for Materials. Materials used in the construction
of Class 3 pressure vessels may be in accordance with the requirements
of an acceptable national or international specification. The manufacturer’s
certificate will be accepted in lieu of Clasifications Register (hereinafter
referred as 'LR') material certificate for such materials.
1.7.2 The
specified minimum tensile strength of carbon and carbon-manganese
steel plates, pipes, forgings and castings is to be within the general
limits of 340 to 520 N/mm2:
1.7.3 The
specified minimum tensile strength of low alloy steel plates, pipes,
forgings and castings is to be within the general limits of 400 to
500 N/mm2, and pressure vessels made in these steels are
to be either seamless or Class 1 fusion welded.
1.7.4 Where
it is proposed to use materials other than those specified in the
Rules for Materials, details of the chemical compositions, heat treatment
and mechanical properties are to be submitted for approval. In such
cases, the values of the mechanical properties used for deriving the
allowable stress are to be subject to agreement by LR.
1.8 Allowable stress
1.8.1 The
term `allowable stress', σ, is the stress to be used in the
formulae for the calculation of scantlings of pressure parts.
1.8.2 The
allowable stress, σ, is to be the lowest of the following values:
where
E
t
|
= |
specified minimum lower yield stress or 0,2 per cent proof stress
at temperature, T, for carbon and carbon-manganese steels.
In the case of austenitic steels, the 1,0 per cent proof stress at
temperature, T, is to be used
|
R
20
|
= |
specified minimum tensile strength at room temperature |
S
R
|
= |
average stress to produce rupture in 100 000 hours at temperature, T
|
T
|
= |
metal
temperature, see
Pt 5, Ch 11, 1.4 Metal temperature.
|
1.8.3 The
allowable stress for steel castings is to be taken as 80 per cent
of the value determined by the method indicated in Pt 5, Ch 11, 1.8 Allowable stress 1.8.2 using the appropriate values
for cast steel.
1.9 Joint factors
1.9.3 Where
a pressure vessel is to be made of alloy steel, particulars of the
welding consumables to be used, including typical mechanical properties
and chemical composition of the deposited weld metal, are to be submitted
for approval.
1.10 Pressure parts of irregular shape
1.11 Adverse working conditions
1.11.1 Where
working conditions are adverse, special consideration may require
to be given to increasing the scantlings derived from the formulae.
In this connection, where necessary, account should also be taken
of any excess of loading resulting from:
-
impact loads,
including rapidly fluctuating pressures,
-
weight of the
vessel and normal contents under operating and test conditions,
-
superimposed
loads, such as other pressure vessels, operating equipment, insulation,
corrosion-resistant or erosion-resistant linings and piping,
-
reactions of
supporting lugs, rings, saddles or other types of supports, or
-
the effect of
temperature gradients on maximum stress.
1.12 Alternative standards for design
1.12.1 Pressure vessels and heat exchangers designed in accordance with an appropriate and
established National or International Code or Standard considered acceptable by LR
may be accepted subject to agreement.
1.12.2 The Code or standard is to fully address the proposed design and provide for an
overall level of safety equivalent to that provided by the Rules which is to be
established and agreed with LR.
1.12.3 For designs already addressed within the Rules, corrosion allowances, wall
thicknesses for pressure boundaries and hydrostatic test pressures are to be in
accordance with the relevant requirements of the Rules irrespective of the
requirements of the Code or standard.
1.12.4 The allowable design stress is to be in accordance with the Code or Standard but is
not to exceed allowable design stress within the Rules.
1.12.5 The requirements in the Rules for materials are to be satisfied.
1.12.6 The mixing of different parts of Codes and Standards is not permitted.
|