Section 5 Components
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Offshore Units, July 2022 - Part 11 Production, Storage and Offloading of Liquefied Gases in Bulk - Chapter 5 Process Pressure Vessels and Liquids, Vapour and Pressure Piping Systems and Offshore Arrangements - Section 5 Components

Section 5 Components

Parent topic: Chapter 5 Process Pressure Vessels and Liquids, Vapour and Pressure Piping Systems and Offshore Arrangements

5.1 Piping system requirements

5.1.1  Piping scantlings
  1. Piping systems shall be designed in accordance with recognised Standards.
  2. The following criteria shall be used for determining pipe wall thickness.

    The wall thickness of pipes shall not be less than:

    where

    t o = theoretical thickness
    t o =

    with

    P = design pressure (MPa) referred to in Pt 11, Ch 5, 2.1 Design pressure
    D = outside diameter (mm)
    K = allowable stress (N/mm2) referred to in Pt 11, Ch 5, 5.2 Stress aspects 5.2.1
    e = efficiency factor equal to 1,0 for seamless pipes and for longitudinally or spirally welded pipes, delivered by approved manufacturers of welded pipes, that are considered equivalent to seamless pipes when non destructive testing on welds is carried out in accordance with Recognised Standards. In other cases an efficiency factor of less than 1,0, in accordance with recognised Standards, may be required depending on the manufacturing process
    b = allowance for bending (mm). The value of b should be chosen so that the calculated stress in the bend, due to internal pressure only, does not exceed the allowable stress. Where such justification is not given, b should be:
    b =

    with

    r = mean radius of the bend (mm)
    c = corrosion allowance (mm). If corrosion or erosion is expected the wall thickness of the piping shall be increased over that required by other design requirements. This allowance shall be consistent with the expected life of the piping
    a = negative manufacturing tolerance for thickness (per cent).

5.1.2 The minimum wall thickness shall be in accordance with recognised Standards.

5.1.3 Where necessary for mechanical strength to prevent damage, collapse, excessive sag or buckling of pipes due to superimposed loads, the wall thickness shall be increased over that required by Pt 11, Ch 5, 5.1 Piping system requirements 5.1.1.(b) or, if this is impracticable or would cause excessive local stresses, these loads shall be reduced, protected against or eliminated by other design methods. Such superimposed loads may be due to; supporting structures, deflections of the ship unit, liquid pressure surge during transfer operations, the weight of suspended valves, reaction to loading arm connections, or otherwise.

5.1.4  Flanges, valves and fittings
  1. Flanges, valves and other fittings shall comply with recognised Standards, taking into account the material selected and the design pressure defined in Pt 11, Ch 5, 2.1 Design pressure. For bellows expansion joints used in vapour service, a lower minimum design pressure may be accepted.
  2. For flanges not complying with a recognised Standard, the dimensions of flanges and related bolts shall be to the satisfaction of LR.
  3. All emergency shutdown valves shall be of the ‘fail-closed’ type. (See Pt 11, Ch 5, 6.2 Testing requirements 6.2.1.(a) and Pt 11, Ch 18, 4.2 ESD valve requirements).
  4. The design and installation of expansion bellows shall be in accordance with recognised Standards and be fitted with means to prevent damage due to over-extension or compression.
5.1.5  Ship unit cargo hoses
  1. Liquid and vapour hoses used for cargo transfer shall be compatible with the cargo and suitable for the cargo temperature.
  2. Hoses subject to tank pressure, or the discharge pressure of pumps or vapour compressors, shall be designed for a bursting pressure not less than five times the maximum pressure the hose will be subjected to during cargo transfer.
  3. Each new type of cargo hose, complete with end fittings, shall be prototype-tested at a normal ambient temperature, with 200 pressure cycles from zero to at least twice the specified maximum working pressure. After this cycle pressure test has been carried out, the prototype test shall demonstrate a bursting pressure of at least 5 times its specified maximum working pressure at the upper and lower extreme service temperature. Hoses used for prototype testing shall not be used for cargo service. Thereafter, before being placed in service, each new length of cargo hose produced shall be hydrostatically tested at ambient temperature to a pressure not less than 1,5 times its specified maximum working pressure, but not more than two fifths of its bursting pressure. The hose shall be stencilled or otherwise marked with the date of testing, its specified maximum working pressure and, if used in services other than ambient temperature services, its maximum and minimum service temperature, as applicable. The specified maximum working pressure shall not be less than 1 MPa.

5.2 Stress aspects

5.2.1  Allowable stress
  1. For pipes, the allowable stress to be considered in the formula for t in Pt 11, Ch 5, 5.1 Piping system requirements 5.1.1.(b) is the lower of the following values:

    Rm/A or Re/B

    where

    Rm = specified minimum tensile strength at room temperature (N/mm2)
    Re = specified minimum yield stress at room temperature (N/mm2). If the stress strain curve does not show a defined yield stress, the 0,2 per cent proof stress applies.

    The values of A and B shall have values of at least A = 2,7 and B = 1,8.

5.2.2  High pressure gas fuel outer pipes or ducting scantlings
  1. In fuel gas piping systems of design pressure greater than the critical pressure, the tangential membrane stress of a straight section of pipe or ducting shall not exceed the tensile strength divided by 1,5 (i.e. Rm /1,5) when subjected to the design pressure specified in Pt 11, Ch 5, 2.2 Cargo system valve requirements 2.2.1. The pressure ratings of all other piping components shall reflect the same level of strength as straight pipes.
5.2.3  Stress analysis
  1. When the cargo design temperature is –110°C or colder, a complete stress analysis, taking into account all the stresses due to weight of pipes, including acceleration loads if significant, internal pressure, thermal contraction and loads induced by hogging and sagging of the ship unit for each branch of the piping system shall be submitted to LR. For temperatures above –110°C, a stress analysis may be required by LR in relation to such matters as the design or stiffness of the piping system and the choice of materials. In any case, consideration should be given to thermal stresses even though calculations are not submitted. The analysis may be carried out according to a Code of Practice acceptable to LR.
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