Chapter 6 - Cargo Transfer
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Chapter 6 - Cargo Transfer

 To ensure the safe handling of all cargoes, under all normal operating conditions and foreseeable emergency conditions, to minimize the risk to the vessel, its crew and the environment, having regard to the nature of the products involved. This will:

  • .1 ensure the integrity of integral liquid product tanks, piping systems and cargo hoses;

  • .2 prevent the uncontrolled transfer of cargo; and

  • .3 ensure reliable means to fill and empty the cargo tank.

6.1 Piping scantlings

6.1.1 Subject to the conditions stated in 6.1.4, the wall thickness (t) of pipes should not be less than:

  • where

    • t0 = theoretical thickness

    • t0 = PD/(2Ke + P) (mm)
  • with
    • P = design pressure (MPa) referred to in 6.1.2

    • D = outside diameter (mm

    • K = allowable stress (N/mm2) referred to in 6.1.5

    • e = efficiency factor equal to 1.0 for seamless pipes and for longitudinally or spirally welded pipes, delivered by approved manufacturers of welded pipes, which are considered equivalent to seamless pipes when non-destructive testing on welds is carried out in accordance with recognized standards. In other cases, an efficiency factor of less than 1.0, in accordance with recognized 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 not less than:

    • with

    • r = mean radius of the bend (mm)

  • c = corrosion allowance (mm). If corrosion or erosion is expected, the wall thickness of piping should be increased over that required by the other design provisions.

  • a = negative manufacturing tolerance for thickness (%).

6.1.2 The design pressure P in the formula in 6.1.1 is the maximum gauge pressure to which the system may be subjected in service, taking into account the highest set pressure on the relief valve on the system.

6.1.3 Piping and piping-system components which are not protected by a relief valve, or which may be isolated from their relief valve, should be designed for at least the greatest of:

  • .1 for piping systems or components which may contain some liquid, the saturated vapour pressure at 45C;

  • .2 the pressure setting of the associated pump discharge relief valve;

  • .3 the scantlings' maximum possible total pressure head at the outlet of the associated pumps when a pump discharge relief valve is not installed; and

  • .4 for systems or components which may be separated from their relief valves and which contain only vapour at all times, the superheated vapour pressure at 45C, assuming an initial condition of saturated vapour in the system at the system operating pressure and temperature.

6.1.4 The design pressure should not be less than 1 MPa gauge except for open-ended lines, where it should be not less than 0.5 MPa gauge.

6.1.5 For pipes, the allowable stress K to be considered in the formula in 6.1.1 is the lower of the following values:

  • where

  • Rm = specified minimum tensile strength at ambient temperature (N/mm2).

  • Re = specified minimum yield stress at ambient temperature (N/mm2). If the stress-strain curve does not show a defined yield stress, the 0.2% proof stress applies.

  • A and B should have values of at least A = 2.7 and B = 1.8. The minimum wall thickness should be in accordance with recognized standards. Where necessary for mechanical strength to prevent damage, collapse, excessive sag or buckling of pipes due to weight of pipes and content and to superimposed loads from supports, vessel deflection or other causes, the wall thickness should be increased over that required by 6.1.1 or, if this is impracticable or would cause excessive local stresses, these loads should be reduced, protected against or eliminated by other design methods. Flanges, valves and other fittings should be in accordance with recognized standards, taking into account the design pressure defined under 6.1.2. For flanges not complying with a standard, the dimensions for flanges and associated bolts should be to the satisfaction of the Administration.

6.2 Piping fabrication and joining details

6.2.1 The provisions of this section apply to piping inside and outside the cargo tanks. However, relaxations from these provisions may be accepted in accordance with recognized standards for open-ended piping and for piping inside cargo tanks except for cargo piping serving other cargo tanks.

6.2.2 Cargo piping should be joined by welding except:

  • .1 for approved connections to shut-off valves and expansion joints; and

  • .2 for any practical vessel building and pipe corrosion protection limits taking into account the provisions stated in 6.2.5 and 6.3 in relation to any additional flanged connections, the use of flanged connections should be limited as far as possible.

6.2.3 Cargo piping for products or residues of products which are subject to the provisions of chapter 4 should be joined by welding.

6.2.4 The following direct connections of pipe lengths without flanges may be considered:

  • .1 Butt-welded joints with complete penetration at the root may be used in all applications.

  • .2 Slip-on welded joints with sleeves and related welding having dimensions in accordance with recognized standards should only be used for pipes with an external diameter of 50 mm or less. This type of joint should not be used when crevice corrosion is expected to occur.

  • .3 Screwed connections, in accordance with recognized standards, should only be used for accessory lines and instrumentation lines with external diameters of 25 mm or less.

6.2.5 Expansion of piping should normally be allowed for by the provision of expansion loops or bends in the piping system:

  • .1 bellows, in accordance with recognized standards and installed in an easily accessible location, may be specially considered; and

  • .2 slip joints should not be used.

6.2.6 Welding, post-weld heat treatment and non-destructive testing should be performed in accordance with recognized standards.

6.3 Flange connections

6.3.1 Flanges should be of the welded-neck, slip-on or socket-welded type. However, socket-welded-type flanges should not be used with an external diameter above 50 mm.

6.3.2 Flanges should comply with recognized standards as to their type, manufacture and test.

6.4 Test requirements for piping

6.4.1 The test provisions of this section apply to piping inside and outside cargo tanks. However, relaxations from these provisions may be accepted in accordance with recognized standards for piping inside tanks and open-ended piping.

6.4.2 After assembly, each cargo piping system should be subject to a hydrostatic test to at least 1.5 times the design pressure. When piping systems or parts of systems are completely manufactured and equipped with all fittings, the hydrostatic test may be conducted prior to installation aboard the vessel. Joints welded on board should be hydrostatically tested to at least 1.5 times the design pressure.

6.4.3 After assembly on board, each cargo piping system should be tested for leaks to a pressure depending on the method applied.

6.5 Piping arrangements

6.5.1 Cargo piping should not be installed under deck between the outboard side of the cargo containment spaces and the skin of the vessel unless clearances required for damage protection (see 2.9) are maintained; but such distances may be reduced where damage to the pipe would not cause release of cargo provided that the clearance required for inspection purposes is maintained.

6.5.2 Cargo piping located below the main deck may run from the tank it serves and penetrate tank bulkheads or boundaries common to longitudinally or transversally adjacent cargo tanks, ballast tanks, empty tanks, pump-rooms or cargo pump-rooms provided that inside the tank it serves it is fitted with a stop valve operable from the weather deck and provided cargo compatibility is assured in the event of piping failure. As an exception, where a cargo tank is adjacent to a cargo pump-room, the stop valve operable from the weather deck may be situated on the tank bulkhead on the cargo pump-room side, provided an additional valve is fitted between the bulkhead valve and the cargo pump. A totally enclosed hydraulically operated valve located outside the cargo tank may, however, be accepted, provided that the valve is:

  • .1 designed to preclude the risk of leakage;

  • .2 fitted on the bulkhead of the cargo tank which it serves;

  • .3 suitably protected against mechanical damage;

  • .4 fitted at a distance from the shell as required for damage protection; and

  • .5 operable from the weather deck.

6.5.3 If a cargo pump serves more than one tank, a stop valve should be fitted in the line to each tank.

6.5.4 Cargo piping installed in pipe tunnels should also comply with the provisions of 6.5.1 and 6.5.2. Pipe tunnels should satisfy all tank provisions for construction, location and ventilation and electrical hazard provisions. Cargo compatibility should be assured in the event of a piping failure. The tunnel should not have any other openings except to the weather deck and cargo pump-room or pump-room.

6.5.5 Cargo piping passing through bulkheads should be so arranged as to preclude excessive stresses at the bulkhead and should not utilize flanges bolted through the bulkhead.

6.5.6. In order to prevent any generation of static electricity, the outlets of filling lines should be led as low as possible in the tanks, except for vessels intended to carry pollution hazard only substances having a flashpoint exceeding 60C or oil products having a flashpoint exceeding 60C.

6.6 Cargo-transfer control systems

6.6.1 For the purpose of adequately controlling the cargo, cargo-transfer systems should be provided with:

  • .1 one stop valve capable of being manually operated on each tank filling and discharge line, located near the tank penetration; if an individual deep well pump is used to discharge the contents of a cargo tank, a stop valve is not required on the discharge line of that tank;

  • .2 one stop valve and break-away fitting at each cargo-hose connection; and

  • .3 remote shutdown devices for all cargo pumps and similar equipment which should be capable of being activated from a dedicated cargo control location and which is manned at the time of cargo transfer and from at least one other location outside the cargo area and at a safe distance from it; cargo controls located in the vessel wheelhouse are acceptable as one of the cargo control locations.

6.6.2 For certain products, additional cargo-transfer control requirements are shown in column o in the table of chapter 17 of the IBC Code.

6.6.3 Pump discharge pressure gauges or readouts should be provided outside the cargo pump-room.

6.7 Vessels' cargo hoses

6.7.1 Liquid and vapour hoses used for cargo transfer should be compatible with the cargo and suitable for the cargo temperature.

6.7.2 Hoses subject to tank pressure or the discharge pressure of pumps should be designed for a bursting pressure not less than 5 times the maximum pressure the hose will be subjected to during cargo transfer.

6.7.3 Drip trays for collecting cargo residues in cargo lines and hoses should be provided in the area of pipe and hose connections under the manifold area.

6.7.4 Each type of cargo hose, complete with end-fittings, should 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 should demonstrate a bursting pressure of at least 5 times its specified maximum working pressure at the extreme service temperature. Hoses used for prototype testing should not be used for cargo service. Thereafter, before being placed in service, each new length of cargo hose produced should 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 should be stencilled or otherwise marked with the date of testing, its specified maximum working pressure and, if used in services other than the ambient temperature services, its maximum and minimum service temperature, as applicable. The specified maximum working pressure should not be less than 10 bar gauge.

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