ᾼ Ņ Üᾍ NᾩᾩŃ Ì Ň ÜÌLL

where:

ᾼL = theoretical thickness (mm )

ᾼ ČÁ

L Ņ ÜĪÅᾙ Ñ Č

with:

Č = design pressure (MPa) referred to in Par 5

Á = outside diameter of pipe (mm )

Å = allowable stress (NÕmmĪ) referred to in Par 6

ᾙ = 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.

ᾎ = allowance for bending (mm ). The value of ᾎ is to 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,

ᾎ is to be:

Ü

ᾎ Ņ ÁᾼL

ĪǾJᾮ

with :

ᾮ = mean radius of the bend (mm )

ᾏ = corrosion allowance (mm ). If corrosion or erosion is expected, the wall thickness of the piping is to be increased over that required by other design requirements. This allowance is to be consistent with the expected life of the piping.

ᾍ = negative manufacturing tolerance of thickness (%).

The minimum wall thickness is to be in accordance with recognized standards.

5. The greater of the following design conditions is to be used for piping, piping systems and compo- nents as appropriate:

(1) 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 45°C or higher or lower if agreed upon by the Society (See 402. 6 (2) of the Rules for Steel Ships Pt. 7 Ch. 5), assuming an initial condition of saturated vapour in the system at the system operating pressure and temper- ature; or

(2) the MARVS of the gas tanks and gas processing systems; or

(3) the pressure setting of the associated pump or compressor discharge relief valve if of sufficient capacity; or

(4) the maximum total discharge or loading head of the gas piping system; or

(5) the relief valve setting on a pipeline system, if of sufficient capacity; or

(6) The design pressure is not to be less than 1.0 MPa gauge except for open ended lines where it should be not less than 0.5 MPa gauge.

6. For pipes made of steel including stainless steel, the permissible stress to be considered in the for- mula for t in Par 4 is the lower of the following values:

ĈᾩÕA or ĈᾙÕÆ

where:

ᾩ

Ĉ = specified minimum tensile strength at room temperature (NÕmm Ī)

Ī

Ĉᾙ = specified minimum yield stress or 0.2% proof stress at room temperature (NÕmm )

A = 2.7 and Æ = 1.8.

For pipes made of materials other than steel, the allowable stress is to be considered by the Society.

7. Where necessary for mechanical strength to prevent damage, collapse, excessive sag or buckling of pipes due to superimposed loads from supports, ship deflection or other causes, the wall thickness is to be increased over that required by Par 4, or, if this is impracticable or would cause ex- cessive local stresses, these loads are to be reduced, protected against or eliminated by other design methods.

8. Gas piping systems are to have sufficient constructive strength. For high pressure gas piping sys- tems, this is to be confirmed by carrying out stress analysis and taking into account:

(1) stresses due to the weight of the piping system;

(2) acceleration loads when significant; and

(3) internal pressure and loads induced by hog and sag of the ship.

9. Flanges, valves and other fittings should comply with recognized standards, taking into account the design pressure defined in Par 5. For bellows expansion joints used in vapour service, a lower minimum design pressure than defined in Par 5. may be accepted.

10. All valves and expansion joints used in high pressure gas systems are to be of an approved type.

11.

The following types of connections may be considered for direct connection of pipe lengths (without flanges):

(1) Butt-welded joints with complete penetration at the root may be used in all applications. For design temperatures below -10°C, butt welds are to be either double welded or equivalent to a double welded butt joint. This may be accomplished by use of a backing ring, consumable in- sert or inert gas back-up on the first pass. For design pressures in excess of 1.0 MPa and de- sign temperatures of -10°C or lower, backing rings are to be removed.

(2) Slip-on welded joints with sleeves and related welding, having dimensions in accordance with recognized standards, are only to be used for open-ended lines with external diameter of 50 mm

or less and design temperatures not lower than -55°C.

(3) Screwed couplings are only to be used for accessory lines and instrumentation lines with ex- ternal diameters of 25 mm or less.

Flanges in flange connections are to be of the welded neck, slip-on or socket welded type. For all

12. piping except open ended line, the following restrictions apply:

(1) For design temperatures lower than -55°C, only welded neck flanges are to be used.

(2) For design temperatures lower than -10°C, slip-on flanges are not to be used in nominal sizes above 100 mm and socket welded flanges are not to be used in nominal sizes above 50 mm .

13.

14.

Piping connections, other than those mentioned in Par 11 and Society.

Post-weld heat treatment is to be required for all butt welds of

12, may be accepted by the

pipes made with carbon, car-

15.

bon-manganese and low alloy steels. The Society may waive the requirement for thermal stress re- lieving of pipes having wall thickness less than 10 mm in relation to the design temperature and

pressure of the piping system concerned.

When the design temperature is -110 °C or lower, a complete stress analysis for each branch of the piping system is to be submitted to the Society. This analysis is to take into account all stress- es due to weight of pipes with gas fuel (including acceleration if significant), internal pressure, thermal contraction and loads induced by movements of the ship. For temperatures above -110°C, a stress analysis may be required by the Society. In any case, consideration is to be given to thermal

stresses, even if calculations need not be submitted. The analysis is to be carried out according to a recognized code of practice.

16. Gas pipes are not to be located less than 760 mm from the ship's side.

17. Gas piping is not to be led through other machinery spaces. Alternatively, double gas piping may be approved, provided the danger of mechanical damage is negligible, the gas piping has no dis- charge sources and the room is equipped with a gas alarm.

18.

19.

An arrangement for purging gas bunkering lines and supply lines (only up to the double block and bleed valves if these are located close to the engine) with nitrogen is to be provided.

The gas piping system is to be installed with sufficient flexibility. Arrangement for provision of the necessary flexibility is to be demonstrated to maintain the integrity of the piping system in all foreseen service situations.

20. Gas pipes are to be colour marked based on a recognized standard(Refer to ISO 14726:2008 Ships and marine technology-Identification colours for the content of piping systems).

21. If the fuel gas contains heavier components that may condense in the system, knock out drums or equivalent means for safely removing the liquid are to be fitted.

22. All pipelines and components which may be isolated containing liquid gas are to be provided with relief valves.

23. Where tanks or piping are separated from the ship's structure by thermal isolation, provision is to be made for electrically bonding to the ship's structure both the piping and the tanks. All gasketed pipe joints and hose connections are to be electrically bonded.

106. System configuration

1. Following two alternative system configurations may be accepted:

(1) Gas safe machinery spaces : Arrangements in machinery spaces are such that the spaces are

(2)

considered gas gas safe. ESD-protected are considered

safe under all conditions, normal as well as abnormal conditions, i.e. inherently

machinery spaces : Arrangements in machinery spaces are such that the spaces non-hazardous under normal conditions, but under certain abnormal conditions

may have the potential to become hazardous. In the event of abnormal conditions involving gas

hazards, emergency shutdown (ESD) of non-safe equipment (ignition sources) and machinery is to be automatically executed while equipment or machinery in use or active during these con-

ditions are to be of a certified safe type.

2. Gas safe machinery spaces are to comply with the following.

(1) All gas supply piping within machinery space boundaries are to be enclosed in a gastight en- closure, i.e. double wall piping or ducting.

(2)

(3)

In case of leakage in a gas supply pipe making shutdown of the gas supply necessary, a sec- ondary independent fuel supply is to be available. Alternatively, in the case of multi-engine in-

stallations, independent and separate gas supply systems for each engine or group of engines

may be accepted.

For single fuel installations (gas only), the fuel storage is to be divided between two or more tanks of approximately equal size. The tanks are to be located in separate compartments.

3. ESD-protected machinery spaces are to comply with the following.

(1) Gas supply piping within ESD-protected machinery spaces may be accepted without a gastight external enclosure on the following conditions:

(A) Engines for generating propulsion power and electric power are to be located in two or more machinery spaces not having any common boundaries unless it can be documented

that the common boundary can withstand an explosion in one of the rooms. Distribution of

engines between the different machinery spaces is to be such that in the case of shutdown of fuel supply to any one machinery space, it is possible to maintain at least 40% of the propulsion power plus normal electrical power supply for sea-going services. Incinerators, in-

ert gas generators or other oil fired boilers are machinery space.

(B) The gas machinery, tank and valve installation

not to be located within an ESD-protected

spaces are to contain only a minimum of

such necessary equipment, components and systems as are required to ensure that any piece of equipment in each individual space maintains its principal function

(C) Pressure in gas supply lines within machinery spaces is to be less than 1.0 MPa, e.g., this

concept can only be used for low pressure systems.

(D) A gas detection system arranged to automatically shutdown the gas supply (also oil fuel supply if dual fuel) and disconnect all non-explosion protected equipment or installations are to be fitted, as outlined in 405 and 406.

(2) For single fuel installations (gas only), the fuel storage is to be divided between two or more tanks of approximately equal size. The tanks are to be located in separate compartments.

107. Gas supply system in gas machinery spaces

1. Gas supply system for gas safe machinery spaces is to comply with the following.

(1) Gas supply lines passing through enclosed spaces are to be completely enclosed by a double pipe or duct. This double pipe or duct is to fulfil one of the following:

(A) The gas piping is to be a double wall piping system with the gas fuel contained in the in- ner pipe. The space between the concentric pipes is to be pressurized with inert gas at a

pressure greater than the gas fuel pressure. Suitable alarms are to be provided to indicate a loss of inert gas pressure between the pipes. When the inner pipe contains high pressure

gas, the system is to be so arranged that the pipe between the master gas valve and the en- gine is automatically purged with inert gas when the master gas valve is closed; or

(B)

The gas fuel piping is to be installed within a ventilated pipe or duct. The air space be- tween the gas fuel piping and the wall of the outer pipe or duct is to be equipped with mechanical under pressure ventilation having a capacity of at least 30 air changes per hour.

This ventilation capacity may be reduced to 10 air changes per hour provided automatic fill- ing of the duct with nitrogen upon detection of gas is arranged for. The fan motors are to

comply with the required explosion

is to be covered by a protection gas-air mixture may be ignited.

protection in the installation area. The ventilation outlet

screen and placed in a position where no flammable

(2) The connecting of gas piping and ducting to the gas injection valves is to be so as to provide

complete coverage by the ducting. The arrangement is to facilitate replacement and/or overhaul of injection valves and cylinder covers. The double ducting is to be required also for gas pipes on the engine itself, and all the way until gas is injected into the chamber. If gas is supplied into the air inlet on a low pressure engine, double ducting may be omitted on the air inlet pipe on the condition that a gas detector is fitted above the engine.

(3)

For high-pressure piping, the design pressure of the ducting is to be taken as the higher of the following:

(A) The maximum built-up pressure: static pressure in way of the rupture resulting from the gas flowing in the annular space;

(B) Local instantaneous peak pressure (ᾬ) in way of the rupture: this pressure is to be taken as the critical pressure and is given by the following expression: