7 Material and General Pipe Design

7.1 Goal

7.1.1 The goal of this chapter is to ensure the safe handling of fuel, under all operating conditions, to minimize the risk to the ship, personnel and to the environment, having regard to the nature of the products involved.

7.2 Functional requirements

7.2.1 This chapter relates to functional requirements in 3.2.1, 3.2.5, 3.2.6, 3.2.8, 3.2.9 and 3.2.10. In particular the following apply:

7.2.1.1 Fuel piping shall be capable of absorbing thermal expansion or contraction caused by extreme temperatures of the fuel without developing substantial stresses.

7.2.1.2 Provision shall be made to protect the piping, piping system and components and fuel tanks from excessive stresses due to thermal movement and from movements of the fuel tank and hull structure.

7.2.1.3 If the fuel gas contains heavier constituents that may condense in the system, means for safely removing the liquid shall be fitted.

7.2.1.4 Low temperature piping shall be thermally isolated from the adjacent hull structure, where necessary, to prevent the temperature of the hull from falling below the design temperature of the hull material.

7.3 Regulations for general pipe design

7.3.1 General

7.3.1.1 Fuel pipes and all the other piping needed for a safe and reliable operation and maintenance shall be colour marked in accordance with a standard at least equivalent to those acceptable to the Organization.^footnote

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

7.3.1.3 All pipelines or components which may be isolated in a liquid full condition shall be provided with relief valves.

7.3.1.4 Pipework, which may contain low temperature fuel, shall be thermally insulated to an extent which will minimize condensation of moisture.

7.3.1.5 Piping other than fuel supply piping and cabling may be arranged in the double wall piping or duct provided that they do not create a source of ignition or compromise the integrity of the double pipe or duct. The double wall piping or duct shall only contain piping or cabling necessary for operational purposes.

7.3.2 Wall thickness

7.3.2.1 The minimum wall thickness shall be calculated as follows:

t = (t₀+ b + c) / (1 – a/100) (mm)

where:

t₀ = theoretical thickness
t₀ = PD / (2.0Ke + P) (mm)
with:
- P = design pressure (MPa) referred to in 7.3.3;
- D = outside diameter (mm);
- K = allowable stress (N/mm²) referred to in 7.3.4; and
- 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 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 shall 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 shall be:
b = D·t₀/ 2.5r (mm)
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 regulations. This allowance shall be consistent with the expected life of the piping; and
a = negative manufacturing tolerance for thickness (%).

7.3.2.2 The absolute minimum wall thickness shall be in accordance with a standard acceptable to the Administration.

7.3.3 Design condition

7.3.3.1 The greater of the following design conditions shall be used for piping, piping system and components as appropriate:^footnote^,^footnote

.1 for systems or components which may be separated from their relief valves and which contain only vapour at all times, vapour pressure at 45°C assuming an initial condition of saturated vapour in the system at the system operating pressure and temperature; or
.2 the MARVS of the fuel tanks and fuel processing systems; or
.3 the pressure setting of the associated pump or compressor discharge relief valve; or
.4 the maximum total discharge or loading head of the fuel piping system; or
.5 the relief valve setting on a pipeline system.

7.3.3.2 Piping, piping systems and components shall have a minimum design pressure of 1.0 MPa except for open ended lines where it is not to be less than 0.5 MPa.

7.3.4 Allowable stress

7.3.4.1 For pipes made of steel including stainless steel, the allowable stress to be considered in the formula of the strength thickness in 7.3.2.1 shall be the lower of the following values:

R_m/2.7 or R_e/1.8

where:

R_m = specified minimum tensile strength at room temperature (N/mm²); and
R_e = specified minimum yield stress at room temperature (N/mm²). If the stress strain curve does not show a defined yield stress, the 0.2% proof stress applies.

7.3.4.2 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 7.3.2 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; supports, ship deflections, liquid pressure surge during transfer operations, the weight of suspended valves, reaction to loading arm connections, or otherwise.

7.3.4.3 For pipes made of materials other than steel, the allowable stress shall be considered by the Administration.

7.3.4.4 High pressure fuel piping systems shall have sufficient constructive strength. This shall 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.

7.3.4.5 When the design temperature is minus 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 hog and sag of the ship shall be carried out for each branch of the piping system.

7.3.5 Flexibility of piping

7.3.5.1 The arrangement and installation of fuel piping shall provide the necessary flexibility to maintain the integrity of the piping system in the actual service situations, taking potential for fatigue into account.

7.3.6 Piping fabrication and joining details

7.3.6.1 Flanges, valves and other fittings shall comply with a standard acceptable to the Administration, taking into account the design pressure defined in 7.3.3.1. For bellows and expansion joints used in vapour service, a lower minimum design pressure than defined in 7.3.3.1 may be accepted.

7.3.6.2 All valves and expansion joints used in high pressure fuel piping systems shall be approved according to a standard acceptable to the Administration.

7.3.6.3 The piping system shall be joined by welding with a minimum of flange connections. Gaskets shall be protected against blow-out.

7.3.6.4 Piping fabrication and joining details shall comply with the following:

7.3.6.4.1 Direct connections

.1 Butt-welded joints with complete penetration at the root may be used in all applications. For design temperatures colder than minus 10°C, butt welds shall be either double welded or equivalent to a double welded butt joint. This may be accomplished by use of a backing ring, consumable insert or inert gas back-up on the first pass. For design pressures in excess of 1.0 MPa and design temperatures of minus 10°C or colder, backing rings shall be removed.
.2 Slip-on welded joints with sleeves and related welding, having dimensions in accordance with recognized standards, shall only be used for instrument lines and open-ended lines with an external diameter of 50 mm or less and design temperatures not colder than minus 55°C.
.3 Screwed couplings complying with recognized standards shall only be used for accessory lines and instrumentation lines with external diameters of 25 mm or less.

7.3.6.4.2 Flanged connections

.1 Flanges in flange connections shall be of the welded neck, slip-on or socket welded type; and
.2 For all piping except open ended, the following restrictions apply:
- .1 For design temperatures colder than minus 55°C, only welded neck flanges shall be used; and
- .2 For design temperatures colder than minus 10°C, slip-on flanges shall not be used in nominal sizes above 100 mm and socket welded flanges shall not be used in nominal sizes above 50 mm.

7.3.6.4.3 Expansion joints

Where bellows and expansion joints are provided in accordance with 7.3.6.1 the following apply:

.1 if necessary, bellows shall be protected against icing;
.2 slip joints shall not be used except within the liquefied gas fuel storage tanks; and
.3 bellows shall normally not be arranged in enclosed spaces.

7.3.6.4.4 Other connections

Piping connections shall be joined in accordance with 7.3.6.4.1 to 7.3.6.4.3 but for other exceptional cases the Administration may consider alternative arrangements.

7.4 Regulations for materials

7.4.1 Metallic materials

7.4.1.1 Materials for fuel containment and piping systems shall comply with the minimum regulations given in the following tables:

Table 7.1: Plates, pipes (seamless and welded), sections and forgings for fuel tanks and process pressure vessels for design temperatures not lower than 0°C.
Table 7.2: Plates, sections and forgings for fuel tanks, secondary barriers and process pressure vessels for design temperatures below 0°C and down to minus 55°C.
Table 7.3: Plates, sections and forgings for fuel tanks, secondary barriers and process pressure vessels for design temperatures below minus 55°C and down to minus 165°C.
Table 7.4: Pipes (seamless and welded), forgings and castings for fuel and process piping for design temperatures below 0°C and down to minus 165°C.
Table 7.5: Plates and sections for hull structures required by 6.4.13.1.1.2.

Table 7.1

PLATES, PIPES (SEAMLESS AND WELDED) ^{1, 2}, SECTIONS AND FORGINGS FOR FUEL TANKS AND PROCESS PRESSURE VESSELS FOR DESIGN TEMPERATURES NOT LOWER THAN 0°C
CHEMICAL COMPOSITION AND HEAT TREATMENT
◆ Carbon-manganese steel
◆ Fully killed fine grain steel
◆ Small additions of alloying elements by agreement with the Administration
◆ Composition limits to be approved by the Administration
◆ Normalized, or quenched and tempered⁴
TENSILE AND TOUGHNESS (IMPACT) TEST REGULATIONS
Sampling frequency
◆ Plates	Each "piece" to be tested
◆ Sections and forgings	Each "batch" to be tested.
Mechanical properties
◆ Tensile properties	Specified minimum yield stress not to exceed 410 N/mm^{2 5}
Toughness (Charpy V-notch test)
◆ Plates	Transverse test pieces. Minimum average energy value (KV) 27J
◆ Sections and forgings	Longitudinal test pieces. Minimum average energy (KV) 41J
◆ Test temperature	Thickness t (mm)	Test temperature (°C)
	T ≤ 20	0
	20 < t ≤ 40³	-20
Notes
1. For seamless pipes and fittings normal practice applies. The use of longitudinally and spirally welded pipes shall be specially approved by the Administration.
2. Charpy V-notch impact tests are not required for pipes.
3. This Table is generally applicable for material thicknesses up to 40 mm. Proposals for greater thicknesses shall be approved by the Administration.
4. A controlled rolling procedure or thermo-mechanical controlled processing (TMCP) may be used as an alternative.
5. Materials with specified minimum yield stress exceeding 410 N/mm² may be approved by the Administration. For these materials, particular attention shall be given to the hardness of the welded and heat affected zones.

Table 7.2

PLATES, SECTIONS AND FORGINGS ¹ FOR FUEL TANKS, SECONDARY BARRIERS AND PROCESS PRESSURE VESSELS FOR DESIGN TEMPERATURES BELOW 0°C AND DOWN TO MINUS 55°C
Maximum thickness 25 mm ²
CHEMICAL COMPOSITION AND HEAT TREATMENT
◆ Carbon-manganese steel
◆ Fully killed, aluminium treated fine grain steel
◆ Chemical composition (ladle analysis)
	C	Mn		Si	S	P
	0.16% max. ³	0.70-1.60%		0.10-0.50%	0.025% max.	0.025% max.
	Optional additions: Alloys and grain refining elements may be generally in accordance with the following
	Ni	Cr		Mo	Cu	Nb
	0.80% max.	0.25% max.		0.08% max.	0.35% max.	0.05% max.
	V
	0.10% max.
	Al content total 0.020% min. (Acid soluble 0.015% min.)
◆ Normalized, or quenched and tempered ⁴
TENSILE AND TOUGHNESS (IMPACT) TEST REGULATIONS
Sampling frequency
◆ Plates			Each 'piece' to be tested
◆ Sections and forgings			Each 'batch' to be tested
Mechanical properties
◆ Tensile properties			Specified minimum yield stress not to exceed 410 N/mm^{2, 5}
Toughness (Charpy V-notch test)
◆ Plates			Transverse test pieces. Minimum average energy value (KV) 27J
◆ Sections and forgings			Longitudinal test pieces. Minimum average energy (KV) 41J
◆ Test temperature			5°C below the design temperature or -20°C whichever is lower
Notes
1.	The Charpy V-notch and chemistry regulations for forgings may be specially considered by the Administration.
2.	For material thickness of more than 25 mm, Charpy V-notch tests shall be conducted as follows:
	Material thickness (mm)		Test temperature (°C)
	25 < t ≤ 30		10°C below design temperature or -20°C whichever is lower
	30 < t ≤ 35		15°C below design temperature or -20°C whichever is lower
	35 < t ≤ 40		20°C below design temperature
	40 < t		Temperature approved by the Administration
	The impact energy value shall be in accordance with the table for the applicable type of test specimen. Materials for tanks and parts of tanks which are completely thermally stress relieved after welding may be tested at a temperature 5°C below design temperature or -20°C whichever is lower. For thermally stress relieved reinforcements and other fittings, the test temperature shall be the same as that required for the adjacent tank-shell thickness.
3.	By special agreement with the Administration, the carbon content may be increased to 0.18% maximum provided the design temperature is not lower than -40°C
4.	A controlled rolling procedure or thermo-mechanical controlled processing (TMCP) may be used as an alternative.
5.	Materials with specified minimum yield stress exceeding 410 N/mm² may be approved by the Administration. For these materials, particular attention shall be given to the hardness of the welded and heat affected zones.

Guidance:
For materials exceeding 25 mm in thickness for which the test temperature is -60°C or lower, the application of specially treated steels or steels in accordance with table 7.3 may be necessary.

Table 7.3

PLATES, SECTIONS AND FORGINGS ¹ FOR FUEL TANKS, SECONDARY BARRIERS AND PROCESS PRESSURE VESSELS FOR DESIGN TEMPERATURES BELOW MINUS 55°C AND DOWN TO MINUS 165°C²
Maximum thickness 25 mm ^{3, 4}
Minimum design temp. (°C)		Chemical composition⁵ and heat treatment		Impact test temp. (°C)
-60		1.5% nickel steel – normalized or normalized and tempered or quenched and tempered or TMCP ^{see note 6}		-65
-65		2.25% nickel steel – normalized or normalized and tempered or quenched and tempered or TMCP^{6, 7}		-70
-90		3.5% nickel steel – normalized or normalized and tempered or quenched and tempered or TMCP^{6, 7}		-95
-105		5% nickel steel – normalized or normalized and tempered or quenched and tempered^{6, 7 and 8}		-110
-165		9% nickel steel – double normalized and tempered or quenched and tempered⁶		-196
-165		Austenitic steels, such as types 304, 304L, 316, 316L, 321 and 347 solution treated⁹		-196
-165		Aluminium alloys; such as type 5083 annealed		Not required
-165		Austenitic Fe-Ni alloy (36% nickel) Heat treatment as agreed		Not required
TENSILE AND TOUGHNESS (IMPACT) TEST REGULATIONS
Sampling frequency
◆ Plates			Each 'piece' to be tested
◆ Sections and forgings			Each 'batch' to be tested
Toughness (Charpy V-notch test)
◆ Plates			Transverse test pieces. Minimum average energy value (KV) 27J
◆ Sections and forgings			Longitudinal test pieces. Minimum average energy (KV) 41J
*Notes*
1.	The impact test required for forgings used in critical applications shall be subject to special consideration by the Administration.
2.	The regulations for design temperatures below –165°C shall be specially agreed with the Administration.
3.	For materials 1.5% Ni, 2.25% Ni, 3.5% Ni and 5% Ni, with thicknesses greater than 25 mm, the impact tests shall be conducted as follows:
	Material thickness (mm)		Test temperature (°C)
	25 < t ≤ 30		10°C below design temperature
	30 < t ≤ 35		15°C below design temperature
	35 < t ≤ 40		20°C below design temperature
	The energy value shall be in accordance with the table for the applicable type of test specimen. For material thickness of more than 40 mm, the Charpy V-notch values shall be specially considered.
4.	For 9% Ni steels, austenitic stainless steels and aluminium alloys, thickness greater than 25 mm may be used.
5.	The chemical composition limits shall be in accordance with recognized standards.
6.	Thermo-mechanical controlled processing (TMCP) nickel steels will be subject to acceptance by the Administration.
7.	A lower minimum design temperature for quenched and tempered steels may be specially agreed with the Administration.
8.	A specially heat treated 5% nickel steel, for example triple heat treated 5% nickel steel, may be used down to –165°C, provided that the impact tests are carried out at –196°C.
9.	The impact test may be omitted subject to agreement with the Administration.

Table 7.4

PIPES (SEAMLESS AND WELDED)¹, FORGINGS² AND CASTINGS² FOR FUEL AND PROCESS PIPING FOR DESIGN TEMPERATURES BELOW 0°C AND DOWN TO MINUS 165°C³
Maximum thickness 25 mm
Minimum design temp.(°C)	Chemical composition⁵ and heat treatment	Impact test
		Test temp. (°C)	Minimum average energy (KV)
-55	Carbon-manganese steel. Fully killed fine grain. Normalized or as agreed.⁶	^{See note 4}	27
-65	2.25% nickel steel. Normalized, Normalized and tempered or quenched and tempered.⁶	-70	34
-90	3.5% nickel steel. Normalized, Normalized and tempered or quenched and tempered.⁶	-95	34
-165	9% nickel steel⁷. Double normalized and tempered or quenched and tempered.	-196	41
	Austenitic steels, such as types 304, 304L, 316, 316L, 321 and 347. Solution treated.⁸	-196	41
	Aluminium alloys; such as type 5083 annealed		Not required
TENSILE AND TOUGHNESS (IMPACT) TEST REGULATIONS
Sampling frequency
◆ Each 'batch' to be tested.
Toughness (Charpy V-notch test)
◆ Impact test: Longitudinal test pieces
*Notes*
1. The use of longitudinally or spirally welded pipes shall be specially approved by the Administration.
2. The regulations for forgings and castings may be subject to special consideration by the Administration.
3. The regulations for design temperatures below -165°C shall be specially agreed with the Administration.
4. The test temperature shall be 5°C below the design temperature or -20°C whichever is lower.
5. The composition limits shall be in accordance with Recognized Standards.
6. A lower design temperature may be specially agreed with the Administration for quenched and tempered materials.
7. This chemical composition is not suitable for castings.
8. Impact tests may be omitted subject to agreement with the Administration.

Table 7.5

PLATES AND SECTIONS FOR HULL STRUCTURES REQUIRED BY 6.4.13.1.1.2
Minimum design temperature of hull structure (°C)	Maximum thickness (mm) for steel grades
Minimum design temperature of hull structure (°C)	A	B	D	E	AH	DH	EH	FH
0 and above	Recognized Standards
down to -5	15	25	30	50	25	45	50	50
down to -10	x	20	25	50	20	40	50	50
down to -20	x	x	20	50	x	30	50	50
down to -30	x	x	x	40	x	20	40	50
Below -30	In accordance with table 7.2 except that the thickness limitation given in table 7.2 and in footnote 2 of that table does not apply.
Notes
'x' means steel grade not to be used.

7.4.1.2 Materials having a melting point below 925°C shall not be used for piping outside the fuel tanks.

7.4.1.3 For CNG tanks, the use of materials not covered above may be specially considered by the Administration.

7.4.1.4 Where required the outer pipe or duct containing high pressure gas in the inner pipe shall as a minimum fulfil the material regulations for pipe materials with design temperature down to minus 55°C in table 7.4.

7.4.1.5 The outer pipe or duct around liquefied gas fuel pipes shall as a minimum fulfil the material regulations for pipe materials with design temperature down to minus 165°C in table 7.4.