Bsi bs en 14398 2 2003 (2006)

4.1.3 Design by calculation and pressure strengthening The pressure retaining capability of vessels manufactured from austenitic stainless steel, strengthened bypressure, shall be calcul

Terms and definitions

For the purposes of this European Standard, the terms and definitions given in EN 14398-1:2003 and the following apply.

A large transportable non-vacuum insulated vessel, exceeding 1000 liters in volume, is designed for one or more cryogenic fluids This vessel comprises an inner container, insulation, various valves and accessories, as well as additional structural framework.

3.1.2 fixed tank (tank vehicle) large transportable vessel permanently attached to a vehicle or to units of running gear used in its stead

A demountable tank is a large transportable vessel that is not permanently affixed to a vehicle When connected to the carrier vehicle, it complies with the regulations set for fixed tanks This tank is specifically designed to be lifted only when it is empty.

3.1.4 inner vessel pressure vessel proper intended to contain the cryogenic fluid

3.1.5 insulation to protect the vessel against heat transfer from the outside atmospheric temperature

Automatic welding involves the automatic control of welding parameters, which can be adjusted to a limited extent either manually or automatically during the welding process to ensure that the specified conditions are maintained.

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The maximum allowable pressure, denoted as \$p_s\$, refers to the highest pressure for which the equipment is designed, as specified by the manufacturer This pressure is defined at a specific location indicated by the manufacturer, typically at the connection point for protective or limiting devices or at the top of the equipment.

3.1.8 relief plate/plug plate or plug retained by atmospheric pressure only which allows relief of excess internal pressure

3.1.9 bursting disc device non-reclosing pressure relief device ruptured by differential pressure It is the complete assembly of installed components including where appropriate the bursting disc holder

Symbols

This European Standard defines several key symbols: $c$ represents the allowance for corrosion in mm, $d_i$ is the diameter of the opening in mm, and $d_a$ denotes the outside diameter of the tube or nozzle in mm The symbol $f$ indicates the narrow side of a rectangular or elliptical plate in mm, while $l_b$ and $l'_b$ refer to the buckling length in mm The number of lobes is denoted by $n$, and $p$ signifies the design pressure as defined in section 4.3.2.2 in bar The allowable external pressure limited by elastic buckling is represented by $p_e$ in bar, $p_k$ indicates the strengthening pressure in bar, and $p_p$ denotes the allowable external pressure limited by plastic deformation in bar The pressure test is indicated by $p_T$ (see section 4.2.3.2) in bar, while $r$ refers to the radius, such as the inside knuckle radius of dished ends and cones in mm The minimum thickness is represented by $s$ in mm, $s_e$ is the actual wall thickness in mm, and $v$ is a factor indicative of the utilization of the permissible design stress in joints or a factor allowing for weakenings Lastly, $x$ denotes the decay-length zone, which is the distance over which the governing stress is assumed to act in mm.

A cross sectional area of reinforcing element mm 2

D a outside diameter e.g of a cylindrical shell mm

D i internal diameter e.g of a cylindrical shell mm

I moment of inertia of reinforcing element mm 4

R e apparent yield stress or 0,2 % proof stress (1 % proof stress for austenitic steel) N/mm 2

R m minimum tensile strength (actual or guaranteed) N/mm 2

K material property used for design N/mm 2

R radius of curvature e.g inside crown radius of dished end mm

S safety factor at design pressure, in relation with Re -

S k safety factor against elastic buckling at design pressure -

S p safety factor against plastic deformation -

Z auxiliary value - v Poisson’s ratio - u out of roundness -

Design options

General

The design shall be carried out in accordance with one of the options given in 4.1.2, 4.1.3 or 4.1.4.

Metallic materials used at cryogenic temperatures shall meet the requirements of the relevant sections of

In the case of 9 % Ni steel, the additional requirements of annex B shall be satisfied.

For carbon and low alloy steels the requirements of EN 1252-2 shall be satisfied.

Design by calculation

All pressure and load-bearing components must be calculated, ensuring that the thickness of the pressure parts of the vessel meets or exceeds the requirements outlined in section 4.3 Additional calculations may be necessary to confirm that the design is adequate for the operating conditions, taking into account dynamic loads.

Design by calculation and pressure strengthening

The pressure retaining capability of vessels manufactured from austenitic stainless steel, strengthened by pressure, shall be calculated in accordance with annex C.

Design by calculation supplemented with experimental methods

In situations where design cannot rely solely on calculations, controlled experimental methods may be employed, provided that the outcomes validate the necessary safety factors outlined in section 4.3 For instance, using strain gauges can effectively measure stress levels to ensure safety compliance.

Common design requirements

General

The requirements of 4.2.2 to 4.2.7 are applicable to all vessels irrespective of the design option used.

Any increase in parameters such as maximum allowable pressure, specific mass of the densest gas, maximum tare weight of the inner vessel, or changes in the nominal dimensions of the inner shell necessitates a reevaluation of the initial design program Additionally, modifications in material type or grade, fundamental shape alterations, reductions in the minimum mechanical properties of the material, or changes in the assembly design—especially regarding support systems between the inner vessel and insulation or protective frames—require a comprehensive review to ensure safety and compliance.

Design specification

To prepare the design of a vessel, it is essential to have the following information: the maximum allowable pressure, the intended fluids, the liquid capacity, dimensions and allowable weight considering vehicle characteristics, the location and allowable loads on fastening points, the filling and emptying rate, and the range of ambient temperature if it differs from 7.2 of EN 14398-1:2003.

A design document must be created, incorporating drawings and any necessary text, which includes the following essential information: definitions of components designed through calculation, pressure strengthening, experimentation, and proven service experience; detailed drawings with dimensions and thicknesses of load-bearing components; specifications for all load-bearing materials, including grade, class, temper, and relevant testing; and types of material test certificates.

The article outlines essential aspects of welding and joining procedures, including the specifics of weld locations, filler materials, and joining techniques It emphasizes the importance of calculations to ensure compliance with standards, alongside a comprehensive design test program Additionally, it addresses non-destructive testing and pressure test requirements, as well as the configuration of piping, which encompasses the types, sizes, and locations of all valves and relief devices Finally, it highlights the details of fastenings used in these processes.

Design loads

The large transportable cryogenic vessel shall be able to withstand safely the mechanical and thermal loads encountered during pressure test and normal operation.

When evaluating design loads for transport, static loads should replace the combination of static and dynamic loads The specified static loads are: twice the total mass in the direction of travel, the total mass at right angles to the direction of travel, the total mass vertically upwards, and twice the total mass vertically downwards.

Each of these loads is considered to act in isolation and includes the mass of the component under consideration.

With the exception of a) the following loads shall be considered to act in combination where relevant : a) test pressure : the value used for validation purposes shall be : bar 3 ,

T p p (1) considered for each element of the vessel e.g shell, courses, head, etc p s is the maximum allowable pressure, in bar.

The vessel shall be capable of holding the pressure test fluid without plastic deformation. b) pressure during operation, p C , where :

C p p p s (2) p L is the pressure, in bars, exerted by the mass of the liquid contents when the vessel is filled to capacity and subject to each load defined in 4.2.3.1, with either :

1) boiling liquid at minimum allowable temperature

2) cryogenic fluid at its equilibrium triple point or melting point temperature;

The reaction forces at the support points of the vessel arise from the weight of the vessel and its contents when subjected to the specified loads Additionally, the load imposed by the piping is influenced by the differential thermal movement between the vessel, the piping, and the insulation.

The article addresses three key scenarios: cooldown, where the vessel is warm and the piping is cold; filling and withdrawal, with both the vessel and piping cold; and transport and storage, where the vessel is cold and the piping is warm Additionally, it highlights the load imposed on the vessel at its support points during the cooling process from ambient to operating temperature and throughout its operation.

Vehicles with vessels that serve as stressed self-supporting components must be engineered to endure the stresses imposed by their structure, along with additional stresses from other sources.

The vessel supports shall be suitable for each load defined in 4.2.3.2 c) plus loads due to differential thermal movements.

The vessel must be segmented by surge plates to ensure stability and restrict dynamic loads as specified in section 4.2.3, unless it is filled to at least 80% of its capacity or is nominally empty Additionally, the cross-sectional area of the surge plate should be a minimum of 70% of the vessel's area.

Current experience with surge plates limiting the capacity to 7 500 l has been shown to meet these requirements.

Surge plates and their connections to the shell must be engineered to withstand stresses from uniformly distributed pressure across the surge plate's surface This pressure is determined by evaluating the mass of liquid between the plates, which decelerates at a rate of 2 g.

Fastening points shall be suitable for fastening the large transportable cryogenic vessel to the vehicle when filled to capacity and subject to each of the loads defined in 4.2.3.

To ensure operational integrity, the fittings and accessories on the upper part of the vessel must be adequately protected against damage from overturning This protection can be achieved through the use of strengthening rings, protective canopies, or specially shaped transverse or longitudinal members that provide effective safeguarding.

The ground-level bearing surface width, defined as the distance between the outer contact points of the right and left tyres on the same axle, must be at least 90% of the height of the centre of gravity of the fully loaded tank-vehicle Additionally, for articulated vehicles, the axle mass of the load-carrying unit of the laden semi-trailer should not surpass 60% of the total nominal laden mass of the entire articulated vehicle.

Piping systems, including valves, fittings, and supports, must be designed to endure various loads, which should be assessed in combination, except for pneumatic pressure tests These loads include: a) a pneumatic pressure test that meets or exceeds the allowable working pressure (\$p_s\$); b) operational pressure that is at least equal to the set pressure of the system's pressure relief device; c) thermal loads as specified in section 4.2.3.2 d); d) dynamic loads; e) the set pressure of thermal relief devices when applicable; and f) loads resulting from pressure relief discharge.

This equipment shall be protected or positioned so as to be protected against the risk of being wrenched off or damaged during transport.

This equipment is designed to maintain leakproofness even if the vehicle overturns The gaskets used must be made from materials that are compatible with the fluids being transported, in compliance with EN 1797 standards.

Each bottom-filling or bottom-discharge opening must have a minimum of two independent shut-off devices installed in series The primary device should be a stop valve that includes protection against mechanical damage.

To prevent leaks of flammable fluids, the first stop valve must be an instant-closing safety device that automatically activates during unintended vehicle movement or fire during filling or emptying Additionally, the closing device should be operable via remote control All vent pipes, including pressure relief devices and purge valves, must connect to a vent pipe for safe discharge, and the control cabinet should be adequately vented to prevent the accumulation of flammable gas.

Fatigue

The design shall take into account the effect of cyclic stress on the inner vessel, outer jacket and their attachments during normal conditions of operation.

In addressing fatigue, it is essential to dimension loads in accordance with section 4.2.3 to effectively manage fatigue effects Special care should be taken with specific details in supports and piping systems to prevent stress raisers.

Corrosion allowance

Corrosion allowance is not required on surfaces in contact with the operating fluid Corrosion allowance is not required on other surfaces if they are adequately protected against corrosion.

Inspection openings

Inspection openings are not required in the vessel, providing the requirements of EN 14398–3 are followed.

NOTE Due to the combination of materials of construction and operating fluids, internal corrosion cannot occur.

Pressure relief

Relief systems shall be designed to meet the requirements given in 4.2.7.1 and 4.2.7.2.

The vessel must have a minimum of two independent pressure relief devices, including at least one relief valve that opens at a pressure not exceeding p s These devices can be installed on a shared line.

A device must safeguard the vessel from excessive pressure caused by normal heat leaks Additionally, multiple devices working in unison should ensure protection against excess pressure resulting from heat leaks with insulation loss, heat leaks without insulation loss while the pressure buildup system is open, and the recycling of any potential combination of pumps.

Excess pressure refers to a pressure that exceeds 110% of the maximum allowable pressure for conditions a) and d), as well as surpassing the test pressure for conditions b) and c).

Relief devices for the vessel shall be in accordance with EN 13648-3 for calculation of sizing.

The pressure relief system shall be sized so that the pressure drop during discharge does not cause the valve to reseat instantly.

Any section of pipework containing cryogenic fluid which can be isolated shall be protected by a relief valve or other suitable relief device.

Valves

Valves shall conform to EN 1626.

Insulation

To safeguard the vessel from external heat transfer, insulation made of low thermal conductivity material is applied at a specific thickness This insulation effectively prevents rapid pressure increases in the cold liquid contained within the vessel.

The insulation shall be covered by an outside cladding, to protect the insulation against collection of humidity or water and against damage.

The insulation material can be polyurethane foam (injected or moulded as formed plates), etc.

Degree of filling

Large transportable non-vacuum insulated vessels for flammable gases must be filled below a level that would cause the liquid volume to reach 95% of the vessel's capacity at the temperature where the vapor pressure equals the safety valve's opening pressure In contrast, these vessels can be filled with non-flammable gases up to 98% of their total volume at the specified loading temperature and pressure.

Means shall be provided to ensure that the above limits are not exceeded.

Electrical continuity

All metallic parts of large transportable non-vacuum insulated vessels designed for carrying flammable gases must maintain electrical continuity These vessels should include attachment points for earthing devices, ensuring that the resistance of the earthing connection is below 5 ohms Additionally, any metal contacts that could lead to electrochemical corrosion should be eliminated.

Design by calculation

General

The dimensions of the vessel shall not be less than that determined in accordance with this subclause.

Vessel

The information in 4.3.2.2 to 4.3.2.6 shall be used to determine the pressure part thicknesses in conjunction with the calculation formulae of 4.3.5.

The actual wall thickness shall be not less than shown in Table 1.

Table 1 —vessel minimum wall thickness vessel

Minimum wall thickness s o in millimetres for reference steel a

3 4 a Reference steel means a steel with a tensile strength of 370 N/mm 2 and an elongation at fracture of 27 %.

For other materials calculate the minimum thickness using the following formula :

R m is the minimum tensile strength of the metal chosen, in Newtons per square millimetre at a temperature not lower than the saturation temperature of the fluid at pressure p s ;

A 5 is the elongation at fracture of the metal chosen, in per cent at the same temperature.

The minimum thickness shall however not be less than the minimum wall thickness defined in chapter 6.8 of the technical annexes of the ADR when other materials are used.

Under these conditions, the reference steel equivalent thickness of the vessel can be determined as follows :

(3) where s e is the actual wall thickness of the inner vessel.

The R m and A5 values must be established at a temperature equal to or above the fluid's saturation temperature at pressure p s, either by referencing the relevant material standard or through a guarantee from the material manufacturer.

The internal design pressure p shall be the greater of p T as defined in 4.2.3.2 a) or p C as defined in 4.2.3.2 b) corrected for operating conditions (i.e times

K ) to take into account the cold properties of the material used It follows that K 20 shall be used in the subsequent formulae where p is shown as the design pressure.

The vessel shall be able to withstand, without permanent deformation, an external pressure of not less than 40 kPa (0,4 bar) above the internal pressure.

The material property K for calculations is defined as follows: for austenitic stainless steels, use 1% proof strength (R e); for carbon steels, aluminum, and aluminum alloys, utilize yield strength (R e) or, if unavailable, 0.2% proof strength; and for carbon steels, the upper yield strength may be applied.

For calculation purposes the material property K of the inner vessel shall be limited to 2/3 of R m the minimum guaranteed tensile strength.

R e and R m shall be the minimum guaranteed values at 20 °C taken from the material standard (see annex E).

For welded tank construction, steel ratios of \$R_e / R_m\$ greater than 0.85 are prohibited The calculation of the \$R_e / R_m\$ ratio must utilize the minimum specified values of \$R_e\$ and \$R_m\$ as indicated in the material inspection certificate.

The allowable values of R e and R m must be established for the material at the operating temperature, which should not be lower than the saturation temperature of the fluid at pressure p s.

R e , R m and E shall be determined from the appropriate material standard (see EN 10028-7:2000 annex F for austenitic stainless steels) or shall be guaranteed by the material manufacturer.

The material shall not be subject to brittle fracture at its minimum operating temperature, see EN 1252-1 and

For steel, the elongation at fracture in % shall be not less than

C 20 t N/mm² a in strength tensile determined

The minimum elongation at fracture for fine-grained steels is set at 16%, while for other steels, it is established at 20% Additionally, for aluminum and its alloys, the elongation at fracture must not fall below 12%.

Elongation and determined tensile strengths are the actual values indicated in the material certificates.

Safety factors are the ratio of material property K over the maximum allowable stress.

In all cases v = 1 shall be used including circumferential seams with permanent backing strip and circumferential joggle joint.

No corrosion allowance is required.

Attachments

For those items attached to the vessel, the allowable stress shall not exceed the lower of 0,75 R e or 0,5 R m

When designing vessel systems, it is essential to consider the temperature and mechanical properties of the components when the vessel is filled to capacity with cryogenic fluid, ensuring that the temperature does not fall below the saturation temperature at pressure $ p_s $.

Piping and accessories

Piping shall be designed for the loads defined in 4.2.3.9 using established piping design methods and safety factors.

Calculation formulae

4.3.5.1 Cylindrical shells and spheres subject to internal pressure (pressure on the concave surface) 4.3.5.1.1 Field of application

Cylindrical shells and spheres where :

For reinforcement of openings, see 4.3.5.5.

The required minimum wall thickness s is : for cylindrical shells : c

4.3.5.2 Dished ends subject to internal pressure

Following calculations the thickness of the dished ends shall not be less than the thickness of the cylindrical shell. Hemispherical ends where D a /D i

10 % torispherical ends where R = D a and r = 0,1 D a and

In the case of torispherical ends 0,001 (s-c)/D a 0,1

NOTE Other end shapes can be used provided suitable calculations are carried out.

4.3.5.2.2 Internal pressure calculation (pressure on concave surface)

The wall thickness of the crown region of dished ends and of hemispherical ends shall be determined using 4.3.5.1.3 for spherical shells with D a = 2 (R + s).

Reinforcement in the crown area of 0.6 D a for torispherical and hemispherical ends must comply with section 4.3.5.5 When utilizing pad type reinforcement, the pad's edge should not exceed 0.8 D a for 10% torispherical ends or 0.7 D a for 2:1 torispherical ends.

4.3.5.2.1.2 Torispherical end knuckle thickness and hemispherical end to shell junction thickness

The required thickness of the knuckle region and hemispherical end junction shall be : for the vessel : v

S K p s D (7) is taken from Figure 5 for 10 % torispherical ends and from Figure 6 for 2:1 torispherical ends as a function of (s-c)/D a Iteration is necessary.

For hemispherical ends a value of 1,1, shall be applied within the distance x from the tangent line joining the end to the cylinder, regardless of the ratio, (s-c)/D a where x = 0 , 5 R s c

D a is the diameter of the end as shown in Figure 4 a) and 4 b).

When there are openings outside the area 0,6 D a the required thickness is found from Figures 5 and 6 using the appropriate curve for the relevant value of d i /D a

The lower curves of Figures 5 and 6 apply when there are no openings outside the area 0,6 D a

When welding a dished end from crown and knuckle components, it is essential that the joint is positioned at a sufficient distance $ x $ from the knuckle This distance must meet specific criteria, with a minimum requirement of at least 100 mm, particularly when the crown and knuckle have different wall thicknesses.

The required wall thickness of the knuckle, denoted as $ s $, is determined by the equation $ R(s - c, x) = 0.5(8) $ It is important to note that the crown and knuckle share the same wall thickness For torispherical ends with a 10% ratio, the relationship is $ x = 3.5s $, while for 2:1 torispherical ends, it is $ x = 3.0s $ A value of $ v = 1.0 $ can be applied if the testing scope aligns with the permissible design stress level or for one-piece ends Additionally, $ v = 1.0 $ is applicable for welded domed ends, excluding hemispherical ends, as long as the weld intersects the crown area of $ 0.6D_a $.

If the ligament connecting adjacent openings does not fall entirely within the 0.6 D a region, it must be at least half the total of the opening diameters Refer to section 4.3.5.5.9 for additional information.

4.3.5.3 Cones subject to internal pressure

For the purposes of 4.3.5.3, the following symbols apply in addition to those given in 3.2 :

A area of reinforcing ring mm 2

D a1 outside diameter of connected cylinder (see Figure 7) mm

D a2 outside diameter at effective stiffening (see Figure 9) mm

D k design diameter (see Figure 7) mm

D S shell diameter at nozzle (see Figure 8) mm

The moment of inertia about the axis parallel to the shell is measured in millimeters (mm) and is influenced by the cone length between effective stiffenings The required wall thickness for the outside corner area is specified in millimeters, as well as the required wall thickness within the corner area Characteristic lengths, denoted as $x_i$ (where $i = 1, 2, 3$), are used to define the corner area, as illustrated in Figures 7a and 7b Additionally, the cone angle is measured in degrees, and the inside radius of the knuckle is also expressed in millimeters.

Cones according to Figure 7 where :

Small ends with a knuckle can be safely assessed and verified as a small end with a corner joint.

Other cone angles may be used providing suitable calculations are carried out.

Openings outside of the corner area (Figure 8) shall be designed as follows : if < 70° design according to 4.3.5.5 using an equivalent cylinder diameter of :

All corner joints shall be subject to the examination required for a weld joint factor of 1,0, see Table 6.

The corner area is that part of the cone where the dominant stresses are bending stresses in the longitudinal direction.

The corner area is defined in Figures 7a) and 7b) by x 1 , x 2 , x 3 calculated from the following equations : c) -

4.3.5.3.6 Internal pressure calculation (pressure on concave surface) a) within corner area

The required wall thickness (s 1 ) within the corner area is calculated from Figures 10.1 to 10.7 for the large end and Figure 10.8 for the small end of a cone using the following variables :

For a corner joint use the curve for = 0

For intermediate cone angles use linear interpolation.

The wall thickness s l in the corner area shall not be less than the required thickness s g outside of the corner area as follows : b) outside corner area

The required wall thickness, s g , outside the corner area is calculated from :

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1 20 k g (13) where for the large end, D k = D a1 - 2 [s 1 + r(1 - cos f) + x 2 sin ]. for the small end, D k is the maximum diameter of the cone, where the wall thickness is s g

4.3.5.3.7 Internal pressure calculation (pressure on the concave surface) > 70°

If r 0,01 D a1 the required wall thickness is :

For the purposes of 4.3.5.4, the following symbols apply in addition to those given in 3.2 : d 1 , d 2 etc opening diameters in mm ;

D 1 , flat end diameters in mm As shown in Figure 12.

Welded or solid flat ends where Poisson's ratio is approximately 0,3, and :

Openings are calculated in accordance with 4.3.5.4.4 but with the C factor multiplied by C A , where C A is given in Figure 11.

The required minimum wall thickness of a circular flat end is :

C and D 1 are taken from Figure 12.

The required minimum wall thickness of a rectangular or elliptical flat end is :

C pS s 0 , 1 e (16) where C E is taken from Figure 13.

4.3.5.5 Openings in cylinders, spheres and cones

In section 4.3.5.5, additional symbols are defined alongside those in section 3.2, including: $ b $ for the width of pad, ring, or shell reinforcement in mm; $ h $ for the thickness of pad-reinforcement in mm; $ l $ for the ligament (web) between two nozzles in mm; $ l_s $ for the length of nozzle reinforcement outstandings in mm; $ s $ for the length of nozzle reinforcement instand in mm; $ s_A $ for the required wall thickness at the opening edge in mm; $ s_S $ for the wall thickness of the nozzle in mm; and $ t $ for the centre-to-centre distance between two nozzles in mm.

Round openings and the reinforcement of round openings in cylinders, spheres and cones within the following limits :

These rules only apply to cones if the wall thickness is determined by the circumferential stress.

NOTE 1 Additional external forces and moments are not covered by this subclause and should be considered separately where necessary.

NOTE 2 These design rules permit plastic deformations of up to 1 % at highly stressed local areas during pressure test. Openings should therefore be carefully designed to avoid abrupt changes in geometry.

The design rules for non perpendicular nozzles shall be based on a perpendicular nozzle, using the dimension of the major elliptical axis or shall be calculated in accordance with EN 13445-3.

Openings may be reinforced by one or more of the following typical but not exclusive methods : increase of shell thickness, see Figures 14 and 15 ;

This article discusses various types of reinforcement in construction, including ring reinforcement illustrated in Figures 16 and 17, pad reinforcement shown in Figure 18, and the increase of nozzle thickness depicted in Figures 19 and 20 Additionally, it covers the combination of pad and nozzle reinforcement as seen in Figure 21.

Where ring or pad reinforcement is used the space between the two fillet welds shall be vented to the outside of the vessel.

The fillet weld on a reinforcing pad shall have a minimum throat thickness of half of the pad thickness.

The through thickness of a fillet weld of each nozzle to shell weld shall be not less than the required thickness of the thinner part.

When the strength of the reinforcing material is less than that of the shell material, design calculations must include an allowance as specified in section 4.3.5.5.5 Conversely, if the reinforcing material's strength exceeds that of the shell material, no allowance for the increased strength is allowed.

When the material property $ K $ of the reinforcement is lower than that of the shell, the cross-section of pad reinforcement and the thickness of nozzle reinforcement should be reduced according to the ratio of $ K $ values before calculating the factor $ v_A $ For a shell subjected solely to internal pressure, where a series of nozzles are connected to the shell via fully penetrating welds, individual reinforcement calculations for each nozzle are unnecessary However, the shell's thickness to withstand internal pressure must be determined using the lower value of the weakening factor, either $ v_A $ from equation (34) or $ v $.

Openings shall also be reinforced according to the following relationship :

The wall thickness must be at least equal to the thickness of the unpierced shell, ensuring a balance between the pressurized area $ A_p $ and the load-bearing cross-sectional area $ A $.

The pressurized area A p and the load bearing cross sectional area A which equals A o + A 1 + A 2 are obtained from Figures 22 to 25.

The load-bearing cross-sectional area must not exceed the maximum limits defined by formula (20) for shells and by formulae (22) or (23) for nozzles, as applicable.

The protrusion of nozzles l S may be included as load bearing cross sectional area up to a maximum length of l's’ = 0,5 ls (18)

The restrictions of 4.3.5.5.7 and 4.3.5.5;8 shall be observed.

If the material property K 1 , K 2 etc of the reinforcing material is lower than that of the shell the dimensions shall comply with : p 2

4.3.5.5.6 Ring or pad reinforcement or increased shell thickness

If the wall thickness of a cylinder or sphere is less than the required thickness $ s_A $ at the opening, adequate reinforcement is achieved when the thickness $ s_A $ is present around the opening over a specified width.

D s c s c b i A A (20) with a minimum of 3 s A (see Figures 16, 17 and 18).

For calculation purposes s A shall be limited to not more than twice the actual wall thickness.

The thickness of pad reinforcement in accordance to Figure 18 preferably shall be not more than the actual wall thickness to which the pad is attached.

Internal pad reinforcement is not allowed.

The width of the pad reinforcement may be reduced to b 1 provided the pad thickness is increased to h 1 according to : h b h b 1 1 (21) and the limits given above are observed.

4.3.5.5.7 Reinforcement by increased nozzle thickness

For calculation purposes s S shall be not more than twice s A

The thickness of the nozzle s S should be not greater than twice s A

The wall thickness s A at the opening shall extend over a width b in accordance with formula (20) with a minimum of

The limits of reinforcement normal to the vessel well are : for cylinders and cones, l s = 1,25 d i s s c ( s s c ) (22) for spheres, l s = d i s s c ( s s c ) (23)

The length l s may be reduced to l s1 provided that the thickness s s is increased to s s1 according to the following : s s 1 s 1 s s l s l (24) and the limits given above are observed.

4.3.5.5.8 Reinforcement by a combination of increased shell and nozzle thicknesses

To reinforce openings, both shell and nozzle thicknesses can be increased simultaneously The calculations for reinforcement should follow sections 4.3.5.5.6 and 4.3.5.5.7 together This increase in shell thickness can be accomplished either by directly increasing the shell thickness or by adding a pad.

Multiple openings are regarded as single openings provided the distance l between two adjacent openings, Figures 24 and 26, complies with :

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If the value of $ l $ is below the threshold specified by formula (25), it is essential to assess whether the cross section between openings can support the applied load Sufficient reinforcement is confirmed if the conditions outlined in formula (17) or (19) are satisfied, as applicable.

Calculations for operating loads

Design validation through experimentation is essential; additional calculations beyond those in section 4.3.5 may be necessary to confirm that stresses from operating loads remain within acceptable limits It is crucial to account for all load conditions anticipated during service, as outlined in section 4.2.3.

In these calculations static loads shall be substituted for static plus dynamic loads.

The analysis shall take account of gross structural discontinuities, but need not consider local stress concentrations.

Annex A provides terminology and acceptable stress limits when an elastic stress analysis is performed.

Acceptable calculation methods include : finite element ; finite difference ; boundary element ; recognised text books, published papers, codes and standards.

Planned and controlled experimental means may be used in order to confirm these calculations, for example, by application of strain gauges to verify stress levels.

Figure 1 — Example of joining stiffening ring to shell

- For design of cylindrical shell : l b = maximum of l b , l b2 ,l b3 ,b b4

- For design of reinforcing elements :

Figure 2 — Determination of buckling length

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Figure 3a) Figure 3b) h/ea 50 b ea + es

1 b ea + 32 es h/ea 50 b ea + es

L is the portion of the shell which acts as part of the reinforcing element and contribute to its effective moment of inertia.

Figure 3 — Determination of reinforcing elements h/e a ≤50 x 1 ≤ min x2 ≤ min ˆ

Figure 4b) — Dished end with nozzle

Figure 4c) — End with knuckle and crown of unequal wall thickness ˆ

Figure 4d) — Weld outside 0,6 D a Figure 4e) — Weld inside 0,6 D a v = 1,0 v = 0,85 or 1,0

Figure 4f) — End welded together from round plate and segments

Figure 5 — Design factors for 10 % torispherical dished ends

Figure 6 — Design factors for 2:1 torispherical dished ends ˆ

Figure 7a) — Geometry of convergent conical shells

Figure 7b) — Geometry of a divergent conical shell

Figure 8 — Geometry of a cone opening

Figure 9 — Geometrical quantities in the case of loading by external pressure

Figure 10.1 — Permissible value v 15K pS for convergent cone with an opening angle = 10°

Figure 10.8 — Permissible value v 15K pS for convergent cone (corner joint) with an opening angle ° to 70°

Type A Type B d = inside diameter of opening d = inside diameter of opening

D i = design diameter D i = design diameter f = short side of elliptical end f = short side of elliptical end

Figure 11 — Opening factor CA for flat ends and plates without additional marginal moment ˆ

Type of flat end design (principle only)

D a r min up to 500 30 over 500 up to 1400 35 over 1400 up to 1600 40 over 1600 up to 1900 45 over 1900 50 and r 1,3 s a) flat end

2 cylindrical part : h 3,5 x s b) forged or pressed flat end 1 knuckle radius :

0,35 c) plate thickness : s 3 s 1 s > 3 s 1 d) plate welded into the shell with welds at both sides of the latter plate thickness : s 3 s 1 s > 3 s 1

Only killed steels are permissible for use When utilizing plate material, it is essential that the weld zone, covering an area of at least 3 s 1, shows no signs of material discontinuities.

0,40 0,45 flat plate welded into the shell from one side only

Figure 12 — Design factors for unstayed circular flat ends and plates

0,35 0,40 ˆ ‰ e) flat plate welded into the shell from both sides ˆ

Rectangular plates Elliptical plates f = short side of the rectangular plate f = short side of the eliptical plate e = long side of the rectangular plate e = long side of the eliptical plate

Figure 13 — Design factor C e for rectangular or elliptical flat plates ˆ

Figure 14 — Increased thickness of a cylindrical shell

Figure 15 — Increased thickness of a conical shell

Figure 16 — Set-on reinforcement ring Figure 17 — Set-in reinforcement ring

Figure 22 — Calculation scheme for cylindrical shells ˆ

Figure 23 — Calculation scheme for spherical shells

Figure 24— Calculation scheme for adjacent nozzles in a sphere or in a longitudinal direction of a cylinder ˆ

Figure 25 — Openings between longitudinal and circumferential direction

Figure 26 — Calculation scheme for adjacent nozzles in a sphere or in a circumferential direction of a cylinder ˆ

General

5.1.1 The manufacturer or his or her sub-contractor, shall have equipment available to ensure manufacture and testing in accordance with the design.

The manufacturer must ensure a robust material traceability system for pressure-bearing components in the inner vessel construction, adhere to design dimensions within specified tolerances, and maintain the required cleanliness of the vessel, associated piping, and any equipment that may come into contact with the cryogenic fluid.

Cutting

Material may be cut to size and shape by thermal cutting, machining, cold shearing or other appropriate method.Thermally cut material shall be dressed back by machining or grinding.

Cold forming

Austenitic stainless steel

Heat treatment after cold forming is unnecessary under specific conditions For operating temperatures down to –196 °C, if the base material's test certificate indicates a fracture elongation (A 5) of at least 30% and the cold forming deformation is 15% or less, or if the residual elongation is at least 15%, heat treatment is not required For temperatures below –196 °C, if the cold forming deformation is 15% or more and the residual elongation is also at least 15%, heat treatment is still not needed Additionally, for formed heads, the base material must show a fracture elongation of at least 40% for wall thicknesses up to 15 mm at temperatures down to –196 °C, at least 45% for wall thicknesses over 15 mm at the same temperatures, and at least 50% for temperatures below –196 °C.

Where heat treatment is required this shall be carried out in accordance with the material standard.

Cold forming deformation can be calculated according to EN 13445-4.

Ferritic steel

Post forming heat treatment is essential for 9% Ni steel when cold forming deformation exceeds 5% This steel must be fully certified as quenched and tempered or double normalized and tempered, and it should undergo stress relief at a temperature of 560 °C.

Heat treatment processes, including forming and stress relieving, can be conducted in multiple stages at temperatures reaching 580 °C To ensure compliance with material standards, a test piece from the parent material must accompany the formed part throughout all heat treatment stages and be tested after the completion of the heat treatment to verify that the mechanical properties meet the specified requirements.

53 b) for the following ferritic steels used for the inner vessel, post forming heat treatment is not required where the forming deformation is not more than 5 % :

1) nickel alloyed steels, suitable for low temperature use ;

2) carbon and carbon-manganese steels : where R m 2 or where 530 < R m 2 and R 0.002 360 N/mm 2

When heat treatment is required, suitable heat treatments after cold forming are nomalising, normalising (double) plus tempering, quenching plus tempering or solution annealing.

The parameters provided by the base material manufacturer in the test certificate serve as guidelines for heat treatments However, alternative heat treatments may be utilized if the procedure is validated and the product, or a representative test piece, is evaluated following forming and heat treatment.

Hot forming

General

Forming must adhere to a documented and qualified procedure that outlines the heating rate, holding temperature, temperature range, and duration of the forming process Additionally, it should include specific details regarding any heat treatment applied to the formed component.

Austenitic stainless steel

Materials must be uniformly heated in a suitable atmosphere, avoiding flame contact, and should not exceed the recommended hot forming temperature If forming occurs after the material's temperature drops below 900 °C, compliance with section 5.3.1 is required.

Ferritic steel

Post-forming heat treatment requirements include: a) 9% Ni steel must undergo double normalization and tempering or quenching and tempering to meet specified material properties, with test pieces provided for testing as per the material standard; b) ferritic steel requires heat treatment according to the material standard to establish its properties, with air-quenched steels needing subsequent tempering and test pieces for verification; however, for normalized steels, post-forming heat treatment is unnecessary if hot forming occurs within the specified temperature range, eliminating the need for additional test pieces.

Manufacturing tolerances

Plate alignment

Except where a tapered transition is provided, misalignment of the surfaces of adjacent plates at welded seams shall be :

For longitudinal seams, the allowable thickness is limited to 15% of the thinner plate, with a maximum of 3 mm In the case of circumferential seams, the limit is set at 25% of the thinner plate's thickness, up to a maximum of 5 mm.

Tapers between surfaces must have a maximum slope of 30° The taper can incorporate the weld width, and if needed, the lower surface can be enhanced with additional weld metal When tapering a plate, it is essential that the thickness of either plate does not fall below the design requirements.

For tapered seams, the distance from either surface of the thicker plate to the center line of the thinner plate must meet specific requirements: for longitudinal seams, it should be at least 35% of the thickness of the thinner plate, while for circumferential seams, it should be no less than 25% of the thickness of the thinner plate.

In no case shall the surface of any plate lie between the centre lines of the two plates.

These requirements are illustrated in Figure 27.

Nomenclature h, h 1 , h 2 = surface misalignments t = thickness of the thinner plate e = distance from the surface of the thicker plate to the centreline of the thinner plate

Figure 27a) — Seam which do not require a taper

Figure 27b) — Seams which do require a taper

Thickness

The vessel's thickness must meet or exceed the design specifications, ensuring that any variations in thickness are gradual and occur after the manufacturing process.

Dished ends

The dishing depth, excluding the straight flange, must meet or exceed the theoretical depth The knuckle radius should not fall below the specified minimum, while the crown radius must remain within the specified maximum Additionally, any profile variations should transition smoothly into the designated shape without abrupt changes.

Cylinders

5.5.4.1 The actual circumference shall not deviate from the circumference calculated from the specified diameter by more than + 1,5 %.

5.5.4.2 The out of roundness u calculated from the expression : out of roundness u = %

Licensed Copy: London South Bank University, London South Bank University, Sat Dec 30 06:21:56 GMT+00:00 2006, Uncontrolled Copy, (c) BSI shall be not more than the values shown in Table 2.

Table 2 — Permitted out of roundness

Permitted out of roundness for Wall thickness to diameter ratio internal pressure external pressure s/D = 0,01 s/D > 0,01

The assessment of out-of-roundness in pressure vessels does not need to account for elastic deformation caused by the vessel's dead weight At nozzle locations, increased out-of-roundness is acceptable if supported by calculations or strain gauge data Single dents or knuckles must adhere to specified tolerances, and dents should be smooth, with their depth not exceeding 1% of their length relative to the generatrix of the shell.

2 % of their width respectively Greater dents and knuckles are permissible provided they have been proven admissible by calculation or by strain measurements.

Irregularities in the profile, as measured by a 20° gauge, must not exceed 2% of the gauge length This limit can be increased by 25% if the irregularities are shorter than one quarter of the shell part's length between two circumferential seams, with a maximum length of 1 meter For larger irregularities, it is necessary to provide calculations or strain gauge measurements to demonstrate that the stresses remain within permissible limits.

Irregularities in the profile at the welded seam, particularly those associated with adjacent "flats," must not exceed the values specified in Table 3.

A conservative method of measurement (covering peaking and ovality) shall be by means of a 20° profile gauge (or template).

The profile gauge, as shown in Figure 29, requires two measurements, P1 and P2, taken on either side of the seam at a specific location The maximum peaking is determined to be equivalent to 0.25 times the sum of P1 and P2.

Measurements should be conducted at intervals of about 250 mm along longitudinal seams to identify the point of maximum peaking value While the use of alternative gauges, such as bridge gauges or needle gauges, is allowed, the maximum allowable peaking value is specified in Table 3.

Vessel ratio wall thickness se to diameter D Maximum permitted peaking s/D 0,025 5 s/D > 0,025 10

For all ratios a maximum permitted peaking is e.

5.5.4.3 Departure of the cylinder axis from a straight line shall be not more than 0,5 % of the cylindrical length,except where required by the design.

Welding

General

The European Standard mandates that the welding method used must be suitable and performed by qualified welders or operators Additionally, it requires that the materials involved are compatible and that a welding procedure test is conducted for verification.

Qualification

Welding procedures shall be approved in accordance with EN 288-4, EN 288-8 or with EN 1418 as applicable.

Welders and welding operators shall be qualified accordance with EN 287-1 or EN 287-2 or to EN 1418 as applicable.

Temporary attachments

Temporary attachments welded to pressure bearing parts shall be kept to a practical minimum.

Temporary attachments welded directly to pressure bearing parts shall be compatible with the immediately adjacent material.

Welding dissimilar metal attachments to intermediate components, like pads that are permanently connected to pressure-containing parts, is allowed It is essential to use compatible welding materials for these dissimilar metal joints.

Before the first pressurization, temporary attachments must be removed from the vessel using chipping or grinding techniques that preserve its integrity Any required repairs through welding must follow an approved welding procedure.

The area of the vessel from where the temporary attachments have been removed shall be dressed smooth and examined by appropriate non-destructive testing.

Welded joints

5.6.4.1 Some specific weld details appropriate to vessels conforming to EN 14398 are given in annex D. These details show sound and currently accepted practice It is not intended that these are mandatory nor should they restrict the development of welding technology in any way.

The manufacturer, in selecting an appropriate weld detail, shall consider : the method of manufacture ; the service conditions ; the ability to carry out necessary non-destructive testing.

Weld details may be used provided their suitability is proven by procedure approval according to EN 288-3,

EN 288-4 or EN 288-8 as applicable.

5.6.4.2 Where any part of a vessel is made in two or more courses, the longitudinal weld seams of adjacent courses shall be staggered A minimum of 100 mm is recommended Joggle joints and backing strips may be used for circumferencial welds only plate thickness up to 8 mm.

5.6.4.3 As the mechanical characteristics of work-hardened austenitic stainless steels can be adversely affected if the material is not welded properly, the additional requirements below shall be applied : the heat input during welding shall be not more than 1,5 kJ/mm per bead to be verified in the procedure qualification test ; the material shall cool down to a temperature of not more than 200 °C between passes ; the material shall not be heat treated after welding.

Non-welded joints

For non-welded joints between metallic and non-metallic materials, it is essential to establish procedures akin to those used for welding These procedures must be adhered to for all joints, and operators must be qualified in these methods Only personnel who have received proper qualification should execute these procedures.

Quality plan

Inspection stages during manufacture of a vessel

During the manufacturing of an inner vessel, several critical inspection stages must be conducted, including the verification of material test certificates and their correlation with the materials used Additionally, the approval of weld procedure qualification records and welders' qualification records is essential The process also involves examining material cut edges, checking the setup of seams for welding with dimensional accuracy, and reviewing weld preparations and tack welds A visual examination of welds is necessary, along with the verification of non-destructive testing Furthermore, testing production control test plates for welds and, if required, for formed parts after heat treatment is crucial, as is the verification of the cleaning of the inside surface of the vessel.

The examination of the completed vessel includes a dimensional check and a pressure test, with a record of any permanent set where necessary.

Additional inspection stages during manufacture of a large transportable cryogenic vessel

During the manufacturing process of a large transportable cryogenic vessel, several key inspection stages are essential These include verifying the cleanliness and dryness of the vessel in accordance with EN 12300, conducting a visual examination of welds that are not covered by section 6.1.1, checking the nameplate and any other specified markings, and performing a thorough examination of the completed vessel, which includes a dimensional check.

Production control test plates

Requirements

Production control test plates for the inner vessel must be created and evaluated according to specific guidelines: one test plate is required for each welding procedure on longitudinal joints per vessel Once 10 consecutive test plates using the same procedure have successfully passed testing, the frequency of testing can be reduced to one test plate for every 50 meters of longitudinal joint for 9% Ni and ferritic steels.

Production control test plates are not required for the outer jacket.

The test results must meet specific criteria: for the weld tensile test (T), the values of R et, R m, and A 5 should not fall below the minimum specified values for the parent metal or the approved welding procedure values The impact test (IW, IH) must adhere to the standards set by EN 1252-1 or EN 1252-2 For the bend test (BF, BR, BS), compliance with section 7.4.2 of EN 288-3:1992 for steels is required Lastly, the macro etch (Ma) should demonstrate a sound build-up of beads and adequate penetration.

Extent of testing

The selection of test specimens from the test plate is determined by the material and thickness, following the specifications outlined in Tables 5 and 6 For reference, the symbols used in Table 5 can be found in Table 4.

The test plate must be adequately sized to accommodate the necessary specimens, including provisions for retests Before cutting the test piece, non-destructive testing should be conducted on the test plate to ensure that the specimens are sourced from sound areas.

Face bend test to EN 910 BF

Root bend test to EN 910 BR

Side bend test to EN 910 BS

Impact test ; weld deposit to EN 875 IW

Impact test ; HAZ to EN 875 IH

Table 5 — Testing of production test plates for steels

Test specimens e 12 1 BF, 1 BR, 1 T, 1 Ma

Fine grain steels normalised or thermo mechanically treated

12 < e 35 3 IW, 3 IH, 1 T, 1 Ma e 12 1 BF, 1 BR, 1 T, 1 Ma

Ni steels up to 9% Ni

12 < e 3 IW, 3 IH, 1 T, 1 Ma e 12 1 BF, 1 BR, 1 T, 1 Ma

Non-destructive testing

General

Non-destructive testing personnel shall be qualified for the duties according to EN 473.

X-ray examination shall be carried out in accordance with EN 1435 or ISO 1106-1 Radioscopy may also be used and shall be carried out in accordance with EN 13068-3.

Extent of examination for surface imperfections

All weld deposits will undergo a visual examination, potentially assisted by a x 5 lens, as outlined in Table 8 for acceptance criteria If there are any uncertainties, surface crack detection will be performed to supplement the examination.

Arc strike contact points and areas from which temporary attachments have been removed shall be ground smooth and subjected to surface crack detection.

Extent of examination for volumetric imperfections

Volumetric imperfections in the vessel will be assessed through radiographic examination, unless a specific justification is provided for using ultrasonic or alternative methods The examination of the main seams on the inner vessel will follow the guidelines outlined in Table 6, while acceptance levels can be found in Table 8.

Hemispherical ends that lack a straight flange must be welded together or to a cylinder, and these welds should be tested as longitudinal welds Additionally, any welds located within a hemispherical end are also required to undergo testing as longitudinal welds.

Table 6 — Extent of radiographic examination for welded seams of the inner vessel

Longitudinal seams T junctions Circumferential seams

NOTE 1 For additional requirements for 9 % Ni steel use annex B.

NOTE 2 Additional testing can be required when pneumatic proof testing is used.

Acceptance levels

6.3.4.1 Acceptance levels for surface imperfections

Table 7 shows the acceptance criteria for surface imperfections.

Table 7 — Acceptance levels for surface imperfections

Lack of penetration 402 Not permitted

Undercut 5011 Where the thickness is less than 3 mm no visible undercut is permitted.

Where the thickness is not less than 3 mm, slight and intermittent undercut is acceptable, provided that it is not sharp and is not more than 0,5 mm.

Excessive penetration 504 Where the thickness is less than 5 mm, excessive penetration shall be not more than 2 mm.

Where the thickness is not less than 5 mm, excessive penetration shall not be more than 3 mm.

Excess weld material 502 Where the thickness is less than 5 mm, excess weld metal shall not be greater than 2 mm and the weld shall blend smoothly.

Where the thickness is 5 mm or greater, the maximum excess weld metal shall not exceed 3 mm and the weld shall blend smoothly.

Reinforcement to be of continuous and regular shape with complete filling of groove.

Grind smooth, acceptable subject to thickness measurement and surface crack detection test.

6.3.4.2 Acceptance levels for internal volumetric imperfections

Table 8 shows the acceptance criteria for internal volumetric imperfections detected by radiographic examination.

Table 8 — Acceptance levels for internal volumetric imperfections

Cracks and lack of sidewall fusion 4011 Not permitted

Incomplete root fusion 4013 Not permitted

Flat root concavity Acceptable if full weld depth is at least equal to the wall thickness and the depth of the concavity is less than

Inclusions (including oxide in aluminium welds) Strings of pores, worm holes parallel to the surface and strings of tungsten.

The maximum length shall be the greater of 7 mm or 2/3 t.

Interrun fusion defects and root defects in multipass weld

The total length of multiple in-line inclusions must not exceed six times the thickness, while the gap between inclusions should be more than twice the length of the largest inclusion.

Area of general porosity visible on a film Acceptable if less than 2 % of projected area of weld

Individual pores 2011 Acceptable if diameter is less than 25 % of the thickness with a maximum of 4 mm

Worm holes perpendicular to the surface 2021 Where the thickness is less than 10 mm, worm holes are not permitted.

Where the thickness is not less than 10 mm, isolated examples are acceptable provided the depth is estimated to be not more than 30 % of the thickness.

Tungsten inclusions 3041 Where the thickness is less than 12 mm, tungsten inclusions are acceptable provided the length is not more than 3 mm.

Where the thickness is not less than 12 mm, tungsten inclusions are acceptable provided the length is not more than 25 % of the thickness.

6.3.4.3 Extent of examination of non-welded joints

Where non-welded joints are used between metallic materials and/or non-metallic materials, the quality plan referred to in 6.1 shall include reference to an adequate technical specification.

This technical specification shall include the description of the requirements for inspection and testing, together with the criteria necessary to allow for the repair of any imperfections.

Rectification

Although unacceptable volumetric or surface imperfections may be repaired by removing the imperfections and rewelding, 100 % of all repaired welds shall be examined to the original acceptance standards.

Pressure testing

Every vessel must undergo a pressure test to confirm its leak tightness This leak tightness can be verified either during the vacuum establishment process or through a separate leak test conducted at pressures reaching the design specifications.

The test pressure shall not be less than the highest of :

1,3 (p s ) bar considered for each element of the vessel e.g shell, head, etc.

During hydraulic testing, the pressure is gradually increased to the test pressure and maintained for 30 minutes before being reduced to the design pressure for a visual inspection of all surfaces and joints The vessel must not exhibit any signs of significant plastic deformation or leakage Pneumatic testing can also be performed under similar conditions; however, due to the higher stored energy involved, it should only be conducted with proper safety measures in place to protect inspectors, employees, and the public.

6.5.2 Vessels which have been repaired subsequent to the pressure test shall be re-subjected to the specified pressure test after completion of the repairs.

6.5.3 Where austenitic stainless steel comes into contact with water the chloride content of the water and time of exposure shall be controlled so as to avoid stress corrosion cracking.

The piping system must undergo a pressure test as specified in section 4.2.3.9 However, mechanical joints and fittings that have proven reliable through satisfactory in-service experience are exempt from strength testing.

General

This annex outlines the guidelines for conducting elastic stress analysis on components of a large vacuum insulated transportable cryogenic vessel under specific operating conditions, focusing on the loads specified in section 4.2.3.

Sections A.4 and A.5 provide alternative criteria for validating design acceptability through elastic analysis, with A.5 specifically addressing local stresses around attachments, supports, and nozzles.

The calculated stresses in the area under consideration are grouped into the following stress categories : general primary membrane stress ; local primary membrane stress ; primary bending stress ; secondary stress.

Stress intensities f m , f L , f b , and f g can be determined from the principle stresses f 1 , f 2 and f 3 in each category using the maximum shear stress theory of failure, see A.2.1.

The stress intensities determined in this way should be less than the allowable values given in A.3 and A.4 or A.5.

Peak stresses are not a concern in this context, as they are primarily important for designs intended for cyclic service The large vacuum insulated transportable cryogenic vessels covered by this standard are not classified as being in cyclic service.

Figure A.1 and Table A.1 serve as guidance for evaluating stress categories and intensity limits in various scenarios It is essential to refer to stress definitions to accurately classify specific stress conditions Section A.4.5 clarifies the rationale behind categorizing thermal stresses into "general" and "secondary" types.

Terminology

Stress intensity

The stress intensity at a specific point is defined as twice the maximum shear stress, which is the difference between the largest and smallest principal stresses In this context, tension stresses are regarded as positive, while compression stresses are viewed as negative.

The principal stresses f 1 and f 2 acting tangentially to the surface at the point under consideration should be calculated from the following equations:

2 is the meridional stress (longitudinal in a cylindrical shell) is the shear stress

Gross structural discontinuity

A gross structural discontinuity significantly influences the overall stress or strain distribution within a structure, acting as a source of stress or strain intensification that impacts a considerable area.

Examples of gross structural discontinuities are :

EXAMPLE 1 end to shell junctions.

EXAMPLE 2 junctions between shells of different diameters or thicknesses.

Local structural discontinuity

A local structural discontinuity, such as small fillet radii, can lead to stress or strain intensification within a limited volume of material However, this localized effect does not significantly alter the overall stress or strain distribution or impact the structure as a whole.

Normal stress

The normal stress is the component of stress normal to the plane of reference; this is also referred to as direct stress.

The distribution of normal stress within a part is typically non-uniform throughout its thickness This stress can be divided into two components: one that is uniformly distributed and represents the average stress value across the thickness, and another that varies depending on the specific location within the thickness of the section.

Shear stress

The shear stress is the component of stress acting in the plane of reference.

Membrane stress

The membrane stress is the component of stress that is uniformly distributed and equal to the average value of stress across the thickness of the section under consideration.

Primary stress

Primary stress arises solely from mechanical loadings and is distributed in a way that prevents load redistribution due to yielding It includes normal and shear stresses necessary for maintaining equilibrium of external and internal forces and moments A key feature of primary stress is its non-self-limiting nature; when it significantly exceeds yield strength, it can lead to failure or substantial distortion Thermal stress, however, is not considered a primary stress Primary stress is further categorized into "general" and "local," with local primary stress defined in A.2.8.

Examples of general primary stress are :

EXAMPLE 1 The stress in a cylindrical or a spherical shell due to internal pressure or to distributed live loads.

EXAMPLE 2 The bending stress in the central portion of a flat head due to pressure.

Primary local membrane stress

Excessive distortion in load transfer can occur in structures when membrane stress, caused by pressure or mechanical loading, interacts with primary effects or discontinuities.

Conservatism dictates that certain stresses should be classified as primary local membrane stresses, despite exhibiting some traits of secondary stresses A region is deemed local if the stress intensity surpasses 110% of the allowable general primary membrane stress within a meridional distance of no more than 0.5 times the radius (R) of the component, and is at least 2.5 times the thickness (s) away from another region where the general primary membrane stress limits are exceeded.

An example of a primary local stress is the membrane stress in a shell produced by external load and moment at a permanent support or at a nozzle connection.

Secondary stress

Secondary stress refers to the normal or shear stress that arises due to the constraints imposed by neighboring components or the self-constraint of a structure A key feature of secondary stress is its self-limiting nature, meaning that local yielding and slight distortions can alleviate the conditions leading to the stress Consequently, failure from a single instance of this stress is unlikely.

An example of secondary stress is the bending stress at a gross structural discontinuity.

Peak stress

Peak stress is characterized by its inability to cause noticeable distortion, making it primarily a concern as a potential source of fatigue cracks Stress that is not highly localized and cannot lead to significant distortion also falls into this category.

EXAMPLE 1 The surface stresses in the wall of a vessel or pipe produced by thermal shock.

EXAMPLE 2 The stress at a local structural discontinuity.

Stress categories and stress limits for general application

Specific criteria, stress categories and stress limits for limited application

Design

Manufacturing and inspection

Comments

Weld detail

Tiêu đề	Cryogenic Vessels — Large Transportable Non-Vacuum Insulated Vessels — Part 2: Design, Fabrication, Inspection And Testing
Trường học	London South Bank University
Chuyên ngành	Cryogenic Vessels
Thể loại	British Standard
Năm xuất bản	2003
Thành phố	London

Định dạng
Số trang	96
Dung lượng	2,01 MB