5.1　General Requirements

5.1.1　Design temperature

Design temperature shall be determined according to the following requirements:

a）Design temperature shall be assumed to be the highest or lowest metal temperature of sidewalls and load-bearing elements under normal operating conditions；

b）Maximum design temperature of the tanks shall not be higher than 120℃；

c）The minimum design metal temperature of the tanks shall consider the minimum daily mean temperature at the site.For the tank without heat tracing and insulation，its design metal temperature shall be the minimum daily mean temperature at the site where the tank is constructed plus 13℃.Under design conditions，if the actual stress of load-bearing element does not exceed 1/3 of the allowable tension stress，consideration of the design metal temperature is not required for tank components that are not exposed to the liquid or vapor being stored.

5.1.2　Design pressure

Design pressure shall be assumed to be the pressure of gas or vapor space above the level in the tank（the volume of gas or vapor space above the highest level in the tank shall not be less than 2% of the volume of total liquid stored）.Positive pressure shall not be less than the set pressure of relief valve，and negative pressure shall not be less than the maximum partial vacuum possibly developed in this space.

5.1.3　Loads

The following loads shall be considered in the design of tanks:

a）Hydrostatic head（density of liquid stored is the weight per cubic meter of liquid at 20℃.In any case，the minimum density shall not be less than 770kg/m 3 ）；

b）Positive gauge pressure and partial vacuum possibly developed during operation；

c）The weight of the tank and its contents；

d）Concentrated load，such as heavy duty instruments，valves installed on the top of the tank；

e）Dynamic load，such as loads resulting from the mixer installed on the top of the tank；

f）The supporting system，both local and integral，including the effect that is predictable from the nature of the foundation conditions；

g）Loads from platforms and stairways and where climatic conditions warrant，excessive snow；

h）Wind loads or seismic loads；

i）Loads resulting from connected piping；

j）The weight of any insulation and lining.

5.1.4　Thickness addition

The thickness addition shall be determined by formula（5.1.4）:

where: c ——Thickness addition（mm）；

c 1 ——Minus deviation of material thickness（determined in accordance with 5.1.4.1）（mm）；

c 2 ——Corrosion allowance（determined in accordance with 5.1.4.2）（mm）.

5.1.4.1　Minus deviation of material thickness

The minus deviation of steel plate thickness shall be in compliance with the requirements specified in material standards.The minus deviation may be neglected，when it is not greater than 0.3mm，and not exceeds 6% of the nominal thickness.

5.1.4.2　Corrosion allowance

The corrosion allowance shall be considered to protect tank subjected to thinning by corrosion，erosion or mechanical abrasion.The requirements in details are prescribed in process datasheets.

5.1.5　Joint efficiency

Joint efficiency shall be determined based on type and position of joint and length ratio of the joint subject to the NDT.See Table 5.1.5.

5.1.6　Allowable stresses of materials and walls

5.1.6.1　Nomenclatures

M ——Ratio of the compressive stress， S c to the maximum allowable compressive stress， S cs （ M = S c / S cs ），less than 1.0；

N ——Ratio of the tension stress， S t ，to the maximum allowable stress for simple tension， S ts （ N = S t / S ts ），less than 1.0；

R ——Inner radius of the wall（mm）；

R 1 ——Radius of curvature of the tank wall in the meridional plane，at the level under consideration（mm）；

R 2 ——Length of the normal to the tank wall at the level under consideration，measured from the wall of the tank to its axis of revolution（mm）；

R 3 ——Horizontal radius of the base of the cone，at any level under consideration（mm）；

S c ——General variable for indicating a compressive stress（which may be either an allowable or computed value，depending on the context in which the variable is used）（MPa）；

S ca ——Allowable compressive stress S ca is lower than S cs because of the presence of a coexistent tensile or compressive stress perpendicular to it（MPa）；

S cc ——Calculated compressive stress at the point under consideration（MPa）；

S cs ——Max allowable longitudinal compressive stress of the wall（for a cylindrical wall，it is determined in accordance with the thickness-to-radius ratio）（MPa）；

S t ——General variable for indicating a tension stress which may be either an allowable or computed value depending on the context in which the variable is used（MPa）；

S ta ——Allowable tensile stress is lower than S ts because of the presence of a coexistent compressive stress perpendicular to it）（MPa）；

S tc ——Computed tensile stress at the point under consideration（MPa）；

S ts ——Max allowable stress for simple tension as given in Table 4.2.2（MPa）；

T 1 ——Meridional unit force of latitudinal arc，in the wall of the tank at the level under conside-ration（ T 1 is positive when in tension，and T 1 is negative when in compression）（N/mm）；

T 2 ——Latitudinal unit force of meridional arc，in the wall of the tank at the level under consideration（ T 2 is positive when in tension，and T 2 is negative when in compression，and in cylindrical sidewalls，the latitudinal unit forces are circumferential unit forces）（N/mm）；

t ——Design thickness of the wall（mm）.

5.1.6.2　Maximum tensile stresses

The maximum tensile stresses in the outside walls of a tank shall not exceed the applicable stress values determined in accordance with the following provisions:

a）If both the meridional and latitudinal unit forces， T 1 and T 2， are tensile or if one force is tensile and the other is zero，the computed tensile stress， S tc ，shall not exceed the applicable value given in Table 4.2.2；

b）If the meridional unit force， T 1 ，is tensile and the coexistent latitudinal unit force， T 2 ，is compressive or if T 2 is tensile and T 1 is compressive，the computed tensile stress， S tc ，shall not exceed a value of the allowable tensile stress， S ta ，obtained by multiplying the applicable stress value given in Table 4.2.2 by the appropriate value of N obtained from Figure 5.1.6.2-1 for the value of compressive stress（ S c = S cc ）and the correlated ratio of（ t - c ）/ R involved.However，in cases where the unit force acting in compression does not exceed 5% of the coexistent tensile unit force acting perpendicular to it，the designer has the option of permitting a tensile stress of the magnitude specified in a）instead of complying strictly with the provisions of this paragraph.In no event shall the value of S ta exceed the product of the applicable joint efficiency for tension as given in Table 5.1.5 and the allowable stress for simple tension shown in Table 4.2.2.

5.1.6.3　Maximum compressive stresses

Except as provided in 5.5.2.3 for the compression-ring region，the maximum compressive forces in the outside wall of a tank shall not exceed the applicable stress values determined in accordance with the following provisions.These rules do not purport to apply when the circumferential stress on a cylindrical wall is compressive（as in a cylinder acted upon by external pressure）.However，values of S cs computed as a）（ R = R 1 when the compressive unit force is latitudinal； R = R 2 when the compressive unit force is meridional），in some degree form the basis for the rules given in b），c），d），which apply to walls of double curvature.

a）If a cylindrical wall，or a portion there of，is acted upon by a longitudinal compressive force with neither a tensile nor a compressive force acting concurrently in circumferential direction，the computed compressive stress， S cc ，shall not exceed a value， S cs ，established for the applicable thickness-to-radius ratio as follows；

For values of（ t - c ）/ R less than 0.00667，

For values of（ t - c ）/R between 0.00667 and 0.0175，

For valuesof（ t - c ）/ R greater than 0.0175，

b）If both the meridional and latitudinal unit forces， T 1 and T 2 ，are compressive and of equal magnitude，the computed compressive stress， S cc ，shall not exceed the value， S ca ，established for the applicable thickness-to-radius ratio as follows.

For values of（ t - c ）/ R less than 0.00667，

For values of（ t - c ）/R between 0.00667 and 0.0175，

For values of（ t - c ）/ R greater than 0.0175，

For austenitic stainless steel low-pressure tanks，for values of（ t - c ）/ R ≤0.0175，if modulus of elasticity of the material at design temperature is less than 2×10 5 MPa，or its yield strength is less than 205MPa，the allowable compressive stress are reduced accordingly in the proportion of the ratio of the allowable compressive stress to 2×10 5 or 205 respectively；

c）If both the meridional and latitudinal unit forces， T 1 and T 2 ，are compressive but of unequal magnitude，both the larger and smaller compressive stress shall be limited to values that satisfy the following requirements:

where:

S l ——Larger compressive stress（MPa）；

S s ——Small compressive stress（MPa）；

S cs ——Allowable longitudinal compressive stress，compuated per a），determined in accordance with the thickness-to-radius ratio；Formula（5.1.6.3-7）is for larger stress， S l ，and Formula（5.1.6.3-8）is for smaller stress， S s （MPa）；

Note:In the previous expressions，if the unit force involved is latitudinal， R shall be equal to R 1 ，if the force is meridional， R shall be equal to R 2 .

d）If the meridional unit force， T 1 ，is compressive and the coexistent unit force， T 2 ，is tensile，except as otherwise provided in e），or if T 2 is compressive and T 1 is tensile，the computed compressive stress， S cc ，shall not exceed a value of the allowable compressive stress， S ca ；determined from Figure 5.1.6.2-1 by entering the computed value of N and the value of（ t - c ）/ R associated with the compressive unit stress and reading the value of S c that corresponds to that point.The value of S c will be the limiting allowable value of S ca for the given conditions；

e）When a local axial compressive buckling stress in a cylindrical shell is primarily due to a moment in the cylinder，then the allowable longitudinal compressive stress S cs or S ca ，as specified in a），b），may be increased by 20%.If the shell bending is due to wind（tank full or empty）or due to earthquake（tank empty），then in addition to the above allowed 20% increase，the allowable buckling stress due to a moment can be increased an additional 1/3.For tanks full or partially full of liquid and for an earthquake induced longitudinal compressive stress，the allowable compressive stress need not be limited for biaxial stress as otherwise may be required by Figure 5.1.6.2-1.

For seismic design，the tank full is usually the worst case.For wind loading，the tank empty and with internal pressure is usually the worst case for local，bending induced compressive force.

5.1.6.4　Maximum shearing stresses

The maximum allowable shearing stresses in welds used for attaching manways，nozzles and their reinforcements or other attachments to the walls of a tank and in section of manway or nozzle necks that serve as reinforcement attachment shall not exceed 80% of the value of the applicable maximum allowable tensile stress， S ts ，given in Table 4.2.2 for the kind of material involved，and shall not exceed 90% of yield strength of the material in case of austenitic stainless steel.Such maximum shearing stresses are permissible only where the loading is applied in a direction perpendicular to the length of the weld and must be reduced where the loading is applied differently.

5.1.6.5　Maximum allowable stresses for wind or earthquake loadings

The maximum allowable stresses for design loadings combined with wind or earthquake loadings shall not exceed 133% of the stress permitted for the design loading condition，and this stress shall not exceed 80% of yield strength unless otherwise specified.

5.1.6.6　Maximum allowable stress values or structural members and bolts

Maximum allowable stress values for structural members and bolts shall meet the following requirements:

a）The maximum stresses in internal or external diaphragms，webs，trusses，columns，and other framing，as determined for any of the loadings listed in 5.1.3 or any concurrent combination of such loadings expected to be encountered in the specified operation，shall not exceed the applicable allowable stresses given in Tables 4.5.1，Table 4.6.2 and Table 5.1.6.6.

b）Except as provided in c），the slenderness ratio（the ratio of the unbraced length， L ，to least radius of gyration， r ），for structural members in compression and for tension members other than rods shall not exceed the following values:

For main compression members-120；

For bracing and other secondary members in compression-200；

For main tension members-240；

For bracing and other secondary members in tension-300.

c）The slenderness ratio of main compression members inside a tank may exceed 120，but not exceed 200.Provided that the member is not ordinarily subject to shock or vibration loads and that the unit stress under full design loadings does not exceed the following fraction of the stress value stipulated in Table 5.1.6.6 for the member's actual L/r ratio:

f =1.6- L /（200 r ）

d）The gross and net cross sections of structural members shall be determined as described in the following provisions:

1）The gross sections of a member at any point shall be determined by summing the products of the thickness and the gross width of each element as measured normal to the axis of the member.The net section shall be determined by substituting for the gross width the net width whick，in the case of a member that has a chain of holes extending across it in any diagonal or zigzag line，shall be computed by deducting from the gross width the sum of the diameters of all holes in the chain and adding the following quantity for each gauge space in the chain；

s 2 /（4 g ）

where: s ——Longitudinal spacing of any two successive holes（mm）；

g ——Transverse spacing of the same two holes（mm）.

2）In the case of angles，the gauge for holes in opposite legs shall be the sum of the gauges from the back of the angle minus the thickness；

3）In determining the net section across plug or slot welds，the weld metal shall not be considered as adding the net area；

4）For splice members，the thickness considered shall be only that part of the thickness of the member that has been developed by the welds or other attachments beyond the section considered；

5）In pin-connected tension members other than forged eyebars，the net section across the pinhole，transverse to the axis of the member，shall be not less than 135%；the net section beyond the pinhole，parallel to the axis of the member，shall be not less than 90% of the net section of the body of the member；The net width of a pin-connected member across the pinhole，transverse to the axis of the member，shall not exceed eight times the thickness of the member at the pin unless lateral buckling is prevented；

e）External structural，or tubular，columns and framing subject to stresses produced by combination of wind and other applicable specified in 5.1.3 may be proportioned for unit stresses 25% greater than those specified in Table 5.1.6.6，if the required section is not less than that required for all other applicable loads combined on the basis of the unit stresses specified in Table 5.1.6.6.A corresponding increase may be applied to the allowable unit stresses in the connection bolts or welds for such members；

f）Allowable design stresses for bolts are established that recognize possible stressing during initial tightening.For flange bolts，these design allowable stresses also recognize additional stressing during overload and testing.

5.2　Design of Bottoms

5.2.1　Thickness of bottom plates

Thickness of bottom plates shall meet the following requirements:

a）Bottom plates

Bottom plates shall have a minimum nominal thickness of 5mm for austenitic stainless steel and 6mm for other materials，exclusive of any corrosion allowance；

b）Annular bottom plates

Annular bottom plates shall have a minimum nominal thickness of 5mm for austenitic stainless steel and have a value specified in Table 5.2.1 for other materials，exclusive of any corrosion allowance.

5.2.2　Construction of bottom plates

Construction of bottom plates shall meet the following requirements:

a）Bottom plates should be of construction with annular（bow）bottom plates；

b）At least a 50mm width of the annular bottom plate will project beyond the outside edge of the weld that attaches the bottom to the sidewall plate，the butt-weld shall extend at least 700mm inside the sidewall；

c）Joints between the bottom plates may be lap-welded，butt-welded or combined lap-and-butt-welded.Butt-joint is preferred；

d）Lap-welded bottom plates under the sidewall shall have the outer ends of the joints fitted and buttwelded to form a smooth bearing for the sidewall plates.Bottom plates under the sidewall that are thicker than 10mm shall be butt welded.The butt-welds shall be made using a backing strip 3mm thick or more，or they shall be butt-welded from both sides.Welds shall be full fusion through the thickness of the bottom plate；

e）When the lap joint is used，the lap width shall not be less than 5 times plate thickness and shall not be less than 30mm.The bottom plates shall be lap-welded above the annular bottom plates，and the lap width shall not be less than 60mm.Three-plate joints in tank bottoms shall not be closer than 300mm from each other and 300mm from the sidewall；

f）Any welding joints in the bottom plates shall not be closer than 300mm.

5.2.3　Sidewall-to-bottom fillet joints

Sidewall to bottom joints shall meet the following requirements:

a）For bottom and annular plate joined to the sidewall，the joining position of the bottom plate shall be machined into a flat surface for assembly with the sidewall；

b）For bottom and annular plates with a nominal thickness 13mm，and less，the attachment between the bottom edge of the lowest course sidewall plate and the bottom plate shall be a continuous fillet weld laid on each side of the sidewall plate.The size of each weld shall not be more than 13mm and shall not be less than the nominal thickness of the thinner of the two plates joined or less than the following values shown in Table 5.2.3；

c）For bottom plates under the sidewall with a nominal thickness greater than 13mm，the attachment welds shall be sized so that either the legs of the fillet welds or the groove depth plus the leg of the fillet for a combined weld are of a size equivalent to the thickness of the annual bottom plate（see Figure 5.2.3）；

d）When the sidewall material has a specified minimum yield strength greater than 248MPa，each weld shall be made with a minimum of two passes.

5.3　Design of Sidewalls

5.3.1　Nomenclatures

A t ——Cross-sectional area，of the interior of the tank at the level under consideration（mm 2 ）；

F ——Summation of the vertical components of the forces in any and all internal or external ties，braces，diaphragms，trusses，columns，skirts，or other structural device or supports acting on the free-body. F shall be given the same sign as p when it acts in the same direction as the pressure on the horizontal face of the free-body；it shall be given the opposite sign when it acts in the opposite direction（N）；

p ——Total pressure（gauge）acting at a given level of the tank under a particular condition of loading， p = p L + p g （MPa）；

p g ——Gas pressure above the surface of the liquid.It is design pressure of a tank. p g shall be positive except in computations used to investigate the ability of a tank to withstand a partial vacuum；in such computations，its value is negative，MPa（gauge）；

p L ——Gauge pressure resulting from the liquid head at the level under consideration in the tank（See the level illustrated in Figure 5.3.1）（MPa）；

W ——Total weight of that portion of the tank and its contents（e.g.the level illustrated in Figure 5.3.1）that is treated as a free-body in the computations for that level. W shall be given the same sign as p when it acts in the same direction as the pressure on the horizontal face of the free-body；it shall be given the opposite sign when it acts in the opposite direction（N）；

φ ——Efficiency of the weakest joint across which the stress under consideration acts（applicable values given in Table 5.1.5）.

See 5.1.6.1 for other Nomenclatures.

5.3.2　Computation of unit forces

At any level of the cylindrical shell selected for free-body analysis of the tank（see Figure 5.3.1），the unit forces shall be computed from the following formulas:

5.3.3　Computation of thickness

5.3.3.1　If T 1 and T 2 are both positive，indicating tension，the larger of the two shall be used for computing the thickness，as shown in the following formulas:

5.3.3.2　If T 1 is positive，indicating tension，and T 2 is negative，indicating compression，or if T 2 is positive，indicating tension，and T 1 is negative，indicating compression，the thickness of tank wall required for this condition shall be determined by assuming different thickness until one is found for which the simultaneous values of the computed tension stress， S tc ，and the computed compressive force， S cc ，satisfy the requirements of 5.1.6.2 b）and 5.1.6.3 d）respectively.

If the unit force acting in compression does not exceed 5% of the coexistent tensile unit force，the computing may be directly performed according to the requirements of 5.3.3.1.The value of the joint efficiency factor φ will not enter into this determination unless the magnitude of the allowable tensile stress is governed by the product φS ts as provided in 5.1.6.2 b）.

5.3.3.3　If T 1 and T 2 are both negative，indicating compression，and of equal magnitude，the thickness of tank wall shall be computed using the following formula:

In this formula， S ca ，has the appropriate value for the thickness-to-radius ratio involved，as prescribed in 5.1.6.3 b）and 5.1.6.3 e）.

5.3.3.4　If T 1 and T 2 are both negative，indicating compression，but of unequal magnitude，the thickness of tank shall be the largest of those thickness values，computed by the stepwise procedure outlined below:

a）Step 1.The thickness values shall be computed from the following formulas:

In both formulas，the value of T ′shall be equal to the larger of absolute values of the two unit forces T 1 and T 2 ； T ″shall be equal to the smaller of absolute values of the two coexistent unit forces T 1 and T 2 ；if the latitudinal unit force（ T 2 ）is larger， R ′= R 1 and R ″= R 2 ；conversely，if the meridional unit force（ T 1 ）is larger， R ′= R 2 and R ″= R 1 .

b）Step 2.The corrosion allowance shall be deducted from each of the two thicknesses computed in Step 1，and the thickness-to-radius ratio，（ t - c ）/ R ，shall be checked for each thickness based on the value of R used in computing t .If both such thickness-to-radius ratios，（ t - c ）/ R ，are less than 0.00667，the larger of the two thicknesses computed in Step 1 will be the required thickness；otherwise，Step 3 shall be followed.

c）Step 3.If one or both thickness-to-radius ratios determined in Step 2 exceed 0.0067，the value of t shall be computed from the following formulas:

d）Step 4.The thickness-to-radius ratios，（ t - c ）/ R ［ R = R ′defined in Step 1 is used for R in connection with Formula（5.3.3.4-3）； R = R ″defined in Step 1 is used for R in connection with Formula（5.3.3.4-4）］，of the two thicknesses computed in Step 3，shall be checked.If both such thickness-to-radius ratios are greater than 0.0175，the larger of the two thicknesses computed in the Step 3 will be the required thickness；otherwise，Step 5 shall be followed.

e）Step 5.If one or more the thickness-to-radius ratios，（ t - c ）/ R ，determined in Step 2 or Step 4 fall between 0.00667 and 0.0175，and the thickness involved was computed using Formula（5.3.3.4-1）or（5.3.3.4-3），a thickness shall be found that satisfies the following formula:

Or if the thickness involved was computed using Formula（5.3.3.4-2）or（5.3.3.4-4），a thickness shall be found that satisfies the following formula:

f）Step 6.A tentative final selection of thickness shall be made from among the thickness values computed in the previous steps.The values of S cc shall be computed for both T 1 and T 2 ，and checked to see that they satisfy the requirements of 5.1.6.3 c）and 5.1.6.3 e）.If the tentative thickness does not satisfy these requirements，the necessary adjustments shall be made in the thickness to make the value of S cc satisfy these requirements.

5.3.4　Minimum thickness of tank wall

The minimum thickness of the tank wall at any level shall be the greatest of the following values:

a）5mm plus the corrosion allowance；

b）Design thickness in accordance with 5.3.3；

c）The minimum nominal thickness of tank wall required for construction，which shall meet the requirements in Table 5.3.4.

5.3.5　Intermediate wind girder

5.3.5.1　For fixed roof tanks，full height of the tank wall shall be used to calculate the stability of the tank under wind loading.

5.3.5.2　The allowable critical pressure of tank shell shall be computed from the following formula:

where:［ p cr ］——Allowable critical pressure of tank shell（kPa）；

D ——Tank inner diameter（m）；

H E ——Equivalent height of tank shell（m）；

t min ——Effective thickness of the thinnest course of tank sidewall（mm）；

H e i ——Equivalent height of course i of tank sidewall（m）；

h i ——Actual height of course i of tank sidewall（m）；

t i ——Effective thickness of course i of tank sidewall（mm）.

5.3.5.3　Design external pressure of tank shell shall be computed from the following formula:

where: p 0 ——Design external pressure of tank shell（kPa）；

ω k ——Characteristic value of wind loading，which shall be computed according to the requirements of GB 50009-2012 and depending on tank height and actual conditions at the site where tank is constructed（kPa）；

q ——1.2 times negative pressure setting of the breather valve of the tank（kPa）.

5.3.5.4　The characteristic value of wind loading， ω k ，shall be computed from the following formula:

where: β z ——Wind vibration coefficient at height Z ， β z =1 for tanks；

μ s ——Shape factor for wind loading，the stagnation point value shall be assumed， μ s =1；

μ z ——Exposure factor for wind pressure；

ω 0 ——Basic reference wind pressure（kPa）.

5.3.5.5　Basic wind pressure shall be 50-year-return wind pressure given in Table E.5 in Appendix E.5 of GB 50009-2012，but shall not be less than 0.3kPa.Besides，the effects of geographical location and local meteorological conditions at the site where the tanks are constructed shall be considered.When local wind velocity data is not available，it shall be determined by comparison and analysis of meteorological and terrain conditions based on the reference wind pressure or long-term data specified for the adjoining region.

5.3.5.6　Exposure factor for wind pressure shall be selected according to the following requirements:

a）For flat or slightly rugged terrain，exposure factor for wind pressure shall be determined based on tank height and terrain exposure categories and per Table 5.3.5.6-1，and middle value shall be computed by the interpolation method.

Terrain exposure may be divided into Categories A，B，C and D:

Category A denotes offshore sea level and island，seashore，lakeshore and desert areas；

Category B denotes fields，villages，forest，hills，and towns and the suburbs of the city with relatively sparse buildings；

Category C denotes urban districts with dense buildings；

Category D denotes urban districts with dense and higher buildings；

b）For the tanks located in the hill areas，exposure factor for wind pressure shall be determined based on the terrain exposure category of flat ground and per Table 5.3.5.6-1，and then is multiplied by the correction factor， η .

For hill peak and slope，the correction factor at its top B may be computed from the following formula:

where: k ——Factor，3.2 for hill peak and 1.4 for hill slope；

θ ——The angle of windward side of hill peak or slope，tg θ =0.3 when tg θ ＞0.3；

Z ——Height of computed tank location above the ground， Z =2.5 H 2 when Z ＞2.5 H 2 （m）；

H 2 ——Full height of hill peak or slope（m）.

For other positions of hill peak and slope，correction factors， η A and η C ，at A，C illustrated in Figure 5.3.5.6 shall be 1.The correction factor， η ，between A and B and between B and C shall be determined by the interpolation method.

η =0.75 to 0.85 for blocked terrains such as interhill basin and valley；

η =1.20 to 1.50 for valley and hill pass having the same direction as wind direction；

c）For the tanks located on the pelagic sea level and island，exposure factor for wind pressure shall be determined based on category A roughness and per Table 5.3.5.6-1，and the correction factor given in Table 5.3.5.6-2 shall be considered.

5.3.5.7　Number of intermediate wind girders and their positions on the equivalent shell shall meet the following requirements:

a）When［ p cr ］≥ p 0 ，no intermediate wind girder is required；

b）When one intermediate wind girder shall be provided，and its position shall be at H E /2；

c）When two intermediate wind girders shall be provided，and their positions shall be at H E /3 and 2 H E /3 respectively；

d）When three intermediate wind girders shall be provided，and their positions shall be at H E /4， H E /2，3 H E /4 respectively，and so on.

5.3.5.8　Positions of intermediate wind girders on actual sidewalls shall meet the following requirements:

a）When intermediate wind girder is located at the thinnest sidewall，its actual distance from the adjacent upper reinforced section is not required to be converted；

b）When intermediate wind girder is not located at the thinnest sidewall，its actual distance from the adjacent upper reinforced section shall be converted by using Formula h i = H e i （ t i / t min ） 2.5 .

5.3.5.9　The required minimum cross-section size of intermediate wind girder shall meet the requirements in Table 5.3.5.9.

5.3.5.10　For attachment between intermediate wind girders and sidewalls，the long leg of the angle steel shall keep horizontal，and its short leg shall be downward.Its long leg is welded to the sidewalls，continuous fillet welding shall be made on the upper side，and intermittent welding may be used on the lower side.Welded joint of intermediate wind girder itself shall be fully-penetrated and fully-fused.

5.3.5.11　The distance between intermediate wind girder and circumferential weld in sidewall shall not be less than 150mm.

5.3.6　Shell plate's arrangement and joint

5.3.6.1　Longitudinal joints on adjacent shells shall be staggered each other，and the stagger shall not be less than at least 300mm.

5.3.6.2　Longitudinal and circumferential welded joints in sideplates shall be butt-welded.

5.3.6.3　The butt-welded construction shall be full penetration（see Figure 5.3.6.3-1 and Figure 5.3.6.3-2）.The design of welded joints shall satisfy the requirements of GB 985.1 and GB 985.2.

5.3.7　Seismic design of tanks

In the area where seismic fortification is required，the design of the tanks shall also conform to the applicable seismic codes.

5.4　Design of Roofs

5.4.1　Nomenclatures

Radius of curvature of dome roof（mm）.

α ——Angle between the direction of T 1 and a vertical line（in a conical surface，it is also one-half of vertex angle of the cone）（°）.

For other Nomenclatures，see 5.1.6.1 and 5.3.1.

5.4.2　Design loads

5.4.2.1　The design of fixed roofs shall be capable of withstanding the following design external loads:

a）Fixed loads:gravity load of tank roof plates and their reinforced members，concentrated load such as heavy duty instruments and valves installed on the top of the tank.When there is insulation，gravity load of the insulation shall be included；

b）Dynamic loads:such as loads resulting from the mixer installed on the top of the tank roof；

c）Additional loads:additional design loads on the horizontal projection of the surface of the roof shall not be less than 1200Pa；when snow load exceeds 600Pa，the exceeded part shall also be included.

5.4.2.2　For design internal pressure，see the requirements of 5.1.2.

5.4.3　Computation of unit forces

5.4.3.1　Tori spherical roofs

At any level of the tori spherical roof，the unit forces shall be computed from the following formulas:

5.4.3.2　Cone roofs

At any level of the cone roof，the unit forces shall be computed from the following formulas:

5.4.4　Computation of thickness

Computation of roof thickness is in accordance with the requirements of 5.3.3.

5.4.5　Minimum thickness of roof

The minimum thickness of the roof shall not be less than the larger of the following values:

a）5mm plus the corrosion allowance；

b）Design thickness determined in accordance with 5.3.3.

5.4.6　Construction of roofs

5.4.6.1　A self-supporting dome roof or cone roof may be used，and a dome roof is preferred.

5.4.6.2　The joints between the roof plates may be butt or lap-welded.

5.4.6.3　When lap-welded joint is used，its width shall be neither less than 5 times plate thickness nor 30mm.The distance between two welds shall not be less than 200mm.

5.5　Design of Roof Knuckle Regions and Compression-ring Girders

5.5.1　Knuckle regions

If a curved knuckle is provided between shell and roof，a ring girder or other form of compression-ring shall not be used in connection with it，and there shall be no sudden changes in the direction of a meridional line at any point.The radius of curvature of the knuckle regions shall not be less than 6%，and preferably not less than 12%，of the diameter of the sidewalls.The thickness of knuckle regions shall satisfy the requirements of 5.3.

5.5.2　Compression-ring girders

5.5.2.1　Nomenclatures

A c ——Net area of the vertical cross section of metal required in the compression-ring region，exclusive of all corrosion allowances（mm 2 ）；

Q——Total circumferential force acting on a vertical cross section through the compression-ring region（N）；

R 2 ——Length of the normal to the roof at the juncture between the roof and the sidewalls，measured from the roof to the tank's vertical axis of revolution（mm）；

R c ——Horizontal radius of cylindrical sidewall at its juncture with the roof of the tank（mm）；

S ts ——Maximum allowable stress value for simple tension（See Table 4.2.2）（MPa）；

T 1 ——Meridional unit force in the roof of the tank at its juncture with the sidewall of circumferential arc（N/mm）；

T 2 ——Latitudinal unit force in the roof of the tank at its juncture with the sidewall of meridian arc（N/mm）；

T 2s ——Latitudinal unit force in the cylindrical sidewall of the tank at its juncture with the roof measured along an element of the cylinder（N/mm）；

t c ——Thickness of the sidewalls considered to participate in resisting the circumferential force acting on compression-ring region（including corrosion allowance）（mm）；

t h ——Thickness of the roof plates considered to participate in resisting the circumferential force acting on compression-ring region（including corrosion allowance）（mm）；

W c ——Width of the sidewalls considered to participate in resisting the circumferential force acting on compression-ring region（mm）；

W h ——Width of the roof plate considered to participate in resisting the circumferential force acting on compression-ring region（mm）；

φ ——Efficiency of meridional joints in the compression-ring region（see Table 5.1.5）.

5.5.2.2　If a curved knuckle is not provided，the circumferential compressive forces must be resisted by other means in the compression-ring region of the tank wall.For compression-ring region，see Figure 5.5.2.2.The widths of compression-ring region of roof and sidewall of tank shall be computed from the following formulas，where the thickness of roof and sidewalls are needed to satisfy the requirements of 5.3，5.4.

5.5.2.3　The magnitude of the total circum-ferential force acting on any vertical cross section through the compression-ring regions shall be computed as follows:

The net cross-sectional area provided in the compression-ring regions shall not be less than that required by one of the following formulas:

Note:When the material is austenitic stainless steel，and its yield strength is less than 205 MPa，the value（103.4）in the Formula（5.5.2.3-2）shall be reduced in the proportion of the ratio of yield strength of this material at design temperature to 205.

5.5.3　Details of compression-ring regions

5.5.3.1　If the Q is negative，indicating compression，then the horizontal projection of the effective compression-ring region shall have a width in a radial direction not less than 0.015 times the horizontal radius of the tank wall at the level of the juncture between the roof and sidewalls.

5.5.3.2　When net cross-sectional area provided in the compression-ring regions can not satisfy the requirements of 5.5.2.3，or when Q is negative and radial width of the horizontal projection of compressionring region can not meet 5.5.3.1，the compression-ring region shall be reinforced by:

a）Thickening the roof and sidewall plates within the compression-ring region；

b）Adding an angle，a rectangular bar，or a horizontally disposed ring girder at the juncture of the roof and sidewall plates；

c）Using a combination of these alternatives.

This additional area shall be arranged so that the centroid of the cross-sectional area of the composite corner compression region lies ideally in the horizontal plane of the corner formed by the two members.In no case shall the centroid be off the plane by more than 1.5 times the average thickness of the two members intersecting at the corner.

5.5.3.3　Such an angle，bar，or ring girder may be located either inside or outside the tank（see Figure 5.5.3.3），and shall have a cross section with dimensions that satisfy the following conditions:

a）If the cross-sectional area is increased，the actual area in the compression-ring region shall satisfy the requirements of 5.5.2.3.

b）The horizontal width of the angle，bar，or ring girder is not less than 0.015 times the horizontal radius， R c ，of the tank wall at the level of the juncture of the roof and the sidewalls except that when the cross-sectional area to be added in an angle or bar is not more than one-half the total area required by 5.5.2.3，the foregoing width requirement for this member may be disregarded if the horizontal projection of the width， W h ，of the participating roof plates alone is equal to or greater than 0.015 R c or with an angle or bar located on the outside of a tank，the sum of the projection of the width， W h ，and the horizontal width of the added angle or bar is equal to or greater than 0.015 R c .

c）When bracing must be provided as specified in 5.5.3.8，the moment of inertia of the cross section around a horizontal axis of compression-ring girder shall be not less than that required by Formula（5.5.3.8）.

5.5.3.4　When the thickness of the vertical leg of an angle，bar ring（vertical arrangement）are not less than that of the top ring wall plates of tank，they may located on the sidewall of the tank and may be built into the sidewall.If this construction is not used，the vertical edge of the compression-ring next to the tank shall make good contact with the wall of the tank around the entire circumference and shall be attached thereto along both the top and bottom edges by continuous fillet welds except as provided in 5.5.3.5.These welds shall be sufficiently sized to transmit to the compression-ring angle or other type reinforced ring that portion of total circumferential force， Q ，which must be carried thereby，assuming in the case of welds separated by the width of a structural member as illustrated in Figures 5.5.3.3（a）and 5.5.3.3（h），that only the weld nearest the roof is effective.In no event，however，shall the size of any weld along either edge of a compression-ring be less than the thickness of the thinner of the two parts joined or 6mm（whichever is smaller），nor shall the size of the corner welds between the shell and a girder bar，such as illustrated in Figures 5.5.3.3（d）and 5.5.3.3（e）be less than the applicable weld sizes in Table 5.5.3.4.The part thicknesses and weld sizes in Table 5.5.3.4 relate to dimensions in the as-welded condition before the deduction of corrosion allowances；with this exception，all other part thicknesses and weld sizes referred to in this paragraph related to dimensions after the deduction of corrosion allowance.

5.5.3.5　If a continuous weld is not needed for strength or as a seal against corrosive elements，attachment welds along the lower edge of a compression-ring on the outside of a tank may be intermittent if:

a）The summation of their lengths is not less than one-half the circumference of the tank；

b）The unattached width of tank wall between the ends of welds does not exceed eight times the tank wall thickness exclusive of corrosion allowance；

c）The welds are sized as needed for strength，but in no case are they smaller than specified in 5.5.3.4.

5.5.3.6　The projecting part of compression-ring shall be placed as close as possible to the juncture between the roof plates and sidewall plates.

5.5.3.7　If a compression-ring on either the inside or outside of a tank is shaped in such a way that liquid may be trapped，it shall be provided with adequate drain holes uniformly distributed along its length.Similarly，if a compression-ring on the inside of a tank is shaped in such a way that gas would be trapped on the underside when the tank is being filled with liquid，adequate vent holes shall be provided along its length.Where feasible，such drain or vent holes should be not less than 20mm in diameter.

5.5.3.8　The projecting part of a compression-ring without an outer vertical flange need not be braced if the width of the projecting part in a radical vertical plane does not exceed 16 times its thickness.With this exception，the horizontal or near-horizontal part of the compression-ring shall be braced at intervals around the circumference of the tank with brackets or other suitable members securely attached to both the ring and the rank wall to prevent that part of the ring from buckling laterally out of its own plane.When bracing is required，the moment of inertia of the cross section of the angle，bar，or ring girder about a horizontal axis shall be not less than that computed by the following formula:

where:

I 1 ——Required moment of inertia for the cross section of a steel compression-ring with respect to a horizontal axis through the centroid of the section（not taking credit for any portion of the tank wall）except that in the case of an angle ring whose vertical leg is attached to or forms a part of the tank wall，the moment of inertia of the horizontal leg only shall be considered and shall be figured with respect to a horizontal axis through the centroid of the leg（mm 4 ）；

Q p ——That portion of the total circumferential force Q p that is carried by the compression-ring angle，bar，or girder as computed from the ratio of the cross-sectional area of the compression-ring to the total area of the compression zone（N）；

R c ——Horizontal radius of the cylindrical sidewall of the tank at its juncture with the roof（mm）；

k ——Constant whose value depends on the magnitude of the angle θ subtended at the central axis of the tank by the space between adjacent brackets or other supports，the value of which shall be determined from Table 5.5.3.8 in which n is the number of brackets or other supports evenly spaced around the circumference of the tank.In no case shall θ be larger than 90°.

5.6　Anchorage

5.6.1　For vertical cylindrical steel welded low-pressure storage tanks，the uplift that results from internal pressure acting on the tank combined with the effect of design wind pressure or seismic loads if specified shall not exceed the summation of the weights of sidewalls，roof（excluding corrosion allowance）and their supporting members；otherwise，tank anchorage shall be provided，or other measures to counterbalance the uplift shall be taken.

5.6.2　Anchorage shall be designed to resist the uplift based on 1.25 times the internal design pressure plus the wind load on the shell and roof based on its projection on a vertical plane.If seismic loads are specified，uplift shall be calculated using internal design pressure plus the seismic loads.Wind and seismic loads need not be combined.

5.6.3　The anchorage shall meet the following requirements:

a）For the allowable stress for simple tension of the anchors，see Table 5.6.3；

b）When corrosion is specified for the anchors，thickness of the anchors and the attachments shall plus corrosion allowance.If bolts are used for anchors，the nominal diameter shall be not less than M24.If the corrosion exists，corrosion allowance for anchor bolts shall be at least 6mm；

c）The anchors shall not be directly attached on the bottoms，and shall be connected to sidewalls through combined pad parts with large rigidity or fixing ring with sufficient size or in other suitable types.Too excessive local stress and deformation of tank walls shall not be caused；

d）When inner diameter of the tank is less than 15m，the bolt spacing（arc length）between anchors shall not be greater than 2m.When inner diameter of the tank is not less than 15m，the bolt spacing（arc length）between anchors shall not be greater than 3m.

5.7　Openings and Reinforcements

5.7.1　Nomenclatures

A ——Total cross sectional area of reinforcement required in the plane under consideration（mm 2 ）；

B ——Effective width of reinforcement（mm）；

C ——Thickness addition（mm）；

D ——Inner diameter of shell（mm）；

d ——Opening diameter，i.e，inner diameter of nozzle plus twice the thickness addition for circular opening；or the finished dimension（chord length at mid-surface of thickness including thickness addition）in the plane under consideration for elliptical or obround openings（mm）；

f r ——Strength reduction factor，i，e，the ratio of allowable stresses of nozzle material to shell material at design temperature.In case，this ratio is greater than 1.0，take f r =1.0；

h 1 ——Effective nozzle height of reinforcement outside the shell（mm）；

h 2 ——Effective nozzle height of reinforcement inside the shell（mm）；

δ ——Calculated thickness of shell at opening（mm）；

δ e ——Effective thickness of shell at opening， δ e = δ n - c （mm）；

δ et ——Effective thickness of nozzle（mm）；

δ n ——Nominal thickness of shell at opening（mm）；

δ nt ——Nominal thickness of nozzle（mm）；

δ t ——Calculated thickness of nozzle（mm）.

5.7.2　Shapes，locations，and maximum sizes of sidewall and roof openings

All openings in the sidewalls，or roofs shall be circular，elliptical，or obround in shape.Where elliptical（or similar shape）or obround connections are employed，the long dimensions shall not exceed twice the short dimension.If the openings is in an area of unequal meridional and latitudinal stresses in the tank wall，the long dimension shall preferably coincide with the direction of the greater stress.

Each opening in the wall of a tank shall be located so that the distance between the outer edge of its reinforcement and any line of significant discontinuity in the curvature of the tank walls（such as the juncture between a roof and sidewalls）is not less than 150mm，or eight times the nominal thickness（including corrosion allowance）of the wall plate containing the opening.The maximum size of the opening shall not exceed 1.5 times the radius of curvature in that portion of the tank wall in which the opening is located.

5.7.3　Applicable dimension of openings

5.7.3.1　The reinforcement requirements given in 5.7.3 and 5.7.6 are primarily intended for the openings no larger than the following sizes:

a）For tanks of inner diameter D =1500mm or less，the maximum opening diameter shall be d ≤ D/ 2，a nd d ≤520mm；

b）For tanks of inner diameter D ＞1500mm，the maximum opening diameter shall be d ≤ D/ 3，and d ≤1 000mm.

5.7.3.2　Openings larger than those mentioned above but still within the limits specified in 5.7.2 shall be given special consideration.The reinforcement shall meet all of the requirements given in 5.7.In addition，special attention shall be given to placing the major portion of the reinforcement as close as practice to the edge of the opening while still providing a reasonably gradual transition in contour from the thickness of the tank wall to the maximum thickness of the reinforcement.Whenever practicable，about 2/3 of the required reinforcement shall be placed within a distance extending d /4 on each side of the opening.

5.7.3.3　The fillet welds should be ground to concave contour，and the inside corners of tank wall or nozzle necks along the edges of the opening shall be rounded to a generous radius.

5.7.4　Maximum opening diameter required no extra reinforcement

5.7.4.1　When single opening in tanks satisfies the following requirements completely，no extra reinforcement shall be provided:

a）For the thickness of shell not larger than 9.5mm，the nominal diameter of nozzle is not larger than DN 80；

b）For the thickness of shell larger than 9.5mm，the nominal diameter of nozzle is not larger than DN 50；

c）For threaded connections，the opening size is not larger than DN 50.

5.7.4.2　The reinforcement required for openings in tank walls for external pressure conditions need to be only 50% of that required in 5.7.5.1 where δ has been determined for external pressure conditions.

5.7.5　Constructions of opening reinforcement

5.7.5.1　Requirements of opening reinforcement for tank walls

The area of required reinforcement for cross section that is perpendicular to the surface of tank walls that passes through the center of the opening shall be determined by:

5.7.5.2　Limits and area of effective reinforcement

When calculating the opening reinforcement，the limits and area of effective reinforcement shall be determined in accordance with the rectangular extent WXYZ in Figure 5.7.5.2.

5.7.5.3　Limits of effective reinforcement

Effective width shall be determined according to the following requirements:

a）Effective width，B，shall be determined from the following formulas，whichever is greater；

b）Effective height shall be computed by formulas（5.7.5.3-2）and（5.7.5.3-3），whichever is less.

Outside height

Inside height

5.7.5.4　Area of reinforcement

Cross sectional area of reinforcement within the limits shall be determined by:

where:

A e ——Area of reinforcement（mm） 2 ； A 1 ——Area available in excess thickness of the tank wall contributing to the area of reinforcement，i.e.the differential value between the effective and calculated thickness of tank，determined by formula（5.7.5.4-2）（mm 2 ）:

A 2 ——Area available in excess thickness of the nozzle wall contributing to the area of reinforcement，i.e.the differential value between the effective and calculated thickness of nozzle，determined by formula（5.7.5.4-3）（mm 2 ）:

A 3 ——Cross section of weld metal（mm 2 ）；

If A e ≥ A ，opening requires no reinforcement；

If A e ＜ A ，opening requires reinforcement，the extra reinforcing area shall be calculated by formula（5.7.5.4-4）:

where:

A 4 ——Cross sectional area of material added as reinforcement within the limit of l reinforcement（see Figure 5.7.5.2）（mm 2 ）.

Material used for reinforcement should usually be the same as that of the shell.When material of lower strength is used for reinforcement，the area of reinforcement shall be increased in inverse proportion to the ratio of allowable stress values of these two materials，But no credit may be taken for the additional strength of any reinforcement having a higher allowable stress value than that of the shell.

5.7.6　Reinforcement of multiple openings

5.7.6.1　When any two adjacent openings are spaced at less than two times their average diameter so that their limits of reinforcement overlap each other（see Figure 5.7.6.1），these two openings shall be reinforced in the plane connecting their centers with a combined reinforcement of an area not less than the sum of the areas required for each opening in accordance with the provisions of 5.7.5.The area of reinforcement between these two openings shall be at least equal to 50% of the total required area for openings.No portion of the cross section shall be considered more than once in a combined area.A series of openings，all on the same center line，shall be treated as successive pairs of openings.

5.7.6.2　When more than two adjacent openings are spaced at less than two times their average diameter，and are provided with a combined reinforcement（see Figure 5.7.6.2），the minimum distance between centers of any two adjacent openings shall be 1 1 / 3 times their average diameter.The area of reinforcement between any two adjacent openings shall be at least equal to 50% of the total required area for these two openings.

When any two adjacent openings，as considered under 5.7.6.3，have a distance between centers less than 1 1 / 3 times their average diameter，no credit for reinforcement shall be given for any of the metal between these two openings.

5.7.6.3　Any amount of adjacent openings in any arrangement may be reinforced by using an assumed opening（its diameter enclosing all adjacent openings）.The diameter of assumed opening shall not exceed the value given in 5.7.3.And no credit reinforcement shall be given for any of the metal of the nozzles.

5.7.7　Pad reinforcement

When reinforcing pads are used，JB/T 4736 should be selected.

5.8　Flush-type Shell Connection

5.8.1　Conditions for providing flush-type shell connection

A tank may have flush-type connections at the lower edge of the shell under the conditions described in a）through c）.

a）The design pressure for the gas vapor space of the tank shall not exceed 13.8kPa；

b）The sidewall uplift from the internal design and test pressure，wind，and earthquake loads shall be counteracted so that no uplift will occur at the cylindrical-sidewall and flat-bottom junction；

c）The longitudinal or meridional membrane stress in the cylindrical sidewall at the top of the opening for the flush-type connection shall not exceed 1/10 of the circumferential design stress in the lowest sidewall course that contains the opening.

5.8.2　Dimensions and details

The dimensions and details of the connection shall conform to Table 5.8.2，Figure 5.8.2 and the rules specified in this section:

a）The maximum width， b 1 ，of the flush-type connection opening in cylindrical sidewall shall not exceed 900mm，and the maximum height of the flush-type connection opening in cylindrical sidewall， h 1 ，shall not exceed 300mm；

b）The thickness of the sidewall plate in the flush-type connection opening shall be at least as thick as the adjacent sidewall plate in the lowest sidewall course；

c）The thickness of the sidewall reinforcing plate shall be of the same thickness as the sidewall plate in the flush connection assembly；

d）The thickness of the bottom transition plate in the assembly shall be 12mm minimum，or when specified，the thickness of the bottom annular plate.

5.8.3　Stress relieving

The completed flush-type connection assembly shall be thermally stress relieved after it is completely welded，inspected and accepted.

5.8.4　Cover plates

Cover plates for flush-type connection shall not be connected with the nozzles with additional loads.

5.8.5　Reinforcement

5.8.5.1　The minimum area of reinforcement over the top of the flush-type connection shall be computed using the following formula:

where:

K 1 ——Reinforcement area coefficient，as given in Figure 5.8.5.1；

t d ——Calculated thickness of the sidewall course in which the connection is located，exclusive of any corrosion allowance（mm）；

h ——Greatest vertical height of the clear opening（mm）.

5.8.5.2　The reinforcement in the plane of the sidewall shall be provided within a height， L ，above the bottom of the opening， L shall not exceed 1.5 h 1 except that L minus h 1 shall not be less than 150mm.Where this exception results in a height， L ，greater than 1.5 h 1 ，only that portion of the reinforcement within a height of 1.5 h 1 shall be considered effective.

Note: L is height of the shell reinforcing plate（mm）.

5.8.5.3　The required reinforcement may be provided by any one or any combination of the following:

a）The shell reinforcing plate；

b）Excess thickness of the shell plate in the assembly greater than the thickness of the adjacent plates（in the lowest sidewall course）；

c）That portion of the neck plate that has a length equal to the thickness of the reinforcing plate.

5.8.5.4　The width of the tank-bottom reinforcing plate at the centerline of the opening shall be 250mm plus the combined thickness of the sidewall plate in the flush-type shell connection assembly and the sidewall reinforcement plate.The thickness of the bottom reinforcing plate shall be computed using the following formula:

where:

b 1 ——Horizontal width of clear opening，（mm）.

The minimum thickness of the bottom reinforcing plate， t b ，shall be 16mm for H =14630mm，18mm for H =17000mm，and 20mm for H =19500mm.The minimum nominal thickness of the bottom reinforcing plate shall not be less than computed thickness plus thickness addition.

Note:For austenitic stainless steel，the value of t b determined by formula（5.8.5.4）shall be increased in proportion to the ratio of 205 MPa to yield strength of this material at design temperature.

5.8.5.5　The minimum thickness of nozzle transition piece and nozzle neck， t n ，shall be 16mm.

5.8.6　Material requirements

The materials of tank sidewall plates，reinforcing plates，bottom reinforcing plates and nozzle neck shall be the same as that of the sidewall plates in the lowest sidewall course.All materials in the flush-type shell connection assembly shall conform to the requirements of Chapter 4 of this standard.The materials of the sidewall plate including the assembly，the reinforcing plate，the nozzle neck attached to the sidewall，the transition piece，and the bottom reinforcing plate shall meet the impact test requirements of Chapter 4 of this standard at design metal temperatures for the respective thickness involved.Notch toughness evaluation for the bolting flange and nozzle neck shall conform to the relevant requirements of Chapter 4 of this Standard.Additionally，the yield strength and tensile strength of the sidewall plate in the flush-type shell connection and the sidewall reinforcing plate shall be equal to or greater than the yield strength and tensile strength of the adjacent sidewall plates.

5.8.7　Connection transition

The connection transition between the flush connection in the shell and the circular pipe flange shall be designed according to the relevant requirements of thisstandard.

5.8.8　Anchorage

Where anchoring devices are used to resist the tank uplift，they shall be spaced so that they will be located immediately adjacent to each side of the reinforcing plates around the opening，while still providing the required anchorage for the tank sidewall.

5.8.9　Foundation

The foundationin the area of a flush-type shell connection shall be locally prepared to support the bottom reinforcing plate of the connection.

5.8.10　Nozzle spacing

Flush-type shell connections may be installed using a common reinforcing pad.However，when this type of construction is employed，the minimum distance between nozzle centerlines shall not be less than 1.5（ b 1 + b 2 +65）mm，or 600mm，whichever is greater.The dimensions b 1 and b 2 may be obtained from Table 5.8.2，Column 3，for the respective nominal flange sizes.Adjacent sidewall flush-type connections that do not share a common reinforcing plate shall have at least a 900mm clearance between adjacent edges of their reinforcing pads.

Note:Here b 2 is the width of opening of adjacent nozzle.

5.8.11　Weld examination

All longitudinal butt-welds in the nozzle and its transition piece，and the first circumferential butt-weld in neck closest to sidewall，excluding neck to flange weld shall be 100% radiographed.The nozzle-to-tank sidewall and reinforcing plate welds and the sidewall-to-bottom reinforcing plate welds shall be examined their entire length using magnetic-particle test.This magnetic-particle test shall be performed on the root pass，on every 13mm of deposited weld metal while the weld is being made，and on the completed weld. qVO4XEao5yNS4ZVECxnCWZhxxVp1HL+g4LhqfZJkEyUZr3/daXZq0CNCpbO5bsWH