UDC
GB
中华人民共和国国家标准
National Standard of the People
′s Republic of China
P
GB 50094-98球形储罐施工及验收规范
Code for construction and
Acceptance of spherical tanks
本英文版为内部资料，仅供参考，以中文版为准。
The Chinese version of standards has precedence to their English translations which are only for internal reference.
Issued on 1998-05-06
Implemented from 1998-12-01
the State Bureau of Technical Supervision
the Ministry of Construction of the People’s Republic of China Jointly issued by
Contents
1 General………3
2 Inspection and Acceptance of Parts and Components………4
2.1 Inspection of Quality Certificate of Parts and Components………4
2.2 Inspection of Tank shell Plates and Test Plate………4
2.3 Inspection of Supports………8
2.4 Inspection of Assembled Weldments………8
2.5 Inspection of Painting, Package and transportation of Parts and Components……8
3 Site Assembling………9
3.1 Inspection and Acceptance of Foundation………9
3.2 Assembling of Spherical Tank………10
3.3 Installation of Parts and Components………13
4 Welding………14
4.1 General Rules………14
4.2 Welding Process Qualification………15
4.3 Selection of Welding Materials and Their Site Control………15
4.4 Welding Application………16
4.5 Repair………20
4.6 Inspection of Size of Spherical Tank Welded………22
5 Inspection of Welds………23
5.1 Visual Inspection of Welds………23
5.3 Radiographic Testing and Ultrasonic Testing………24
5.4 Magnetic Powder Testing and Dye Penetrant Testing………25
6 Post Weld Heat Treatment of the Whole………27
6.1 General Rules………27
6.2 Heat Treatment Process………27
6.3 Requirements for Heat Insulation………28
6.4 Temperature Measuring System………29
6.5 Treatment of Support Foot………29
7 Test Plate of Product Welding………30
7.1 Requirements for Preparation of Test Plate of Product Welding………30
7.2 The Preparation and Test of the Test Plate………30
8 Pressure Test and Airtight Test………31
8.1 Pressure Test………31
8.2 Airtight Test………33
9 Handing Over and Acceptance………34
Appendix A Low Temperature Spherical Tanks………35
A.1 General Rules………35
A.2 Inspection and Acceptance of Tank Shell Plates………35
A.3 Assembling………35
A.4 Welding………35
A.5 Post Weld Heat Treatment of the Whole………36
A.6 Product Test Plate………37
A.7 Inspection of Welds………37
A.8 Pressure Test………37
Appendix B Name of Different Parts of Spherical Tank, Numbering of Zones, Tank Shell Plates and Welds of Spherical Tank………38
1 General
1.0.1 In order to make the spherical tanks (hereinafter referred to as spherical tank) in site
construction be advance in technology, reasonable in economy, safe and practical and to guarantee the quality, this Code is worked out.
1.0.2 This Code applies to carbon steel and alloy steel welded spherical tank of orange-petal
type or mix type supported with columns with design pressure ≥0.1Mpa but ≯4 Mpa and nominal capacity ≥50M3。
This Code does not apply to following spherical tank: (1) Spherical tank under nuclear radiation;
(2) Non-fixed (truck or ship carried) spherical tank; (3) Spherical tank of double-layer structure;
(4) St requiring fatigue analysis; (5) Spherical tank expansion formed.
1.0.3 The construction and acceptance of spherical tank shall include following scope: 1.0.3.1 The tank shell and its pressure parts and components connected shall be differentiated
in following scope:
(1) The first circumferential welds in welding connection of the tank connection pipe and the outer piping;
(2) The first thread in thread connection of the tank connection pipe and the outer piping; (3) The first flange seal face in flange connect of the tank connection and the outer piping..
1.0.3.2 Pressure seal heads, flat covers and their fasteners of the openings of spherical tank. 1.0.3.3 Non-pressure elements of supports, tie rods, pad plates and bottom plates connected
to the tank shell.
1.0.4 For spherical tank with design temperature ≤-20℃, stipulation in Appendix A of this
Code shall apply.
1.0.5 The contractor of the spherical tank shall have qualification certificate for site
assembling and welding of spherical pressure vessels issued by labor department.
1.0.6 Before installation of spherical tank, the contractor must inform the labor departments
at provincial, regional and municipal level where the user or installation unit of the spherical tank is. Also the contractor shall make a report to the inspection organization authorized by the safety supervision institution for boilers and pressure vessels under the provincial labor department for inspection and shall accept its site supervision and inspection.
1.0.7 The spherical tank shall be constructed in accordance with design drawings. In case it
is necessary to make modification, it must be agreed with original designer and the documents for design modification must be signed.
shall also be in conformity with relevant national standards and specifications in force.
2 Inspection and Acceptance of Parts and Components
2.1 Inspection of Quality Certificate of Parts and Components
2.1.1 The contractor shall inspect technical quality documents of product quality certificates
furnished by manufacturers.
2.1.2 Factory certificates for parts and components of tank shell plates, manholes, connection
pipes, flanges, reinforcing pieces, supports and tie rods of the spherical tank shall include following contents:
(1) Ex-factory Quality Certificates of parts and components;
(2) Product inspection reports issued by the supervision organization under labor department;
(3) Papers approving material substitution;
(4) Quality certificate of materials and reports on re-testing;
(5) Non-destructive testing reports on steel plates, forging, parts and components; (6) Ultrasonic testing reports on sides of tank shell;
(7) Non-destructive testing reports on bevels and welds; (8) Testing reports on test plates hot-press formed; (9) Testing reports on product welding test plates.
2.2 Inspection of Tank shell Plates and Test Plate
2.2.1 The structural type of tank shell shall be in conformity with requirements of design
drawings, no piece of shell plates shall be spliced.
2.2.2 The tank shell plates supplied by manufacturers shall not have defects of crack, bubble,
scar, folding or slag inclusion. In case there is, a repair shall be made in accordance with what specified in 4.5 of this Code.
2.2.3 Spot test shall be made to the thickness of tank shell plates. The actual thickness
measured shall not be less than nominal thickness minus negative error of the steel plate. The quantity for spot test shall be 20% of quantity of shall plates, and for each zone, it shall not be less than 2 pieces. For upper and lower poles, it shall not be less than 1 piece. For each piece of tank shell plate, the test shall not be less than 5 points. Spot test by double shall be made in case any in-qualification found in the spot test. In case it is still not qualified, test piece by piece shall be made to tank shell plates.
2.2.4 The profile size of tank shell plates shall meet following requirements:
2.2.4.1 The allowable clearance between the sample plate to test the curvature of tank shell
plates and tank shell plates and the sample plates shall meet what specified in Table 2.2.4 – 1. (Figure 2.2.4 – 1).
Table 2.2.4 – 1
Allowable Clearance between Sample Plate and Tank Shell Plates and Sample Plates Length of chord of tank shell
plate (m)
Length of chord of sample plate (m)
Allowable clearance,
e (mm)
≥2 2 3
<2 Same as the length of chord of
tank shell plate 3
Figure 2.2.4-1 Inspect Curvature of Tank Shell Plate (unit: mm) 1—sample plate；2—tank shell plate
2.2.4.2 The allowable error for the geometric size of tank shell plates shall meet what
specified in Table 2.2.4- 2 (Figure 2.2.4 – 2).
2.2.5 The welding bevels of tank shell plates shall meet following requirements: 2.2.5.1 The surface quality of the bevels flame cut shall meet following requirements:
(1) The degree of plane shall be ≤0.04 times of nominal thickness of the tank shell plate (δn), and not > 1mm.
(2) The surface shall be smooth and the surface roughness (Ra) shall be ≤25μm;
(3) The limit space between defects (Q) shall be ≥0.5m.
Table 2.2.4 – 2 Allowable Error for Geometric Size of Tank Shell Plate
Item Allowable error (mm)
Length of chord in length direction L1, L2, L3 ±2.5
Length of chord in any width direction, B1, B2, B3 ±2
Length of chord of diagonal lines D ±3
Distance between tow diagonal lines 5
Note: For tank shell plates with less rigidity, length of arc may be inspected. The allowable error shall meet what specified in first three items in the Table.
(4) Slag and oxidation scales shall be removed. The surface of the bevel shall not have any defect of crack or lamination. For the tank shell plates made of the steel with standard tensile strength >540 Mpa, the surface of the bevel shall be spot tested with magnetic powder or dye penetrant and there shall be no defect of crack, lamination or slag inclusion. The quantity for spot test shall be 20% of shell plate quantity. In case any unallowable defect is found, re-test shall be made in double. In case there is still unallowable defect, test shall be made piece by piece.
2.2.5.2 The allowable error for geometric size of bevels shall meet following requirements
(Figure 2.2.5).
(1) The allowable error for the angle of the bevel (α) shall be ±2°30′；
(2) The allowable error for the obtuse side (P) and the depth of the bevel (h) shall be ± 1.5mm.
2.2.6 Ultrasonic spot testing shall be made to the full range 100mm from sides of the tank
shell plates. The quantity for spot testing shall not be less than 20% of total quantity of tank shell plate, and not less than 2 pieces for each zone, not less than 1 piece for upper and bottom poles. For tank shell plates requiring ultrasonic testing, a spot test of ultrasonic testing shall be made. The quantity for spot test shall be the same as that for the spot test of the sides. The test method and the test results shall meet what specified in the national standard in force the
Non-destructive Testing of Pressure Vessels JB4730. The class for qualification shall meet
requirements of design drawings. In case there is any unallowable defect, re-test shall be made in double. In case there is still unallowable defect, test shall be made piece by piece.
2.2.7 In case the thickness of adjoining plates is ≥3mm or 1/4 larger than the thickness of
thinner plate, the side of thicker plate shall be cut to hypotenuse (Figure 2.2.7). The thickness of the end after cutting shall be the thickness of the thinner plate.
2.2.8 The manufacturer shall provide at least 6 pieces of product welding test plates as well as the test plates necessary for assessing welding process for each spherical tank. The size shall be 180mm x 650mm.The material of test plates shall be qualified and they shall also have same thickness and same steel number of the tank shell plates. The bevel type of the welding test plates shall be same as that of tank shell plates.
Figure 2.2.4 – 2 Inspection of Geometric Size of Tank Shell Plate (Unit: mm)
Figure 2.2.5 Inspection of Geometric Size of the Bevel of Tank Shell Plate (Unit: mm)
Figure 2.2.7 Requirements for Reducing the Thickness of Thicker Plate in Welding Tank Shell Plates of Different Thickness
2.3 Inspection of Supports
2.3.1 The allowable error for the total length of the supports shall be 3mm.
2.3.2 The supports, after welding to the bottom plate, shall be vertical. The allowable error
for the verticality shall be 2mm. (Figure 2.3.2).
Figure 2.3.2 Inspection of Error of Verticality of Support and Bottom Plate (Unit: mm)
2.3.3 The error for the linearity of the total length of the supports shall be ≤1/1000 of total
length, and not be > 10mm.
2.4 Inspection of Assembled Weldments
2.4.1 After assemble welding of the upper part of the support of sectors and the equator plate,
the curvature shall be inspected by using a sample plate with length of the chord not less than 1m.
The clearance must not be >3mm. The allowable error for the linearity of the upper part of the support shall be 1/1000 of the length of upper part of the support. The drift of the position of axis shall not be > 2mm.
2.4.2 After assemble welding of manholes, connection pipes and tank shell plates, the
allowable error for the positions of openings of the manholes, connection pipes as well as the allowable error for the length of extension, the curvature of tank shell plates and the installation of the flange of connection pipes shall meet requirements in 3.3.1 of this Code.
2.5 Inspection of Painting, Package and transportation of Parts
and Components
2.5.1 Rust shall be removed both from inside and outside of tank shell plates. Both sides
shall be applied with two passes of primer. Weldable painting shall be applied within a range of 50mm from the edge inside and outside. The marks of the numbering of tank shell plates the steel number and furnace batch number on each tank shell plate shall be framed with white painted.
2.5.2 In transporting and storing, tank shell plates shall be packed with steel structure
supports and closely tied to the supports by using tie yokes. The convex of the tank shell plate shall be upward. Flexible material of wooden blocks shall be cushioned between tank shell plates. The number of plates eclipsed should not be more than 6. Total weight of each package should not be more than 30t.
2.5.3 Flanges, manholes and sample plates should be transported in packages. Tie rods and
levers should be bundled.
2.5.4 Anti-rust grease shall be applied to surfaces of all processed pieces. The threads of tie
rods shall be protected properly to avoid any damage.
2.5.5 The other requirements for inspection, packing and transportation of parts and
components of tank shells, supports and tie rods shall meet relevant stipulations in national standard in force the Painting, Packing and Transportation of Pressure Vessels JB2536.
3 Site Assembling
3.1 Inspection and Acceptance of Foundation
3.1.1 Before installation of spherical tank, inspection and acceptance shall be made to the
size of different parts of the foundation. (Figure 3.1.1). The allowable error shall meet what specified in 3.1.1 of this Code. Construction shall not be done until the strength of foundation concrete is not less than 75% of design strength.
Figure 3.1.1 Inspection of Size of Different Parts of Foundation 1—Anchor bolts；2—Reserved holes for anchor bolts
Table 3.1.1 Allowable Error for Size of Different Parts of Foundation Serial
No. Item Allowable error
spherical tank capacity
<1 000m3 ±5 mm
1 Diameter of center circle of foundation
(D1) spherical tank capacity
≥1 000m3 ±Di/2 000 mm
2 Position of foundation 1°
3 Distance between foundation centers of adjoining supports (S) ±2 mm 4 Distance between center of the anchor bolt of support foundation and
the foundation center circle (S1)
±2 mm
5 Distance between reserved hole of anchor bolt of support foundation and the foundation center (S2)
±8 mm Elevation of upper surface of different support foundation -D1/1000mm, and not lower than –15mm Foundation fixed
with anchor bolts Difference of foundation elevations of adjoining supports
4 mm Elevations of upper
surfaces of foot plates of support foundation -6 mm 6 Foundation elevation Foundation fixed with pre-embedded
foot plates Difference of elevations of foot plates of adjoining support foundations
3 mm
Foundation fixed with anchor bolts 5 mm 7
Level of upper surface of single
support foundation Foundation fixed with pre-embedded foot plates 2 mm
Note: D1 is design inside diameter of spherical tank.
3.2 Assembling of Spherical Tank
3.2.1 Before assembling of spherical tank, the numbering of each tank shell plate and welds
shall be made. The numbering of tank shell plates should be made along 0°→90°→180°→ 270°→0° of spherical tank. The tank shell plate with number of 1 shall be put at the position over 0°or close to 0°in the direction to 90°. In case the upper and lower poles are using tank shell plates of football petal type, plates arrangement drawing for upper and lower poles shall be drawn and the number of tank shell plates and welds shall be marked. The name of
different parts of spherical tank shall meet what specified in B.0.1 ~ B.0.3 of Appendix B of this Code. Numbering should be in conformity with stipulations in B.0.4 of Appendix B of this Code.
3.2.2 When assembling spherical tank, tools and calipers may be used to adjust the clearance
and displacement of tank shell plates. Assembling shall not be made in force.
3.2.3 When assembling tank shell plates, the clearance, displacement and sharp corner shall
meet following requirements:
3.2.3.1 In the case of hand arc welding, the clearance for matching should be 2±2mm; in the
case of gas shielded welding with cored welding wires, the matching clearance should be 3 ±1mm; in the case of other welding methods, the matching clearance should be determined BY WPS.
3.2.3.2 The displacement for matching tank shell plate, b, shall not be >1/4 of nominal
thickness of the tank shell plate, and not be >3mm (Figure 3.2.3 -1 and Figure 3.2.3 - 2). In case the thickness of two plates is different, the difference of the thickness of two plates may not be counted.
Figure 3.2.3-1 Displacement of Matching for Assembling Tank Shell Plates of Same Thickness
Figure 3.2.3-2 Displacement of Matching for Assembling Tank Shell Plates of Different Thickness
3.2.3.3 Sharp corners shall be inspected by using a sample plate with length of chord not less
than 1m (Figure 3.2.3 – 3). The sharp corner shall be calculated according to following formula, and not be > 7mm:
E = l1 – l 2 (3.2.3 – 1)
l 2 = |R – R 0| (3.2.3 – 2)
In which E ---- value of sharp corner (mm)
shell plate at the place of the largest sharp corned (mm);
l 2 --- Radial distance between the sample plate and standard tank shell plate
(mm);
R ---- Design inside radius or outside radius of tank shell (mm);
R0 ---- Curvature radius of the sample plate (mm).
Figure 3.2.3 – 3 Inspection of Sharp Corner in Assembling Tank Shell Plates (Unit: mm)
3.2.3.4 The inspection of the clearance, displacement and sharp corner in assembling should
be made at each 500mm along butt joints as one measuring point.
3.2.4 After assembling of equator zone of spherical tank, the error for the level of equator
line of each tank shell plate should not be > 2 mm. The error for the level of equator line of adjoining two tank shell plates should not be > 3 mm. The error for the level of equator line of any two tank shell plates should not be > 6 mm.
3.2.5 When assembling spherical tank, the distance the sides of following welds shall not be
less than 3 times of the thickness of tank shell plate, and not less than 100mm:
3.2.5.1 Longitudinal welds of adjoining two zones;
3.2.5.2 Fillet welds of support and tank shell to the butt welds of tank shell plates;
3.2.5.3 The connection welds of spherical tank manholes, connection pipes, reinforcing
rings and connection plates and the tank shell to the butt welds of tank shell plates as well as the welds between them.
3.2.6 When assembling spherical tank, the difference of maximum diameter and minimum
diameter of the spherical tank shall be controlled. On completion of assembling, the difference should be less than 3 ‰ of design inside diameter of the spherical tank, and not be > 50mm.
3.2.7.1 In case the supports are aligned with iron pads, the height of each group of iron pads
shall not be less than 25mm, and also should not be more than 3 pieces. The bevel iron pads shall be used in pair and contacted closely. On completion of alignment, tack welding shall be firm.
3.2.7.2 After alignment of the installation of supports, the verticality of supports shall be checked both in radial and circumferential directions of spherical tank. In case the height of the support is ≤8m, the allowable error for the verticality shall be 12mm. In case the height of the support is over 8m, the allowable error for the verticality shall be 1.5‰ of the height of support, and not > 15mm.
3.2.8 When installing tie rods, they shall be tightened symmetrically and uniformly. The deflection at the middle of the tie rods should be controlled according to following calculated value (Figure 3.2.8).
Figure 3.2.8 Measurement of Deflection at the Middle of the Tie Rod 1—Tie line；2—Tie rod；3—Pin shaft
Δ = 5.42 × 10 –4·(L4 cosθ ) 1 / 3
(3.2.8) In which,
Δ ---- Deflection at the middle of the tie rod (cm);
L ----Distance between pin shafts at two ends of the tie rod (cm); θ ---- Angle of elevation (°).
3.3 Installation of Parts and Components
3.3.1 The installation of pressure elements of manholes and connection pipes shall meet
following requirements:
3.3.1.1 Allowable error for the position of the opening shall be 5mm;
3.3.1.2 The difference of the diameter of the opening and the diameter of the assembled piece
3.3.1.3 Allowable error for the extended length and the position of the connection pipe shall
be 5mm;
3.3.1.4 The flange face of the connection pipe shall be vertical to the center axis of the
connection pipe, unless the design specifies. The flange faces shall be horizontal or vertical. The error must not exceed 1% of outside diameter of the flange (in case the outside diameter of the flange is <100mm, it shall be calculated as 100mm), and not be > 3mm;
3.3.1.5 With the center of the opening as a circle, and with the diameter of the opening as the
radius, beyond this range, check the curvature by using a sample plate with the length of chord not less than 1m, the clearance must not be > 3mm;
3.3.1.6 The reinforcing rings shall be close to the tank shell plates.
3.3.2 The connection plates of the spherical tank shall be close to the tank shell and shall be
welded before heat treatment. In case the fillet welds between the connection plates and the tank shell is continuous welds, vent gap of 10mm shall be reserved at the place where rain is not easy to flow in. The allowable error for the installation of the connection plates shall be 10mm.
3.3.3 The parts and components, which shall affect the entire heat treatment of the spherical
tank and affect the water-filling settlement, shall be fixed to the spherical tank after heat treatment and after settlement test.
4 Welding
4.1 General Rules
4.1.1 The welder engaging spherical tank welding must have valid certificate issued by labor
department. The type of steel, the welding process and the welding position the welder is going to apply welding shall be in conformity with the items the welder was tested.
4.1.2 The welding machine selected shall meet the requirements of welding process.
4.1.3 In any of following cases, welding shall not be applied until effective measures are
taken.
4.1.3.1 In raining or snowing weather;
4.1.3.2 Wind velocity exceeds 8m/s; in case of gas shielded welding, wind velocity exceeds
2m/s;
4.1.3.3 Ambient temperature is -5℃ or below; 4.1.3.4 Relative humidity is 90% or over.
Note: The ambient temperature and relative humidity for welding shall be measured 0.5 ~ 1m from
the surface of the spherical tank.
4.1.4 The welding method for the spherical tank should be hand arc welding, automatic
submerged arc welding.
4.2 Welding Process Qualification
4.2.1 Before welding spherical tank, welding process shall be evaluated in according with
the national standard in force the Evaluation of Welding Process for Steel Pressure Vessels
JB4708.
4.3 Selection of Welding Materials and Their Site Control
4.3.1 The selection of welding materials shall meet following stipulation:
4.3.1.1 Welding materials shall have quality certificates with them. The quality certificates
of the electrodes and cored welding wires for hand arc welding shall include chemical composition, physical performance and content of diffusion hydrogen of melt metal.
4.3.1.2 The electrodes for hand arc welding shall meet what specified in the national
standard in force the Carbon Steel Electrodes GB/T5117 and the Low Alloy Steel Electrodes
GB/T5118. The cored welding wires shall meet what specified in the national standard in
force the Carbon Steel Cored welding wires GB10045. The welding wires for submerged arc welding shall meet what specified in the national standard in force the Wires for Melt
Welding GB/T14957 and the Welding Wires for CO2 Shielded Welding GB/T8110.
4.3.1.3 For butt welds of the tank shell and the welds directly welded to the tank shell, coated
electrodes of low hydrogen must be used. The electrodes and cored welding wires shall be re-tested for hydrogen diffusion according batch numbers. The test method for hydrogen diffusion shall be in accordance with the national standard in force the Method for
Measuring Hydrogen in Electrode Melting Metal GB/T3965. The actual content of
hydrogen diffusion after baking shall meet what specified in Table 4.3.1.
Table 4.3.1
Content of Diffusion Hydrogen in Low Hydrogen Electrodes and Cored welding wires Type of electrodes and cored welding wires Content of hydrogen diffusion (ml/100g)
E4315 E4316 ≤8
E5015 E5016 ≤8
E5515 – X E5516 – X ≤6
E6015 – X E6016 - X ≤4
Cored welding wire ≤6
meet what specified in the national standard in force the Flux for Carbon Steel Submerged
Arc Welding GB5293 and the Flux for Low Alloy Submerged Arc Welding GB12470.
4.3.1.5 CO2 for shielding shall meet what specified in the national standard in force the CO2
for Welding HG/T2537. Argon for shielding shall meet what specified in the national
standard in force the Argon GB4842. Before using, CO2 cylinder should be put upside down
for 24 hours and all water drained.
4.3.2 Site control of welding materials shall meet following stipulations:
4.3.2.1 Welding material shall be kept, baked and issued by assigned special person; 4.3.2.2 Before using, the welding material shall be baked according to product instructions, It may also be baked according to baking temperature and time set in Table 4.3.2. The electrodes baked shall be kept in a oven at temperature of 100 ~ 150℃ and when it is to be used , take it out. The coating of the electrodes shall have no peeling or notable crack.
Table 4.3.2 Baking Temperature and Time for Electrodes and Fluxes Type Baking temperature (℃) Baking time (h)
Low hydrogen coated electrode 350 ~ 400 1
Melting type 150 ~ 300 1
Flux
Sintering type 200 ~ 400 1
4.3.2.3 For hand arc welding, an oven of constant temperature, which is up to product
standard, shall be provided at site. The electrodes shall not be kept in the oven for more than 4 hours. If it is over 4 hours, they shall be re-baked at original baking temperature. The electrodes shall not be re-baked for more than two times.
4.3.2.4 No foreign material shall be mixed in the flux. In case there is any foreign material in
the flux, the flux shall be cleaned or replaced.
4.3.2.5 Before using, any rust or dirt shall be removed from the welding wires.
4.4 Welding Application
4.4.1 Before welding, bevels shall be inspected. Rust, water, oil or dust shall be removed
from the surface and from the range at least 20mm from both sides of the bevel.
4.4.2 Pre-heating and post heating shall meet following stipulations:
4.4.2.1 The pre-heating temperature shall be in accordance with the WPS. For the steel of
Table 4.4.2 Pre-heating Temperature for Common Use Steel ( ℃ ) Steel type Thickness of steel (mm) 20R 16MnR 15MnVR 15MnVNR 07MnCrMoVR 20 — — — 75 ~ 125 25 — — 75 ~ 125 100 ~ 150 32 — 75 ~ 125 100 ~ 150 125 ~ 175 38 75 ~ 125 100 ~ 150 125 ~ 175 150 ~ 200 50 100 ~ 150 125 ~ 175 150 ~ 200 150 ~ 200 75 ~ 100
4.4.2.2 The welds requiring pre-heating before welding, the temperature of inter-layer in
welding application shall not be lower than lower limit of pre-heating temperature.
4.4.2.3 Any of following welds shall be post weld heat treated immediately after welding:
(1) Thickness is over 32mm, and the standard tensile strength of the material is >540Mpa; (2) Low alloy steel of thickness over 38mm;
(3) Butt welds of insert type connection pipe and tank shell; (4) Post weld heat treatment specified by WPS.
4.4.2.4 Post weld heat treatment shall be in accordance with WPS as well as following
requirements:
(1) Post weld heat treatment temperature shall be: 200 ~ 250℃; (2) Post weld heat treatment time shall: 0.5 ~ 1 hour.
4.4.2.5 Temperature for pre-heating and post- heating shall be uniform. The width at the two
sides of welds center, at pre-heating zone and post-heating zone shall be 3 times of plate thickness, and not be < 100mm.
4.4.2.6 The temperature for pre-heating, post-heating and inter-layer temperature shall be
measured symmetrically at 50mm away from welds center. For each piece of welds, the measuring points shall not be less than 3 pairs.
4.4.2.7 For welds not requiring pre-heating, in case the temperature of the wledment is lower
than 0℃, welding shall not be applied until the range 100mm from the place to weld is pre-heated to 15℃.
4.4.2.8 For connection pipes and manholes which have high restrain, and the ambient
temperature is lower than 5℃, the range for pre-heating shall be expanded.
4.4.2.9 In accordance with energy condition in the area of construction, pre-heating and
post-heating may be electric heating or flame heating. Pre-heating and post-heating may be done at the back of welds.
4.4.3 Positioning welding and the welding of tools and calipers shall meet following
requirements:
4.4.3.1 Welding shall be applied in accordance with WPS;
4.4.3.2 If pre-heating is necessary, it shall be done in the range at least 150mm from the
center of welding;
4.4.3.3 The positioning welding shall be applied to the back of preliminary welding layer.
The quality requirements for positioning welding shall be the same as the formal welding. In case there is any crack, it must be removed.
4.4.3.4 The length of positioning welding shall be over 50mm and the space should be 250 ~
300mm. The arc striking and arc closing of positioning welding shall be in the bevel.
4.4.3.5 When welding temporary welds of tools and calipers, the arc striking and arc closing
shall all be in tools, calipers or in welds. It is strictly prohibited to strike arc or close arc in non-welding position.
4.4.4 The determination and control of the energy of welding line shall meet following
requirements:
4.4.4.1 The energy of welding line shall be set in the WPS according to the material,
thickness, welding position and pre-heating temperature of the tank shell.
For the steel plate with standard tensile strength over 540Mpa and the carbon steel with thickness over 38mm as well as the low alloy steel with thickness over 25mm, the energy of welding line must be measured and controlled strictly.
4.4.4.2 The control of energy of welding line shall be calculated according to following
formula:
Q = 60 I U (4.4.4) V
In which, Q ---- Energy of welding line (J/cm);
I ---- Current in welding (A); U ---- Voltage of arc (V); V ---- Welding speed (cm/min).
4.4.4.3 In hand arc welding, the energy of line may be controlled through the range of the
length of welding pass of each electrode which is pre-determined by the range of allowable energy of line.
4.4.4.4 In automatic welding and submerged arc welding with cored welding wires, energy
of line may be controlled in accordance with the WPS by selecting proper welding speed.
4.4.5 In hand arc welding, the welding sequence of the spherical tank and the arrangnent of
welders shall meet following requirements:
4.4.5.1 In case the spherical tank is assembled in zones, the longitudinal joints of the zones
circumferential joints between zones.
4.4.5.2 In case the spherical tank is assembled in sectors, the welding sequence shall follow
the principle of longitudinal joints firstly and then circumferential joints.
4.4.5.3 The arrangement of welders shall be uniform and welding shall be applied
synchronously.
4.4.6 When welding double-face butt welds with hand arc welding, after welding one side,
the root of the back shall be cleaned. In case carbon arc air planner is used in cleaning, after root cleaning, sand wheel shall be used to rectify planed channel and carbon penetration layer shall be ground off. Visual inspection, magnetic powder and dye penetrant testing shall be used for inspection. For steel with standard tensile strength over 540Mpa, after root cleaning, it is a must to use magnetic powder and dye penetrant testing to inspect.
In root cleaning of the welds, the metal of welds of positioning welding shall be removed. The shape of the bevel after root cleaning shall be same.
4.4.7 In auto and semi-auto welding with cored welding wires, the welding sequence in
welding the spherical tank shall meet following requirements:
4.4.7.1 On completion of the assembling of the spherical tank, the welding sequence shall be
arranged follow the principle of longitudinal joints first and then circumferential joints.
4.4.7.2 When welding longitudinal joints, the arranging of welding machines shall be
uniform and symmetrically and the welding shall be applied synchronously.
4.4.7.3 When welding circumferential joints, the arranging of welding machines shall be
symmetrically and welding shall be applied in same rotation direction.
4.4.8 In welding, the side of arc striking shall be backward arc striking method. At arc
closing side, the arc pit shall be fully filled. The connections of multi-layer welding layers shall be staggered.
4.4.9 In the case of the interruption of any pass of the welding, measures to avoid any crack
shall be taken in accordance with the process requirement. Before re-welding, a check shall be made to confirm that there is no crack, then the welding can be applied.
4.4.10 Steel stamp of welder’s code shall be made at the assigned place 50mm away from the
welds of the spherical tank and a record shall be made. For the spherical tank which allows no stamp, it shall be recorded in arrangement drawings.
4.4.11 The welding of the parts and components of manholes, connection pipes and supports
shall meet following requirements:
4.4.11.1 The welding for the butt welding of forged flange and the tank shell, apart from that
the welding materials shall be same as that for the welding of the tank shell, the welding process shall be same as that for the steel of higher strength.
4.4.11.2 The welding of the supports, connection plates and the tank shell, apart from that the
welding materials should be the one matching the steel of lower strength, the welding process shall be same as that that for the steel of higher strength.
4.4.11.3 The fillet welds of the tank shell and the reinforcing rings, connection pipes and
supports shall be transited smoothly.
4.5 Repair
4.5.1 Any defect of the spherical tank caused in manufacturing, storage or transportation
shall be repaired.
4.5.2 The repair of surface defect shall meet following requirements:
4.5.2.1 The surface defect of the spherical tank and the welding trace of tools and calipers
shall be removed by sand wheel grinding. The actual thickness after grinding shall not be < design thickness. The depth of grinding shall be < 5% of nominal thickness of tank shell plate, and not exceeding 2mm. If it exceeds, remedy welding shall be applied.
4.5.2.2 In welding repairing surface defect of tank shell plate, the area of each repair shall be
within 50 cm2. In case there are two or more places repaired, the distance between sides of any two repairs shall be > 50mm. The total area of repair of surface of each tank shell plate shall be <5% of the area of that tank shell plate.
In case the shape of the defects of scraping or the defects caused during forming is mild, remedy welding may be applied directly. In case the direct deposit welding may cause crack, a sand wheel may be used to remove the defect, and then apply remedy welding. The surface of welds after repair shall be ground to be mild and smooth or to be a mild convex surface with 1:3 down slope, and the height shall be less than 1.5mm.
4.5.2.3 The surface defects of welds shall be removed by using a sand wheel. After grinding
off the defect, in case the surface of welds is lower than the base metal, a remedy welding shall be applied. In case the welds surface only need grinding, the grinding shall be done in the way to make it smooth or be a down slope of 1:3.
4.5.2.4 The over cut of two sides of welds and the crack at welds foot must be ground off by
using a sand wheel to make it smooth or a down slope of 1:3 (Figure 4.5.2 - 1). The depth of grinding off the over cut and welds foot must not be > 0.5 mm, and the actual thickness of the tank shell after grinding must not be < design thickness. In case it is not up to this requirement, a remedy welding shall be applied.
Figure 4.5.2 – 1 Grinding off the Welding Defects Along Both Side of Welds by Using a Sand Wheel
4.5.2.5 In welding repairing defects of welds over cut and welds foot crack, a sand wheel
shall be used to grind off the defects to make it a concave channel facilitating welding, and then welding shall be applied. The length of remedy welding shall not be < 50mm. For the spherical tank with standard tensile strength over 540 Mpa, one pass of tempered welding pass shall be added onto the remedy welding pass (Figure 4.5.2 – 2). After welding, grind off surplus metal of welds.
Figure 4.5.2 - 2 Tempered Welding Pass in Remedy Welding
1—Remedy welding pass；2—Tempered welding pass；3—Base metal；4—Welds metal
4.5.2.6 In case preheating is necessary in remedy welding, preheating shall be done in a
range with repairing place as the center and a radius of 150mm. The preheating temperature shall take the upper limit. The energy of welding line shall be within specified scope. In welding short welds, the energy of line shall not take the lower limit. After remedy welding, post weld heat treatment, if required, shall be done immediately.
4.5.3 The repair of the inside defects in welds shall meet following requirements:
4.5.3.1 An appropriate welding method shall be selected according to the reason causing the
defects and the repair process shall be worked out.
4.5.3.2 Before repairing, ultrasonic testing should be used to determine the position and
depth of the defect and to determine the side to repair.
4.5.3.3 In case the removal of the inside defect uses carbon arc air planner, a sand wheel shall
be used to remove carbon penetration layer and grind the welds to be transited smoothly. Remedy welding shall not be applied until it is magnetic powder tested or dye penetrant tested and qualified. The depth air planned shall not exceed 2/3 of plate thickness. In case the defect still not yet removed, after remedy welding, air planning shall be made at another side.
4.5.3.4 The length of remedy welding shall not be < 50mm.
4.5.3.5 In case pre-heating is necessary in remedy welding, the pre-heating temperature shall
be the upper limit of the required value. After remedy welding, post weld heat treatment, if required, shall be done immediately. The energy of line shall be within specified scope. In welding short welds, the energy of line shall not take the lower limit.
4.5.3.6 At same position (inside and outside of the welds shall be deemed as one position
separately), the time of repairing shall not exceed two. For the welds repaired for two times and not yet qualified, reliable technical measures shall be taken and repair shall not be done until it is approved by the person in charge of technique of the organization.
4.5.3.7 The positions, times and test results of remedy welding shall be recorded.
4.5.4 Non-destructive testing shall be made to the spherical tank after repairing in accordance
with following stipulations::
4.5.4.1 After removal of all defects and after remedy welding, magnetic powder testing and
dye penetrat testing shall be made.
4.5.4.2 In case the depth for remedy welding of the surface defects exceeds 3mm (calculated
from the surface of the tank shell plate), a radiographic testing shall be made.
4.5.4.3 After repairing of inside defects of the welds, a radiographic testing or ultrasonic
testing shall be made. The method selected shall be the same as the method with which the defect was found.
4.6 Inspection of Size of Spherical Tank Welded
4.6.1 After welding, the sharp corners shall be inspected in accordance with the method in
3.2.3.3 of this Code. The value of the sharp corner shall not be > 10mm.
4.6.2 After welding, the inside diameters of the sections at two poles and at equator section
shall be inspected and they shall meet following requirements:
4.6.2.1 The difference of the three, the ID at two poles, the maximum ID at equator and the
minimum ID, shall be < 7/1000 of design ID, and not be > 80mm;
4.6.2.2 The difference of the ID at two poles, the maximum ID at equator and the minimum
ID and the design ID shall all be < 7/1000 of design ID, and not be > 80mm.
4.6.3 The verticality of the supports of spherical tank after welding shall meet what specified
in 3.2.7.2 of this Code.
4.6.4 After welding, manholes and connection pipes shall meet what specified in 3.3.1 of this
5 Inspection of Welds
5.1 Visual Inspection of Welds
5.1.1 After welding, a visual inspection shall be made to the welds. Before inspection, fused
slag and scales, spatters shall be removed.
5.1.2 The surface quality of welds shall meet following stipulations:
5.1.2.1 The welds and the heat-affected zone shall not have any defect of crack, bubble, over
cut, slag inclusion, pit or in-full welding.
5.1.2.2 The size of welding foot of fillet welds shall meet requirements of design drawings. 5.1.2.3 The width of welds shall be 1 ~ 2mm wider than each side of the bevel.
5.1.2.4 The surplus height of but welds shall meet the requirements in Table 5.1.2. Table 5.1.2 Surplus Height of Butt Welds (mm)
Surplus height of welds Depth of welds (δ)
Hand arc welding Submerged arc welding
Gas shielded welding with cored welding wires
≤12 0 ~ 1.5 0 ~ 3 0 ~ 3
12 <δ≤25 0 ~ 2.5 0 ~ 3 0 ~ 3
25 <δ≤ 50 0 ~ 3 0 ~ 3 0 ~ 3
>50 0 ~ 4 0 ~ 3 0 ~ 3
Note: The depth of welds means the thickness of base metal in singe face welding, and the depth from the center of obtuse side of the bevel to the surface of base metal in double-face welding. Two sides shall be calculated separately.
5.1.3 The surface after removal of tools and calipers shall not have any defect of crack,
bubble, over cut, slag inclusion, pit or in-fill welding.
5.2 Qualification of Non-Destructive Inspection Personnel
5.2.1 The non-destructive inspection personnel for spherical tank shall have relevant
qualification certificate of boiler and pressure vessels non-destructive inspection
personnel issued by labor department.
5.2.2 Non-destructive personnel of Class I may conduct relevant non-destructive operation,
recording test data and sorting test papers under the direction of the personnel of Class II and III. Personnel of Class II and Class III may evaluate test results and sign test reports.
5.3 Radiographic Testing and Ultrasonic Testing
5.3.1 The radiographic testing and ultrasonic testing of welds shall be done in accordance
with the national standard in force the Non-destructive Inspection of Pressure Vessels
JB4730. For radiographic testing of welds, X ray testing or γray full screen exposure testing
may be used. The quality requirements for radiographic images shall not be less than Class AB.
5.3.2 For butt welds of spherical tank, any of following shall be 100% radiographic tested or
ultrasonic tested in accordance with the method set in the design drawings:
5.3.2.1 Welds of carbon steel spherical tank with nominal thickness over 38mm; 5.3.2.2 Welds of 16MnR steel spherical tank with nominal thickness over 30mm; 5.3.2.3 Welds of 15MnVR steel spherical tank with nominal thickness over 25mm; 5.3.2.4 Welds of spherical tank with standard tensile strength over 540MPa;
5.3.2.5 Welds of spherical tank needs air pressure test;
5.3.2.6 Welds of spherical tank containing flammable and toxic and extreme or high
dangerous hazard medium specified in drawings;
5.3.2.7 Butt welds of insert type connection and the tank shell;
5.3.2.8 Welds covered in the circle with center of the opening as the circle center and 1.5
times of opening diameter as the radius, and the welds connecting connection pipe with nominal diameter over 250mm and the long neck flanges, connection pipes;
5.3.2.9 Welds covered by reinforcing rings.
5.3.3 Radiographic testing shall be made to butt welds in case the nominal thickness of the
tank shell is ≤38mm.
5.3.4 All butt welds, except those specified in 5.3.2 of this Code, are allowable to be locally
inspected. The testing method shall be in accordance with what specified in drawings. The length of inspection shall not be less than 20% of each piece of welds. The local position shall include all crossed welds and some locations welded by each welder.
5.3.5 Re-test of welds shall meet following stipulations:
5.3.5.1 For welds 100% radiographic or ultrasonic tested, in any of following cases, they
shall be radiographic or ultrasonic re-tested:
(1) Spherical tank of material with standard tensile strength over 540Mpa and the nominal thickness over 20mm;
(2) Spherical tank of nominal thickness over 38mm; (3) Those re-test specified in design drawings.
all crossed welds. Result of two tests shall meet standard for qualification respectively.
5.3.6 The standard for qualification for non-destructive inspection of butt welds shall be in
conformity with what specified in the national standard in force the Non-destructive
Inspection of Pressure Vessel JB4730. For butt welds 100% radiographic tested, Class II is
qualified. For butt welds locally radiographic tested, Class III is qualified. For butt welds 100% ultrasonic tested, Class I is qualified. For butt welds locally ultrasonic tested, Class II is qualified.
5.3.7 For radiographic or ultrasonic tested welds, in case any defect is found, after removal
of defects and repairing, the repaired welds shall be re-tested by using the original testing method till they are qualified. For locally tested welds and the re-tested welds, in case any defect is found, spot test by double shall be made to the extended position of the defect. In case spot test by double is still unqualified, test shall be done to all welds welded by that welder.
5.3.8 Spherical tank made of steel with standard tensile strength over 540Mpa, radiographic
or ultrasonic testing shall be made 36 hours after welding; for spherical tank of other steel, 24 hours after welding.
5.3.9 Before radiographic or ultrasonic testing of welds, marks shall be made to the positions
to be tested according to drawings and welds arrangement drawings. For radiographic testing, sketches for film arrangement shall be made.
The numbering of the films in radiographic testing should consist of the number of welds and the sequence number of the film. The sequence numbering of films for longitudinal welds should be 1, 2, 3 …. downward while for circumferential welds, 1, 2, 3 …. From 0°→90° →180°→270°→0°.
5.4 Magnetic Powder Testing and Dye Penetrant Testing
5.4.1 Magnetic powder or dye penetrant testing shall be made to following locations of
spherical tank before pressure test (in case post weld heat treatment is necessary for whole spherical tank, it shall be done before post weld heat treatment):
5.4.1.1 Inside and outside surfaces of butt welds of the tank shell;
5.4.1.2 Inside and outside surfaces of butt welds of manholes and connection pipes with
nominal diameter ≥250mm;
5.4.1.3 Inside and outside surfaces of welds of connection pipes and the tank shell; 5.4.1.4 Outside surfaces of reinforcing rings, pad plates, supports and other fillet welds; 5.4.1.5 Locations after grinding off the trace of tools and calipers and the locations of the
tank shell after defect repairing and grinding.
5.4.2 Magnetic powder or dye penetrant re-test shall be made after spherical tank pressure
include all crossed welds, inside and outside surfaces of welds of connection pipes and the tank shell, outside surface of reinforcing rings, pad plates, supports and other fillet welds as well as welds of each welder, locations after grinding off the trace of tools and calipers and the locations of the tank shell after defect repairing and grinding.
5.4.3 Magnetic powder and dye penetrant testing shall be done in accordance with the
national standard in force the Non-destructive Inspection of Pressure Vessels JB4730 and shall also meet following requirements:
5.4.3.1 Magnetic powder and dye penetrant testing shall be done after the defects found in
radiographic and ultrasonic testing are repaired and qualified. Spherical tank made of steel with standard tensile strength over 540Mpa, magnetic powder or dye penetrant testing shall be done 36 hours after welding; for spherical tank of other steel, 24 hours after welding.
5.4.3.2 Before magnetic powder or dye penetrant testing, the part to be tested shall be ground
to show metal and the welds shall be transited to the base metal smoothly.
5.4.3.3 Magnetic powder testing shall use round channel A – 30 / 100 standard test film.
Sensitivity test shall be done to front and back respective under same operation condition.
5.4.3.4 For magnetic powder testing, after removal of preliminary magnetic trace shown,
testing shall be done again. It can be confirmed if the magnetic trace shown again as previous one.
In case the magnetic trace shown is difficult to judge it as defect trace, the surface shall be repaired to be smooth and then tested.
5.4.4 The standard for qualification in magnetic powder and dye penetrant testing shall meet
following stipulation:
5.4.4.1 None of following defects shall be found:
(1) Any crack and white point;
(2) Any showing of transversal defect;
(3) Any showing of linear defect with length over 1.5mm; (4) Any showing of round defect with single size ≥2mm.
5.4.4.2 In a welds area of 35mm x 100mm, the accumulated length of defect shown shall not
be > 2mm.
5.4.5 Any defect found in magnetic powder or dye penetrant testing shall be ground or
repaired in accordance with what specified in 4.5.2 of this Code and a re-test shall be made to that location by using original test method till it is qualified.
6 Post Weld Heat Treatment of the Whole
6.1 General Rules
6.1.1 In any of following cases, spherical tank shall be post weld heat treated for the whole
before pressure test:
6.1.1.1 Post weld heat treatment required by design drawing;
6.1.1.2 Spherical tank to contain LPG, liquefied ammonia and other medium of stress
corrosive;
6.1.1.3 Spherical tank made of carbon steel with nominal thickness over 34mm (in case the
preheating temperature is over 100℃, nominal thickness is over 38mm) and spherical tank made of 07MnCrMoVR steel;
6.1.1.4 Spherical tank made of 16MnR steel with nominal thickness over 30mm (in case the
preheating temperature is over 100℃, nominal thickness is over 34mm);
6.1.1.5 Spherical tank made of 15MnVR steel with nominal thickness over 28mm (in case
the preheating temperature is over 100℃, nominal thickness is over 32mm);
6.1.1.6 Spherical tank of other low alloy steel of any thickness.
6.1.2 Following conditions shall be ready before post weld heat treatment: 6.1.2.1 Welding connecting pressure pieces of spherical tank is completed; 6.1.2.2 Non-destructive inspection before heat treatment is completed;
6.1.2.3 The product welding test plate is put at the outer side of the high temperature zone of
the spherical tank heat treatment;
6.1.2.4 Heating system is adjusted and qualified;
6.1.2.5 Connection pipe not related to heat treatment is blind blocked;
6.1.2.6 The bolts connecting spherical tank and ladders, platforms have been loosened; 6.1.2.7 Measures for anti rain, anti wind, anti fire and power failure prevention have been
taken.
6.2 Heat Treatment Process
6.2.1 Temperature for heat treatment shall meet requirements of design drawings. In case the
design drawings have not requirements for it, the temperature for heat treatment for common use steels may be selected according to Table 6.2.1.
Table 6.2.1 Temperature for Heat Treatment for Common Use Steel Steel number Temperature for heat treatment (℃)
20R 625±25 16MnR 625±25 +25 15MnVR 570 -20 15MnVNR 565±15 07MnCrMoVR 565±20
6.2.2 The minimum holding time in heat treatment shall be calculated according to the
thickness of butt welds of thickest steel plate as 1 hour for every 25mm, and shall not be <1 hour.
6.2.3 When heating, temperature rising may not be controlled at 300℃ and below. When it
is over 300℃, speed for temperature rising shall be controlled at 50 ~ 80℃/hour.
6.2.4 When falling temperature, the speed for temperature falling should be controlled at 30
~ 50℃/hour at the temperature from heat treatment temperature down to 300℃. When it is below 300℃, it can be cooled naturally in air.
6.2.5 At the stage over 300℃, the difference of temperature between any two temperature
measuring points on the tank shell must not be > 130℃.
6.3 Requirements for Heat Insulation
6.3.1 In heat treatment, insulation materials, which may resist highest temperature, have no
corrosive to spherical tank, lower unit weight, less heat conduction coefficient and is easy for construction, shall be selected.
6.3.2 The insulation materials shall be dry and not damped.
6.3.3 The insulation layer shall be close to the tank shell surface and the local gap should not
be > 20mm. The joints shall be tight. In multi-layer insulation, the joints of different layers shall be staggered. During heat treatment, the insulation layers shall not be loose or peeling off.
6.3.4 All manholes, connection pipes and connection plates of spherical tank shall be
insulated. Insulation shall be made to the supports within a range not less than 1 meter calculated down from the lower side of the welds of the supports and the tank shell.
6.3.5 During temperature holding time, the temperature at outer surface of the insulation
6.4 Temperature Measuring System
6.4.1 The temperature measuring points shall be arranged on the tank shell surface evenly.
The space between adjoining temperature measuring points should be < 4.5m. One temperature measuring point shall be arranged respectively in a range 200mm away from the upper and lower manholes and from the side of circumferential welds of the tank shell plate. One temperature measuring point shall be arranged to the product welding test plate. The total temperature measuring points shall not be less than what specified in Table 6.4.1.
Table 6.4.1 Quantity of Temperature Measuring Point
Volume of spherical tank (m3) 50 120 200 400 650 1 000 2 000 ≥4 000 Quantity of temperature measuring point 8 8 12 12 12 16 24 36 6.4.2 The thermocouple used in temperature measuring may be fixed onto the outer surface
of the tank shell by percussion welding or bolts (Figure 6.4.2). The thermocouple and compensation wire shall be fixed.
Figure 6.4.2 Method for Fixing Thermocouple in Temperature Measuring 1—Channeled nut；2—Tack welds；3—Tank shell；4—Bolt；5—Thermocouple
6.4.3 Temperature shall be recorded continuously and automatically. The thermocouple and
recording instruments shall be adjusted and in valid period. The accuracy shall be up to ± 1%.
6.5 Treatment of Support Foot
6.5.1 During heat treatment, tie rods and anchor bolts shall be loosened. Moving device and
displacement measuring unit shall be installed to the bottom of anchor plate of the supports.
6.5.2 During heat treatment, actual displacement shall be monitored and the displacement of
the support foot shall be adjusted according to the calculated value of displacement. For changing of temperature of each 100℃, one adjustment shall be made. The moving of support foot shall be mild and slow.
6.5.3 After heat treatment, verticality of supports and deflection of tie rods shall be measured
7 Test Plate of Product Welding
7.1 Requirements for Preparation of Test Plate of Product Welding
7.1.1 The steel number, thickness and the heat treatment process of the test plate shall be
same as that for the tank shell.
7.1.2 The test plate shall be welded by the welder who is going to weld the spherical tank
under same welding condition and with same welding process.
7.1.3 According to the position of welding application, for each spherical tank, one piece of
test plate shall be prepared respectively for horizontal welding, vertical welding, flat welding and overhead welding. The size of the test plate shall be 360mm x 650mm.
7.1.4 Visual inspection and 100% radiographic or ultrasonic testing shall be made to welds
of the test plate. When cutting the test plate, the defect may be kept away.
7.1.5 For the spherical tank needs post weld heat treatment, the product test plate shall be
heat treated together with the spherical tank.
7.2 The Preparation and Test of the Test Plate
7.2.1 The size, cutting, test method of the test plate and the criteria for qualification shall
meet relevant stipulations in the national standard in force the Steel Made Pressure Vessels
GB150.
7.2.2 For spherical tank made of 20R steel with thickness over 25mm, of 16MnR steel,
15MnVR steel, 15MnVNR steel and 07MnCrMoVR steel with thickness over 38mm, in case the design temperature is lower than 0℃, a low temperature Charpy（V-notch）impact test shall be made to the heat affected zone and the welded metal according to the design temperature of spherical tank and the test temperature specified in drawings.
7.2.3 Re-test shall meet following requirements:
7.2.3.1 In case the product test plate is not qualified in the tensile test or bend test, it is
allowable to cut double test plates for unqualified item from the original test piece or from another test piece welded at same time with the spherical tank for re-test.
7.2.3.2 In case the impact test is not up to requirements, another group (3 pieces) of test plate
may be cut from original test plate to test. The criteria for qualification shall be: the average value of impact power for the 6 test pieces of 2 groups shall not be lowered than specified value. It is allowable that the impact power for 2 test pieces may be lower than specified values, in which, it is allowable that only one can be 70% lowered than the specified value.
7.2.3.3 In case the result of re-test is still not qualified, the welding test plate of the spherical
tank shall be judged as not qualified. In this case, reasons shall be analyzed. It is allowed to re-heat treat the test plate and the spherical tank it represented. However, the heat treatment
process shall be worked out again and then re-test in accordance with the requirements of this Code.
8 Pressure Test and Airtight Test
8.1 Pressure Test
8.1.1 Before pressure test, the spherical tank shall have following conditions:
(1) The welding of the spherical tank and the connection with parts and components have been completed and they are qualified after inspection;
(2) The strength of secondary grouting of the foundation is up to the requirements for the strength;
(3) Post weld heat treatment has been done to spherical tank, which needs post weld heat treatment. The product welding test plate is qualified after inspection;
(4) The welds of reinforcing rings have been leakage tested with compressed air of 0.4 ~ 0.5 Mpa and qualified;
(5) The alignment of the supports and the adjustment of the tie rods have been completed.
8.1.2 Gases must not be used to replace the liquid in pressure test, unless it is specified in
design drawings.
8.1.3 During pressure, a pressure gauge of same scale and qualified after calibration shall be
installed respectively at the top and bottom of the spherical tank. The accuracy shall not be less than 1.5 grade. The range of scale of pressure gauges should be 2 times of test pressure, and shall not be < 1.5 times of and not be > 4 times of test pressure. The diameter of the pressure gauge should not be < 150mm.
8.1.4 During pressure test, it is strictly prohibited to impact or strike the spherical tank. 8.1.5 Hydraulic test shall meet following stipulations:
8.1.5.1 For hydraulic test, clean water shall be used as the medium;
8.1.5.2 For hydraulic test of spherical tank of carbon steel, 16MnR steel and normalized
15MnVR steel, the temperature of water used in the test shall not be lower than 5℃. For spherical tank of other low alloy steel (except low temperature spherical tank) the temperature of water used in the test shall not be lower than 15℃. In case the temperature is risen due to the lacking of ductility of material caused by the thickness of the plate, the temperature of water used in the test shall also be raised correspondingly.
8.1.5.3 The test pressure in hydraulic test shall be specified by the design drawings, and not
lower than 1.25 times of design pressure of the spherical tank. For the reading of the test pressure, the one of the pressure gauge at the top of the spherical tank shall apply.
(1) During test, a vent port shall be provided at the top of the spherical tank. Air in the spherical tank shall be completely vented when filling the liquid. During the test, the outer surface of the spherical tank shall be dry;
(2) During test, the pressure shall be risen slowly. Keep the pressure for 15 minutes when the pressure is up to 50% of test pressure. Check all welds and connection places of the spherical tank. Continue the pressure rising after confirming that there isn’t any leakage; (3) Keep the pressure for 15 minutes when the pressure is up to 90% of test pressure. Check
it again and continue the pressure rising after confirming there isn’t any leakage;
(4) Keep the pressure for 30 minutes when the pressure is up to the test pressure. Then fall the pressure to 80% of test pressure and check. If there isn’t any leakage or abnormal, it is qualified;
(5) On completion of the hydraulic test, water shall be drained completely. Water shall not be drained to the ground locally.
8.1.6 Air pressure test shall meet following stipulations:
8.1.6.1 Safety measures shall be taken for air pressure test, which shall be approved by the
person in charge of safety work of the organization. The test shall be supervised and checked by the safety department of the organization. Two or more safety valves and emergency vent valves shall be provided in air pressure test.
8.1.6.2 The test pressure of the air pressure test shall meet what specified in design drawings. 8.1.6.3 Air or nitrogen shall be used as the medium of the air pressure test. The temperature
of the medium shall not be less than 15℃.
8.1.6.4 The air pressure test shall be done in accordance with following steps:
(1) Keep the pressure for 5 ~ 10 minutes when the pressure is up to 10% of test pressure. A preliminary check for leakage shall be made to all welds and connection places of spherical tank. Continue the pressure rising after confirming there isn’t any leakage; (2) Keep the pressure for 10 minutes when the pressure is up to 50% of test pressure. When it
is confirmed that there isn’t any abnormal, the test pressure shall be risen stage by stage at a pressure of 10% of test pressure for each stage. Keep it for 10 ~ 30 minutes. Then fall to design pressure to check. If there isn’t any leakage or abnormal, it is qualified; (3) The pressure shall be unloaded slowly.
8.1.6.5 In air pressure test, the fluctuation of the environment temperature shall be monitored
as well as the reading of the pressure gauge. No over pressure shall happen.
8.1.6.6 The safety valves used in the air pressure test shall meet following requirements:
(1) Safety valves shall be the products manufactured by the manufacturer having manufacturing license and the products are up to technical standard;
(2) The safety valves must be calibrated and qualified;
(3) The begin-to-open pressure of the safety valves shall be set at 0.05Mpa of the test pressure.
