1.1 Overall construction scheme
Automatic welding process of hydraulic lifting flip chip
Take the 20000m3 inner floating roof tank as an example, the hydraulic lifting inverted automatic welding process is used for construction, and the construction process flow chart is shown in the following figure.
The tank bottom plate and tank wall plate are deeply prefabricated in the production base of the department, and the imported gantry automatic cutting machine is used to cut and cut the material and groove processing in one time.
CO2 gas shielded automatic welding shall be adopted for the outer seam of the longitudinal seam and the circumferential seam of the oil tank, and CO2 gas shielded semi-automatic welding shall be adopted for the inner seam; Submerged arc welding+broken wire welding is adopted for oil tank bottom plate.
Construction process flow chart of hydraulic lifting flip chip automatic welding
Before the prefabrication of the base plate, the plate arrangement drawing shall be drawn and shall meet the following requirements
The diameter of the row plate at the tank bottom should be enlarged by 0.1% - 0.2% according to the design diameter;
The minimum size of the edge plate along the radius direction of the tank bottom shall not be less than 700mm;
The butt joint of arched edge plate should adopt unequal clearance, and the outer clearance should be 6-7mm; The inner clearance should be 8-12mm;
The width of the center plate shall not be less than 1000mm and the length shall not be less than 2000mm;
The distance between any adjacent weld joints of the base plate shall not be less than 200mm.
The allowable deviation of the size of the center plate shall comply with the provisions of the following table

Allowable deviation of size of cambered edge plate:

Wall panel prefabrication
The wall panel prefabrication mainly includes three processes: plate material inspection, cutting and blanking, and rounding. The factory construction is carried out. The wall panel prefabrication process flow is as follows:
Before the prefabrication of wall panels, the layout drawing shall be drawn according to the design requirements, construction specifications and actual arrival specifications of steel plates, and submitted to the design and supervision unit for approval, and shall meet the following requirements:
The longitudinal joints of the bottom ring wall panels should be staggered one by one in the same direction, and the spacing should not be less than 500mm;
The distance between the longitudinal weld of the bottom ring wall plate and the butt joint of the tank bottom edge plate shall not be less than 200mm;
The distance between the outer edge of the tank wall opening nozzle or opening nozzle reinforcing plate and the tank wall longitudinal weld shall not be less than 200 mm; The distance from the circumferential weld shall not be less than 100 mm;
The distance between the butt joint of the wrapped channel steel and the longitudinal weld of the tank plate shall not be less than 200mm;
The width of the wall panel shall be 1800mm, and the length shall not be less than 6000mm.
The allowable deviation of wall panel size shall conform to the following table
The prefabricated wall panels are stored and transported with special moulds.
After the wallboard is rolled, it should be upright on the platform and checked with a template. The vertical direction shall be checked with a straight sample plate, and the gap shall not be greater than 1mm; The arc template shall be used for inspection in the horizontal direction, and the gap shall not be greater than 4mm. In order to ensure the quality in the rolling process, special arc striking mould shall be used. Due to the angular deformation in the automatic welding of the vertical seam, a certain amount of clearance is required to be reserved when checking the radian of the two ends with the template when the wall plate is rounded, so as to ensure that the angular deformation of the vertical seam is zero after the automatic welding of the vertical seam.
1.2 Oil tank installation scheme
Foundation acceptance
Before the installation and construction of the tank bottom, the foundation acceptance work should be completed first, which is mainly to retest the orientation, elevation and levelness of the foundation. The key point is to ensure the levelness of the surface of the foundation concrete ring beam, the radial width of the ring beam, etc. The surface concavity and convexity of the asphalt sand layer should be less than the specified value, and the surface of the asphalt sand layer should be flat and compacted, without prominent bulges, pits and penetrating cracks.
Before laying the bottom plate, the oil tank foundation shall be rechecked and accepted according to the provisions of the foundation design construction drawing and the Code for Construction and Acceptance of Vertical Cylindrical Steel Welded Oil Tanks (GB128-90). The relevant technical requirements are:
The allowable deviation of foundation center elevation is ± 20mm;
The height difference between any two points in every 10m arc length of the ring beam shall not be greater than 6mm, and the height difference between any two points in the whole circumference length shall not be greater than 12mm;
The surface of asphaltic sand cushion shall be flat and dense, without prominent lifting, depression and penetrating cracks. The inspection methods and technical requirements are shown in the table.

The concavity and convexity of the asphalt sand layer surface shall be checked by the following methods: draw the distribution map of measuring points on the basis of the map, measure the elevation of each point with a level gauge, and the difference between the elevation of measuring points on the same circumference and the calculated elevation shall not be greater than 12mm.
Draw the outer circle line of the edge plate at the bottom of the tank according to the radius calculated by multiplying the design diameter by 0.1% - 0.2%, mark it with paint, draw the center line of the center plate and the position of the long strip center plate. After all are checked, lay and weld the base plate, and then start the plate laying.
Firstly, the arched edge plate shall be paved, and the irregular plate of the bottom plate shall be numbered in advance. The irregular plate of the bottom plate shall be assembled according to the number on the site. The irregular plate of the bottom plate shall be fixed with clamps immediately after laying. Each plate shall be equipped with three clamps to prevent deformation after welding, as shown in the figure:
When laying the center line strip plate, the cross center line and circle center on the foundation shall be moved to the steel plate, and obvious marks shall be made. Then, the center strip base plate at the bottom of the tank shall be laid, the base plate shall be welded, the center plate shall be laid, and finally the fan-shaped center plate shall be laid. During lifting, the plate shall be lifted into the tank by a crawler crane.
When welding the tank bottom plate, first spot weld the outer side of the edge plate, then the short seam of the center plate, and then the long seam of the center plate. The spot welding of the center plate shall be conducted symmetrically from the center to the outside, and the contraction joint shall not be spot welded, but shall be welded in zones according to the welding sequence.
The remaining butt joint of the edge plate and the large circle contraction joint (tortoiseshell joint) connected with the center plate shall be assembled and welded after the large angle seam of the wall plate and the tank bottom is welded.
The anti-deformation measures for butt weld of edge plate are shown in the figure:
After the tank bottom is welded, a vacuum leak test shall be conducted, and the negative pressure value of the test shall not be less than 53Kpa.
Tank top installation
The tank top assembly procedure is shown in the figure below
Marking and positioning of tank bottom
Tank top assembly procedure diagram
Mark the installation circle of the top ring wall plate on the tank bottom plate, and spot weld a piece with the size of 80 every 300mm along the inner side of the circumference × 60、 δ 10 Position the baffle plate to ensure the ovality of the wall plate, and the installation diagram of the top ring wall plate
The top ring wall panel shall be assembled according to the plate arrangement drawing. After assembly and welding, the allowable deviation of its upper opening level and plumb shall comply with the following table.
Table of allowable deviation for assembly welding of top ring wall plate
After the top ring wall plate is inspected to be qualified, install the wrapped angle steel. Before assembly, the camber and warpage shall be checked on the steel platform with arc template. The assembly welding sequence of the wrapped angle steel is: angle steel butt joint → internal broken fillet weld → external lap continuous fillet weld. After assembly and welding, the local allowable deviation of the wrapped angle steel higher than the wall plate is ± 4mm. The wrapped angle steel should be close to the wall plate, and its gap should not be greater than 2mm.
After the installation of the eleventh and tenth rings of wall panels, the construction of single-layer two-way meridian dome latticed shell will be carried out. The construction quality of the reticulated shell shall meet the requirements of the Technical Conditions for the Construction of the Single-layer Two-way Meridian Dome Reticulated Shell Roof of Vertical Cylindrical Steel Welded Oil Tank.
When assembling the top plate, draw the position line of each top plate on the edge angle steel and the groove steel ring of the temporary support frame, and weld the assembly positioning baffle.
The top plate shall be mounted symmetrically on both sides of the axis at the same time.
Wall panel installation
Before the wall panel assembly, the prefabricated wall panel shall be rechecked and can be assembled only after it is qualified.
While assembling and welding the second circle of wall panels, install the expansion ring and hydraulic lifting device.
After the tank top is assembled, the top ring and the outer ring of the second ring of wall plate and the third ring of wall plate shall be welded according to the layout drawing, and a hole shall be left at one of the longitudinal joints, and the tensioning device shall be installed, and the other longitudinal joints shall be welded.
Arrange the hydraulic lifting frame evenly. The lifting frame shall be set at a flat place and the weld bead shall be staggered to avoid affecting the radiographic inspection. The hydraulic lifting frame shall be arranged as required.
Lay a piece at the bottom of the hydraulic lifting frame δ 18 base plate, and measure the perpendicularity of the lifting frame in two directions with a level gauge or a plumb bob attached, and fix it with the tank bottom plate by spot welding after alignment, and use ∠ 80 × 8 Make diagonal bracing for reinforcement.
At 300mm from the bottom edge of the tank wall plate, install the [20 # expansion ring to ensure the ovality of the wall plate assembly and prevent the tank body from deformation during lifting. The expansion ring is connected with the tank wall with a gantry clamp, pin and anti-slip baffle. When installing the expansion ring, level it with a level gauge to prevent the tank body from tilting during lifting.
Install the hydraulic lifting device and hydraulic control pipeline, check whether all implements are normal after preparation, and then prepare for jacking.
Start the oil pump for jacking, and stop lifting when the wall panel is jacked to the predetermined height. Tighten the tensioning device to align the current ring wall panel with the upper ring wall panel, install the plug, spot weld the circumferential seam, fix the wall panel, weld the reserved contraction joint, and then weld the circumferential seam. Round the tank wall.
Repeat the above steps to complete the assembly of the remaining rings of wall panels.
Labor protection and accessory installation
A. Manufacturing and installation of winding ladder
At the same time of the wall panel assembly, weld the prefabricated winding ladder reinforcement plate, side plate, step and tripod parts on the corresponding positions of the body wall panel. After the wall panel assembly is completed, install the handrail and other connectors.
B. Connecting pipe installation
Before installation, the accessories shall be positioned and marked according to the design drawings, and the holes can be opened only after the size is checked to be correct. In order to reduce the thermal stress caused by the opening and welding, before the opening of the manhole on the tank wall and the transparent hole on the tank top, the reinforcing arc plates shall be welded on the upper and lower sides to reduce the generation of internal stress.
The allowable deviation of the extension length of the attachment nozzle is ± 5mm, the deviation of the nozzle center shall not be greater than 10mm, and the curvature of the opening reinforcement plate shall be consistent with the curvature of the tank body.
After the reinforcement ring of the opening is welded, the tightness of the welding shall be checked, and it is qualified if there is no leakage.
C. Installation of reinforcing ring
When assembling the stiffening ring, the curvature shall be fully checked while installing and adjusting, and the welding deformation shall be taken into account. The deformation measures shall be taken to prevent the concavity at the joint.
Water filling test of oil tank
The water filling test shall meet the following requirements:
Before the water filling test, all welds related to the tightness test shall not be painted;
Fresh water shall be used for water filling test, and the water temperature shall be higher than 5 ℃;
During the water filling test, the observation of foundation settlement should be strengthened. In the water filling test, if the foundation has an impermissible settlement, the water filling should be stopped, and the test can be continued after treatment;
In case of any abnormality during water filling, water filling shall be stopped immediately. In case of leakage, water shall be drained to the lower edge of the leakage for repair, and water shall be refilled until qualified;
During water filling and drainage, the transparent hole shall be opened and the foundation shall not be soaked in water;
Water supply and drainage pipes available Ф two hundred and seventy-three × 7 Seamless steel pipes, water supply and drainage valves shall be inspected and qualified before use.
The water filling test shall check the following contents:
Tank bottom tightness test: during the water filling test, observe the surrounding of the foundation, and it is qualified if there is no leakage.
Tank wall strength and tightness test: fill water to the highest design operating level, keep it for 48 hours, and the weld is free of leakage, and the wall plate is free of abnormal deformation.
Foundation settlement observation: set a certain number of observation points (20 points) evenly along the circumference at the lower part of the tank wall (200mm from the tank bottom) to observe the tank settlement. The datum point for settlement observation is set at a point 5m away from the tank foundation.
Each oil tank shall be observed and recorded before water inflow; Then fill water. When the water level rises to 1/2 of the tank height, stop water inflow and conduct settlement observation. After 24 hours, conduct settlement observation again, and compare with the data observed last time to calculate the actual uneven settlement; If the allowable error is not exceeded, continue to fill water to 3/4 of the tank height, and then observe; When the allowable differential settlement is not exceeded, the water can be filled to the maximum level and observed after 48 hours. When the settlement does not exceed the allowable error and is relatively stable, the water can be discharged. When the settlement changes significantly, the maximum level should be maintained and regular observation should be carried out every day until the settlement is stable.
If the settlement is not allowed or the settlement deviation exceeds the allowable deviation value, or the foundation ring beam has sudden settlement, cracking and other phenomena. The water inflow shall be stopped immediately, and the construction unit, the supervision unit and the design unit shall be notified immediately, and the construction can be continued after treatment.
1.3 Tank welding construction scheme
Welding of tank bottom plate
The tank bottom plate is divided into two parts: the tank bottom center plate and the arched edge plate. The gas shielded semi-automatic welding for backing, broken wire submerged arc welding for filling and cover welding are adopted for the welding of the tank bottom center plate; The arc edge plate at the tank bottom shall be welded by gas shielded semi-automatic welding; The welding of the large shrinkage joint between the center plate of the tank bottom and the arched edge plate adopts the welding process of gas shielded semi-automatic welding for backing and broken wire submerged arc welding for filling the cover.
First install the bow edge plate, and weld the outer 300mm of the butt joint between the edge plates. Electric welders are evenly distributed on the tank edge, and weld at the same time. To prevent welding deformation, arc plate shall be used for reinforcement before welding.
The whole center plate is symmetrically arranged by 4 sets (sets) of welding machines and welded from the center to the periphery. In order to prevent welding deformation, anti-deformation clamps are added at both ends of the large plate before welding. When welding the gallery plate, the channel steel is used to reinforce the side of the large plate, and four 8T counterweights are used to press on the side of the large plate.
After the large fillet weld is completed, weld the rest of the inner side of the edge plate first, then weld the large circle contraction joint between the edge plate and the arched edge plate, and use I12 as the back bar to reinforce the entire tortoiseshell ring joint before welding,
Welding of tank wall plate
CO2 gas shielded automatic transverse welding and vertical welding are used for the welding of longitudinal and circumferential seams of oil tank wall plates
The tank wall plate shall be welded with longitudinal seam first and then with circumferential seam. Welders shall be evenly distributed and welded in the same direction.
During welding, the outer side shall be welded first and then the inner side. Before welding the inner side, the welding root shall be cleaned.
After all the welds are welded, the wooden hammer shall be used to strike the weld to correct the weld deformation and disperse and reduce the internal stress generated during welding.
The welding of T-shaped fillet weld between bottom ring wall plate and tank bottom plate shall meet the following requirements:
The electrode shall be alkaline low hydrogen electrode;
During welding, it is advisable to weld the inside first and then the outside, and several welders shall be evenly distributed in the same direction for backward welding to reduce deformation;
Reducing the welding deformation energy is also an effective means to control the deformation. Therefore, when welding 10000 m3 oil tank, multi-pass rapid welding is adopted. See Figure 8 for the weld bead distribution
Figure 8 "T" type fillet weld
Note: The welding process of T-shaped weld shall be welded in sequence of 1 → 2 → 3
K1＝ δ、  K2＝（1～1.5）＊ δ、  h＝ δ
Welding of tank top
First weld the internal intermittent weld, then weld the circumferential rib joint weld. It is advisable to use double-sided fillet welding, and finally weld the external continuous weld. For the long seam of the sector plate splicing, it is advisable to adopt the symmetrical welding method of the seam separation, and the welding shall be carried out from the center to the outside.
For the welding of the arch roof plate and the wrapped angle steel, the outer side shall be continuously welded, and the welders shall be symmetrically and evenly distributed, and the welding shall be carried out in the same direction.
1.4 NDT scheme for oil tank
Preparation basis
GB50128-2014 Code for Construction and Acceptance of Vertical Cylindrical Steel Welded Oil Tanks
JB4730-94 Nondestructive Testing of Pressure Vessels
Detection range
Inspection of tank bottom plate
For the T-shaped weld on the bottom plate of the butt welding tank, after the root pass is welded, the penetrant flaw detection shall be carried out within the range of 300mm in three directions. After all welding is completed, the magnetic particle flaw detection or penetrant flaw detection shall be carried out again, and the results meet the requirements of Class II.
Within 300mm of the outer end of each butt weld on the edge plate of the tank bottom, radiographic inspection shall be carried out, and the results meet the requirements of Class III.
Inspection of tank wall plate
The joint of tank wall shall be subject to radiographic inspection. The flaw detection results of the first to third rings of wall plates meet the requirements of Class II, and the rest of the wall plates meet the requirements of Class III.
Each longitudinal joint of the bottom ring wall plate shall be taken as two 300mm for radiographic inspection, one of which shall be close to the bottom plate.
All tank wall T-shaped welds with thickness greater than 10mm shall be subject to radiographic inspection.
Tank wall longitudinal weld: take 300mm of each plate thickness of each welder for radiographic inspection within the initial 3m, and then take 300mm of each 30m weld and its tail for radiographic inspection regardless of the number of welders. 25% of all flaw detection parts shall be located at the T-joint.
Tank wall circumferential weld: for each plate thickness of each welder, take 300mm for radiographic inspection within the initial 3m, and then take 300mm for radiographic inspection within every 30m weld and its tail, regardless of the number of welders.
After the welding of the bottom ring wall plate and the bottom edge plate of the tank and the water filling test, a magnetic particle flaw detection shall be carried out on the fillet welds inside the tank respectively. The inspection results shall be free of any cracks or rows of air holes, and Class II is qualified.