YANG Wei, LIU Xinshang, HU Xuefeng

(The Boiler and Pressure Vessel Safety Inspection Institute of Henan Province, Luohe 450000, He′nan, China )

Abstract:This paper mainly introduces the scientific cutting and hoisting construction technology before the large spherical tank (hereinafter referred to as spherical tank) moving and loading, so as to better ensure the construction quality of field assembly and welding in the process of spherical tank moving and loading.

Keywords: spherical tank; moving and loading; cutting and hoisting technology

1 Introduction

Due to the large volume and diameter of the large spherical tank and the limitation of its removal, hoisting and transportation, it can not be lifted and transported as a whole. This kind of spherical tank moving construction technology is different from the new spherical tank construction, and it is not the general definition of major maintenance and moving of special equipment[1]. How to ensure that the original spherical tank parts will not be damaged in the process of dismantling and hoisting, and at the same time, it is convenient for the assembly and welding construction of the spherical tank after dismantling, so as to ensure the safety performance of the spherical tank after construction; Cutting, hoisting and transportation are the key links in the process of dismantling. This paper briefly introduces the construction technology of spherical tank cutting and hoisting based on the case of spherical tank moving in an enterprise.

2 Project overview

2.1 Project name

Two 1 000 m3liquid ammonia spherical tanks(as shown in Figure 1)of Haohua Junhua Group Co., Ltd. are removed and transported to another site for installation.

Figure 1 1 000 m3 liquid ammonia spherical tank

2.2 Main quantities

Two 1 000 m3liquid ammonia spherical tanks were removed and reinstalled.

2.3 Scope of work

After dismantling, two 1 000 m3liquid ammonia spherical tanks were transported to another site for reassembly, welding, nondestructive testing, heat treatment, pressure test, platform ladder, anti-corrosion and cold insulation.

2.4 Design parameters of spherical tank

The design parameters of Liquid ammonia spherical tank is shown in Table 1, and the shel material is Q345R(normalizing)

Table 1 Parameters of spherical tank

2.5 Construction unit

Jianglian Heavy Industry Group Co., Ltd. has the qualification of spherical tank design and manufacturing, and has been engaged in the construction of new spherical tank and relocation for many years. It has rich experience in spherical tank construction, and its ability and qualification meet the requirements of spherical tank relocation construction of this project.

3 Demolition construction organization

3.1 Key technical points of main construction steps

3.1.1 Construction procedure→spherical tank replacement→obstacle clearance→dismantling of supporting equipment→scaffolding→spherical tank body slice cutting demolition.

3.1.2 Spherical tank replacement

After the owner coordinates the relationship between all parties, all pipeline valves are closed and blind plates are set to seal the pipeline, the spherical tank is soaked with water, washed and purged, and it is required to pass the test after washing, purging and replacement[2].

3.1.3 Obstacle removal

In order to ensure the construction site hoisting and transportation work smoothly, it is necessary to remove the obstacles around the construction site and transportation road that affect the construction work.

3.1.4 Removal of pipelines and auxiliary equipment

1) Purging and replacement to meet the fire conditions.

2) First equipment, then valve, then pipeline.

3) If it can be disconnected at the flange, do not use fire as much as possible.

4) Process pipeline removal sequence: first up and then down, first large and then small.

5) Removal of auxiliary equipment: all auxiliary equipment affecting hoisting and transportation shall be removed one by one in sequence and transported away.

3.1.5 Spherical tank removal

1) First remove the upper polar band, then remove the lower polar band, and finally remove the equatorial plate.

2) When cutting, the double head flame magnetic cutting machine is used to cut according to the original weld position, and the angle of the cross head is adjusted to 45°～ 50° for inclined cutting (as shown Figure 2), so that the cutting machine can cut along the preset track and positioning cutting depth without deviation from the weld width. At the same time of cutting off all the original welds, the spherical shell plate is formed into an asymmetric X-shaped groove on both sides (the ratio of outer 7 to inner 3) (as shown Figure 3). The quality of the groove cut can fully meet the requirements of the relevant standards of our country, which facilitates the processing of the groove after disassembly and reassembly[3].

Figure 2 The double head flame magnetic cutting machine

Figure 3 Asymmetric X-shaped groove

3) The equatorial spherical plate is divided into 4 pieces for cutting, lifting and removal, and the upper and lower polar spherical plates are cut, lifted and removed as a whole, so that the whole spherical tank is cut into 6 pieces as shown in Figure 4.

Figure 4 The equatorial spherical plate

4) The lifting lug used in hoisting shall be processed and welded as required before cutting the spherical shell, and the lifting lug shall be made of steel plate with the same material as spherical tank and the thickness is not less than 36 mm.

5) When cutting, the positioning block shall be welded and fixed with fixture while cutting.

6) The total height of the spherical tank in this construction is about 15 m, and the farthest lifting position is about 25 m. According to the weight, height and construction site conditions of the parts to be hoisted, a 300 ton crane is used. The equatorial spherical plates are divided into four pieces for hoisting and removal, and the upper and lower polar spherical plates are cut, hoisted and removed as a whole. At the same time, it shall be loaded and fixed in the flatbed truck and transported to the installation site.

7) After the spherical shell plate is transported to the installation site, the groove shall be polished. The allowable deviation of groove is: anglea±2.5°; the blunt edgep±1.5°; the surface finish meets the requirements of GB/t12337-2014 standard[4]is 2.5 ua.

3.2 Construction equipment and material plan

One 300 ton crane, two electric welding machines, two sets of gas cutting tools (automatic, manual), a batch of lifting sling and rigging, steel plate is 25～30 mm, several welding electrodes, and several bottles of cutting gas (oxygen, acetylene).

3.3 personnel plan

Two on site construction management personnel, one welder for special equipment, one cutter, three lifting workers, one riveter and two small workers.

3.4 Hoisting and relocation

3.4.1 Equipment hoisting scheme

1) The difficulty of equipment installation in this project is the hoisting of spherical shell plate. Because the spherical shell plate with legs is a length overrun equipment, it is difficult to lift the equipment.

2) Lifting and relocation procedure

Dismantling and hoisting→transportation and hoisting→unloading and hoisting→field installation.

3) Work to be done before cutting and lifting operation:

(1) The ground treatment of the construction site is completed, and the road is unobstructed;

(2) The crane in place meets the hoisting requirements and has gone through relevant hoisting procedures;

(3) The lifting lug of equipment lifting point has been welded.

4) Lifting lug and wire rope

1 set of 300 ton crane, 1 pair of 50 t standard tubular lifting lug for main lifting lug. The main hoisting rope shall be no less than 6 * 37 steel wire rope.

5) Precautions

(1) Site foundation requirements: the foundation bearing capacity is greater than 15 N/cm2. The area is about 50 m2

(2) Precautions: the road along the way must meet the transportation requirements, the auxiliary equipment must be stable, and the corresponding fixed measures must be taken to prevent damage;

(3) During hoisting, all aspects of coordination and careful organization shall be strengthened to ensure hoisting safety.

3.4.2 Brief introduction of hoisting task in this scheme

This hoisting task: single 1 000 m3after dismantling, the spherical tank is composed of 6 spherical skin plates (4 equatorial plates and 2 upper and lower polar tops), with a maximum weight of 45 tons. This hoisting task is to hoist the spherical skin of 2 spherical tanks is shown in Table 2.

Table 2 Hoisting task

3.4.3 Preparation before hoisting[5]

1) Fabrication and installation of lifting lug

According to the design confirmation, the lifting lug of this scheme is selected on the ball skin body, and the lifting lug is welded on the ball skin with the same base material lifting block[6], with specifications of 150 mm×150 mm and thickness is not less than 36.

2) foundation treatment measures

Because the driving and operation area of the main crane is the concrete pavement of the plant road, there is no need for site hardening treatment.

3.4.4 Hoisting

The selection of crane is the key to hoisting.

3.4.5 Selection of main hoisting parameters

The selection of main hoisting parameters is shown in Table 3.

Table 3 Selection of main hoisting parameters

Requirements for main crane: 300 ton truck crane, crane pole 26.3～30.6 m, rotation radius 12～18 m, rated lifting capacity 40～64.5 t, auxiliary crane is 50 t truck crane for tail sliding.

1) Selection of wire rope

Six steel wire ropes of ∅24 are used for dismantling and assembly.

2) Lifting layout

The crane station shall be in accordance with the following demolition plan 6(shown in Figure 6) and installation plan 7(shown in Figure 7), and the maximum layout error shall not exceed 3 m.

Figure 6 Demolition plan

Figure 7 Installation plan

3) Check and confirm before hoisting

(1) Check the weight of equipment hoisting.

(2) Whether the positioning block is welded firmly.

(3) Working radius of crane.

(4) Hoisting capacity of crane.

(5) The crane passes the daily inspection.

(6) Remove all obstacles in the lifting area.

(7) Whether the weather conditions meet the hoisting requirements.

4) Sign lifting order

The project department shall organize relevant departments and relevant professional and technical personnel to conduct comprehensive inspection and demonstration. After confirming that the requirements for hoisting are met, the manager will sign the hoisting order.

5) Trial hoisting

After all the preparations are completed and checked to be correct, the trial hoisting is carried out. The trial hoisting time is about 3 min. The trial hoisting requires that the ball should leave the crane to bear the force. The contents of the trial hoisting inspection are whether there are any problems with all the lifting rigging, crane load and foundation changes; check whether the positioning block and ball skin are abnormal.

6) Hoisting steps and sequence[7]

There are two lifting blocks of equatorial belt plate. The ball skin is vertical to the ground. The top is 1 500 mm below the ground. There is one on the left and one on the right. The left and right lifting blocks are about 2 500 mm away from the edge of the ball skin. The size of lifting block is 200 mm×200 mm, thickness is not less than 36 mm. There are 4 lifting blocks for the upper, lower and top plates, and the center radius of the upper and lower poles is 2 m, which is evenly distributed in a ring, as shown in Figure 8 and Figure 9.

Figure 8

Figure 9

4 Lifting equipment and personnel planning

4.1 Lifting equipment

One 300 ton truck crane, one 50 t truck crane, two wire ropes (≥ ∅24 mm,L=8 m) and four wire ropes (≥∅24 mm,L=4 m), hemp rope (∅20 mm) is 50 m.

4.2 Lifting labor plan

One technician, one crane worker (with operation certificate), one riveter, one electric welder (with operation certificate), one gas welder and one assistant worker.

5 Safety technical measures

1) Before organizing the construction, the construction scheme shall be prepared by the personnel with corresponding construction experience and qualification according to the corresponding specifications and standards and approved by the company.

2) Establish the construction quality assurance system of the project, and clarify the responsibilities of relevant responsible persons.

3) The cleaning and replacement of spherical tank before construction must pass the inspection before construction.

4) All construction management and operation personnel shall receive relevant knowledge training before entering the site.

5) Organize the construction in strict accordance with the construction scheme and relevant equipment operation procedures[8].

6) In case of special circumstances in the construction process, it shall be reported to the leaders of the company for approval.

6 Detection of spherical tank group before welding

Before group welding, according to the STANDARD of NB/T47013-2015 Non-destructive Testing of Pressure Equipment and relevant standards, the original spherical shell plate shall be 100% ultrasonic reinspected and the entire area of 100% original weld perimeter width within 100 mm shall be tested as gradeiby ultrasonic testing before the spherical tank group. The 100% magnetic particle detection of spherical shell plate groove is gradei. The shape and size of the 6 welds to be welded before group welding should be checked that the staggered edge quantity is no more than 3 mm and the angle of the edge is no more than 7 mm. The practice shows that the original spherical shell plate has no deformation and no new defect when the spherical tank is constructed according to the cutting and lifting construction technology described in this paper before moving. The test fully meets the relevant requirements.

7 Conclusions

Compared with the newly-built spherical tank, the field construction of large-scale spherical tank is complicated, difficult and technically demanding. Especially in the process of dismantlement, if the construction can not be organized scientifically, the original spherical tank shell may be damaged or even scrapped due to improper dismantlement, or due to the backward construction technology, the safety and quality of the reconstructed spherical tank will be affected after the spherical tank shell is disassembled. Therefore, scientific organization of cutting and hoisting plays an important role in ensuring the quality of spherical tank shell materials.