Metal pressure vessel is widely used in chemical, petroleum, machinery, metallurgy, nuclear energy, aviation, aerospace and other departments, is the core of the production process essential equipment, pressure vessel generally consists of cylinder, head, flange, sealing element, opening and took over, bearing and so on six big parts container ontology, according to the requirements of the weld stress intensity, can be divided into ABCD grade.
Scope of application | Classification of welded joints of main pressurized parts of vessels | |||
Butt joint | Lap and corner joints | |||
A | B | C | D | |
Steel welded single-layer containers, multi-layer wrapped containers, hot jackets and forged welding containers with design temperature > -20℃. Design temperature ≤-20℃ containers, should also comply with GB150-C provisions | The longitudinal joints of the cylinder part (except the longitudinal joints of the multi-layer packing container laminates), the circular joints of the spherical head and the cylinder, all the splicing joints in various types of convex heads, and the joints of the embedded pipe and the shell butt connection. | Annular joints for shell parts, joints for tapered head segments connected with nozzles, joints for long neck flanges connected with nozzles, except joints that have been specified as class A, C and D. | Flat cover, tube plate and cylinder non-butt joint joint, flange and shell, pipe connection joint, inner head and cylinder lap joint and multi-layer packing container laminate longitudinal joint. | Nozzles, manholes, flanges, reinforcement rings and other joints connected with the shell, except those specified as class A and B. |
It can be seen that the welded joints of the main compression part of the container are divided into four categories: A, B, C and D, as shown in the table.
a) The longitudinal joints of the cylinder part (except the longitudinal joints of the laminate layer of the multi-layer packing container), the circumferential joints of the spherical head connected to the cylinder, all the split-welded joints of various types of convex heads, and the joints of the butt connection between the embedded pipe and the shell are all class A welded joints.
b) The annular joints of the shell part, the joints connected with the small end of the conical head and the joints connected with the pipe, and the joints connected with the long neck flange and the pipe shall all belong to class B welding joints, except those already specified as class A, C and D welding joints.
c) Non-butt joints of flat cover, tube plate and cylinder, joints of flange and shell and pipe, lap joints of inner head and cylinder, and longitudinal joints of laminates of multi-layer packing containers are all class C welded joints.
d) Joints connected with the shell, such as nozzles, manholes, flanges and reinforcing rings, belong to class D welding joints, except those already specified as class A and B welding joints.
It is recommended to use submerged arc welding, electrode arc welding, argon arc welding, or A combination of them for type A and B joints. CO2 can be used for the butt weld between the nozzle and flange.
Note: GAS WELDING is generally not allowed for pressure REQUIREMENTS.MANUAL GTIG SUBMERGED ARC WELDING IS RECOMMENDED.
2.1 Arc initiation and arc closure
Should be in the arc or groove in the arc, prohibited in the non-welding parts of the arc, welding seam should be on the arc plate arc, arc pit should be filled.
2.2 Prevent arcs
Avoid arcs between ground wire, power line, welding holder and weldment.
2.3 Polishing and repair welding of arc pit
The arc pit at the arc scrape should be polished to make it uniformly transition to the surface of the base material. If the thickness of the base material after grinding is less than the specified value, it needs to be welded.
2.4 Fillet weld of compression component
Its root should be guaranteed to be welded through, the foot should be smooth transition.
2.5 Welding wire energy
The line energy of each pass shall not be higher than the qualified value.
2.6 welding
The joints of each weld pass should be staggered as far as possible.
2.7 clear root
Double-sided welding requires cleaning the weld root to expose the front backing weld metal. For automatic welding, if the test can guarantee the penetration, can not do root cleaning treatment.
2.8 Requirements for arc joints
Penetration and fusion should be ensured
2.9 Interlayer temperature
During the welding process, the temperature between layers should not exceed the specified range. When the weldment is preheated, the interlayer temperature should be controlled not lower than the preheating temperature.
2.10 Requirements for welding interruption
Each weld should be welded as far as possible. When the welding is interrupted, the welding parts sensitive to cold cracks should take post-heating and slow cooling measures in time. When rewelding, it is still necessary to preheat according to regulations.
2.11 Hammer to improve welding quality
When it is necessary to use hammer to improve welding quality, the welding of the first layer of weld and cover layer should not be hammered.
2.12 Removal of arc starting plate, arc ending plate and test plate
The arc starting plate, arc ending plate and product welding test plate should not be dismantled by hammer.
Time | Check the main items |
Before welding | Base metal, welding material Welding equipment, current, voltmeter Welding groove, joint assembly and cleaning Welder qualification Welding process document |
Shi welding process | Welding specification parameters Perform welding process Implementation of technical standards Implementation of drawing requirements |
After welding | Actual welding records Appearance and size of welded joint Post heating, post welding heat treatment Product welding test plate Nondestructive testing Withstand voltage test Test for compactness |
3.1 Appearance quality of welding
3.1.1 The appearance, shape and size of the weld shall meet the requirements of technical standards and design drawings, and the surface shall not have cracks, pores, arc pits and spatter.
3.1.2 Class C and D welds shall have smooth transition with the base metal. Where the drawing does not specify the height of the solder, the thickness of the thinner part of the solder is taken. For the solder pin of the reinforcing ring, when the reinforcing ring is greater than or equal to 8mm, the solder pin is equal to 70% of the thickness of the reinforcing ring, and not less than 8mm.
3.1.3 For steels with standard tensile strength σb > 540MPa, containers made of austenitic stainless steel, cryogenic containers, spherical tanks and containers with a welded joint coefficient of 1.0, the welded joint surface shall not have bite edges. The depth of bite edges on the surface of welded joints of containers other than the above shall not be greater than 0.5mm, the continuous length of bite edges shall not be greater than 100mm, and the total length of bite edges on both sides of the welded joints shall not exceed 10% of the length of the welded joints.
3.1.4 Residual height of Class A and B welded joints Residual height of class A and B welds shall not be greater than 10% of the weldment thickness and shall not be greater than 3mm. The width of class A and B welded joints is generally 1-2mm wider than the width of each side of the groove.
