[introduction] composite steel pressure vessel is commonly used in some steel as base, a steel or non-ferrous metal as a composite layer, two metal plates formed by hot rolling or explosive forming process such as composite method. The basic structure is mainly to meet the requirements of strength and stiffness, generally with low carbon steel or low alloy steel; and the cladding is mainly to meet the corrosion resistance requirements of chromium and chromium nickel stainless steel, nickel base alloy, copper alloy or titanium plate for general use. Complex layers usually only account for 10%-20% of the total thickness. Therefore, the composite plate both have special properties of precious metals (such as corrosion resistance), but also save a lot of stainless steel or titanium and other precious metals, in which can greatly reduce the cost and technical requirements, has great economic value. Therefore, the composite steel plate in the petroleum, chemical, marine, medical, food industry and military production has been more and more widely used. In addition, as the composite plate to withstand the pressure of pressure vessel, the working medium almost has a strong corrosive substances, so the manufacturing process is very strict, here we will mainly talk about some of the composite steel pressure vessel manufacturing process and requirements, to discuss with the big house.
1 composite board preparation
Composite steel plate base layer and compound layer of material due to the need to set. In general, the overseas projects in the base material for the SA516-70, the composite layer material for the SA240-304L stainless steel composite plate is more commonly used. Composite steel plate shall meet the following conditions:
(1) composite plate should meet the user requirements and the corresponding standard requirements of steel and austenitic stainless steel with steel plate should meet the SA264 standard, a complete quality certificate accurately and clearly, and ensure the smooth surface. Attention should be emphasized that the heat treatment should be a single sheet of air cooling and not to be put in a state of air and cold air cooling which leads to the reduction of the corrosion resistance of the clad layer.
(2) composite steel plate shall not have harmful appearance defects. The basic and complex layer is combined with the combination of minimum area should be accounted for more than 95% of the total area, local unbound area shall not exceed 58cm2; have greater stress on processing (such as stamping head) or when using a large load (such as tube plate) of the composite steel plate should require 100% combination. The surface of the base layer and the surface of the shallow defect, if it can not be worn off, the total surface area of the total surface of the defect is not more than 20% of the composite area. At the same time, the surface quality of the compound layer should be adapted to the composite method, the thickness is uniform and the tolerance should be in accordance with the specified value.
(3) on the mechanical properties of composite steel plate, its tensile strength and elongation principle should be equal to or greater than the parent material (base material); bending test standard should be the base material and the same thickness of the same compound layer and the base shear strength of not less than 140MPa; 3 samples of bending joint the two bend portion of both sides cannot have the stratification above 50mm.
(4) the ultrasonic testing of the composite steel plate shall be carried out in the time of entering into the factory, and shall not have the phenomenon of stratification beyond the standard and the contract. The repair of composite plates, as well as the marking and marking, and so on, are the same as the control of the raw materials of the general steel pressure vessel.
2 cylinder under the material
(1) the butt welding between the cylinder and the end of the composite steel plate, the diameter of the two should be in agreement (the length of the inner circumference of the control should not be greater than 3mm).
(2) the plate is subjected to bending during the rolling process, which is called the neutral layer and the circumference of the neutral layer is the same as that of the 0. According to the head of the neutral layer Zhou Changlai to determine the length of the tube expansion is reasonable. In addition, the diameter of the neutral layer of the composite plate cylinder or the head is smaller than that of the middle diameter:
L=π (Di-2Yh)
In the formula, Di: the measured diameter of the head Yh: the distance from the inner wall of the neutral layer of the head
(3) in both longitudinal and girth welds, the misalignment of the composite plate cylinder and the butt joint of the end plate shall not exceed 50% of the thickness of the plate, and shall not be greater than 2mm.
3 cylinder layout
The cylinder layout, namely the first cylinder in a clockwise direction, and then in the barrel mark all take over the position and diameter of hole, and according to the longitudinal seam stagger over hole principle to determine the length and width of plate, longitudinal weld from the edge of the distance should be greater than 100mm.
4 welding
(1) welding method of composite steel plate, can be determined according to the material, thickness, size of groove joints and construction conditions, usually by manual arc welding, submerged arc welding, submerged arc welding, CO2 welding and argon arc welding.
(2) clad steel plate and double layer and transition layer electrode selection: SA516-70+SA240-304L composite plate, base by E-5015 electrode, E309-16 electrode layer, compound layer with E347-16 electrode is more appropriate; such as SA516-70+SA240-304L composite plate, base optional E-5015 electrode, E309MoL-16 electrode layer, double layer E316L-16 electrode is suitable.
(3) preparation: according to the basic selection of suitable thickness of groove type, pay attention to a complex processing stage of 5mm, avoid the coating material into the weld in the primary welding caused cracks.
(4): for the welding welding sequence, welding seam is generally the first base inside, outside in turn pick root, using carbon arc gouging welding blade root, removal of slag and slag, and then fill the post welding weld base; grinding in the clad side with the angle of grinding wheel, after passing the examination, then inside welding transition layer, and finally welding layer. When welding, should strictly control the inner weld height away from the base, double layer interface 1mm-1.5mm, double layer must not be welded to the weld welding, transition layer is only one layer, the welding metal should be completely covered with grass, and cover the complex layers of 0.5mm-1.5mm, should adopt smaller line energy welding transition layer, in order to prevent the base metal into the complex layer caused by weld defects.
5 other requirements
(1) cutting, bending or deep drawing of composite steel plate, should be put in the lower layer of the complex, it is necessary to set a protective layer, in order to prevent the surface of the composite layer on the surface scratch.
(2) the bending or deep drawing of composite steel plate should be used in cold rolling process, when it is forced to use hot processing, we must pay attention to the following points: before heating, oil and dirt should be removed.Low; heating time is 2min/mm, and not more than 15mm; solid fuel heating flame or not directly contact layer, and the temperature distribution is uniform, to prevent carburization; should be avoided in the sensitized temperature range (550 DEG -850 DEG) processing, in order to prevent intergranular corrosion; heating atmosphere should be maintained by reduction of oxygen, of not according to different materials; composite layer should control the heating temperature range, the best processing after air cooling.
(3) because of the different thermal expansion coefficients of 2 kinds of metal, the residual stress in the heat treatment process is likely to increase, so it is necessary to eliminate stress annealing. When it is not necessary to eliminate stress annealing, it is necessary to use the appropriate method according to the use of the container. The base material for low carbon steel, the thickness of base metal < -25mm, does not need to eliminate stress; when the thickness of base metal > 25mm-28mm, if the preheating temperature is over 100 DEG C need not eliminate stress; when the thickness of base metal > 38mm, to eliminate the residual stress.
(4) because of the dilution effect of the base weld on the complex layer, it is easy to reduce the content of chromium, nickel and other alloying elements in the complex layer of the weld metal. Therefore, when welding, welding transition layer of high chromium nickel steel should be used, such as welding, weld to obtain two-way organization, to avoid a lot of martensite, welding cold crack.
(5) before welding, ventilation should first remove the air pipe; when the CO2 gas shielded welding composite plate, should ensure that adequate protection of gas flow, to avoid air intruding into the welding zone; after welding, welding spatter on the mouth should be cleaned timely; the length of wire extension should not be too long to 10mm-15mm.
(6) in addition to the pattern of composite steel plate fixed weld X-ray detection or ultrasonic testing, the cladding weld all should also be made to test the weld penetration test, no cracks on the surface; weld inspection can not be immediately after welding, the best in test methods available before annealing, coloring, magnetic particle or ray detection can.
(7) with carbon steel stainless steel lining pipe end should be (4+/-1) mm cladding layer, should also take over the inner wall of the container into the stainless steel (4+/-1) mm.
(8) the surface of the compound layer with corrosion protection requirements should be treated by pickling and passivation, in order to improve the anti cracking ability.
Test of 6 composite steel plate pressure vessel
Pressure vessel, due to sealing, pressure and medium and other reasons, prone to explosion, burning fire and endanger personnel, equipment and property safety and even environmental pollution accidents. Therefore, the application of composite steel plate pressure vessels in the manufacturing, the specialized agencies designated by regulations, in accordance with the requirements of users, regulations and standards to implement supervision and inspection and technical inspection. The main test items and methods are:
(1) physical inspection. Using the methods of visual inspection, measuring and inspection, nondestructive testing, physical and chemical performance test, hydraulic pressure test, the appearance and inner quality of the pressure vessel body and main parts were examined.
(2) the main items tested: the pressure element material, the size and appearance of weld forming quality, quality, quality, internal assembly device and safety accessories are complete and valid, expanding quality, compression elements of each geometric position and pressure resistance etc..
(3) performance: pressure vessel technical review and inspection of the entities as needed to check its performance test, the provisions of the technical and economic indicators, such as the consumer needs to deal with complex layers of intergranular corrosion test.
(4) the key test of composite layer and the base layer are combined welding defect parts, mainly slag and hot crack, once exceed the standard, must be repaired until qualified.
(5) inspection of the inward angle deformation of the longitudinal weld.
In summary, the manufacturing process of composite steel pressure vessel and pressure vessel are still very different, mainly in the control of raw materials, processing, welding groove group of control to more precise control and heat, to ensure and improve the quality of manufacturing. The practice has proved that the quality of the composite plate pressure vessel made by the above requirements is stable, and there is no problem in the actual use.