| The metal composite pipe is composed of two or more different metal pipes.Since it has advantages of both parent pipes and flyer pipes,the combination properties of metal composite pipes are comprehensive that a single metal pipe does not have.Metal composite pipes with excellent performance such as high-temperature resistance,abrasion resistance,high specific strength and high conductivity can be obtained and widely used in urban construction,oil and gas industry,chemical industry,energy environmental protection and nuclear facilities,as well as aerospace and other fields.There are many kinds of processes for making metal composite pipes,including drawing method,expansion method,spinning method,hot extrusion method,explosive welding method,centrifugal aluminum heat method,medium frequency induction heating brazing method and surfacing molding method.Among them,the explosive welding method can realize the combination of hundreds of kinds of metal combination,so it becomes the most promising metal composite process.The explosive cladding,also known as explosive welding,is a process of making use of explosive energy generated by the explosive to drive the flyer plate(pipe)at a suitable speed to impact on the base plate(pipe)so that the two plates(pipes)to form a strong combination.After more than 70 years of researching and developing,the explosive welding process is developing rapidly.Especially the metal plate explosive welding has formed a certain scale.Compared with the metal plate explosive welding process,metal pipe explosive welding process is more complex.In addition to big explosive dosage,low energy efficiency,vibration,dust and other serious pollution problems encountered in the process of metal composition,the internal explosive welding of pipes is usually faced with difficulties to charge the explosive,uneven charge,serious ablation of the inner wall,mold versatility and loss and other serious problems.And the literature on the metal pipe explosive welding from the exterior which can be found is very limited,and development of this area is slow.This paper focuses on the main problems of metal pipe explosive,and aims to achieve large-scale industrial production to carry out the following work.At present,the explosives used for the metal explosive welding are mainly emulsion explosives,expanded ammonium nitrate explosives,and expanded ammonium oil explosives.These explosives made by adding modifiers through sieving on site are poor in storage stability and poor uniformity,as well as detonation instability and other issues,which seriously affects the quality of explosive welding and is not conducive to safe production.When those kinds of explosives are used for the internal explosive of the metal pipe,the semi-sealing of the pipe structure and the adhesion of the explosive can cause difficulties in charging and uneven charge.Furthermore the critical dimensions of steady detonation of the above-mentioned explosive are relatively large,which requires that the thickness of charge must be adequate.In order to overcome the pipe rupture caused by the ultra explosive dose,usually steel mold constraints are added outside the parent pipe.And this constraint is poor versatility,for different diameters of the base pipe require different constraints of steel mold,and under the influence of explosive loading and the mold wears,and is short in life.In addition,explosives in the round pipe in the semi-closed structure of the explosive will form thousands of degrees Celsius high temperature,resulting in complex pipe wall serious ablation phenomenon,increasing the second operation cost of the composite pipe.In this paper,starting from the metal detonating cord,through innovation of the process and improvement of the formula the metal explosive cord is obtained,and it will be used as explosives in a metal pipe explosive welding which is originally used as blasting equipment in the expansion of detonation.Metal explosive cord with high energy density,small stable detonation critical diameter,the detonation velocity is reasonable,safe and reliable,suitable for long-term storage and long-distance transport and can achieve industrial production.As a kind of columnar structure explosives,it helps to solve problems of difficult charge in metal pipe explosive welding,and the uneven charge.Based on the new ideas and new breakthroughs in the explosive welding of metal pipes,the protection of the inner wall is carried out in order to solve the problem of ablation damage in the inner wall when the metal pipe is exploded.In the choice of protective materials,the standard is cheap,wide source,easy to use,good bonding.After the comprehensive analysis the final choice is the liquid water.On the basis of this,the composite system of the underwater explosive welding of metal pipes was designed,and the feasibility test of underwater explosive welding system was analyzed based on Q235 steel pipe and 1060 aluminum pipe.The results show that the bonding strength of aluminum-steel composite pipe is 3.27MPa,which is much higher than that of CJ/T192-2004 standard 0.2MPa and 0.5MPa stipulated in SY/T6623 standard.Feasibility test shows that the underwater explosive system can effectively solve the problem of ablation damage of inner pipe,and the combined strength of composite pipe is much higher than the standard of urban construction industry and oil and gas industry.In addition,with the Q235 steel pipe and the 1060 aluminum pipe as the base and coated pipes respectively,the influence of explosive quantity on the composite pipes was explored and the underwater explosive welding experiments were done using four different specifications of the explosive cord without deep surface cleaning treatment of the base and coated pipes.The results show that the aluminum-steel composite pipe obtained with the explosive cord of outer diameter of 5mm and the linear density of about 14.7g/m is superior.The microstructure observation of the bonding interface shows that the aluminum-steel interface gives the appearance of wave-like interface which is a wave-like interface between microwave and small wave by judging the wavelength and magnitude.Compared with the large wave-like or small wave-like interface,this wave-shaped interface usually represents that the composite pipe has a higher bonding strength.Through the discussion of the mechanism of the formation of the classical wave-like interface,the main reason for the formation of the irregular wave interface is presented in this paper.In the internal combustion of the metal pipe composite test,the cracking phenomenon at the end of the composite pipe often appears.In this paper,the PVDF piezoelectric thin film sensor is firstly used to measure the dynamic parameters of the explosive welding,which is significant for the study of the explosive welding of the metal pipe in the absence of dynamic observation.The impact pressure of the aluminum layer on the steel layer in the aluminum-steel underwater explosive was measured by using the PVDF piezoelectric thin film sensor.The results show that the impact pressure between parent pipe and flyer pipe increases along the detonation direction.The microstructures of the interface at the beginning,middle and end of the composite pipe show that the interface is transformed from the initial interface with the fissure interface to the middle of the flat and straight interface,and finally to the wavy interface at the end of the detonation.The changing process of the microstructure of the interface intuitively reflects the change of the impact pressure and energy in the bonding process of the metal pipe.This paper gives an explanation about this phenomenon from the reflection process of the underwater shock wave in the inner wall of the composite pipe.The study of this phenomenon will help to change the charge structure,save a number of explosives and improve the quality of composite.Based on the research situation of the external explosive of the metal pipe,the heat transfer pipe which is widely used in heat exchange system is used as the background of the application.Through the change of the structure of metal explosive cord,an asymmetric metal pipe explosive system was designed.It was used to weld the 1070 aluminum pipe to 10100 thread copper pipe.The wide-angle three-point bending experiment of composite pipe samples shows the excellent macroscopic mechanical properties of the aluminum-copper composite pipe.The samples were sampled to be observed by scanning electron microscope.The results showed that a part of the aluminum layer had been completely pressed into the depression of the copper pipe thread.Most of the metal interface is a direct bond,but in some copper layer cavities metal melting blocks and melting layer forms.The high magnification backscattering picture of the interface between the aluminum layer and the copper pipe top platform shows that even after the bending test,the bonding interface with the micro-pattern feature remains tightly bonded and that no separation occurs.The interface between the aluminum layer and the copper pipe thread cavity has a large area of melting blocks and melting layer,and there are micro-cracks and cavities in these melting zones,indicating that the region is a weak region of the interface.The results show that the percentage of Al and Cu atoms in the vicinity of the crack is about 2 to 1 by using Energy Disperse Spectroscopy,which is consistent with the intermetallic compound of CuAl2,which is a brittle intermetallic compound.It is an internal factor in the development of cracks in these areas. |
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