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At pipelining, welding of circular nonrotatable pipe joints is one of the main technological operations. To perform this operation, different welding methods are used: manual electric arc welding with piece coated electrodes, semi-automatic electric arc welding with powder cored wire with flux-distribution method, automatic multi-layer welding in shielding gas environment with continuous cross section GMAW wire or powder cored wire, contact continuous fusion welding, laser welding, etc.).
In the E. O. Paton Electric Welding Institute works on development of new technology and equipment for electric arc automatic welding are carried out. A technical project of a set of equipment, technology and welding materials for automatic electric arc welding of nonrotatable pipe joints with powder cored wire with forced formation of weld metal is elaborated.
The technology prescribes realization of all the passes of the weld joint by the method “bottom-up” in orbits with two welding heads of the welder in fully automatic mode with programmable control.
The program starts after installation of the suspension member with welding heads at pre-mounted guide belts. A system of sensors (tracker system) provides flow of current data on the position of the welding head, on the travel speed, angle of inclination of the wire, frequency and amplitude of vibration of the electrode wire, linear heat input of welding and the parameters of arc burning.
As operator’s task there remains installation of the apparatus to the start position and its removal after completion of welding, and effective response on activation of the alarm system in the case of error in the program run. The control system provides diagnostics of state and technical parameters of the welding heads.
At welding nonrotatable pipe joints with forced weld forming (electrogas welding) molten metal of the weld puddle is held against runoff with a forming tool (sliding piece, backing). The melting space is filled with melted filler metal of the powder cored wire. At that on the surfaces of the forming tools a layer of welding slag produced at cored wire melting is deposited.
- welder channel for feeding cored wire;
- contact tip;
- powder cored wire;
- coolant supply;
- coolant removal;
- forming sliding piece;
- slag crust;
- the weld.
Realization of such a process at change of the spatial position of the weld puddle has become possible due to the control of the position of the electrode and selection of its composition able to generate at melting required amounts of slag and gas. Thus the process is based on account and control, according to the weld position in space, of effect of the forces of gravity, arc pressure and gas flow, and the forces of interfacial tension. In the process of displacement of the apparatus in orbit along the pipe joint, the electrode wire is displaced along the melting space, and the angle of inclination of the electrode wire with respect to the tangent line to the periphery of the pipe is changed according to the position of the weld puddle in space. At that the weld puddle, by means of forming tools, is held in set zone due to the tracker system.
Flowchart of control of apparatus with control of the level of the weld puddle
- welding wire feed mouthpiece;
- welding wire;
- welding arc;
- light radiation of the arc;
- weld puddle;
- water-cooled sliding piece.
Intratubal self-propelled centrator
Welding of the root weld is performed on a copper or a ceramic backing ring. To form the reverse roll of the joint root, in the section spreader backing a shaped groove with needed shape is provided. The backing is formed of separate elements with special design installed on the intratubal centrator. At section spreading the backing forms a continuous ring that tightly adjoins the pipe joint. The surface of the weld in all spatial positions of welding is formed in forced way with a special tool – a sliding piece that moves together with the welding head in orbit by the pipe, with provision of formation of the weld with given dimension, shape and state of surface.
Forming sliding pieces
The inner self-propelled hydraulic or pneumatic centrator is placed in the pipeline being welded. For alignment of the pipe edges, a centering mechanism is mounted on it, this comprises sets of presses between which a segment backing ring is installed. All the parts of the backing ring are in contact by the whole circumference of the pipe. Accurate positioning of the backing ring at the joint being welded is performed by the centering mechanism, and its fixation – with clamps. From the joint that is just welded to the next one the centrator moves autonomously. The control panels of the centrator are placed at the end of the rod and at the head of the centrator.
Welding of the weld root of nonrotatable pipe joints
The root weld is made at outside of the pipe joint with application of a self-propelled intratubal centrator with a special backing ring. In following passes grooving is filled, and facing weld is formed. In each pass grooving is filled by 5 … 8 mm (depending on the pipe wall thickness).
Automatic welding system «BUTT JOINT» of new generation
Purpose function of the welding system – welding of nonrotatable pipe joints of main pipelines with forced weld formation, with automatic welding of the weld root on intratubal centrator with a backing ring. The guide belt is positioned on the pipe beforehand, with accurate orientation along the joint.
Welding of main pipeline pipe joints
Performance specification of the automatic welding system «BUTT JOINT - Auto» of new generation
|Diameter of welded pipes||530 … 1420 mm|
|Wall thickness||8 … 32 mm|
|Welding current at DC 100||280 … 500 А|
|Arc voltage, V||24 … 32 V|
|Diameter of electrode wire||1,6; 2,0; 2,4 mm|
|Electrode wire feed rate||150 … 500 m/h|
|Welding head displacement speed||Up to 75 m/h|
|Overhang length of electrode wire||20 … 45 mm|
|Correction of the position of the electrode end, across the butt||±12 mm|
|Control of frequency of vibrations of electrode wire with respect to the axis of the butt||Automatically depending on the mode|
|Amplitude of vibrations||0 … 12 mm|
|Control of feed of electrode wire by depth of grooving||±7 mm|
|Time for mounting apparatus to the butt joint||1 … 3 min.|
|Machine time for welding one joint (at operation of 2 heads simultaneously) on pipes with diameters 1020 – 1420 mm||6 … 12 min.|
Development of equipment for welding main pipeline nonrotatable pipe joints Welding heads with automatic control units
Development of software for welding process control and logging
Graphical representation of the record of pipe joint automatic welding with one welding head
Powder cored wire for nonrotatable pipe joint arc welding with forced weld forming
Typical mechanical properties of weld metal and the welded joint made with cored wire
|Temporary breaking strength, MPa||Yield strength, MPa||Elongation, %||Contraction, %||Impact energy KV at –40 °C, J|
|720 … 760||at least 590||at least 17||at least 60||at least 47|
Content of diffusion hydrogen in weld metal is within 5 ml/100 g.
To make welded joints of steels of grades X70 and X80, special powder cored wires with diameters 1,6; 2,0 and 2,4 mm are developed. Mechanical properties of weld metal and the welded joint are given in the table
Automatic arc welding of nonrotatable pipe joints with powder cored wire with forced forming
Macrosections of pipe butt joint made with automatic electric arc welding with powder cored wire with forced weld forming in two passes.
Outward form of welded pipe butt joint made with automatic electric arc welding with powder cored wire with forced weld forming.
Application of the system «BUTT JOINT» at construction of main pipelines
- At system servicing personnel staff structure from 8 to 16 persons, productivity of construction of a pipeline with diameter 1420 mm is from 3 to 6 joints per hour. Maximal experience of operation is gained at construction of pipelines with diameters 1020 mm, 1220 mm and 1420 mm (pipelines Urengoy – Center, Shebelinka – Izmail, Urengoy – Pomary – Uzhgorod, Khiva – Biyneu, Yamal – Western border, Yamal – Volga region and others, with linear sections from 193 to 1750 km). Productivity of pipelining in steady state mode of operation is within 25 and 40 joints per shift. The share of repair during regular operation is not more than 3 %.
Construction and reconstruction of the energy carrier (crude oil, oil products and gas) transportation systems is an actual problem in development of power engineering.
Application of the method of weld forced forming has provided stable high characteristics of quality, and perfect geometry of welds. The welding method can quickly enough be adapted for jointing pipes made of steels differing by composition and properties, and geometric parameters of pipes. Project of a set for construction of offshore pipelines from pipe-laying barges is elaborated.
Today large volumes of construction and reconstruction of main pipelines in CIS states are planned. Construction and reconstruction volume, according to the plans, is up to 10 thousand km during the next 5 years. Realization of such projects makes need in application of technologies and equipment corresponding to modern level of engineering and technology and providing high rates of construction under different geographical and climatic conditions.
The new set of equipment, technology and materials for automatic arc welding of main pipeline nonrotatable pipe joints being produced by characteristics of productivity and quality corresponds to, and by a number of characteristics surpasses the world achievements and is able to solve this problem.