CS256071B1 - A method of arc welding of suspension noses to hanging tubes - Google Patents

Abstract

The arc welding method is suitable for welding joint plates to webs and hanging noses to pipes. Welding is performed by machine arc welding with a melting electrode in a protective atmosphere or protective gases simultaneously with two welding torches that move during welding! in the opposite direction. At the end of welding, it is advantageous to reduce the welding current to 50% of the nominal value.

Description

BACKGROUND OF THE INVENTION The present invention relates to a method of arc welding of suspension noses to suspension tubes in power engineering for the production of heat exchangers and superheater walls by dimensional welding in a horizontal position from above, wherein:. the suspension nose is in the vertical position and the pipe is in the horizontal position.

Welding joints are manufactured at the manufacturers of power equipment by means of pendant nose - pendant tube by manual arc welding with a coated electrode. The type of electrode used is chosen as the steel tube stage, the lower alloy steel stage of the given suspension nose-tube combination. Pre-welding as well as additional heat treatment of the entire weld after welding is determined in turn by the stages of higher alloy steel.

The method of manual arc welding by a coated electrode is relatively laborious and inefficient. It requires demanding preparation of the joints before welding, determining the correct position of the hanging nose on the pipe and moving it to the pipe with at least two stitches. Stitching requires separate preheating for some material combinations. In the case of coated electrode welding, the most common procedure is the gradual formation of two longitudinal welds, first on one side and then on the other side of the suspension nose. The connection of the tubing is most often done on the nose surfaces. The slag residue should be removed after the joint has been made. The produced hanging pipe with welded noses is finally annealed in the furnace.

The quality of the produced electrode-coated electrode bends varies widely. The quality of joints is also influenced by the welder himself, his disposition, qualification and craftsmanship. Quality control of joints is possible only on the surface appearance. Frequent joint failures are deformations, in particular the deflection of the suspension nose from the desired plane. For some suspension nose - pipe steels, the occurrence of cracks is also possible, especially cold hydrogen - induced cracks. Additional mechanical compensation of suspension nose deformations is often impossible due to the low plastic properties of the joints. The occurrence of martensite in the weld and heat affected area is also a major cause of cracks in some suspension nose-pipe combinations, but especially when welding high-alloy refractory steel suspension noses to low-alloy refractory steel tubes. Cracks occur especially at the beginning of the weld. Their occurrence is more common when welding with lower specific heat inputs (below 10 kj / cm).

The aforementioned disadvantages are largely eliminated by welding the hinged nose to the hinged tube with a melting electrode by a fillet weld in a horizontal position when the dimension weld joint around the perimeter of the hinged nose and hinged tube is produced by two-arc welding of up to 150 welding seams And, I burn on an arc of 20 to 25 V and a welding speed of 150 to 500 mm / min simultaneously with two burners, the essence of which is that they move in the opposite direction.

When welding the suspension nose to a depth of 6 mm, it is advantageous if the welding torches are kept in marginal positions at the beginning and at the end of welding for 1 to 5 seconds at rest, when welding the suspension nose above a depth of 6 mm When finishing the weld on the front flat perform! welding torches movement in transverse direction.

By comparing the manual welding by the coated electrode with the method according to the invention, the method according to the invention is substantially more advantageous. It ensures higher under-connectivity, higher quality and, in particular, uniformity of quality of manufactured joints. In the process according to the invention, the productivity increases up to twice the current state of welding the suspension noses to the tubes by an arc-coated electrode. For machine dosing and positioning of suspension noses, e.g. computer, further productivity gains can be expected in the production of joints, as the by-product preparation times are further reduced. By pulling the current at the end of the weld up to 50% of the nominal current, a more regular transition is created, the crater fills better, and the weld susceptibility to crater cracking is also reduced. After the oven has been preheated, the suspension nose is pressed against the oven with a force of 50 to 1000 N using a fixture. The dimension weld joint is made in a horizontal position from above by two burners moving simultaneously on both sides of the nose along a set rectilinear or curved path.

The burner inlet position is 1 to 5 mm in front of the front nose front plane and the burner outlet position is 1 to 5 mm behind any nose front plane. In the inlet and outlet positions, the burners are always on the opposite side of the nose. Dimensional joints are formed on the nose and pipe faces by holding the welding process and the burners in the exit position without moving for a period of 1 to 5 seconds depending on the sheet depth or by a small additional movement of the burners in the transverse direction. The first method of dimension weld production on the face is recommended for sheets of thickness less than 6 inm, the second method for sheets of thickness over 6 mm.

The method according to the invention has proved to be particularly suitable, in particular for welding the suspension noses to pipes of the following dimensions, a suspension nose of thicknesses of 4 to 10 mm and a width of 30 to 100 mm, suspension tubes with a wall thickness of 4 to 10 mm.

The method according to the invention has been practically tested when welding pendulum noses of thicknesses of 6, 8 and 10 mm and widths of 30 to 50 mm of low-alloy and high-alloy refractory steels to 0 32 x 5 and 0 x 38 mm of low-alloy refractory steels.

258071

Welded joints were made with double-arc welding parameters by counter-welding with a melting electrode in a protective atmosphere of 80% argon and 20% carbon dioxide at a gas flow rate of 16 l / min, base material low-alloy heat-resisting steel, 6 mm nose thickness of high-alloy heat-resistant steel 230 to 240

A, arc voltage 22 V, welding speed 200 mm / min, chromium-molybdenum filler material (C 312).

Tests of the performance of the joints produced according to the invention have confirmed the high integrity of the joints, the fulfillment of the trade standard in terms of form and weld section and also the satisfactory heat resistance.

Claims (3)

1. Method of arc welding of pendant noses to pendant tubes by a melting electrode, by fillet weld in a horizontal position, when the fillet weld joint around the entire circumference of the contact surface of the pendulum nose and pendant tube is made by two-arc welding by fusion electrode, in particular a welding current of 150 to 300 A, a voltage of 20 to 25 V arc and a welding speed of 150 to 500 mm / min at the same time by the torch burners, characterized in that they move in the opposite direction. We claim: 2. The method of arc welding of the suspension noses to a depth of 6 mm according to item 1, characterized in that the welding torches are held in the marginal positions at the beginning and at the end of the welding for a period of 1 to 5 seconds in which. 3. The method of arc welding of the suspension nose above a depth of 6 mm according to claim 1, characterized in that the welding torches move in the transverse direction at the end of the weld on the front face.