DD205354A1 - METHOD FOR WELDING REPAIR OF DEVICED PRESSURE FAULTS AND PIPING ELEMENTS - Google Patents

Abstract

The invention relates to a method for the weld repair of geschaedigter pressure vessels and piping elements, wherein the damaged areas are mechanically or thermally processed and prewarmed as well as the same kind or type foreign filler material is introduced in layers. In order to fully restore the utility value properties, a crack-preventing treatment of the additional material to be introduced in layers and caterpillars is to be achieved. This is achieved in that at least every second layer of the introduced weld material is cold worked and machined to 2/3 of the original height and that applied after filling to the original wall thickness an additional weld with an edge distance to the base material and after cooling down to the original wall thickness is mechanically processed.

Description

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Title of the invention

Process for the repair of damaged pressure vessels and piping elements

Field of application of the invention

The invention relates to a method for the repair of damaged damaged pressure vessels and piping elements, in particular such pressure vessels and Rojir! L, Eif üngselemente whose wall as a result EroeiVer effect'eines medium and / or by mechanical, thermal or chemical influences or their combined attack, partially is destroyed. ' ^m * ""'

Characteristic of the known technical solutions

It is known that crack damage to boiler drums in power * plants are eliminated by individual cracks or Rißfelder removed mechanically and the removed material is replaced by species-specific or alien additional materials. Depending on the nature of the filler material, this process is followed by a heat treatment. However, this method has the decisive disadvantage that only cracks up to a limited depth are eliminated, breakthroughs or the often occurring radiographs or mechanical, thermal or chemical (or their combination) continuous destruction of the wall can not be set in 3tand.

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It is also known a method for repair welding of severely crack damaged boiler drums, the cracks in the form of a continuous trough to a wall weakening of the boiler drum ground to 80 % , the adjacent areas polished to a bare metal and trough start, interruption and end to prevent van Einbrandstellung and to secure the weld pool with the mold shape matched cover and filling parts are provided, the Kesseltroramel is preheated during welding of Pufferlägen in the trough to 150 ⁰ C such that both sides next to and below the trough, a preheating, and that of the alien Welding filler material from the center of the middle is introduced alternately to both sides of the trough according to the following welding sequence as a load-bearing cross-section:

- The total to be welded trough length is halved, divided into each trough sections and at the same time with two welders from the trough means alternately to both trough sides for filling and cover layers after the steps

• Welding the middle third

• Welding of one outside and one inside third

• Welding the other outer and the other inner thirds

welded ·

- Welding the buffer layers in two layers, wherein the welding of the following seam and layer the previous melted to 50 % and the penetration into the wall is kept small;

- Welding the filling and cover layers in three layers, wherein the first layer of about middle buffer layer to the trough side, the second layer is introduced from about middle first layer to the other side of the trough and the third layer in the part formed by the two troughs;

as well as the passages created during welding are ground «

By this method has been achieved that

- the utility value characteristics of the damaged component

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restored to a limited extent and - the material reserves of the damaged component better

be used.

However, this method is a pure build-up welding method to a present after the completion of the crack field nocn crack-free base material on the inside of boiler drums. Due to the various types of damage present, however, it is not suitable for repairing partial wall breakthroughs. In addition, this method exclusively describes a repair variant of the inner wall of a boiler drum.

Object of the invention

The aim of the invention is to repair by means of welding process a damage to the above-mentioned way pressure vessel or pipe element so that a full restoration of the use of ten States of the pressure vessel or the pipe elements is guaranteed.

Explanation of the essence of the invention

The invention has for its object to introduce the filler so that caterpillar and layerwise a crack-preventing processing is possible.

This is achieved in that according to the invention at least every second layer of the introduced weld metal cold worked and machined to 2/3 of the original height and that after filling up to the original wall thickness applied an additional weld with a margin distance zürn base material and after the '"cooling machined to the original wall thickness mechanically

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embodiment

In one embodiment, the invention is explained in detail.

According to the invention, the wall, which has been broken by an erosive steam action on a steam collector made of steel 12 Ch 1 MF, should be repaired according to the invention.

To this end, the edge zone of the damaged area which has been closed by the damage process is mechanically smoothed with minimum material removal and prepared for welding at a flank angle of maximum 20 °. Depending on the geometric shape of the wall opening prepared for welding, the injection of a suitably designed and adapted weld pool protection · De takes place after the filler material has been applied. Local preheating of the collector takes place in the area of the damaged area to be repaired (dimension: IO χ wall thickness s around the damage area) to the following temperatures:

- For Ni-Fe filler metals to 100 - 150 ⁰ C (in high nickel Ni-Fe filler material, the heat treatment can be omitted) and

- For similar filler materials to 250 - 350 ⁰ C.

These preheat temperatures are maintained throughout the welding process.

When welding with a bath fuse, the filler material is introduced continuously by means of manual arc welding, combined as TIG and manual arc welding when welding without a fuse.

The layer-wise introduction of the filler material is such that when welding with a bath fuse the structure of the weld layers takes place so that the weld material is introduced in layers, beginning at the flanks, to the middle of the breakthrough. It is welded with 3.25 mm diameter electrodes at minimum current, avoiding oscillations.

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When welding without a thermal fuse, the root welding is carried out in at least 2 layers by means of the TIG process and then proceeded as in welding without a bath fuse. After each weld bead and each position the welding direction is changed. Each situation is z. B. cold pressed by pressing, blasting, pressing or hammering (below Rekristalliesationstemperatur) and then abraded to 2/3 of its seam height.

After filling the breakthrough until reaching the original wall thickness, the application of an additional layer to the Füllschweißgut, wherein a distance of about * 2 mm to the base material is maintained.

After cooling down this additional layer this is sanded down again to the original wall thickness. The heat post-treatment, which is only necessary when using filler materials of the same kind, which must be carried out within 72 hours after cooling of the weld metal, takes place at 720 - 750 ^° C. The holding time in the example given is 150 minutes. Within the specified period of 72 hours, the pressure vessel must not be loaded (also transport is not permitted).

By the invention it is achieved that

1. introduced the filler material with the lowest amount of heat in crawler and layerwise welding direction change, thereby keeping the amount of shrinkage stresses as a result of welding to a minimum and unwanted structural changes are largely limited,

2. a compressive residual stress is generated by the cold deformation, which leads to the fact that the remaining stresses due to welding are further reduced,

3. any defects caused during welding and / or occurring as a result of the cold deformation and surface defects, eg. B. too high degree of deformation or microcracks, are eliminated and for the following situation an optimal seam preparation is created as a prerequisite for a fault-free weld metal,

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a complete homogenization of the weld metal is achieved by applying an additional layer and the associated tempering effect for the cover layer of the welded joint. The subsequent mechanical processing of the additional layer leads to a completely notch-free adaptation of the weld metal to the surface geometry of the component and to eliminate the shrinkage effect by this position «

the edge distance between additional layer and base material causes the negative effects metallurgical notches along the fusion line and in the heat affected zone in the base layer adjacent to the base material degraded by the tempering effect and the negative influences along the melting line of the additional layer are displaced in the compared to the base material tougher weld metal .

by the achieved structural and property improvement of the weld metal the damaged component material economically and technically optimal exploitable, the required effort for the repair is much lower than in previously applied repair process (fitting change, patch welding) is.

Claims (2)

invention claim 1. A method for welding repair damaged damaged pressure vessels and piping elements, the damaged areas are mechanically or thermally processed and preheated and same kind or artfremder filler material is introduced in layers, characterized in that at least every other layer of the introduced weld metal cold formed and 2/3 of the original Height is mechanically processed and that applied after filling to the original wall thickness, an additional weld with an edge distance from the base material and machined after cooling to the original wall thickness mechanically. 2 «method according to item 1, characterized in that the filler introduced from the flanks beginning to the middle in layers and after each weld bead and each layer, the welding direction is changed.