DE2704021A1 - Preventing propagation of cracks in pipes - by intermediate ring with transverse metal texture welded into pipe - Google Patents

Abstract

A device for limiting the length of cracks in a pipeline consists of an intermediate ring or rings welded into the pipe, each ring being of the same material as the rest of the pipe but having its rolling or forging texture oriented perpendicularly to that of the main part of the pipe. Pref. the intermediate ring is thicker than the remainder of the pipe, with a gradual transition from the standard pipe thickness to the increased thickness of the ring itself. Used in particular for pipes and ducts in nuclear power plant, to prevent the propagation of brittle fractures along the pipe. With nuclear power plant, in particular, diffulties arise if other conventional methods of preventing crack propagation, such as jackets or reinforcing sleeves around the pipe, are used. These impede access for routine testing and surveillance. The method obviates this difficulty and enables the entire pipe to be inspected.

Description

Arrangement to limit crack length in pipelines

The invention relates to an arrangement for limiting the length of cracks in pipelines.

In plant construction, such as in nuclear power plants, pipelines are used used, the media lead, which with high pressure and / or high temperature are equipped.

As a result of local stress concentration and possibly existing material weaknesses brittle fractures can occur, which then occur due to the slower stress reduction in the axial direction of the pipe, usually at high speed. at Supply pipelines have already cracked several hundred meters in length. This fact is due to the fact that both seamless and welded Pipes the crack plane occurs as normal to the membrane tension and the crack propagation takes place in the axial direction. The problem, the possible one, has therefore existed for a long time Limit crack length to a certain level.

To solve this problem, it is known to increase the voltage by means of magnification the pipe wall, by pulling on collars or by pulling on a second pipe to diminish. These measures have the disadvantage, especially in reactor construction, that the non-destructive testing is hindered or made impossible.

Furthermore, voltage peaks can be caused by the changed temperature profile and the changed voltage curve occur. It is also known, the crack arrest fracture toughness value the pipeline by using a material with a different chemical Increase composition. Here it has been shown to be disadvantageous that the good Weldability is lost and thus the quality of the necessary joint welds is reduced.

The invention has the task of creating a pipeline, which limits the crack length to a selectable level and the disadvantages shown avoids.

The problem is solved in that in the axial direction of the pipeline seen intermediate rings are welded in that the intermediate rings are made of the same Material like the other pipeline parts and that the rolling or forging textures of the intermediate rings approximately at right angles to the textures of the other pipeline parts get lost.

The invention is based on the findings of fracture mechanics, which state that the crack arrest fracture toughness value by the in a material existing microstructure is influenced. The measure according to the invention is the crack arrest fracture toughness value in the area of the intermediate rings by approx. 50% the remaining pipeline parts increased.

The progress compared to the known can still be seen in that no welding problems occur and that the accessibility for a non-destructive Material testing is guaranteed.

In a further embodiment it is proposed that the wall thickness the intermediate rings are reinforced and that the transition from the wall thickness the remaining pipeline parts gradually to the increased wall thickness of the intermediate rings he follows.

This measure achieves once that the membrane tension is decreased compared to the membrane tension of the remaining pipeline parts and on the other hand, through the gradual increase in wall thickness, stress peaks as well a deflection of an ongoing brittle fracture in the radial direction can be avoided.

The pipeline according to the invention is illustrated by means of schematic drawings explained.

1 shows a partial area of the pipeline according to the invention 2-4 show different configurations of an intermediate ring according to a section the line A-A of Fig. 1 Fig. 1 shows the portion of a pipeline 1 which consists of pipeline parts 2 and welded-in intermediate rings 3. Depending on the area of application of the pipeline, the pipeline parts 2 can have a length of up to to have several hundred meters before an intermediate ring 3 is used again whose width usually does not exceed approx. 30 cm. The textures 4 of the The material structure of the pipeline parts 2 run in the axial direction of the pipeline 1 or as a normal for the membrane tension of the pipeline parts 2.

In contrast, the textures 5 of the material structure of the intermediate ring run 3 approximately at right angles to the textures 4 of the pipeline parts 2 or parallel to Membrane tension of the intermediate ring 3. The desired direction of the textures 5 of the Intermediate ring 3 is determined by the corresponding deformation direction during manufacture achieved. Since the intermediate ring is designed to be relatively narrow, it can be preferred can be manufactured as a rolled-out ring. The small width of the intermediate ring allows the introduction of high deformation and good through-hardening. The crack arrest fracture toughness value of the intermediate ring, which due to the position of the texture 5 is already about 50% compared the crack arrest fracture toughness value of the remaining pipeline parts 2 is increased, can further improved by the aforementioned high deformation and the good through-hardening will.

To further increase the crack arrest fracture toughness value, the The wall thickness of the intermediate ring is reinforced. The contour of the reinforcement a For example, t can have the shape of the embodiment shown in FIGS. As can be seen from these figures, the transition takes place from the wall thickness ~ t of the remaining pipeline parts 2 gradually increasing the wall thickness of the intermediate ring, around stress peaks and a deflection of an ongoing brittle fracture in the radial direction to avoid.

With the arrangement according to the invention, a effective crack length limitation for pipelines created.

Claims (2)

Claims arrangement for crack length limitation in pipelines, characterized in that seen in the axial direction of the pipeline (1) intermediate rings (3) are welded in that the intermediate rings (3) are made of the same material as the other pipeline parts (2) exist and that the rolling or forging textures (5) of the intermediate rings (3) approximately at right angles to the textures (4) of the remaining pipeline parts (2) run. 2. Arrangement according to claim 1, characterized in that the wall thickness the intermediate rings (3) are reinforced and that the transition from the wall thickness (t) the remaining pipeline parts (2) to increase the wall thickness of the intermediate rings (3) done gradually.