EP1985919B1 - Surface-blasted steam generator parts or power plant components - Google Patents

Description

The invention is directed to a steam generator component or a steam generator assembly or a power plant component which at least substantially consists of an alloyed, in particular chromium-containing, material and at least partially, in particular essentially, treated by surface blasting (shot-peening / shot-blasting) is. Furthermore, the invention is directed to a method for producing a steam generator component or assembly or power plant component, which / essentially consists of an alloyed, in particular chromium-containing material in which a component or assembly surface or component surface, in particular a pipe inner surface by means of surface jets (shot -peening / shot-blasting).

Steam generator components or power plant components are particularly exposed to the oxidizing conditions of the steam with which they come into contact, especially on the steam side of steam generators of power plants. Superheater and / or reheater stages of steam generators are therefore already today partially or substantially made of austenitic materials, in particular austenitic steels, with a chromium content of 18 wt .-%, wherein the austenitic material for improving and the oxidation behavior of these materials by surface blasting (shot-peening / shot-blasting) is treated. In particular in Japanese power plants with steam temperatures around 600 ° C such treated materials are used.

In surface-blasting or shot-peening / shot-blasting processes, the area exposed to treatment particles or blast particles, in the case of pipelines usually the inner surface of the respective pipe, is deformed, which causes a migration, i. the diffusion of chromium from the parent material, i. the matrix to which the treated surface benefits and occurs. As a result, a thin, chromium-rich layer forms on the treated surface, which counteracts the growth of epitaxial and topotactic layers. During surface blasting (shot-peening / shot-blasting) blasting material of the same type is blown against the surface to be treated. This promotes the diffusion of chromium from the matrix of the base material into this layer and thus the oxidation resistance of this layer.

In the chromium-rich austenitic steels used hitherto in the superheater and reheater zone, with an average chromium content of ≥18% by weight, a deformation of the treated inner pipe surface of the respective material structure is up to a depth of 100 by means of the shot-peening or shot-blasting method μm, which leads to the formation of a corresponding chromium-rich layer. From the depth of the microstructure (matrix), chromium diffuses into this treated layer and enriches it with chromium. On this chromium-rich layer, the growth of spinel and magnetite layers under the conditions prevailing in the respective power plant components compared to untreated surfaces is much slower and thus on the steam side, with which these surfaces are related, the oxidation behavior of the material used and treated improved.

In power plant construction, the tendency is now to build power plants with steam temperatures of over 600 ° C and even ≥ 700 ° C are operated. At these high steam temperatures, the problem of steam-side oxidation of power plant components or steam generator components is increasingly becoming the focus of attention. In particular, there is also the problem that the chromium-containing steels used hitherto have an austenitic structure in the case of martensitic or surface-treated chromium contents of ≥18% by weight and are no longer sufficiently resistant to oxidation or extremely high in the steam temperatures expected during operation of the power plants of this new generation expensive material use.

The invention is therefore based on the object to provide a solution with which materials are made available to steam generators with outlet temperatures of ≥ 700 ° C in power plant components, in particular steam generator components, sufficient strength, especially creep rupture strength, and sufficient corrosion resistance and oxidation resistance exhibit.

In a steam generator component or a steam generator assembly or a power plant component of the type described, this object is achieved with the features of claim 1. In a method for producing a steam generator component or assembly or power plant component which essentially consists of an alloyed, in particular chromium-containing material, in which a component or assembly surface or component surface, in particular a pipe inner surface, by means of surface-blasting (shot-peening / shot-blasting) blasting), this object is achieved according to the invention with the features of claim 12. Advantageous embodiments emerge from the respective subclaims.

The invention is based on the recognition that it is possible in the steam generators of new-generation power plants, the outlet temperatures of over 600 ° C, in particular ≥ 700 ° C, have significantly reduced their chromium content compared to the steel grades used previously Use steels or steel materials when surface areas exposed to oxidizing conditions, since they are essentially pipelines, ie the inner surfaces of the corresponding tubes or tubular bodies, are treated by shot-peening / shot-blasting and then into the power plant, in particular the steam generator, to be installed. This makes it possible to use steel grades that are on the one hand relatively inexpensive, but on the other hand also required for the now high temperatures, sufficient strength and the corresponding strength behavior and the necessary oxidation but also have corrosion resistance. The necessary oxidation resistance at these temperatures can now be achieved by the fact that the water; Liquid or steam leading side - the steam side - of the respective component or the respective assembly or the respective power plant component, in particular the inner surface of tubular bodies, by means of surface-blasting (shot-peening / shot-blasting) is treated. In this case, then accumulates in the matrix of the respective material, in particular steel material, existing chromium, in particular by forming a Cr ₂ O ₃ layer on the treated (outer) surface of the material. Experience has shown that by means of the surface-beam method (shot-peening / shot-blasting) a chromium enrichment in the correspondingly treated layer by about 50% is possible. It is thus possible by means of the method according to the invention, for example Steel grades having an average chromium content of 9 wt .-% with an outside layer on the material to provide, usually on the inner surface of a tube, which then - after the treatment - an average chromium content of about 12 wt. % and thus is sufficiently resistant to oxidation even under the conditions of new power plant generations at steam outlet temperatures of ≥ 700 ° C.

Surprisingly, contrary to other expert expectations, it has been found that this improvement in the oxidation behavior or the achievement of sufficient oxidation resistance on the steam side is not associated with a simultaneous deterioration of the high temperature corrosion behavior of the treated steam generator component or the respectively treated steam generator component group or the respective power plant component on the flue gas side. The application of surface blasting or shot-peening / shot-blasting to lower chromium steels, ie steels having a chromium content of ≤ 18% by weight, was the general fear of the art that the use of this process would result in unfavorable chromium distribution could result in the treated material. The enriched in the steam-side or treated layer chromium in the form of chromium oxides is diffused from the base matrix, ie the main body of the material in this layer. Since no chromium is supplied to the material from the outside, this diffusion leads to this chromium or these chrome particles no longer being present elsewhere in the material. It was now to be feared that this could lead to a reduced chromium content on the side of the respective component opposite the treated side, ie on the outside of the pipe for a pipe. There at Power plant components, the outside of these pipes is exposed to the corrosive and aggressive conditions flowing past the flue gas streams, they must have a sufficient corrosion behavior, ie a sufficient corrosion resistance. For this purpose, the surfaces exposed to the flue gas must also have a certain chromium content. If the chromium content in these surfaces decreases, this reduces the corrosion resistance of the component. It was therefore feared that while treating the inner surface of the pipe by means of surface peening (shot-peening / shot-blasting), an increased or sufficient oxidation resistance could be achieved, but a reduced or reduced corrosion resistance would occur on the opposite outer surface.

Furthermore, it was feared that the welding behavior of the material on its outer surface and its inner surface or its non-surface-treated and its surface-treated side would be different due to the induced unequal distribution of the chromium content, so that was expected when welding these components with difficulties.

The document JP 2005298878A shows accordingly a surface blasting method in which is dispensed with the diffusion effect of the material surface chromium from the outside.

While these problems are of less importance for steel grades with a chromium content of ≥ 18% by weight, because there is a sufficient amount of chromium to ensure the necessary steam-side oxidation resistance and flue gas-side corrosion resistance even in problematic cases, because of the relatively high chromium content, There were fears in the art that this could no longer be guaranteed with low-alloy steels, ie steels with a significantly lower chromium content. In particular, the aspect still comes into play here, that as a further component, the sufficient creep rupture strength of the material must be guaranteed.

In particular, the high temperature corrosion resistance, ie the corrosion resistance on the flue gas side of a steam generator with chromium contents below 18 wt .-% shows an exponential worsening. Investigations have shown that the material removal in the form of a weight loss in mg / cm ² and thus the reduction of the corrosion resistance of the material at chromium contents below 20 wt .-%, especially below 18 wt .-%, increases very strong. In particular, the high temperature corrosion increases with increasing temperature, ie increasing material temperature, so that the high temperature corrosion resistance, especially in the power plants of the next generation, which will work with significantly higher steam outlet temperatures, this problem is given particular weight. Measures that could bring about a reduction in the high-temperature corrosion behavior of a material are therefore not regarded as realistically feasible measures.

Surprisingly, however, it has now been found that the method according to the invention leads to a sufficient resistance to oxidation of the components / assemblies / components without impairing the corrosion resistance.

Surprisingly, it has been found that, in particular, materials which have a ferritic microstructure with an average chromium content of ≦ 8% by weight or a martensitic microstructure with an average chromium content of ≦ 14% by weight, in particular in the range from 9 to 12% by weight. -% have, surface blasted for use as a steam generator component or steam generator assembly or power plant component even with the loads at Exit temperatures of ≥ 600 ° C, in particular ≥ 700 ° C occur, can be used or such structures can be selected for surface blasting.

In particular, this application possibility arises when the corresponding components or surfaces by means of surface blasting with a material used for the same material or the same structure and / or material or a material is treated with respect to the material higher chromium content or what the invention provides in an embodiment.

With the invention it is possible to equip steam generators with high steam parameters, in particular steam generators with steam outlet temperatures of ≥ 700 ° C., with steam generator components or assemblies or power plant components which are sufficiently temperature-stable and, in addition, sufficiently resistant to corrosion and sufficiently resistant to oxidation. In particular, the invention also steels with ferritic or martensitic structure can be used, which do not have a high chromium content. For example, martensitic steels with the material designation T91 / P91 or T92 / P92 are suitable steels which, in addition to their strength, have the necessary corrosion resistance and oxidation resistance to atmospheres and environments prevailing in steam generators with outlet temperatures of ≥ 700 ° C. in addition to their strength. From these materials, a variety of steam generator components and power plant components can be produced, such as membrane walls, spiral wound steam generator walls, connecting lines, steam and water bottles, injection coolers, heating surfaces, collectors and Manifolds, support tube bulkheads, support tubes, transition pieces, etc. In particular highly stressed header and piping as well as membrane walls of new 700 ° C power plants with steam outlet temperatures of ≥ 700 ° C can be produced with the steam generator components according to the invention. As with the steels used hitherto at lower steam outlet temperatures, the use of the shot-peening or shot-blasting method or surface blasting results in the growth of a spinel or magnetite layer on the correspondingly treated surface, ie, cold-worked and plastically deformed by surface blasting and due to the resulting as a result of the treatment, having a relation to the base material matrix increased chromium content having surface much slower compared to untreated surfaces. Thus, it is only necessary to select high temperature steels for this new generation power plant type, which are then rendered oxidation resistant by surface blasting or shot-peening / shotblasting treatment on the vapor side surface.

Martensitic steels having an average chromium content of 9-12% by weight have proven to be particularly suitable materials. The terms ferritic or martensitic refer to the respective formed material structure.

The surface blasting or shot peening / shot blasting is carried out in particular under such conditions or conditions are set such that the treated component or assembly surface or power plant component surface up to a material depth of 200 μm, preferably up to 100 μm, is or can be influenced in their microstructure and / or is or will be influenced. As part of this layer thickness of up to 200 microns or up to 100 microns, the desired Chromanreicherung forms. Due to the thin layer thickness of this structural layer exposed to the surface structure, the solidification resulting in this layer is negligible due to the small layer thickness in relation to the wall thickness of the respective component or component group or the respective component component, so that the strength of the treated component or the treated component group or Power plant component remains essentially unchanged. The usually in the foreground strength-enhancing effect of shot peening plays in the surface rays (shot-peening / shot-blasting) according to the invention, not at all, he should rather play no role. The only decisive factor is the possibility resulting from the use of this method of influencing the outer layer or an outer layer region of the respective workpiece or component (for example a pipe inner surface) such that an enrichment with chromium takes place in this region.

The conditions of the surface blasting or shot-peening / shot-blasting are adjusted so that in the treated surface or the treated layer an increase in strength in the range of +50 - +150 HV, in particular of about +100 HV based on Sets the original hardness of the material / material. The surface blasting is not only irradiated with the same material or the same material or the same material as the treated material or with a material with a higher chromium content than the base material, but it can also ceramic blown materials, glass beads or the like can be used. In particular, however, is the same material or the same material or the same material material used. For this purpose, for example, a wire of the identical material chopped finely, optionally rounded off at its ends and then blown with the aid of a fluid jet on the material surface to be treated.

The surface blasting or shot-peening / shot-blasting is usually carried out with a jet pipe with an end-side 360 ° jet nozzle, so that on the inside blasting material passed through the pipe and then brought through the blasting nozzle to the inner surface of pipes or of the respectively treated pipe can be. This works with a volume flow of up to 9 m ³ / min and a maximum blowing pressure of 0.7 MPa. In this case, the jet nozzle is passed through the pipe to be treated at a nozzle feed rate of 100-800 mm / min. The "shot-blasting" effect is to form on the treated side of the material a layer cold-formed by shot-blasting or surface blasting. Below this cold-formed layer is located in the matrix of the base material, a diffusion zone. From the diffusion zone, chromium diffuses through the cold-formed layer and forms on the outside, ie above the cold-formed layer, an oxide layer, in particular a Cr ₂ O ₃ layer, above which the topotactic and epitaxial layers are formed later in the operating state. However, the Cr ₂ O ₃ layer reduces Fe diffusion and reduces magnetite growth.

Claims (15)

1. Steam-generator part or assembly or power-station component, consisting at least substantially of an alloyed, chromium-containing construction material which consists at least in part, in particular substantially, of a construction material treated by means of surface blasting, characterised in that said part, assembly or component consists at least substantially of a construction material which has a ferritic structure having a mean chromium content of ≤ 8 % by weight or a martensitic structure having a mean chromium content of ≤ 14 % by weight, and at least one surface of said part, assembly or component comprising such a structure is treated at least in part by means of surface blasting, the conditions for the surface blasting being set such that the structure of the treated surface of the part, assembly or component is influenced down to a material depth of 200 µm, preferably to 100 µm, and such that there exists a strain-hardened or cold-worked layer and a diffusion zone which is formed in the matrix below the strain-hardened or cold-worked layer.
2. Steam-generator part or assembly or power-station component according to claim 1, characterised in that the surface of the part, assembly or component is treated by means of surface blasting using a material of the same type or same structure and/or same composition as the construction material, or using a material which has a higher chromium content than the construction material.
3. Steam-generator part or assembly or power-station component according to either claim 1 or claim 2, characterised in that the surface of the part, assembly or component is a constituent of a part or an assembly or a power-station component which is installed on the steam side of a steam generator, the steam outlet temperature of which is ≥ 600 °C, in particular ≥ 700 °C.
4. Steam-generator part or assembly or power-station component according to any of the preceding claims, characterised in that said part, assembly or component is or forms a constituent of an effective heating surface, a membrane wall, a spiral-wound steam-generator wall, a connecting duct, a steam separator, a water bottle, an injection cooler, an effective heating surface, a collector, a distributor, a supporting-pipe partition, a supporting pipe, a connecting piece or a steam generator of a power plant.
5. Steam-generator part or assembly or power-station component according to any of the preceding claims, characterised in that the construction material is a ferritic or a martensitic steel.
6. Steam-generator part or assembly or power-station component according to any of the preceding claims, characterised in that the construction material is a material having a mean chromium content of ≤ 9 % by weight.
7. Steam-generator part or assembly or power-station component according to any claims 1 to 5, characterised in that the construction material has a martensitic structure having a mean chromium content in the range from 9 to 12 % by weight.
8. Steam-generator part or assembly or power-station component according to any of the preceding claims, characterised in that the construction material is a martensitic material with the specification T91, P91, T92 or P92.
9. Steam-generator part or assembly or power-station component according to any of the preceding claims, characterised in that the conditions for the surface blasting are set such that the treated surface of the part, assembly or component has an increased hardness of from + 50 to + 150 HV, in particular + 90 to + 110 HV, in relation to the matrix of the construction material.
10. Steam-generator part or assembly or power-station component according to any of the preceding claims, characterised in that the conditions for the surface blasting are set such that the strength of the treated part, assembly or power-station component remains substantially the same.
11. Steam-generator part or assembly or power-station component according to any of the preceding claims, characterised in that the surface of the part, assembly or component treated by means of surface blasting is the inner surface of a pipe.
12. Method for producing a steam-generator part or assembly or power-station component which is composed substantially of an alloyed, chromium-containing construction material, in which a surface of a part, assembly or component, in particular an inner surface of a pipe, is treated by means of surface blasting, characterised in that, to carry out the surface blasting, a surface of a part, assembly or component is selected which has a ferritic structure having a mean chromium content of ≤ 8 % by weight or a martensitic structure having a mean chromium content of ≤ 14 % by weight, and the conditions for the surface blasting are set such that the structure of the treated surface of the part, assembly or component is influenced down to a material depth of 200 µm, preferably to 100 µm, and such that there exists a strain-hardened or cold-worked layer enriched with chromium and a diffusion zone which is formed in the matrix below the strain-hardened or cold-worked layer.
13. Method according to claim 12, characterised in that the surface blasting is performed using a material of the same type or same structure and/or same composition as the structure of the surface-blasted surface, or is performed using a material having a chromium content higher than that of the construction material of the surface.
14. Method according to either claim 12 or claim 13, characterised in that a surface of a part, assembly or component is selected which has a ferritic structure having a mean chromium content in the range from 9 to 12 % by weight.
15. Method according to any of claims 12 to 14, characterised in that the conditions for the surface blasting are set such that the hardness of the treated surface of the part, assembly or component is increased to a hardness of from + 50 to + 150 HV, in particular + 90 to + 110 HV, in relation to the matrix of the construction material.