WO1997028289A1

WO1997028289A1 - Iron-based spray material for producing a corrosion-resistant coating, process for producing the coating and use of the coat

Info

Publication number: WO1997028289A1
Application number: PCT/EP1997/000384
Authority: WO
Inventors: Jeffrey Luster; Horst Seifahrt; Gary Heath
Original assignee: Castolin S.A.
Priority date: 1996-02-01
Filing date: 1997-01-29
Publication date: 1997-08-07
Also published as: DE19603515C1

Abstract

A part exposed to hot gas corrosive stresses caused by sulphur, chlorine and other corrosive compounds is thermally sprayed with an iron-based material having the following composition: 10.0-33 wt.% Al; < 10.0 wt.% Cr; < 10.0 wt.% Ta, Ti and/or Zr; < 5.0 wt.% Nb and/or Mo; < 6.0 wt.% Si; < 2.0 wt.% Y, Hf and/or Ce; < 2.0 wt.% C; the remainder being iron. The sprayed material forms a corrosion-resistant coating of 0.1 to 2.0 mm thickness on the sprayed part.

Description

Iron-based spraying material for producing a corrosion-resistant coating. Manufacturing process for the coating and use of the layer

The invention relates to an iron-based spray material for producing a corrosion-resistant coating on a part - exposed to hot gas corrosion by sulfur, chlorine and other corrosion-triggering compounds - by means of thermal spraying. In addition, the invention includes a suitable method and uses of such a coating.

Known protective coatings against hot gas corrosion are produced by means of alloys based on nickel, cobalt or iron, which mainly contain chromium and aluminum as alloying elements.

For example, EP 0 652 297 AI describes an alloy with 12-18 atom% AI and 0.1-10 atom% Cr, which should have good thermal shock resistance and relatively good mechanical properties at temperatures of 800 ° C.

EP 0 625 585 A1 discloses an iron-based alloy with good oxidation resistance with the following composition: C <0.02; N <0.02; Si <1.0; Mn <1.0; Cr 15.0-26.0; AI 4.5 - 8.0; Sm 0.05-0.30; Zr 0.01-0.10 and Hf 0.005-0.10% by weight.

From WO 93/23 581 an iron aluminide with the composition 30.0-40.0 atom% Al; 0.01-0.4 atom% of Zr and 0.01-0.8 atom% of boron, the rest of Fe with corrosion-resistant properties are known. Knowing this state of the art, the inventor has set himself the goal of creating a further improved coating based on iron, which can be used in a variety of ways.

The teaching of the independent claims leads to the solution of this problem, the subclaims indicate favorable further developments.

According to the invention, a coating is applied by thermal spraying, the alloy composition of which is in% by weight as follows:

AI 10.0 to 33.0;

Cr <10.0;

Ti, Ta and / or Zr <10.0;

Nb and / or Mo <5.0;

Si <6.0;

Y, Hf and / or Ce <2.0;

C <2.0

Fe rest.

Each of the elements Cr, Si, C or each of the element groups Ti, Ta and / or Zr and Nb and / or Mo can be found in the alloy, even if only in a range of about 0.01% by weight %. The element group Y, Hf and / or Ce is also conceivable.

The application takes place according to further features of the invention by arc wire spraying, autogenous flame spraying, high-speed flame spraying or plasma flame spraying.

It has proven to be advantageous to use the spray material for this process with proportions of elements such as they are outlined in at least one of claims 7 to 21.

In tests, agglomerated or wire-shaped spray materials - such as cored wire - have proven their worth.

The coating according to the invention can be used with great success on surfaces of fin walls, valve seats, superheater pipes, heat exchangers or the like. against hot gas corrosion caused by sulfur, chlorine and other compounds.

Further advantages, features and details of the invention result from the following description of preferred exemplary embodiments.

EXAMPLE 1;

The relatively short service lives of superheater tubes in a coal dust combustion system for power generation, which are very heavily stressed by hot gas corrosion, should be extended by a thermally sprayed protective coating prior to installation in the boiler.

To carry out the work, the high-speed flame spraying process should be used with the following powdered spray material produced by agglomeration with a particle size distribution of 22.5 / 45 μm and the following composition in% by weight:

AI 22.0;

Cr 1, 5;

Ta, Ti, Zr 2, 0;

Nb 0.1;

Si 1.0;

C 0.5;

Fe rest

The preparation by blasting and the spraying process were carried out in the spraying workshop using a mechanical movement device for the spray gun and workpiece.

After checking the planned layer thickness of 0.3 to 0.4 mm of the sprayed-on layer, the superheater tubes were welded together and installed in the boiler. When the incineration plant was stopped for maintenance at a time when uncoated pipes had to be replaced, the coated surface of the treated pipes was checked for corrosion attack and the layer thickness of the coating. There was only a very small, flat attack on it. From the values found, it can be deduced that the service life of the pipes has been extended by about three times before they are replaced.

EXAMPLE 2;

A very strong corrosion was found on the fin wall of a waste incineration plant near the grate; the tube walls take part in the combustion process there. In these systems, further difficulties are caused by the high humidity of the combustion gases in this area, as a result of which the tube walls have to be repaired or partially replaced after a relatively short time.

An attempt should now be made to increase the service life by thermal spraying or to apply a layer which can be replaced without problems after wear; the costs should be reduced very significantly.

The autogenous flame spraying process was chosen to create the coatings in situ, and the following composition (in% by weight) as powdered spraying material:

AI 24.0

Cr 5.0

Ti 6.0,

Nb 0.01; Si 0.5;

Y 0.2; C 0.4;

Fe rest.

The grain size range was between 37/105 μm, the suggested layer thickness between 0.5 and 0.6 mm.

After blasting with corundum and subsequent spraying in situ, the layer thickness was measured and a visual inspection was carried out.

During the next regular overhaul of the system, it was found that the protective layer applied had a barely detectable attack.

EXAMPLE 3

During overhaul work on a stationary gas turbine, an increased corrosion attack was detected in the gas outlet duct, which had been triggered by incorrect operation.

An attempt should now be made to apply a sprayed layer by arc wire spraying. A filler wire with the calculated composition (in% by weight) of:

AI 18.0;

Cr 2.0;

Nb 0.01; Si 0.1;

C 0.1;

Fe rest.

The spray coating was done on site. The layer thickness to be repaired was up to 1.2 mm in some places. The The area to be coated had a total surface area of 0.5 m ³ .

After blasting and spraying, the sprayed-on layer was tested and the edges resulting from the spraying were reworked. The quality or the density of the layer could be determined at the processed points.

When checking after one year of inactivity, no defects were found in the applied layer.

EXAMPLE 4

On the seats of the exhaust valves of a slowly rotating marine diesel engine - and in the vicinity - during the overhaul, severe corrosion attacks, for example blow-throughs, were found, which had been triggered by a high sulfur content in the heavy fuel oil. Tests have now been carried out on these diesel engines with a plasma-sprayed coating. An agglomerated powdery material with a particle size distribution of 45/90 μm and a composition (in% by weight) of:

AI 15.0

Cr 8.0

Ta 0.5

Ti 1.0

Mon 0.5

Si 0.5

Ce 0.1

C 1.0

Fe rest. After the usual preparation by pre-blasting with broken steel gravel and final blasting with corundum, the coating was applied with a layer thickness of 0.2-0.4 mm by plasma flame spraying.

During the maintenance work after a running time of 5000 hours, no damage to the spray layer due to corrosion could be found either during the visual inspection or when measuring the layer thickness. A further check will now take place during the next maintenance work.

EXAMPLE 5;

In the suction ducts in front of the filter system of a thermal power plant, increased corrosion caused by sulfur and chlorine compounds in the hot gas was found in some places during the annual maintenance work - especially at the duct bends.

At the operator's request, a coating of the attacked areas should now be carried out using an autogenous wire flame spraying process.

A filler wire newly developed for corrosion-resistant coatings with the following composition (in% by weight) was used as the spray material for this work:

AI 23.0

Cr 7, 0

Ti, Ta, Zr 0.5

Mon 0.5

Si 0.1

C 1, 2

Fe rest For coating, the removed parts were subjected to the following work steps instead of the power plant:

(a) cleaning the corrosion products;

(b) preparation by blasting with steel gravel;

(c) spraying the protective layer.

After a standing time of 8000 hours, the spray coat was checked at the next maintenance stop. The layer was found to have very little attack. Nothing stood in the way of renewed use within 8000 hours.

EXAMPLE 6;

On a filter system of a chemical waste incineration plant, a strong corrosion attack was found on the inlet side for the hot gases after a relatively short running time of the plant (500 hours).

After removing the corroded parts, they should be protected by a coating applied using the high-speed flame spraying process. The particle size distribution of the wettable powder was between 5/22 μm and the chemical composition (in% by weight)

AI 22.0

Cr 1.0 Ti 0.5,

Nb 0.01;

Si 0.01;

C 0.3;

Fe rest. After the coating had been prepared and sprayed on, the parts were reinstalled in the filter system and the system started up. After several checks, a three-fold improvement in service life was also found here.

Claims

PATENT CLAIMS

1. Iron-based spray material for producing a corrosion-resistant coating on a hot corrosion load by means of part exposed to sulfur, chlorine and other corrosion-promoting compounds by means of thermal spraying, characterized by the following composition:

AI 10.0-33% by weight;

Cr <10.0 wt.

Ta, Ti and / or Zr <10.0% by weight of Nb and / or Mo <5.0% by weight

Si <6.0% by weight

Y, Hf and / or Ce <2.0% by weight

C <2.0% by weight

Fe rest

2. Spray material according to claim 1, characterized gekennzeich¬ net that it has an aluminum content between 15.0 to 25.0 wt .-%, preferably 18.0 to 22.0 wt .-%, has.

3. Spray material according to claim 1, characterized gekennzeich¬ net that it has a chromium content between 0.01 to 8.0 wt .-%, preferably 0.1 to 5.0 wt .-%.

4. Spray material according to claim 1, characterized gekennzeich¬ net that it has a silicon content between 0.01 to 4.0 wt .-%, preferably 0.1 to 3.0 wt .-%, has.

5. Spray material according to claim 1, characterized gekennzeich¬ net that it has a tantalum, titanium and zirconium content between 0.01 to 8.0 wt .-%, preferably 0.1 to 6.0 wt .-%.

6. Spray material according to claim 1, characterized by a tantalum content between 0.01 to 8.0 wt .-%, preferably 0.1 to 6.0 wt .-%.

7. Spray material according to claim 1, characterized by a titanium content between 0.01 to 8.0 wt .-%, preferably 0.1 to 6.0 wt .-%.

8. Spray material according to claim 1, characterized by a zirconium content between 0.01 to 8.0 wt .-%, preferably 0.1 to 6.0 wt .-%.

9. Spray material according to claim 1, characterized gekennzeich¬ net that it has a niobium and molybdenum content between 0.01 to 3.0 wt .-%, preferably 0.1 to 2.0 wt .-%.

10. Spray material according to claim 1, characterized by a niobium content between 0.01 to 3.0 wt .-%, preferably 0.1 to 2.0 wt .-%.

11. Spray material according to claim 1, characterized by a molybdenum content between 0.01 to 3.0 wt .-%, preferably 0.1 to 2.0 wt .-%.

12. Spray material according to claim 1, characterized gekennzeich¬ net that it has an yttrium, hafnium and cerium content between 0.01 to 1.0 wt .-%, preferably 0.1 to 0.5 wt .-%.

13. Spray material according to claim 1, characterized by an yttrium content between 0.01 to 1.0 wt .-%, preferably 0.05 to 0.5 wt .-%.

14. Spray material according to claim 1, characterized by a hafnium content between 0.01 to 1.0 wt .-%, preferably 0.05 to 0.5 wt .-%.

15. Spray material according to claim 1, characterized by a cerium content between 0.01 to 1.0% by weight, preferably 0.05 to 0.5% by weight.

16. Spray material according to claim 1, characterized gekennzeich¬ net that it has a carbon content between 0.01 to 1.5 wt .-%, preferably 0.05 to 1.0 wt .-%, has.

17. Spray material according to at least one of claims 1 to 16, characterized in that it is designed as a cored wire or as a filled tube wire.

18. Spray material according to at least one of claims 1 to 16, characterized in that it is an agglomerated powdered material.

19. A process for producing a corrosion-resistant coating on a hot gas corrosion-stressed part exposed to sulfur, chlorine and other corrosion-promoting compounds by means of thermal spraying of an iron-based material of the following composition:

AI 10.0 33% by weight Cr <10.0% by weight

Ta, Ti and / or Zr <10.0 wt. Nb and / or Mo <5.0 wt. - Si <6.0% by weight

Y, Hf and / or Ce <2.0% by weight

C <2.0% by weight

Fe rest

in a layer thickness between 0.1 and 2.0 mm.

20. The method according to claim 19, characterized in that the coating is applied in the arc wire spraying process.

21. The method according to claim 19, characterized in that the coating is applied by autogenous flame spraying.

22. The method according to claim 19, characterized in that the coating is applied by high-speed flame spraying.

23. The method according to claim 19, characterized in that the coating is applied by plasma flame spraying.

24. Use of a corrosion-resistant coating against hot gas corrosion, which is produced with a spray material according to at least one of claims 1 to 18 and / or according to the method of at least one of claims 19 to 23, on parts of large-scale combustion plants.

25. Use of a corrosion-resistant coating against hot gas corrosion, which is produced with a spray material according to at least one of claims 1 to 18 and / or according to the method of at least one of claims 19 to 23, on parts of refuse incineration plants. WO 97/28289

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26. Use of a corrosion-resistant coating against hot gas corrosion, which is with a spray material according to at least one of claims 1 to 18 and / or according to the method at least one of claims 19 to 23, on parts of thermal power plants for burning coal or oil.

27. Use of a corrosion-resistant coating against hot gas corrosion, which with a spray material according to at least one of claims 1 to 18 and / or according to the method at least one of claims 19 to 23 and / or with a spray material according to at least one of claims 6 to 21 , is manufactured on parts of engines or engines that are subject to high thermal loads.

28. Use of a corrosion-resistant coating against hot gas corrosion, which is produced with a spray material according to at least one of claims 1 to 18 and / or according to the method of at least one of claims 19 to 22, on highly stressed parts of extraction systems or filter systems.