CA1076812A - Process of cleaning an austenitic steel surface - Google Patents
Process of cleaning an austenitic steel surfaceInfo
- Publication number
- CA1076812A CA1076812A CA299,772A CA299772A CA1076812A CA 1076812 A CA1076812 A CA 1076812A CA 299772 A CA299772 A CA 299772A CA 1076812 A CA1076812 A CA 1076812A
- Authority
- CA
- Canada
- Prior art keywords
- corundum
- blasting
- mixture
- cleaning
- austenitic
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B24—GRINDING; POLISHING
- B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
- B24C1/00—Methods for use of abrasive blasting for producing particular effects; Use of auxiliary equipment in connection with such methods
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
- Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
- Cleaning By Liquid Or Steam (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
An austenitic steel surface is cleaned of ferritic contaminations and other impurities by blasting it with a wet abrasive mixture containing 40-90%, by volume, of corundum of an average grain size of 0.2 to 0.6 mm and of triangular habit. This wet abrasive mixture is accelerated and applied to the surface under a gas pressure of 2.5 to 5.5 atmospheres, 0.8 to 3 kg of corundum being applied per 100 cm2 of the surface to be cleaned.
Before the surface has dried, a rinsing liquid is applied thereto.
An austenitic steel surface is cleaned of ferritic contaminations and other impurities by blasting it with a wet abrasive mixture containing 40-90%, by volume, of corundum of an average grain size of 0.2 to 0.6 mm and of triangular habit. This wet abrasive mixture is accelerated and applied to the surface under a gas pressure of 2.5 to 5.5 atmospheres, 0.8 to 3 kg of corundum being applied per 100 cm2 of the surface to be cleaned.
Before the surface has dried, a rinsing liquid is applied thereto.
Description
` 1076812 This invention relates to a process of cleaning surfaces of austenitic materials, particularly to remove ferritic contaminations, by means of an abrasive mixture of corundum and a liquid blas~edonto the surface ~`
to be cleaned.
Austenitic chromium-nickel steels are known for their resistance to corrosion but, when subjected to corros;ive conditions, particularly for a pTolonged time, they may~suffer damage which may soon require a shutdown of a plant in view of the safety riskO On the other hand, a passive film forms on stainless steels and protects such materials against the corrosive action of numerous fluids, the passive film may be removed entirely or local-ly under certain conditions. Active regions are then formed, which may be dissolved at a high rate because they form local couples with the passive environment. The resulting forms of corrosion are typical only for stain-less steels and include particularly pitting and intercrystalline corrosion.
As these forms of corrosion on austenitic surfaces may be initiated by fer ritic iron, it is necessary to keep austenitic surfaces of workpieces as free as possible from ferritic iron and from firmly adherent deposits in order to avoid these forms of corrosionO This is usually accomplished by removing the surface layer, e.g. by grindingO To ensure a maximum life of such workpieces, their surface is cleaned once more after a certain time of use. For this purpose, a mixture of corundum and water is blasted onto the surface to be cleanedO The resulting efects range from washing to polishing and even to the removal of residues which are due to the use of the workpiece , and of slight ferritic contaminationsO On theother hand, the use of this known blasting process for treating surfaces of austenitic materials which have not been treated before does not result in the high surface finish and purity, required for vessels of nuclear reactors, for example.
It is an object of the invention to improve the process des-cribed above so that surfaces of austenitic materials are cleaned thoroughly of all impurities, such as grease, oil, ferritic contaminations, 1~7~ii81~
roll scale and scale which is due to a heat treatment~ without the need for prior machining.
It is a more particular object of this invention to prevent the corrosion of austenitic surfaces as much as possible by removing ferritic iron and adherent coatings therefrom without impacting the ferritic iron particles in the surface under excessive pressure, and rinsing the removed contaminations away before they have dried onto the surface.
It is a specific object of the present invention to obtain thor-ough cleaning of austenitic surfaces without the risk of hammering together surface cracks under high impact pressures of the abrasive cleaning mixtureO
This avoids the possibility of superficially closing surface cracks and thus permitting faulty work pieces to pass a quality test to which they are submitted after cleaning, superficially closed cracks being readily sub-ject to subsequent corrosion.
It is yet another specific object to avoid surface deformations during the cleaning process due to high impact pressures of the cleaning mixture on the surface and conversion of the austenite to martensite due thereto. Martensite would be subject to corrosion.
:
The above and other objects and advantages are accomplished in accordance with this invention by blasting a surface of an austenitic mate~i_ ~l with an abrasive mixture consisting, by volume, of 40~0 to 90~ of corun-dum and 601o to 101 of a liquid, the corundum having an average grain size of 0.2 to o.6 mm and the corundum being of triangular habit. By "being of triangular habit" I mean having a plurality of sharp edges. The abrasive ; blasting mixture is accelerated and applied to the austenitic material surface by a compressed gas under a low pressure in the range of 2.5 to 5.5 atmospheres, the gas pressure increasing in direct proportion to the liquid content in the mixture~ From o.8 to 3 kg of corundum is applied per 100 cm2 of the austenitic material surface to be cleaned, and a rinsing liquid is ' ~07681~
applied to the blasted surface before the surface has dried.
For most prevailing operating conditions and austenitic materials, the preferred corundum content in the abrasive blasting mixture is from 50% to 60%, by volume, in which case the preferred gas pressure is about 402 atmospheresO
The preferred average corundum grain si7e of about 0.4 mm and the preferred amount of corundum applied per 100 cm2 of surface is 2 kgo The preferred amount of rinsing liquid applied to the surface before it has dried is 1 to 10 liters per 100 cm of blasted surface. `
The technique applied in the blasting process is generally con-ventional, as exemplified in United States patent No. 2,605~59~, dated August 5, 1952. In such conventional surface cleaning methods, an abrasive blasting slurry is pumped to a blasting nozzle and compressed gas is deliver-ed to the nozzle in a direction substantially normal to the flow of the abrasive blasting slurry to cause substantial envelopment of the compressed gas by the slurry whereby the slurry is accelerated and delivered as a jet to the surface to be cleaned. In the process according to this inven~
tion, the blasting jet is directed substantially perpendicularly against the surface to be cleaned.
As the abrasive blasting mixture of the invention is accelerated ~`
by a compressed gas~ preferably compressed air~ at the indicated pressure, the action of the corundum particles is similar to the action in a dry ~`
blasting process because the liquid skin which encloses each corundum parti-cle is destroyed`!to a high degree by the compressed gas and can no longer dampen the impact of the corundum particle on the surface to be cleanedO
As a result, the surface of the austenitic material is thoroughly cleaned but ferritic iron particles are not forced into the surface of the material by the impact because of the relatively low pressure~ It will be under-stood that the gas pressure must be increased as the liquid content of ` 1al7683L2 the corundum-liquid mixture is increasedO
Whereas it has been found that the use of a gas under a pressure which is selected in dependence on the liquid content enables the surface to be cleaned to a degree which has not been achieved before by a mere blasting, the degree o~ purity which is required particularly in nuclear reactors is not achieved. The desired characteristics can be ensured only if the blasted surface is also rinsed with a liquid which is applied ;
to the surface before it has driedO This measure appears to prevent a re-adherence of the contaminations on the surface. It is not significant for the process whether'additional rinsing liquid is applied simultaneously with the cleaning blast or subsequently, provided that wet conditions are main-tained. The rinsing has the additional advantage that any residual ferritic iron on the cleaned surface becomes visible. The work piece may then be sub-jected to an additional cleaning treatment. The above indicated amoun~ of rinsing liquid will ensure adequate rinsing of the b~àsted surface.
Water may be used as the rinsing liquid and the liquid in the abrasive blasting mixture.
If surfaces having a particularly high finish are required, a cleaning pickling liquor, eOg. dilute nitric acid, is applied to the surface when the same has been blasted with the corundum-liquid mixture and before the surface is rinsed.
We have found that, by combining the specific abrasive blasting mixture, gas pressure and amount of corundum applied to the austenitic material surface to be cleaned, with rinsing the blasted surface before it has dried, excellent cleaning of the surface was obtained without any cracks in the surface being hammered closed by the impact of the blasting mixtureO
While it was predictable that a lowered impact pressure would prevent this phenomenon, it was unexpected that this lowered blasting pressure will -not reduce the effectiveness of the cleaningO However, extended experiments i 10~681Z
have shown that highly effective cleaning of austenitic material surfaces was obtained with the process herein disclosed and that the removal of sur-face impurities could even be enhanced above the extent obtained by dry blasting with this process although surface cracks were not closed thereby.
While we can only speculate about the physical reasons for this result at this time, we assume, without being bound by this theory, that the relatively high corundum content in the wet blasting mixture produces a multiplicity of small chiseling impacts on the surface to clean the same thoroughly. The corundum particles thus chisel the ferritic iron and other impurities out of the austenitic material surface without, however, causing and substantial deformation thereof.
This effect requires the combination of all the steps in the process, including the shape and si~e of the corundum grains. They must be of triangular habit, i.e. have a plurality of sharp edges, to enable them to chisel the undesirable impurities out of the austenitic surface without substantially deforming it. Round particles, or particles with rounded edges, would not serve this purpose but would tend to hammer cracks in the surface closed.
In view of the assumed operation of the corundum grains of trian- ;
- 20 gular habit as a multiplicity of tiny chisels impacted upon the surface to be cleaned, it could be expected that the particles would be smashed or their sharp edges would be rounded after short use so that a repeated use of the corundum in this cleaning process would not be possible, thus making it uneconomical. Unexpectedly, we have found this not to be the case and that up to about 50 cleanings can be effectively carried out with this pro-cess with the same corundum chargeO Used blasting material may readily be cleaned in a centrifugal separator and can then be reused for blastingO
The ferritic contam:inations remaining on the blasting material are not significant~
~076812 The amount of impurities abraded from the surface depends on the amount of corundum applied thereto within the indicated range. We have found that blasting the abrasive mixture at a rate of 1 to 2 kg/100 cm2 was required when a corundumwater mixture containing 40% corundum was used under a gas pressure of 6 atmospheres to remove scale which had been formed by a heat treatment. Blasting material at a rate of 2 to 3 kg/100 cm2 was required to remove roll scale. All specimens inspected were free of ferrites when material had been removed from the surface by blasting to a depth of about 10 to 15 microns. Blasting material at a rate of about : :~
1 to 2 kg per 100 cm2 and about 6 kg/min. was required to remove impurities I~ ;
consisting of grease oil, ferrite dust, and scale formed by annealing. The blast cone had a diameter between 20 and 200 mm on the blasted surface.
The blasting noz71es used to discharge the abrasive mixture onto the austenitic surface may be spaced at a distance of 50 to 500 mm, preferably about 200 mm, the blasting cones at ~he point of impact on the surface having diameters of 20 to 150 mm, preferably about 50 to 70 mm. ;
~.~
':.
.
to be cleaned.
Austenitic chromium-nickel steels are known for their resistance to corrosion but, when subjected to corros;ive conditions, particularly for a pTolonged time, they may~suffer damage which may soon require a shutdown of a plant in view of the safety riskO On the other hand, a passive film forms on stainless steels and protects such materials against the corrosive action of numerous fluids, the passive film may be removed entirely or local-ly under certain conditions. Active regions are then formed, which may be dissolved at a high rate because they form local couples with the passive environment. The resulting forms of corrosion are typical only for stain-less steels and include particularly pitting and intercrystalline corrosion.
As these forms of corrosion on austenitic surfaces may be initiated by fer ritic iron, it is necessary to keep austenitic surfaces of workpieces as free as possible from ferritic iron and from firmly adherent deposits in order to avoid these forms of corrosionO This is usually accomplished by removing the surface layer, e.g. by grindingO To ensure a maximum life of such workpieces, their surface is cleaned once more after a certain time of use. For this purpose, a mixture of corundum and water is blasted onto the surface to be cleanedO The resulting efects range from washing to polishing and even to the removal of residues which are due to the use of the workpiece , and of slight ferritic contaminationsO On theother hand, the use of this known blasting process for treating surfaces of austenitic materials which have not been treated before does not result in the high surface finish and purity, required for vessels of nuclear reactors, for example.
It is an object of the invention to improve the process des-cribed above so that surfaces of austenitic materials are cleaned thoroughly of all impurities, such as grease, oil, ferritic contaminations, 1~7~ii81~
roll scale and scale which is due to a heat treatment~ without the need for prior machining.
It is a more particular object of this invention to prevent the corrosion of austenitic surfaces as much as possible by removing ferritic iron and adherent coatings therefrom without impacting the ferritic iron particles in the surface under excessive pressure, and rinsing the removed contaminations away before they have dried onto the surface.
It is a specific object of the present invention to obtain thor-ough cleaning of austenitic surfaces without the risk of hammering together surface cracks under high impact pressures of the abrasive cleaning mixtureO
This avoids the possibility of superficially closing surface cracks and thus permitting faulty work pieces to pass a quality test to which they are submitted after cleaning, superficially closed cracks being readily sub-ject to subsequent corrosion.
It is yet another specific object to avoid surface deformations during the cleaning process due to high impact pressures of the cleaning mixture on the surface and conversion of the austenite to martensite due thereto. Martensite would be subject to corrosion.
:
The above and other objects and advantages are accomplished in accordance with this invention by blasting a surface of an austenitic mate~i_ ~l with an abrasive mixture consisting, by volume, of 40~0 to 90~ of corun-dum and 601o to 101 of a liquid, the corundum having an average grain size of 0.2 to o.6 mm and the corundum being of triangular habit. By "being of triangular habit" I mean having a plurality of sharp edges. The abrasive ; blasting mixture is accelerated and applied to the austenitic material surface by a compressed gas under a low pressure in the range of 2.5 to 5.5 atmospheres, the gas pressure increasing in direct proportion to the liquid content in the mixture~ From o.8 to 3 kg of corundum is applied per 100 cm2 of the austenitic material surface to be cleaned, and a rinsing liquid is ' ~07681~
applied to the blasted surface before the surface has dried.
For most prevailing operating conditions and austenitic materials, the preferred corundum content in the abrasive blasting mixture is from 50% to 60%, by volume, in which case the preferred gas pressure is about 402 atmospheresO
The preferred average corundum grain si7e of about 0.4 mm and the preferred amount of corundum applied per 100 cm2 of surface is 2 kgo The preferred amount of rinsing liquid applied to the surface before it has dried is 1 to 10 liters per 100 cm of blasted surface. `
The technique applied in the blasting process is generally con-ventional, as exemplified in United States patent No. 2,605~59~, dated August 5, 1952. In such conventional surface cleaning methods, an abrasive blasting slurry is pumped to a blasting nozzle and compressed gas is deliver-ed to the nozzle in a direction substantially normal to the flow of the abrasive blasting slurry to cause substantial envelopment of the compressed gas by the slurry whereby the slurry is accelerated and delivered as a jet to the surface to be cleaned. In the process according to this inven~
tion, the blasting jet is directed substantially perpendicularly against the surface to be cleaned.
As the abrasive blasting mixture of the invention is accelerated ~`
by a compressed gas~ preferably compressed air~ at the indicated pressure, the action of the corundum particles is similar to the action in a dry ~`
blasting process because the liquid skin which encloses each corundum parti-cle is destroyed`!to a high degree by the compressed gas and can no longer dampen the impact of the corundum particle on the surface to be cleanedO
As a result, the surface of the austenitic material is thoroughly cleaned but ferritic iron particles are not forced into the surface of the material by the impact because of the relatively low pressure~ It will be under-stood that the gas pressure must be increased as the liquid content of ` 1al7683L2 the corundum-liquid mixture is increasedO
Whereas it has been found that the use of a gas under a pressure which is selected in dependence on the liquid content enables the surface to be cleaned to a degree which has not been achieved before by a mere blasting, the degree o~ purity which is required particularly in nuclear reactors is not achieved. The desired characteristics can be ensured only if the blasted surface is also rinsed with a liquid which is applied ;
to the surface before it has driedO This measure appears to prevent a re-adherence of the contaminations on the surface. It is not significant for the process whether'additional rinsing liquid is applied simultaneously with the cleaning blast or subsequently, provided that wet conditions are main-tained. The rinsing has the additional advantage that any residual ferritic iron on the cleaned surface becomes visible. The work piece may then be sub-jected to an additional cleaning treatment. The above indicated amoun~ of rinsing liquid will ensure adequate rinsing of the b~àsted surface.
Water may be used as the rinsing liquid and the liquid in the abrasive blasting mixture.
If surfaces having a particularly high finish are required, a cleaning pickling liquor, eOg. dilute nitric acid, is applied to the surface when the same has been blasted with the corundum-liquid mixture and before the surface is rinsed.
We have found that, by combining the specific abrasive blasting mixture, gas pressure and amount of corundum applied to the austenitic material surface to be cleaned, with rinsing the blasted surface before it has dried, excellent cleaning of the surface was obtained without any cracks in the surface being hammered closed by the impact of the blasting mixtureO
While it was predictable that a lowered impact pressure would prevent this phenomenon, it was unexpected that this lowered blasting pressure will -not reduce the effectiveness of the cleaningO However, extended experiments i 10~681Z
have shown that highly effective cleaning of austenitic material surfaces was obtained with the process herein disclosed and that the removal of sur-face impurities could even be enhanced above the extent obtained by dry blasting with this process although surface cracks were not closed thereby.
While we can only speculate about the physical reasons for this result at this time, we assume, without being bound by this theory, that the relatively high corundum content in the wet blasting mixture produces a multiplicity of small chiseling impacts on the surface to clean the same thoroughly. The corundum particles thus chisel the ferritic iron and other impurities out of the austenitic material surface without, however, causing and substantial deformation thereof.
This effect requires the combination of all the steps in the process, including the shape and si~e of the corundum grains. They must be of triangular habit, i.e. have a plurality of sharp edges, to enable them to chisel the undesirable impurities out of the austenitic surface without substantially deforming it. Round particles, or particles with rounded edges, would not serve this purpose but would tend to hammer cracks in the surface closed.
In view of the assumed operation of the corundum grains of trian- ;
- 20 gular habit as a multiplicity of tiny chisels impacted upon the surface to be cleaned, it could be expected that the particles would be smashed or their sharp edges would be rounded after short use so that a repeated use of the corundum in this cleaning process would not be possible, thus making it uneconomical. Unexpectedly, we have found this not to be the case and that up to about 50 cleanings can be effectively carried out with this pro-cess with the same corundum chargeO Used blasting material may readily be cleaned in a centrifugal separator and can then be reused for blastingO
The ferritic contam:inations remaining on the blasting material are not significant~
~076812 The amount of impurities abraded from the surface depends on the amount of corundum applied thereto within the indicated range. We have found that blasting the abrasive mixture at a rate of 1 to 2 kg/100 cm2 was required when a corundumwater mixture containing 40% corundum was used under a gas pressure of 6 atmospheres to remove scale which had been formed by a heat treatment. Blasting material at a rate of 2 to 3 kg/100 cm2 was required to remove roll scale. All specimens inspected were free of ferrites when material had been removed from the surface by blasting to a depth of about 10 to 15 microns. Blasting material at a rate of about : :~
1 to 2 kg per 100 cm2 and about 6 kg/min. was required to remove impurities I~ ;
consisting of grease oil, ferrite dust, and scale formed by annealing. The blast cone had a diameter between 20 and 200 mm on the blasted surface.
The blasting noz71es used to discharge the abrasive mixture onto the austenitic surface may be spaced at a distance of 50 to 500 mm, preferably about 200 mm, the blasting cones at ~he point of impact on the surface having diameters of 20 to 150 mm, preferably about 50 to 70 mm. ;
~.~
':.
.
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process of cleaning a surface of an austenitic material, which comprises the steps of blasting the surface with an abrasive mixture consist-ing, by volume, of 40% to 90% of corundum and 60% to 10% of a liquid, the corundum having an average grain size of 0.2 to 0.6 mm and the corundum grains being of triangular habit, the abrasive blasting mixture being accelerated and applied to the austenitic material surface by a compressed gas under a pressure in the range of 2.5 to 5.5 atmospheres, the gas pressure increasing in direct proportion to the liquid content in the mixture, and 0.8 to 3 kg of corundum being applied per 100 cm2 of the austenitic steel surface to be cleaned; and applying a rinsing liquid to the blasted surface before the surface has dried.
2. The cleaning process defined in claim 1, wherein the abrasive blasting mixture contains 50% to 60%, by volume, of corundum.
3. The cleaning process defined in claim 2, wherein the gas pressure is about 4.2 atmospheres.
4. The cleaning process defined in claim 1, or 2, or 3, wherein the average grain size of the corundum is about 0.4 mm and about 2 kg of corundum is applied per 100 cm2 of the surface to be cleaned.
5. The cleaning process defined in claim 1, or 2, or 3, wherein 1 to 10 liters of the rinsing liquid is applied per 100 cm of the blasted surface.
6. The cleaning process defined in claim 1, or 2, or 3, wherein the austenitic steel surface contains ferritic contaminations and the contamina-tions are removed by blasting the surface and applying the rinsing liquid thereto.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AT385477A AT347809B (en) | 1977-06-01 | 1977-06-01 | PROCEDURE FOR CLEANING AUSTENITIC MATERIAL SURFACES, IN PARTICULAR FERRITIC CONTAMINATION |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1076812A true CA1076812A (en) | 1980-05-06 |
Family
ID=3556338
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA299,772A Expired CA1076812A (en) | 1977-06-01 | 1978-03-28 | Process of cleaning an austenitic steel surface |
Country Status (6)
| Country | Link |
|---|---|
| AT (1) | AT347809B (en) |
| CA (1) | CA1076812A (en) |
| CH (1) | CH609604A5 (en) |
| GB (1) | GB1562475A (en) |
| NL (1) | NL168436C (en) |
| SE (1) | SE7714197L (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4287689A (en) * | 1979-10-30 | 1981-09-08 | Rca Corporation | Method for improving the quality of low frequency output of a video disc pickup stylus |
-
1977
- 1977-06-01 AT AT385477A patent/AT347809B/en not_active IP Right Cessation
- 1977-12-08 CH CH1503977A patent/CH609604A5/en not_active IP Right Cessation
- 1977-12-14 NL NL7713818A patent/NL168436C/en not_active IP Right Cessation
- 1977-12-14 SE SE7714197A patent/SE7714197L/en not_active Application Discontinuation
-
1978
- 1978-02-07 GB GB489578A patent/GB1562475A/en not_active Expired
- 1978-03-28 CA CA299,772A patent/CA1076812A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| SE7714197L (en) | 1978-12-02 |
| CH609604A5 (en) | 1979-03-15 |
| ATA385477A (en) | 1978-05-15 |
| GB1562475A (en) | 1980-03-12 |
| AT347809B (en) | 1979-01-10 |
| NL168436C (en) | 1982-04-16 |
| NL168436B (en) | 1981-11-16 |
| NL7713818A (en) | 1978-12-05 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |