1、I .I c BSI M*37 70 = Lb2Llbb9 00993b 4 I M. 37, October, 3970 UDC 629.7 : 620.183.2 INCORPORATED BY ROYAL CHARTER Telephone: 01-629 9ooo BRITISH STANDARDS INSTITUTION 2 PARK STREET LONDON WlA 2BS Telegrams: STANDARDS LONDON W1 BRITISH STANDARD : AEROSPACE SERIES METHOD FOR THE ETCH INSPECTION OF MET
2、ALLIC MATERIALS AND COMPONENTS CONTENTS Page Page Foreword . .1 3. EQUIPMENT AND SPECIAL CONSIDERATIONS 3.1 Processing equipment . -3 3.2 Viewing aids . .3 3.3 In-situ applications . -3 1.1 scope . - 2 4.1 Eyesight , .3 1.2 Purpose of etch inspection . 2 4.2 Fatigue . .3 1.3 General considerations.
3、- 2 4.3 Viewing conditions . .4 1.4 Approvals . - 2 4.4 safety requirements . .4 METHOD 4. PERSONNEL 1. GENERAL APPENDICES A. Etch inspection technique sheet . .4 2. PROCEDURE 2.1 Introduction . . 2 B. Typical process solutions for the etching of 2.2 Operations . .2 various materials . .6 FOREWORD T
4、his British Standard, prepared under the authority of the Aerospace Industry Standards Committee, is one of a series on the nondestructive testing and inspection of aerospace materials, components and structures. Other standards in this series will cover radiographic, ultrasonic, magnetic particle a
5、nd penetrant methods. The standard is intended to provide a method for carrying out etch inspection of metallic materials and components used in the aerospace industry. Consideration may subsequently be given to the preparation of further standards describing specific applications of etch inspection
6、 techniques. British Standards: This standard makes reference to the foiiowing: BS 1134. Centre-line-average height method for the assessment of surface texture. BS 4000. Sizes of papers and boards. DEF 151. Anodizing of aluminium and aluminium alloys. DEF 162. The treatment and protection of very h
7、igh tensile steels. DEF 2331. Protective PX-1 dyed and undyed. DTD 901. Process spiication-cleaning and preparation of metal surfaces. *Ministry of Defence Specications: *Ministry of Technology: Obtainable fromH.M.S.0. Price 10s (50) net /- . .- M. 37, October, 1970 METHOD 1. GENERAL 1.1 SCOPE 1.1.1
8、 This British Standard describes a method for carry- ing out etch inspection of metallic materials and com- ponents and describes some of the widely accepted etching solutions currently in use. 1.1.2 The materials covered by the standard are grouped 8s follows; Ferrous metals (1) Plain carbon, mediu
9、m and low alloy steels. (2) High alloy (corrosion and heat-resisting) steels. (3) Copper alloys. (4) Aluminium alloys. (5) Magnesium alloys. (6) Titaniumalloys. 0 Nickel and cobalt base alloys. Non-ferrous merals 1.2 PURPOSE. OF ETCH INSPECTION 1.2.1 Etch inspection is employed to examine the surfac
10、e conditions (see 1.2.2) of metallic materials to reveal or accentuate any variations of these conditions using either differential chemical or electrolytic attack. It may be applied at one or more stages in the manufacturing processes of a part or assembly and also subsequently in service. 1.2.2 Et
11、ching may be used to inspect for the following pincipal surface conditions: (1) Variations in grain size and flow. (2) Segregation. (3) Grinding abuse. (4) Faulty heat treatment. (5) Inclusions. (6) Cracks and folds. 1.3 GENEXAL CONSIDERATIONS 1.3.1 The initial surface texture of the material or com
12、- wnent should be commensurate with obtaining satisfactory results from the process used and the degree of inspection required. For components, the surface texture should generally be better than 6.3 pm (250 micro-inches) CLA. For materials, the surface finish should not exceed 12.5 pm (500 micro-in
13、ches) (=LA*. 23.2 Consideration should be given to the following effects caused by etching: (1) Change of overall dimensions. (2) Change of surface finish. (3) Modification of fatigue properties. (4) Production of hydrogen embrittlement of surface L3.3 The actual etching process (listed in 2.2.2 Op.
14、 10) may be carried out by: (1) Chemical etching, i.e. immersion in a solution, or (2) Electrochemical etching, Le. immersion in an layers. application of a solution to localized areas. electrolyte and the passage of direct current. *As dened in BS 1134, Centre-line-average height method for assessm
15、ent of surface texture. 2 Because of the greater degree of control which is neces- sary when etching electrochemically, the process is con- fined generally to the less reactive metals, and also to workpieces where greater dimensional changes or an electro-polishing action can be tolerated. NOTE. Agi
16、tation of the solution in both (i) and (2) is desirable. 1.4 APPROVALS 1.4.1 The preparation of all solutions, the installation of the equipment and the entire procedure shall be under the control of a responsible person functioning by agreement between the contracting parties. 1.4.2 It is strongly
17、emphasized that etch inspection shall not be carried out except as part of an accepted inspection schedule prepared under the control of the responsible person acting with the approval of the Design Authority. 2. PROCEDURE 2.1 INTRODUCTION 2.1.1 The particular etchant composition and etching time to
18、 be used shall be chosen having due regard to: (1) The material to be inspected (see 1.1.2). (2) The surface condition to be investigated (see 1.2.2). (3) The extent of attack that can be tolerated (see 1.3.2). 2.1.2 The procedure consists of pretreatment, the etching process, inspection, and post-t
19、reatment. It shall be con- tinuous, with a minimum of delay between each of the operations listed in 2.2.1 to 2.2.4. (See also Appendix A and Fig. 1.) 2.1.3 If delays are anticipated, the process should not be started. However, if unforseen delays arise after commence- ment of the process, the mater
20、ial or component should be hot-rinsed and dried off, the process then being restarted when the line is fully operative. It may be necessary to apply a temporary corrosion preventative in accordance with DEF 2331. 2.2 OPERATIONS 2.2.1 Pretreatment. The preparation of the workpiece for etching shall c
21、omply with the relevant stress-relieving and cleaning requirements of DTD 901, using one or a com- bination of the following operations: 0p.l. De-scale to remove heavy surface contamination. This may be carried out by mechanical or chemical means. Op. 2. Dry or wet-blast to remove surface oxides. Th
22、e size of media and time of blasting shall be minimal and selected to suit the hardness of the surface and also to avoid the peening effect in masking the flaws. Op. 3. Stress-relieve where necessary. Op. 4. De-grease. Op, 5. Mask all areas not requiring etching with a suit- able material that is no
23、t affected by the solution, such as PVC adhesive tape or film. Op. 6. Rinse in cold running water. Op. 7. Electro-polish to produce a chemically clean and smooth surface when a high degree of fnish is required. Op. 8. Chemically clean using an alkaline cleaner. Op. 9. Rinse in cold running water. I
24、i b BSI M237 70 lb24bb OO370 2 p I 2.2.2 The etching process. The etching operation shall continue as follows : Op. 10. Etching in accordance with therelevant sections of the table in Appendix B. Op. 11. Rinse in cold running water. Op. 12. De-smut, if specified in Appendix By to remove chemical res
25、idues remaining from the etching operation by immersing in the chemical solution specified in the relevant process instruction. Op. 13. Rinse in cold running water. Op. 14. Neutralize, where necessary, to eliminate further surface reactions by the application of suitable chemical solutions. Op. 15.
26、Rinse in cold running water. Op. 16. Immerse in hot water and dry off. Op. 17. Remove all traces of masking. Op. 18. Hydrogen de-embrittle, when specified in the relevant process instruction for the material concerned. 2.2.3 Inspection Op. 19. Inspect to the requirements of the acceptance standard.
27、2.2.4 Post-treatment. The workpiece shall be treated using one or both of the following stages: Op. 20. Remove the etch structure by mechanical means to prevent possible detrimental effect of the etch process on the mechanical properties. Op. 21. Apply a corrosion preventative in accordance with DEF
28、 2331. 3. EQUIPMENT AND SPECIAL CONSIDERATIONS 3.1 PROCESSING EQUIPMENT 3.1.1 Chemical etchant tanks. The size of the tanks con- taining the etchant shall be such that they will contain the workpiece; the tanks shall be constructed of materials that are non-reactive to the solution employed, and, if
29、 necessary, shall be capable of maintaining the specified process temperatures. Agitation of the solution shall be possible, Where size permits, covers to the tanks shall be used to protect the solution between periods of use. 3.1.2 Electrolytic etchant tanks. The size of the tanks con- taining the
30、etchant shall be such that they will contain the workpiece; the tanks shall be constructed of materials that are non-reactive to the solution employed. Temperature control and agitation of the electrolyte shall be provided. The cathode may be the tank and/or individual plates carried from the cathod
31、e bars. It shall be possible to main- tain uniform current density especially when treating hollow and complex shapes, e.g. by the use of auxiliary cathodes or work shrouds. Adequate electrical supply with current and voltage control, and instrumentation shall be provided. A high standard of cleanli
32、ness should be main- tained in respect of clamps, busbars, etc. 3.1.3 Rinse tanks. Tanks containing the rinse water shall be capable of containing the workpiece and be con- structed of corrosion resistant materials. The rinse tank shall be supplied with an adequate supply of cold running water. The
33、location of entry and exit (preferably over a weir) should be such as to produce the fullest possible circulation and/or agitation within the tank. The hot rinse tank shall have a supply of water and shall be capable of maintaining the contents at the required elevated temperature. M. 37, October, 1
34、970 3.1.4 ControI and maintenance of solutions. The solutions in the tanks shall be maintained at a constant level. The efficiency of the solution shall be regularly maintained in accordance with the instructions stated in Appendix B. The frequency of analysis of the solutions is dependent upon the
35、work load. Mechanical aids, e.g. floating glass or plastics capsules, should be used, where applicable, to prevent unduly high evaporation rates. 3.1.5 Extraction and ventilation. Adequate fume extraction shall be provided in accordance with the relevant Home Office requirements. To comply with loca
36、l byelaws it may be necessary to clean the extracted air before it is dis- charged into the atmosphere. Extractor ducts should be regularly cleaned to remove all deposits, in order to maintain the efficiency of the system. Adequate ventilation with clean warm air should be provided to replace that r
37、emoved by the extraction equip- ment. 3.2 VIEWING AIDS Viewing aids such as low power mamers and binoculars shall be of good optical quality, free from serious distor- tion and chromatic aberration. Use of the etch method for the in-situ examination of a component contained within an assembly or str
38、ucture is not generaliy recommended for routine inspection. However, if this method is used, special consideration shall be given to the following: (1) Adequate masking. (2) COnGnement of the chemicals. (3) Possible proximity of dissimilar materials. (4) The application of pretreatment and post-trea
39、tment. 3.3 IN-SITU APPLICATIONS 4. PERSONNEL 4.1 EYESIGHT The eyesight of ail personnel engaged in etch inspection shall be regularly checked. 4.2 FATIGW 4.2.1. Personnel who work steadily at the inspection of etched components will become fatigued due to the sustained concentration that is required
40、. The length of time before an inspector becomes fatigued will depend on numerous factors, the principal ones being listed below : (1) Physical condition of the inspector (Le. tired or fresh). (2) Environmental conditions such as temperature, humidity, freshness of air, noise level and location. (3)
41、 Viewing conditions. (As the magnification increases so does the rate of fatigue.) (4) Surface appearance of etched components. (Bright etches generally increase the rate of fatigue.) (5) The surface condition being inspected for. (The greater the concentration required, the more rapid the fatigue.)
42、 4.2.2 It is dicult to lay down a standard procedure, due to the number of variables which can influence fatigue, but experience has shown that continuous viewing should be limited to : 3 M. 37, October, 1970 ES1 M*37 70 M 3b24bb9 0099373 (1) without magnification, 1% hours to 2 hours ; (2) up to xl
43、5 magnification, 1 hour to 1% hours; (3) above x 15 magnification, special considerations apply. 4.3 VIEWING CONDITIONS The optimum viewing conditions for etched surfaces is when the lighting is oblique to the angle of view and such that highlights are avoided. Generally, high intensity light source
44、s are not required but a low power independent light source is essential. 4-! Ambient background light levels in the inspection area should be subdued and not exceed 250 lux. A suitable light source for the inspection of etched surfaces is a flexibly mounted 40 W to 60 W floodlight. For brightly etc
45、hed surfaces it may be necessary to fit a diffusing screen to the lamp in order to reduce reflected highlights from the surface of the component. 4.4 SAFETY REQUIREMENTS Precautions shall be taken to ensure adequate protection of personnel when handling corrosive acids and other harmful chemicals. A
46、PPENDIX A ETCH INSPECTION TECHNIQUE SHEET The etch inspection technique sheet should be of A4 size m accordance with BS 4o00, and should include the minimum details shown in Fig. 1. The precise format of the technique sheet should be agreed between the contracting parties. The additional details to
47、be stated on the sheet will usually include such items as work shrouds, nature and position of any additional electrodes used, jigs and ktures, current densities, etc. 4 M. 37, October, 1970 Company name and address ETCH INSPECTION TECHNIQUE SHEET Sheet . , of sheets Component title: Manufacturing o
48、r overhaul stage: Purpose of inspection: F -_ Technique sheet Ref. No PART No. Component material specitlation: Ara to be inspected: Acceptance standard : c Prepared by: Date: Date: I Associated documents and diagrams: BS references, etc. I Approved by: - OP. - 1 2 - Procedure Reqd Detaiis De-scale
49、Dry/wet-blast 3 Stress relieve I I 4 5 - 6 7 - Rinse (cold runuing water) Electro-polish 8 9 - Clean Rinse (cold running water) I+ 10 11 12 - Rinse (cold runninp: water) I I De-smut Rinse (cold running water) 13 14 - Neutralize Rinse (cold running water) 15 16 17 - Hot wash and dry Remove masking 18 19 - Hydrogen de-embrite Inspect 20 21 - - Remove etch I Apply corrosion preventative I I ADDITIONAL DETAILS: Fig. 1. Example of etch inspecon technique sheet 5 M. 37, October, 1970 6 O c -2 .z Sa O c *$ .g SN & 2 2 2 La o (d 8 .“ c .2 El mo ao g .z as - O c *g .g S(N
