·Table of Contents
·Aeronautics and Aerospace
NDE of Flight Hardware Exported to Aircraft Manufacturers in Europe and USA - an appraisal from Indian Aircraft Manufacturer
P. VIJAYARAGHAVAN B. CHATTERJEE
HINDUSTAN AERONAUTICS LIMITED
BANGALORE - 5 6 0 0 1 7. INDIA
In the international scenario, civil aircraft building is dominated by consortium in Europe and USA. Some of the flight hardware are subcontracted to Asian countries.
All flight hardware are subjected to stringent Non destructive evaluation, to the required standard and specification of the customer.Aircraft manufacturers are very particular about the training and certification of NDE personnel, and insists for the certification system existing in their countries. This holds good for some of the equipments and consumables also. In certain cases, for the common process, different parameters and process control checks of different periodicity are stipulated.
This paper attempts to cite such problems, solutions and the area where uniformity can be attempted, which can be acceptable to the industries in Aerospace sector of countries of same and different origin.
When a subcontractor of flight hardware caters to multinationals in Aerospace sector of countries of same and different origin namely Europe and USA , during NDE many problems arise. For instance, for a common process, different parameters and process control checks of different periodicity are stipulated. though most of them have been solved, still in certain cases there is scope to rationalise.
Training and certification of NDT personnel:
Though the topics of "Harmonization of NDT certification" is discussed in many of international forums , yet a solution is not sighted in the near future. Here is a classic example depicting the difficulties faced by NDT personnel in Aerospace sector. NDT personnel evaluating flight hard wares are required to certified to Level III from professional bodies like ASNT, PCN etc, Then they have to certified as per NAS 410 (which supersedes MIL STD 410 ), over and above this they have to pass the supplier level III examination in specific paper..However France based aerospace manufacturers do not recognise ASNT qualifications, and also their system is having centralised certification system for level I, II and III.and personnel certified to level III from French official NDT body (COFREND ), need not take examination as per NAS 410 or company specific examinations. However the recertification is by examination only, once in five years.
This means that a sub contractor supplying flight hardware to US and Europe based prime contractor shall have level III, who should take a series of examinations to certify the components by required NDT methods.
Procedure to be written separately for each customer (Europe and USA based ). Internal company procedure of the manufacturer is not acceptable to them. One more procedure citing the customer's specification and other standards to be written with full details. Merely citing their specification and standards are not sufficient.
Only Penetrant materials approved as per the document QPL AMS 2644 which supersedes QPL MIL -25135 is approved. So all the Penetrant materials are imported , since indigenously available products are not listed in QPL.
For dry developer spray, on the recommendation of one European customer electro static spray equipment was bought. Here the developer can not be re cycled as done in cloud chamber (powder storm cabinet), and also developer application on bulk of smaller components was difficult. For economical reason as well as for bulk application of smaller components powder storm cabinet is under procurement, as a common method of the dry developer application, agreeable to both the customers.
Manual spray wash to remove the excess surface penetrant was being removed by using ordinary pipes. US customer insisted upon using tricon jet nozzle for getting a fan shaped coarse water spray . here process improvement was observed. To check the effectiveness of water rinsing in removing the background fluorescence UV lamps are installed in the wash stations. Though most of the company specs does not call for intensity checking of these lamps, one UK based company calls for weekly check of this.
Regarding test panels for penetrant system performance check, Ni-Cr panels and TAM panels (artificial defect standards) are used. US companies require both master and working panels and also calls for calibration annually. Where as Europe based companies calls for only working panels , and do not insists for annual calibration.
Vapour degreasing is a common method of removing surface contaminants like oil , grease etc, acceptable to all. However recently some European companies are switching to alkaline degreasing because of ecological reason of ozone depletion by trichloro ethylene contained in vapour degreasing.
For components which undergoes metal smearing operations like grinding, machining, abrasive cleaning , blasting etc, etching is a must, for removal of smeared metal over defects (In microns levels depending on material, process etc )to facilitate penetrant inspection.
Though same Aluminium alloys are used for both US and European customers for some of the components, US company recommends sodium hydroxide etching, whereas European co insists on sulphochromic etching. Though the end result achieved is same i.e. removal of smeared metal in the material to a few micron level.
Two separate process lines involving lot of tests, process control checks, calibration of the instruments connected with the baths and operator fatigue can be avoided if a common method for this process is agreeable .
Inspection of the components undergone Fluorescent penetrant process, are done in a dark room under UV light (black light). The intensity of UV light is measured on the inspection surface at a fixed distance. This changes from spec to spec, from 800 microwatt per cm.sq to 3000 microwatt per cm.sq. under same conditions and also at different conditions. Same thing applies to visible light.
To check the brightness of in use fluorescent penetrant with the unused (hold out sample) most of the customer specifications calls for simple comparison on a filter paper or dilution with methylene chloride and measure the intensity output by UV radiometer, Which is a simple and practicable test. However one US customer insisted on this check as per ASTM E 1135. It was found that the manufacturer of of this particular instrument (Photofluorimetry) in US was defunct. However the instrument was sourced from Italy to tide over the situation.
Process control checks and calibration of the instruments:
While not much difficulties are faced in process control check and calibration in the other conventional methods like radiography, ultrasonic and eddy current test methods. Some difficulties are experienced while performing penetrant and magnetic particle testing methods due to diversified process control check requirements and their periodicity. In the last 5 years this has narrowed down when the companies come out with fully revised and up dated version of their specification.
When there are differences in the periodicity in process control checks and calibration between the customer specification, the minimum periodicity is practiced. For example, if one spec calls for monthly check of UV light intensity and the other calls for a weekly check, then weekly check is carried in the installation to the satisfaction of both the customer.
After scrutinising the customer specifications (US and Europe origin) of process control check and calibration requirements for penetrant inspection , areas having common requirements and periodicity have been left out and areas where distinct differences have been observed are given in table I (Latest issues as on April 2000 are considered for comparison).
|UV light intensity
||Daily/weekly FN 1
||Daily FN 3
|Fluorescent penetrant brightness
|Hydrophilic emulsifier concentration
|Dry developer appearance
|Water content of WW Flu Pen
||As per MIL-STD -45662
||As per MIL-STD -45662
|Table 1: |
Europe 1 2 3 - Companies in Aerospace sector of European base
US 1 2 - Companies in Aerospace sector of American base
FN 1 - daily /weekly checks depending on the intensity measured
FN 2 - Test intervals may be extended provided the known defect panels
adequately monitors the performance of penetrant materials
FN 3 - This company cites in their spec, Process control and calibration checks
as given in ASTM E 1417, but adds, the requirements of UV intensity is 1200 micro watts/cm sq.
Most of the US and Europe based companies do not insist on using lipophilic emulsifier, (method B). In some cases choice between hydrophilic emulsifier (method D) and lipophilic emulsifier is given. French based aerospace company forbids the use of lipophilic emulsifier. Recently one US based co insisted on using lipophilic emulsifier . clarification was requested to know if there is any specific reason for this. Answer is still awaited.
Regarding concentration of Hydrophilic emulsifier, French aerospace company requires that the concentration should not exceed 5% , but American usage provides concentrations up to 20%.
During process control check of dry developer, most of the US companies and Europe companies cite the requirement as per ASTM E 1417, i.e. 10 or more specks observed will render the developer to discard. French aerospace co simply states that no fluorescent grains observable during weekly check, and does not quantify.
Magnetic particle Inspection :
Flaw shims are used on the components to check the adequacy of magnetisation during Magnetic particle testing. One American company has pointed out in one of their audits for calibration and periodicity for this shims, which is not mentioned in any of the available specification and also details mentioned by shim manufacturer.
On equipment using timer to control current duration during mag particle test, timer check once in six month is called for in ASTM E 1444. This was carried using oscilloscope to the accuracy of ±
0.1 second, Since The American company did not accept the calibration with manual stop watch for accuracy purpose. This timer calibration is not called for in the Europe based company specifications.
US company specification states, to use ammeters that indicate the actual current applied to the heads or coil. Where as Europe company specifications gives a detailed chart for correction factors for conversion of current reading, read on ammeters to peak values. As for periodicity of Ammeter calibration is considered, it is Annually as per European companies and half yearly as per American companies.
During audits, ISO auditors question the calibration status of X-ray control panel for Kv. mA meters, timer, and temperature gauges on film dryers. There is no mention of this in any of the radiographic standards available or company specifications, only Densitometer calibration and developer activity check is given in detail. However , A leading European engine manufacturer has detailed this in the company specification on Radiography, which reads as under. This has pacified the ISO auditors.
" It is generally accepted that radiographic inspection is a self regulating process, the quality of the final film or real image being assessed visually against the requirement of sensitivity, density, contrast, definition, etc. Exposure and processing parameters are given as guide lines. Minor alterations may be necessary to achieve correct image results.
In view of the above , it is NOT necessary to carryout calibration on electrical meters (KV and MA)or timers on x-ray equipment control panels or on timers and temperature gauges on processing units ".
Regarding penetrameters , which are used for qualifying the image quality, European companies recommends DIN wire penetrameters. However American companies recommends ASTM plaque type penetrameters. When one set of penetrameters to MIL STD 453 was received from an American source to be used on castings for a prime contractor in US , they made certain observation. On scrutiny it was found that the penetrameter material was steel but SS (stainless steel )was engraved on the pentameters. When this was pointed to the supplier, they agreed for the lapse, asked to remove the wording SS from penetrameter or ask for a full replacement. This is only to cite , how a small mistake can lead to non conformance during audits.
One European company has called for Radiographic inspection of wrought products, the reason given is to find out 0.5 mm dia inclusions which may be missed by Ultrasonic inspection. In the subsequent para, it is stated as, when an Indication is found during x-ray inspection of the pan cake , the defect shall be investigated or confirmed by Ultrasonic. These two instructions are contradictory and confuses the user.
Aluminum alloy cast billets of 300 mm dia and above are supplied by a European manufacturer, certified to 2mm FBH single indication as per ASTM E 127 block standards, by ultrasonic immersion testing using longitudunal waves and by spiral scanning . I t is a fact that ASTM E 127 does not specify any FBH (Flat bottom hole blocks )beyond a metal distance of 158 mm. When clarification was sought from the supplier, they are not willing to give technical information on calibration blocks .
It is assumed that, they may be scanning the billet for only half thickness at a time, but however since a international reference standard is quoted, the procedure adopted to be made clear. ASTM can solve such problems by stating why FBH blocks are not made and certified beyond a metal distance of 158 mm or issue a procedure of scanning billets of higher dia to the specified FBH.
Conclusion and recommendation :
Establishing common procedure for the process , process control check requirements , calibration of equipment , materials required for the NDT methods, quantitative and qualitative assessment wherever applicable , for common process and materials requires the full cooperation , coordination , technical and administrative resources of all the industries in Aerospace sector of countries of same and different origin .
Authors would like to acknowledge their gratitude for the Management of M/S Hindustan Aeronautics Limited in encouraging to present this paper in 15th WCNDT. And thank all the NDT personnel and Chief of Quality for their support.