1、AEROSPACERECOMMENDEDPRACTICESubmitted for recognition as an American National StandardPROCEDURE FOR INSPECTION OF INSERVICEAIRBORNE ACCUMULATORS FOR CORROSION AND DAMAGELand Sea Air and SpaceFor Advancing MobilityThe Engineering SocietyINTERNATIONAL400 Commonwealth Drive, Warrendale, PA 15096-0001Is
2、sued 1996-11ARP4150FOREWORDThis SAE Aerospace Recommended Practice (ARP) is intended as a guide toward standard practiceand subject to change to keep pace with experience and technical advance.TABLE OF CONTENTS1. SCOPE .22. REFERENCES23. REVIEW OF SERVICE HISTORY.23.1 Background.23.2 Review 24. INSP
3、ECTION 34.1 General .34.2 Inspection Program .35. RECOMMENDATIONS .66. NOTES86.1 Key Words 8FIGURE 1 Critical Stress / Corrosion Areas5FIGURE 2 Single Point Inspection for Assembled Accumulator7Reaffirmed 2011-03SAE Technical Standards Board Rules provide that: “This report is published by SAE to ad
4、vance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.” SAE reviews each technical report at least
5、every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. Copyright 2011 SAE International All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means
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7、ues your input. To provide feedbackon this Technical Report, please visit http:/www.sae.org/technical/standards/ARP4150SAE ARP4150- 2 -1. SCOPE:This SAE Aerospace Recommended Practice (ARP) is intended as a guide in establishinginspection procedures to determine the condition of inservice accumulato
8、rs. A minimum inspectionprogram is recommended to determine the existence of corrosion and damage. Recommendationsare also provided for corrective action if it is determined that the environment is contributing to thedeterioration of the surface protection system treatments.2. REFERENCES:2.1 SAE Pub
9、lications:Available from SAE, 400 Commonwealth Drive, Warrendale, PA 19111-5094.2.2 U.S. Document Publications:Available from DODSSP, Subscriptions Services Desk, Building 4D, 700 Robbins Avenue,Philadelphia, PA 19111-5094.3. REVIEW OF SERVICE HISTORY:3.1 Background:Accumulators are designed for the
10、 service life of the aircraft, however, under certainenvironmental conditions the surface protection system can deteriorate and allow corrosion,which in turn can lead to early stress corrosion type failures. Since the accumulator is chargedwith a high pressure gas, the results of such failure can be
11、 extremely violent. Failure of anaccumulator can result in aircraft structural damage and may result in injury to nearby personnel.3.2 Review:Accumulators are generally installed on aircraft and not removed for service. There are,however, certain conditions that can lead to early failures. The most
12、obvious of these are asfollows:3.2.1 Installation and Environment Causes: Cavities or fluid traps in the end caps or under themounting clamps can retain moisture which will adversely act on the corrosion protectivesystem. The rate of corrosion will be greater on some installations than on others due
13、 to theirmore severe operating environment.Installations exposed to moist salty air, waste water, or corrosive cleaning solvents will, losetheir protective finish much faster than those operating under clean dry conditions.SAE ARP4150- 3 -3.2.2 Use of Poor Quality Gas: The inadvertent use of moist n
14、itrogen or air to service theaccumulator can cause loss of the internal corrosion protection system. Some configurations,such as those with permanently closed gas chambers are especially susceptible to this problemsince the air chambers are not necessarily inspected during normal refurbishment activ
15、ities. Itis recommended that high purity, cryogenically pumped, industrial grade nitrogen be used toreduce the chance of introducing moisture into the accumulator.3.2.3 Damage Caused During Normal Maintenance:3.2.3.1 Damage to the protective coating will allow corrosion pitting, which will allow ear
16、ly failure dueto stress corrosion action.3.2.3.2 Nicks or scratches can induce high localized stress levels which will appreciably reduce thestructural life.3.2.4 Improperly Manufactured or Installed Parts:3.2.4.1 Sharp internal corners from improper machining cause high stress concentrations and re
17、ducelife.3.2.4.2 Deficient plating / coating processes allow early corrosion pitting, which in turn allows failuresdue to stress corrosion.3.2.4.3 Improper material heat treating can reduce the material fatigue life.3.2.4.4 Improper installation of parts can cause high stress concentrations and redu
18、ce life.4. INSPECTION:4.1 General:A general inspection program should be established to determine the service life probability foreach particular accumulator installation. The inspection period may be determined from asampling program over different inservice periods. The inspection program should b
19、e aimed atdetermining problems related to corrosion, since structural problems related to heat treatment orbuilt in stress risers will not be apparent at the normal maintenance levels.Disassembly inspection should include visual magnetic particle (ferromagnetic parts) and /orfluorescent penetrant (n
20、on magnetic parts). The alternate ultrasonic method for in placeinspection described is only good for detection of fatigue cracking. Usually stress corrosioncracks develop rapidly and scheduled inspections can miss the cracks.4.2 Inspection Program:In order to be effective the program should consist
21、 of the following:SAE ARP4150- 4 -4.2.1 Inspection for Corrosion and Damage: A program shall be set up to require the inspection forcorrosion of all units returned for servicing. In addition the parts should be inspected forunusual nicks, scratches, or manufacturing tool marks in excess of drawing r
22、equirements, thatcould be a source of stress risers. As a minimum this inspection should consist of using abright light and low power (approximately 2 to 3 power) magnifying glass to detect corrosion onthe pressure shell and end cap portions of the assembly. A manual or instruction should beprepared
23、 for an inspection “How To“. In some cases more sophisticated equipment will berequired to inspect hard to get at areas.Figure 1 shows some typical areas of concern on two common accumulator end capconfigurations. Moisture can enter the areas around the highly stressed thread, lock ring, andend cap
24、areas and cause corrosion.It is good practice to inspect the interior surfaces of the gas chamber. This chamber is normallycharged with non-corrosive dry nitrogen, however experience has shown that inadvertent use ofmoist air can cause extensive corrosion damage.4.2.2 Corrective Action: When corrosi
25、on is found, corrective action must be taken. When a mildcase of corrosion exists as defined by the light surface discoloration without pitting all signs of discoloration should be removed and the affected surface protected prior to assembly. Heavierindications of corrosion involving surface pitting
26、 shall be inspected for indications of stresscorrosion cracks. Nondestructive inspection is recommended; e.g; magnetic particle inspectionor fluorescent inspection as recommended by the manufacturer. Discard the parts which showcrack indications. Further use of the remaining parts normally requires
27、removal of thecorrosion, blending of the pits, and restoration of the corrosion protective coating to the originalstate. Internal corrosion on the accumulator cylinder must be considered on an individual basisbased on the cylinder configuration. Generally no repair can be accomplished except rework
28、tooriginal condition, since the internal finish affects both static and dynamic sealing.NOTE: Contact the manufacturer for the dress-out limits, finishes, and the possible stressrelief requirements. Any rework that is beyond the overhaul manual / design limitsrequires approval of the applicable gove
29、rnment agencies or the airworthinessauthorities. Since many accumulators are standard off the shelf items it is often moreeffective to replace these assemblies rather than to rework the defective parts.SAE ARP4150- 5 -FIGURE 1 - Critical Stress/Corrosion AreasTypical End Cap ConfigurationSAE ARP4150
30、- 6 -4.2.3 Recording Process: A program should be initiated to record and track corrosion problemsdiscovered during inspection. Proper recordings and tracking will make it possible to separatethe repetitive from the one of a kind problems and take fleet wide corrective action whenrequired. Installat
31、ions found to be prone to corrosion shall be subject to repetitive inspectionsaimed at time intervals based upon the severity of the problem at the finding and correcting theoverall fleet problems. If it is determined that a fleet wide problem exists, a plan should be set up to methodicallyinspect a
32、ll the field units within a reasonable time. The surest method of inspection is todisassemble the unit and proceed with a visual inspection.Sometimes, however, an alternate method of in place inspection can be developed which canboth expedite the program and reduce inspection costs. One method that
33、has been usedsuccessfully is to use an ultrasonic transducer installed in a lucite wedge shaped to theaccumulator contour. This tool is calibrated to a standard and will pick up defects in installedequipment. Refer to Figure 2.When an acceptable ultrasonic inspection method has been established the
34、detailed inspectionprocedure (for fatigue cracks at a known location on the part) shall include: the ultrasonictransducer type, size, and operating frequency; the lucite wedge incident angle (for properangle of refraction) and the search unit placement on the part being inspected.A sketch or photogr
35、aph of the Cathode Ray Tube (CRT) trace showing the crack / no-crackresponses shall also be provided. The detailed ultrasonic inspection procedure shall also givethe accept / reject criteria based on the position and the amplitude of the ultrasonic signal as itrelates to the reference notch shown in
36、 Figure 2.5. RECOMMENDATIONS:Some installations can expose accumulators to harsh environmental conditions. If adequateprotection has not been provided on new or serviced units it is recommended that corrective actionbe taken, and protection be added prior to installation.Both aircraft and accumulato
37、r manufacturers can be of help in the selection of protective methods. It is further recommended that the prime aircraft manufacturer inform all operators, eithercommercial or military, of the problem and provide corrective action for the future productionaircraft. Threads can be protected by primer
38、s or nonsetting sealants during assembly. Moisturecavities or fluid traps can be filled with various types of sealant compounds. Exterior surfaces canbe protected by paints. Refer to Figure 1 for areas of recommended protection.In any case, care should be exercised as to both the type of primers and
39、 sealants and theirapplication to ensure that they are compatible with the installation environment, systemtemperature, and will not impair future accumulator disassembly.SAE ARP4150- 7 -FIGURE 2 - Single Point Inspection for Assembled Accumulator of One TypeSAE ARP4150- 8 -6. NOTES:6.1 Key Words:Aerospace, accumulator, hydraulic, pneumaticPREPARED BY SAE SUBCOMMITTEE A-6A, FLUID POWER SYSTEMS OFCOMMITTEE A-6, AEROSPACE FLUID POWER, ACTUATION AND CONTROL TECHNOLOGIES
