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SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions.
Copyright © 2007 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, electronic, mechanical, photocopying, recording,
or otherwise, without the prior written permission of SAE.
TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada)
Tel: 724-776-4970 (outside USA)
Fax: 724-776-0790
Email: CustomerService@sae.org
SAE WEB ADDRESS: http://www.sae.org
AEROSPACE
MATERIAL
SPECIFICATION
Issued OCT 1999
Revised SEP 2007
Superseding AMS-C-27725A
Coating, Corrosion Preventative,
for Aircraft Integral Fuel Tanks
for Use to 250 °F (121 °C)
RATIONALE
AMS-C-27725B results from a five-year update, clarification of test requirements, and addition of a nonchromated
classification for fuel tank coatings.
1. SCOPE
1.1 Form
This specification covers three types of corrosion preventative coatings for protection of aircraft integral fuel tanks.
1.2 Application
The coating materials covered by this specification are typically applied to the interior of aircraft integral fuel tanks to
protect against corrosion from fuel contaminants, but usage is not limited to such applications. They are suitable for use in
a service temperature range from -65 to +250 °F (-54 to +121 °C).
1.3 Classification
The corrosion-preventative coatings covered by this specification shall be of the following types.
Type 1 - A two-component polyurethane coating with less than 420 g/l Volatile Organic Compound (V.O.C.) content.
Type 2 - A two-component polyurethane coating with less than 720 g/l V.O.C. content.
Type 3 - Non-chromated coating with less than 420 g/l V.O.C. content
1.4 Safety - Hazardous Materials
While the materials, methods, applications, and processes described or referenced in this specification may involve the
use of hazardous materials, this specification does not address the hazards which may be involved in such use. It is the
sole responsibility of the user to ensure familiarity with the safe and proper use of any hazardous materials and to take
necessary precautionary measures to ensure the health and safety of all personnel involved.
2. APPLICABLE DOCUMENTS
The issue of the following documents in effect on the date of the purchase order forms a part of this specification to the
extent specified herein. The supplier may work to a subsequent revision of a document unless a specific document issue
is specified. When the referenced document has been cancelled and no superseding document has been specified, the
last published issue of that document shall apply.
AMS-C-27725B
Copyright SAE International
Provided by IHS under license with SAE Licensee=Defense Supply Ctr/5913977001
Not for Resale, 12/04/2007 21:18:08 MSTNo reproduction or networking permitted without license from IHS
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SAE AMS-C-27725B - 2 -
2.1 SAE Publications
Available from SAE International, 400 Commonwealth Drive, Warrendale, PA 15096-0001, Tel: 877-606-7323 (inside
USA and Canada) or 724-776-4970 (outside USA), www.sae.org.
AMS 2471 Anodic Treatment of Aluminum Alloys, Sulfuric Acid Process, Undyed Coating
AMS 2473 Chemical Film Treatment for Aluminum Alloys General Purpose Coating
AMS 2629 Fluid, Jet Reference
AMS 2825 Material Safety Data Sheets
AMS 3276 Sealing Compound, Integral Fuel Tanks and General Purpose, Intermittent Use to 360 °F (182 °C)
AMS 3819 Cloths, Cleaning, for Aircraft Primary and Secondary Structural Surfaces
AMS 4045 Aluminum Alloy Sheet and Plate, 5.6Zn - 2.5Mg - 1.6Cu - 0.23Cr (7075; -T6 Sheet, -T651 Plate)
Solution and Precipitation Heat Treated
AS5505 Requirements for Accreditation of Testing Laboratories for Organic Coatings
AS9100 Quality Systems - Aerospace - Requirements
ARP1917 Clarification of Terms Used in Aerospace Metals Specifications
2.2 PRI Publications
Available from Performance Review Institute, 161 Thorn Hill Road, Warrendale, PA 15086-7527, Tel: 724-772-1616,
www.pri-network.org.
PRI QPL-AMS-C-27725 Products Qualified Under AMS-C-27725
PD 2000 Procedures for an Industry Qualified Product Management Process
2.3 ASTM Publications
Available from ASTM International, 100 Barr Harbor Drive, P.O. Box C700, West Conshohocken, PA 19428-2959,
Tel: 610-832-9585, www.astm.org.
ASTM B 36 Brass Plate, Sheet, Strip and Rolled Bar
ASTM D 257 DC Resistance or Conductance of Insulating Materials
ASTM D 740 Standard Specification for Methyl Ethyl Ketone
ASTM D 1200 Viscosity by Ford Viscosity Cup
ASTM D 1353 Nonvolatile Material in Volatile Solvents for Use in Paint, Varnish, Lacquer and Related Products
ASTM D 1475 Density of Liquid Coatings, Inks, and Related Products
ASTM D 1974 Methods of Closing, Sealing, and Reinforcing Fiberboard Boxes
ASTM D 3960 Volatile Organic Compound (VOC) Content of Paint and Related Coatings
ASTM D 3335 Standard Test Method for Low Concentrations of Lead, Cadmium, and Cobalt in Paint by Atomic
Absorption Spectroscopy
ASTM D 3363 Standard Test Method for Film Hardness by Pencil Test
2.4 U.S. Government Publications
Available from the Document Automation and Production Service (DAPS), Building 4/D, 700 Robbins Avenue,
Philadelphia, PA 19111-5094, Tel: 215-697-6257, http://assist.daps.dla.mil/quicksearch/.
PPP-C-96 Can, Metal, 28 Gage and Lighter
FED-STD-791 Lubricants, Liquid Fuels, and Related Products, Methods of Testing
MIL-PRF-23699 Lubricating Oil, Aircraft Turbine Engine, Synthetic Base, NATO Code 0-156
MIL-PRF-83282 Hydraulic Fluid, Fire Resistant, Synthetic Hydrocarbon Base, Aircraft
MIL-DTL-85470 Inhibitor, Icing, Fuel System, High Flash NATO Cold Number S-1745
MIL-A-8625 Anodic Coatings for Aluminum and Aluminum Alloys
MIL-C-5541 Chemical Conversion Coatings on Aluminum and Aluminum Alloys
Copyright SAE International
Provided by IHS under license with SAE Licensee=Defense Supply Ctr/5913977001
Not for Resale, 12/04/2007 21:18:08 MSTNo reproduction or networking permitted without license from IHS
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SAE AMS-C-27725B - 3 -
2.5 ISO Publications
Available from American National Standards Institute, 25 West 43rd Street, New York, NY 10036, Tel: 212-642-4900,
www.ansi.org.
ISO/IEC 17025 General Requirements for the Competence of Testing and Calibration Laboratories
3. TECHNICAL REQUIREMENTS
3.1 Materials
The basic ingredient shall be polyurethane for Types 1 and 2 with curing agents, thinners, and additives suitable for
various application methods including brushing, dipping, and spraying. Type 3 shall not contain any chromium or chromium
compounds. Incidental chromium content in Type 3 coatings shall not exceed 5 ppm. The basic ingredients for the Type 3
coatings are not specified, providing the material will meet the performance requirements set forth in this specification and
is suitable for various application methods including brushing, dipping, and spraying. All three types of coatings, when
tested in accordance with ASTM D 3335, shall not contain any cadmium or cadmium compounds and shall not contain
more than .06 % of lead or lead compounds.
3.2 Properties
The coating, when prepared in accordance with the manufacturer’s instructions shall conform to the requirements shown
in Table 1, determined in accordance with specified test methods in Table 1.
TABLE 1 - APPLICATION PROPERTIES
Paragraph Property
Requirement
Type 1
Requirement
Type 2
Requirement
Type 3 Test Method
3.2.1 Surface
appearance
Smooth,
uniform, and
free of film
porosity and
irregularities
Smooth,
uniform, and
free of film
porosity and
irregularities
Smooth,
uniform, and
free of film
porosity and
irregularities
4.6.5.1
3.2.2 Density,
variation from
acceptable
qualification
sample listed on QPL,
percent ±5 ±5
±5
4.6.5.2
3.2.3 Volatile Organic
Compound
Content (VOC)
g/l, max 420 720
420 4.6.5.3
3.2.4 Viscosity, seconds
Initial
After Application Life
13 to 23
≤35
10 to 20
≤20
13 to 23
≤35
4.6.5.4
4.6.5.4
3.2.5 Application life,
hours, min
4 4
4
4.6.5.5
3.2.6 Drying time,
hours max at
standard conditions
2 2
2
4.6.5.6
3.2.7 Coating shall be fully cured within 21 days at standard conditions for Types 1 and 3, and within 14 days at
standard conditions for Type 2. Types 1, 2, and 3 shall also be fully cured within 24 hours at standard conditions
followed by 24 hours at 140 °F ± 2 (60 °C ±1) and 50 ± 5 percent relative humidity when tested in accordance with
4.6.5.7. The cured coating shall have a minimum pencil hardness of “F” when tested in accordance with 4.6.5.22.
Copyright SAE International
Provided by IHS under license with SAE Licensee=Defense Supply Ctr/5913977001
Not for Resale, 12/04/2007 21:18:08 MSTNo reproduction or networking permitted without license from IHS
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SAE AMS-C-27725B - 4 -
3.2.8 Resistance to Water
The cured coatings shall show no blistering, softening in excess of 1 hardness unit, leaching, corrosion extending more
than 1/8 inch (3.2 mm) beyond the scribe mark or in from the edge of the panel, loss of adhesion, or other visible
deleterious effect when tested as specified in 4.6.5.8.
3.2.9 Resistance to Salt Water and Fuel
The cured coatings shall show no blistering, softening in excess of 1 hardness unit, leaching, shrinkage, corrosion
extending more than 1/8 inch (3.12 mm) beyond the scribe mark or in from the edge of the panel, loss of adhesion, or
other visible deleterious effect when tested as specified in 4.6.5.9.
3.2.10 Resistance to Engine Oil
The cured coatings shall show no blistering, softening in excess of 1 hardness unit, leaching, shrinkage, loss of adhesion,
or other visible deleterious effect when tested as specified in 4.6.5.10.
3.2.11 Resistance to Hydraulic Fluid
The cured coatings shall show no blistering, softening in excess of 1 hardness unit, leaching, shrinkage, loss of adhesion,
or other visible deleterious effect when tested as specified in 4.6.5.11.
3.2.12 Fuel Contamination
The nonvolatile extractable materials contributed by the cured coatings in contact with the jet reference fluid shall not be
more than 20 mg per 100 ml when tested as specified in 4.6.5.12. Not more than a slight discoloration or tarnish shall be
present on a freshly polished copper strip.
3.2.13 Low-Temperature Flexibility
The cured coatings shall withstand the low-temperature test specified in 4.6.5.13 without cracking, checking, crazing, or
loss of adhesion.
3.2.14 Peel Strength, Sealing Compound to Coating Material
Sealing compound conforming to AMS 3276, Class B-2, applied to the cured coating material shall have a peel strength of
not less than 20 pounds force per inch (3503 N/m) when tested as specified in 4.6.5.14. There shall be no adhesive failure
between the coating and the sealing compound except for bubbles and knife cuts.
3.2.15 Adhesion, Coating Material to Sealing Compound
The coating material applied to sealing compound conforming to AMS 3276, Class B-2, shall not cause cracks in the
sealing compound when tested as specified in 4.6.5.15. Cracks in the cured coating shall be permissible, but the cured
coating shall not flake from the sealant.
3.2.16 Repairability
The cured coating shall show no blistering or loss of adhesion when tested as specified in 4.6.5.16.
3.2.17 AccelErated Storage Stability
After storing as specified in 4.6.5.17, coating material shall be capable of meeting the initial viscosity requirements and the
requirements for dry time and application life specified in Table 1.
3.2.18 Resistance to Iron Chloride
The cured coatings shall show no blistering or softening, and the panels shall show no corrosion when tested as specified
in 4.6.5.20.1. After immersion, the cured coatings shall have a resistance of at least 5.0 megohms per mil of thickness
when tested as specified in 4.6.5.20.2.
Copyright SAE International
Provided by IHS under license with SAE Licensee=Defense Supply Ctr/5913977001
Not for Resale, 12/04/2007 21:18:08 MSTNo reproduction or networking permitted without license from IHS
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SAE AMS-C-27725B - 5 -
3.2.19 Resistance to Simulated Microbial By-Products
The cured coatings shall show no blistering, softening, or shrinkage when tested as specified in 4.6.5.21. There shall be
not more than 5 percent loss of coating when subjected to the tape test. Removal of coating immediately adjacent to the
scribe and obviously caused by coating cracking during scribing shall not be cause for rejection.
3.3 Quality
The coatings, as received by purchaser, shall be uniform in quality and condition, as free from foreign materials as
commercially practicable and free from imperfections detrimental to the usage of the compound. There shall be no
separation of ingredients that cannot be readily dispersed by hand mixing.
4. QUALITY ASSURANCE PROVISIONS
4.1 Quality System of Manufacturer
Before submitting a product for qualification to this specification for the purpose of being listed on the PRI QPL, the
manufacturer must have a quality system in place which holds a third party accreditation to AS9100.
4.2 Responsibility for Inspection
The manufacturer of the product shall supply all samples needed for required tests and shall be responsible for the
performance of all required tests. Purchaser reserves the right to sample and to perform any confirmatory testing deemed
necessary to ensure that the product conforms to specified requirements.
4.3 Classification of Tests
4.3.1 Acceptance Tests
Surface appearance (3.2.1), density (3.2.2), volatile content (3.2.3), viscosity (3.2.4), application life (3.2.5), drying time
(3.2.6), and force cure time (3.2.7) are acceptance tests and shall be performed on each batch.
4.3.2 QualificaTion Tests
All technical requirements are qualification tests and shall be performed prior to the initial shipment of coating to a
purchaser, when a change in ingredients and/or processing requires re-approval as in 4.5.4, and when purchaser deems
confirmatory testing to be required. All qualification testing is to be carried out by a laboratory which is independent of the
manufacturer and is accredited per ISO 17025 and AS5505.
4.4 Sampling and Testing
Shall be as follows:
4.4.1 For Acceptance Tests
Sufficient coating compound shall be taken at random from each batch to perform all the required tests. A batch shall be
the quantity of material run through a mill or mixer at one time. The number of determinations for each required test shall
be as specified in the applicable test procedure or, if not specified herein, not less than three, except that multiple testing is
not required for viscosity, application life, drying time, and forced cure time.
4.4.1.1 A statistical sampling plan, acceptable to purchaser, may be used in lieu of sampling as in 4.4.1.
Copyright SAE International
Provided by IHS under license with SAE Licensee=Defense Supply Ctr/5913977001
Not for Resale, 12/04/2007 21:18:08 MSTNo reproduction or networking permitted without license from IHS
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SAE AMS-C-27725B - 6 -
4.4.2 For Qualification Tests
Samples shall consist of approximately 2 gallons (7.6 L) of material. The material shall be furnished in containers of the
type to be used in filling contract orders. Samples shall be identified as follows and forwarded to the activity responsible for
testing, as designated in the letter of authorization from the activity responsible for qualification:
COATING, CORROSION PREVENTATIVE
For Aircraft Integral Fuel Tanks for Use to 250 °F (121 °C)
AMS-C-27725 TYPE (1, 2 or 3)
MANUFACTURER’S IDENTIFICATION
NAME OF MANUFACTURER
LOT NUMBER
DATE OF MANUFACTURE
SUBMITTED BY (NAME) (DATE) FOR QUALIFICATION TESTS IN ACCORDANCE WITH AMS-C-27725B UNDER
AUTHORIZATION
(REFERENCE AUTHORIZING LETTER)
4.5 Approval and Reapproval
4.5.1 Coating supplied to this specification shall be listed, or approved for listing, on the qualified products list, PRI QPL-
AMS-C-27725.
4.5.2 Qualification testing, review of test results, approval, re-approval and recertification of qualification for QPL listing
shall be in accordance with PD 2000.
4.5.3 Recertification of qualification is required every three years. Recertification consists of a letter certifying that there
have been no changes in the material ingredients, manufacturing processes, or site of production since
qualification and that the product meets all of the requirements of this specification. In addition a test report shall
be provided from a lab of the manufacturer’s choosing, showing compliance with all of the qualification tests.
4.5.4 Manufacturer shall use ingredients, manufacturing procedures, processes, and methods of inspection on
production coating which are essentially the same as those used on the approved (qualified) sample. If necessary
to make any change in product formulation, raw materials, basic methods of processing, or plant site,
manufacturer shall submit for reapproval a statement of the proposed changes in ingredients and/or processing
and, when requested, sample coating. Production coating made by the revised procedure shall not be shipped
prior to receipt of reapproval.
4.5.5 The manufacturer shall submit a statement of any proposed changes per 4.5.4 to PRI for review by the applicable
SAE G-8 Qualified Products Group (QPG). The QPG may elect to reapprove without testing, or they may require
partial or full requalification testing to be performed before the manufacturer may ship product with the PRI QPL-
AMS-C-27725 seal.
4.6 Test Methods
Testing shall be as follows:
4.6.1 Standard Conditions
4.6.1.1 Test Conditions
Standard laboratory conditions shall be 77 °F ± 2 (25 °C ± 1) and 50 ± 5% relative humidity. Except as otherwise specified
herein, all test specimens shall be cured under these conditions.
Copyright SAE International
Provided by IHS under license with SAE Licensee=Defense Supply Ctr/5913977001
Not for Resale, 12/04/2007 21:18:08 MSTNo reproduction or networking permitted without license from IHS
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SAE AMS-C-27725B - 7 -
4.6.1.2 Standard Tolerances
Unless otherwise specified herein, Table 2 shows standard tolerances applied throughout test methods.
TABLE 2 - STANDARD TOLERANCES
Measurement
Units Tolerance
Temperatures ±2 °F (±1 °C)
Days ±2 hours
Hours ±5 minutes
Minutes ±10 seconds
Inches (mm) ±0.010 inch (0.25 mm)
4.6.2 Preparation of Test Panels
4.6.2.1 Description of Panels
Panels sizes and quantities shall be as shown in Table 3. Test panels shall be cut to the required dimensions prior to
chemical treatment.
a. Class A: Bare aluminum al