DOT/FAA/AR-95/81 **Corrosion of Aluminum Alloys in the Presence** **of
Fire-Retardant Aircraft Interior Materials**

FAA Technical Center

Atlantic City Airport,

NJ 08405

October, 1995

Final Report

This document is available to the public through the National Technical
Information Service, Springfield, Virginia 22161

NOTICE

> This document is disseminated under the sponsorship of the U.S.
> Department of Transportation in the interest of information exchange.
> The United States Government assumes no liability for the contents or
> use thereof.

U.S. Department of Transportation

**Federal Aviation Administration**

+-----------------+---------------+------+----------------+-----------+
| 1\. Report No.  | 2\.           |      | 3\.            |           |
|                 | Government    |      | Recipient's    |           |
| DO              | Accession No. |      | Catalog No.    |           |
| T/FAA/CT-94/110 |               |      |                |           |
+-----------------+---------------+------+----------------+-----------+
| 4\. Title and   |               |      |                |           |
| Subtitle        |               |      |                |           |
|                 |               |      |                |           |
| Corrosion of    |               |      |                |           |
| Aluminum Alloys |               |      |                |           |
| in the Presence |               |      |                |           |
| of              |               |      |                |           |
| Fire-Retardant  |               |      |                |           |
| Aircraft        |               |      |                |           |
| Interior        |               |      |                |           |
| Materials       |               |      |                |           |
+-----------------+---------------+------+----------------+-----------+
|                 |               |      |                |           |
+-----------------+---------------+------+----------------+-----------+
| 7\. Author(s)   |               |      |                |           |
|                 |               |      |                |           |
| > Dr. J. E.     |               |      |                |           |
| > Talia and Dr. |               |      |                |           |
| > J. Chaudhuri  |               |      |                |           |
+-----------------+---------------+------+----------------+-----------+
| 9\. Performing  |               |      |                |           |
| Organization    |               |      |                |           |
| Name and        |               |      |                |           |
| Address         |               |      |                |           |
|                 |               |      |                |           |
| National        |               |      |                |           |
| Institute for   |               |      |                |           |
| Aviation        |               |      |                |           |
| Research/       |               |      |                |           |
|                 |               |      |                |           |
| Mechanical      |               |      |                |           |
| Engineering     |               |      |                |           |
| Department      |               |      |                |           |
|                 |               |      |                |           |
| Wichita State   |               |      |                |           |
| University      |               |      |                |           |
|                 |               |      |                |           |
| Wichita, KS     |               |      |                |           |
| 67260-0035      |               |      |                |           |
+-----------------+---------------+------+----------------+-----------+
|                 |               |      |                |           |
+-----------------+---------------+------+----------------+-----------+
| 12\. Sponsoring |               |      |                |           |
| Agency Name and |               |      |                |           |
| Address         |               |      |                |           |
|                 |               |      |                |           |
| U. S.           |               |      |                |           |
| Department of   |               |      |                |           |
| Transportation  |               |      |                |           |
|                 |               |      |                |           |
| Federal         |               |      |                |           |
| Aviation        |               |      |                |           |
| Administration  |               |      |                |           |
|                 |               |      |                |           |
| Technical       |               |      |                |           |
| Center          |               |      |                |           |
|                 |               |      |                |           |
| Atlantic City   |               |      |                |           |
| International   |               |      |                |           |
| Airport, NJ     |               |      |                |           |
| 08405           |               |      |                |           |
+-----------------+---------------+------+----------------+-----------+
|                 |               |      |                |           |
+-----------------+---------------+------+----------------+-----------+
| 15\.            |               |      |                |           |
| Supplementary   |               |      |                |           |
| Notes           |               |      |                |           |
|                 |               |      |                |           |
| FAA COTR: Dr.   |               |      |                |           |
| Thomas Flournoy |               |      |                |           |
+-----------------+---------------+------+----------------+-----------+
| 16\. Abstract   |               |      |                |           |
|                 |               |      |                |           |
| This research   |               |      |                |           |
| project was to  |               |      |                |           |
| evaluate the    |               |      |                |           |
| potential for   |               |      |                |           |
| fire-retardant  |               |      |                |           |
| materials used  |               |      |                |           |
| in aircraft     |               |      |                |           |
| interiors to    |               |      |                |           |
| cause corrosion |               |      |                |           |
| of aluminum     |               |      |                |           |
| structural      |               |      |                |           |
| alloys. Service |               |      |                |           |
| Difficulty      |               |      |                |           |
| Reports (SDR's) |               |      |                |           |
| were reviewed   |               |      |                |           |
| for several     |               |      |                |           |
| aircraft types, |               |      |                |           |
| and the most    |               |      |                |           |
| frequent        |               |      |                |           |
| locations for   |               |      |                |           |
| corrosion were  |               |      |                |           |
| identified as   |               |      |                |           |
| fuselage,       |               |      |                |           |
| windows, and    |               |      |                |           |
| frames.         |               |      |                |           |
|                 |               |      |                |           |
| Laboratory      |               |      |                |           |
| experiments     |               |      |                |           |
| were designed   |               |      |                |           |
| and conducted   |               |      |                |           |
| for corrosion   |               |      |                |           |
| testing of      |               |      |                |           |
| common aircraft |               |      |                |           |
| structural      |               |      |                |           |
| alloys (Al      |               |      |                |           |
| 2024-T3 and Al  |               |      |                |           |
| 7075-T6) in the |               |      |                |           |
| presence of     |               |      |                |           |
| Ultrasuede,     |               |      |                |           |
| Glenlivit, and  |               |      |                |           |
| Highland Wool,  |               |      |                |           |
| common interior |               |      |                |           |
| materials.      |               |      |                |           |
| Accelerated     |               |      |                |           |
| corrosion test  |               |      |                |           |
| results showed  |               |      |                |           |
| that, for most  |               |      |                |           |
| test            |               |      |                |           |
| conditions,     |               |      |                |           |
| corrosion was   |               |      |                |           |
| increased for   |               |      |                |           |
| all three       |               |      |                |           |
| fire-retardant  |               |      |                |           |
| materials       |               |      |                |           |
| compared to     |               |      |                |           |
| baseline tests  |               |      |                |           |
| without fire    |               |      |                |           |
| retardants.     |               |      |                |           |
| Chemical        |               |      |                |           |
| composition     |               |      |                |           |
| from EDAX       |               |      |                |           |
| studies of the  |               |      |                |           |
| fire-retardants |               |      |                |           |
| revealed        |               |      |                |           |
| substantial     |               |      |                |           |
| halogens in     |               |      |                |           |
| Ultrasuede and  |               |      |                |           |
| Glenlivit, but  |               |      |                |           |
| negligible      |               |      |                |           |
| halogens in     |               |      |                |           |
| Highland Wool.  |               |      |                |           |
| Thus, the       |               |      |                |           |
| corrosion       |               |      |                |           |
| results cannot  |               |      |                |           |
| be attributed   |               |      |                |           |
| solely to       |               |      |                |           |
| halogens.       |               |      |                |           |
| Sulfur, which   |               |      |                |           |
| is present in   |               |      |                |           |
| substantial     |               |      |                |           |
| amounts in both |               |      |                |           |
| Glenlivit and   |               |      |                |           |
| Highland Wool,  |               |      |                |           |
| could be        |               |      |                |           |
| another cause   |               |      |                |           |
| for corrosion   |               |      |                |           |
| observed with   |               |      |                |           |
| these           |               |      |                |           |
| materials.      |               |      |                |           |
+-----------------+---------------+------+----------------+-----------+
| 17\. Key Words  |               | 18\. |                |           |
|                 |               | Dist |                |           |
| Fire Retardant  |               | ribu |                |           |
|                 |               | tion |                |           |
| Corrosion       |               | S    |                |           |
|                 |               | tate |                |           |
|                 |               | ment |                |           |
|                 |               |      |                |           |
|                 |               | This |                |           |
|                 |               | docu |                |           |
|                 |               | ment |                |           |
|                 |               | is   |                |           |
|                 |               | a    |                |           |
|                 |               | vail |                |           |
|                 |               | able |                |           |
|                 |               | to   |                |           |
|                 |               | the  |                |           |
|                 |               | pu   |                |           |
|                 |               | blic |                |           |
|                 |               | thr  |                |           |
|                 |               | ough |                |           |
|                 |               | the  |                |           |
|                 |               | Nati |                |           |
|                 |               | onal |                |           |
|                 |               | T    |                |           |
|                 |               | echn |                |           |
|                 |               | ical |                |           |
|                 |               | Inf  |                |           |
|                 |               | orma |                |           |
|                 |               | tion |                |           |
|                 |               | Serv |                |           |
|                 |               | ice, |                |           |
|                 |               |      |                |           |
|                 |               | Spri |                |           |
|                 |               | ngfi |                |           |
|                 |               | eld, |                |           |
|                 |               | VA   |                |           |
|                 |               | 2    |                |           |
|                 |               | 2161 |                |           |
+-----------------+---------------+------+----------------+-----------+
| 19\. Security   | 20\. Security |      |                |           |
| Classif . (of   | Classif. (of  |      |                |           |
| this report)    | this page)    |      |                |           |
|                 |               |      |                |           |
| Unclassified    | Unclassified  |      |                |           |
+-----------------+---------------+------+----------------+-----------+

Form DOT F 1700.7 ( ) Reproduction of completed page authorized

**TABLE OF CONTENTS**

Page

EXECUTIVE SUMMARY vii

1\. INTRODUCTION 1

2\. CORROSION CASES FROM AIRCRAFT SERVICE

DIFFICULTY REPORTS 1

3\. SUMMARY OF SERVICE DIFFICULTY REPORTS 5

4\. LABORATORY CORROSION EXPERIMENTS 8

5\. EVALUATION OF CORROSION 9

6\. CORROSION RESULTS 12

7\. CHEMICAL COMPOSITION OF THE FIRE-RETARDANT MATERIALS 30

8\. CONCLUDING REMARKS 34

9\. REFERENCES 35

**LIST OF FIGURES**

Figure Page

1\. Corrosion Cases from Service Difficulty Reports 6

2\. Corrosion Incidents by Location 7

3\. Assembly of Sandwich Test Specimen 9

4\. Micrograph of Al 7075-T6 With Ultrasuede, 100^o^F, 90% RH, 21 Days
10

(Severe Corrosion, 100 Points)

5\. Micrograph of Al 2024-T3 With Glenlivit, 100^o^F, 90% RH, 14 Days.
11

(Moderate Corrosion, 50 Points)

6\. Micrograph of Al 7075-T6 With Highland Wool, 70^o^F, 50% RH, 7 Days
11

(Minimal Corrosion, 5 Points)

7\. Al 2024-T3 With Ultrasuede, 100^o^F, 90% RH, 21 Days (50 Points) 12

8\. Al 2024-T3 With Ultrasuede, 130^o^F, 90% RH, 14 Days (80 Points) 13

9\. Al 7075-T6 With Ultrasuede, 70^o^F, 50% RH, 21 Days (40 points) 13

10\. Al 7075-T6 Alclad With Ultrasuede, 130^o^F, 90% RH, 21 Days (40
Points) 14

11\. Al 2024-T3 With Glenlivit, 100^o^F, 90% RH, 21 Days (65 Points) 14

12\. Al 2024-T3 Alclad With Glenlivit, 130^o^F, 50% RH, 14 Days (80
Points) 15

13\. Al 7075-T6 Alclad With Glenlivit, 130^o^F, 50% RH, 21 Days (55
Points) 15

14\. Al 2024-T3 With Glenlivit, 130^o^F, 90% RH, 21 Days (85 Points) 16

15\. Al 2024-T3 With Highland Wool, 70^o^F, 90% RH, 7 Days (40 Points)
16

16\. Al 7075-T6 With Highland Wool, 130^o^F, 50% RH, 7 Days (45 Points)
17

17\. Al 2024-T3 Alclad With Ultrasuede, 130^o^F, 90% RH, 14 Days (Cross
Section) 17

18\. Al 7075-T6 With Ultrasuede, 70^o^F, 90% RH, 14 Days (Cross Section)
18

19\. Al 7075-T6 With Glenlivit, 70^o^F, 50% RH, 14 Days (Cross Section)
18

20\. Al 7075-T6 With Glenlivit, 70^o^F, 50% RH, 21 Days (Cross Section)
19

**LIST OF FIGURES (CONTINUED)**

Number Page

21\. Al 2024-T3 Alclad With Highland Wool, 130^o^F, 90% RH, 21 Days
(Cross Section) 19

22\. Al 7075-T6 With Highland Wool, 70^o^F, 90% RH, 14 Days (Cross
Section) 20

23\. Average Corrosion Rating of Fire Retardants

with Al 2024-T3 (at 70^o^F/90% RH) 25

24\. Average Corrosion Rating of Fire Retardants

with Al 2024-T3 (at 100^o^F/50% RH) 25

25\. Average Corrosion Rating of Fire Retardants

with Al 2024-T3 (at 130^o^F/50% RH) 26

26\. Average Corrosion Rating of Fire Retardants

with Al 2024-T3 (at 130^o^F/90% RH) 26

27\. Average Corrosion Rating of Fire Retardants

with Al 2024-T3 Alclad (at 130^o^F/50% RH) 27

28\. Average Corrosion Rating of Fire Retardants

with Al 2024-T3 Alclad (at 130^o^F/90% RH) 27

29\. Average Corrosion Rating of Fire Retardants

with Al 7075-T6 (at 70^o^F/50% RH) 28

30\. Average Corrosion Rating of Fire Retardants

with Al 7075-T6 (at 130^o^F/50% RH) 28

31\. Average Corrosion Rating of Fire Retardants

with Al 7075-T6 (at 130^o^F/90% RH) 29

32\. Average Corrosion Rating of Fire Retardants

with Al 7075-T6 Alclad (at 130^o^F/50% RH) 29

33\. Average Corrosion Rating of Fire Retardants

with Al 7075-T6 Alclad (at 130^o^F/90%RH). 30

34\. EDAX Analysis of Fire-Retardant Ultrasuede 31

35\. EDAX Analysis of Fire-Retardant Glenlivit 32

36\. EDAX Analysis of Fire-Retardant Highland Wool 33

**LIST OF TABLES**

Table Page

1\. Reference Specimens 10

2\. Aluminum Control Specimens without Fire Retardant 21

3\. Average Corrosion Rating for Aluminum Specimens with Ultrasuede 22

4\. Average Corrosion Rating for Aluminum Speimens with Glenlivit 23

5\. Average Corrosion Rating for Aluminum Specimens with Highland Wool
24

6\. Elements Associated with Fire Retardants Present in Ultrasuede,
Glenlivit,

and Highland Wool. 34

**EXECUTIVE SUMMARY**

This research project was to evaluate the potential for fire-retardant
materials used in aircraft interiors to cause corrosion of aluminum
structural alloys. This work was initiated based on evidence of some
corrosion problems in general aviation, small business jets, and
commuter aircraft in areas near fire-retardant interior fabrics. Service
Difficulty Reports (SDR) data were studied to measure the magnitude of
the problem. Corrosion incidences were reviewed for several aircraft
types, and the most frequent locations for corrosion were identified as
fuselage, windows, and frames.

Laboratory experiments were designed and conducted for corrosion testing
of common aircraft structural alloys (Al 2024-T3 and Al 7075-T6) in the
presence of aircraft interior materials. Tests were conducted for
Ultrasuede, Glenlivit, and Highland Wool, common interior materials.
Accelerated corrosion test conditions included ambient and high
temperatures and high-humidity conditions. Control specimens of the
aluminum alloys were tested as a baseline without exposure to the fire
retardants. Results show that, for most test conditions, corrosion was
increased for all three fire-retardant materials compared to the
baseline tests without fire retardants. Chemical composition from EDAX
studies of the fire-retardants revealed substantial halogens in
Ultrasuede and Glenlivit, but negligible halogens in Highland Wool. Thus
the corrosion results cannot be attributed solely to halogens. Sulfur,
which is present in substantial amounts in both Glenlivit and Highland
Wool, could be another cause for corrosion observed with these
materials.

**[1. INTRODUCTION.]{.underline}**

The purpose of this research was to investigate the potentially
corrosive behavior of upholstery, floor, and wall covering material,
currently used in the interiors of general aviation and commuter
aircraft. Halogen salts have commonly been used to provide such
materials a level of fire retardancy. Federal Aviation Regulations (FAR)
23.853 and 25.853 established the requirement for fire retardancy of
seat cushions, and Advisory Circular AC 25.853-1 also addresses their
flammability requirements. However, service difficulty reports indicate
that the fire-retardant products which are currently being used might be
responsible for severe corrosion in aircraft interiors \[1,2,3\].

General corrosion and corrosion due to fire retardants in particular are
a strong function of environment. Alert No. 161, 1991\[4\], states:

\"Reports continue to be received concerning rapidly induced corrosion
possible from various flame-retardant fabrics used in aircraft
interiors. The latest reports involve a Jetstream 3101 and the
Gulfstream Commander 900, both of which had Ultrasuede 357 installed in
the cabin interior. Extensive corrosion was found on panels and
stringers where the material had been attached. Reports have been
received on a wide range of aircraft, including amateur-built, with
corrosion caused by the salts (usually bromide or chloride salts) which
are used to increase the flame retardancy of materials.

Fabrics which have been treated with any of the above salts can be
extremely corrosive when exposed to moisture of any nature. Corrosion
occurs very rapidly and is difficult to detect without removing the
material. In general, the more synthetic material in a fabric, the more
salts required to provide the desired flame retardancy. Metal surfaces
contacting this type of interior fabric must be properly treated in
order to avoid corrosion. Zinc chromate primer will not provide the
required corrosion protection. The use of acid etching and wash primer
treatment will provide protection.\"

This Alert and the cited Service Difficulty Reports implicating
fire-retardant materials in accelerated metal corrosion suggested that a
research program should be conducted to quantify this corrosion problem.
The program should include review of SDR\'s and laboratory experiments
to quantify corrosion of typical aircraft metals in the presence of
fire-retardant materials currently in use.

**[2. CORROSION CASES FROM AIRCRAFT SERVICE DIFFICULTY
REPORTS.]{.underline}**

Data were obtained from several pertinent sources including General
Aviation Airworthiness, \"Alerts,\" aircraft maintenance logs (Cessna),
and the FAA Service Difficulty Report data base for FAR part 23 aircraft
\[4,5\]. An extensive search of the Service Difficulty Report data base
was done to identify corrosion attributed to a fire-retardant treatment.

Aircraft that have had corrosion due to the use of fire-retardants and
have been cited in the data base are classified below. A brief summary
of the description of the corrosion as listed in the narrative is also
given.

**[PIPER]{.underline}**

Aircraft model PA28161, serial number 287916185;

A report of corrosion under rear seat. The possible cause was leakage at
rear seat window causing wetness of the fire-retardant insulation around
fitting.

Aircraft model PA23250, serial number 234405291;

A report of corroded longeron tube. Suspected cause was a water leak at
the left window where water soaked the side wall insulation.
Fire-retardant insulation resting on the tubing triggered corrosion.

Aircraft model PA23250, serial number 277654176;

A report of corrosion on 17134-44 tube and frame 3039206 at station
153.87 below door. Suspected cause was that the flame retardant
insulation had gotten wet and held water against the tubing. Corrosion
on the tube was found below the battery box.

Aircraft model PA23250, serial number 277554032;

A report of corrosion on 17134-44 tube at station 153.87 on right and
left tubes. Suspected cause was that the corrosion was caused by
flame-retardant.

Aircraft model PA23250, serial number 277754158;

A report of corrosion at station 153.87 on right side at cabin step.
Holes were put in tubes with scribe. This was probably caused by a
window leaking water and trapped by fiber glass insulation against the
tube.

Aircraft model PA28140, serial number 2825805;

A report of corrosion under left rear seat in the steel plate and rivet
heads; corrosion was found to have extended through half the thickness
of the plate. The possible cause was the fire-retardant insulation under
the seat holding water.

Aircraft model PA28151, serial number 287415687;

A report of steel fittings corrosion. The possible cause was the wet
fire-retardant insulation which was in contact with these steel parts.

Aircraft model PA28161, serial number 288116316;

A report of corrosion on the surface of the fitting P/N 62448-03 behind
the fiberglass insulation in the lower cockpit. The possible cause of
this corrosion was the moisture retained by the fiberglass insulation in
contact with the fittings.

Aircraft model PA28161, serial number 287816067;

Corrosion reported on right rear spar and left rear spar in the fittings
6244803 and 6244802 respectively. Moisture leaking in from a side window
caused the fiberglass insulation to become saturated. This insulation
contacts the fitting, the worst corrosion was noted under the
insulation, but very little corrosion was noted on the exposed portion
of the fitting outside the aircraft.

Aircraft model PA28181, serial number 288090326;

A report of corrosion in the fittings 6244802 and 6244803 located at
lower fuselage. The fittings were located inside the flap torque
tubewell, behind flap pillow blocks, and the submitter suggested that
the fire-retardant insulation held water and caused the corrosion.

Aircraft model PA28181, serial number 287890373;

A report of corrosion on plates 6244803 and 6244802 under rear seat.
Possible cause was the fire-retardant insulation packed under the rear
seat became soaked with water and caused these steel plates to corrode.

Aircraft model PA32300, serial number 327940243;

A report of corrosion on the fitting assembly 6538861 in the right wing
attachment. Corrosion had built up on steel rear spar attaching plate
and cabin caused by the fiber glass insulation holding water. There were
no drain holes forward of this bulkhead.

Aircraft model PA60600, serial number 600016;

Corrosion was reported on longerons 210028510, 210028525, and 210028506
on the extruded H sections. This seemed to have been caused by water
leaking through windows and being held by the longerons and
fire-retardant insulation materials.

Aircraft model PA23160, serial number 231626;

Corrosion reported in frame 1716206 on the lower fuselage. It appeared
that moisture was collecting at the point of contact of insulation on
the tube causing the corrosion.

Aircraft model PA23250, serial number 273335;

A report of corrosion on frame 3039205 in the fuselage. The corrosion
appeared to be caused by fire-retardant insulation between the fuselage
frame and the aircraft skin.

Aircraft model PA34200, serial number 3474T0131;

Corrosion reported on bracket 6252200 on the windshield. During
inspection it was found that the sponge type fire-retardant insulation
in this area trapped water from a leaking windshield seal.

**[BEECH]{.underline}**

Aircraft model 35A33, serial number CD277;

Corrosion reported on the stringers in the cabin right corner, and
pitting was formed on the inside surface of skin and stringers. This was
probably caused by a leaking door seal which allowed moisture to enter
and then became retained in the fire-retardant insulation.

Aircraft model B60, serial number P336;

Corrosion found extensively on structural fuselage in the cabin. This
seemed to have been caused by moisture trapped in the fire-retardant
insulation around structural members.

Aircraft model 58, serial number TH513;

Report of corrosion on the floor supports 0024400291, 0024400294,
0024400293, and 0024400292 from FS151-FS171. The corrosion reported was
intergranular corrosion. Cause of this corrosion was speculated to be
from the floor fire-retardant insulation holding water due to a leaking
frame door seal.

**[MOONEY]{.underline}**

Aircraft model M20J, serial number 240210;

Corrosion reported on tubes 340155021 and 340155061 in the frame. The
cause for corrosion was water retained by the fire-retardant insulation.

Aircraft model M20J, serial number 241098;

Corrosion reported on tubing 340155 at the window area. It was revealed
that the fire-retardant insulation was soaked with moisture from leaking
windows caused the corrosion.

Aircraft model M20J, serial number 240839;

Corrosion reported on tubing 340117 at the window area. Corrosion was
caused by soaked fire-retardant insulation, caused by leaks around left
cockpit windows.

Aircraft model M20J, serial number 240414;

A report of corrosion on the fuselage tube below pilot\'s window.
Corrosion was caused by window leakage soaking the fire-retardant
insulation.

Aircraft model M20J, serial number 240712;

Corrosion was reported on the structure in the fuselage. The problem
seemed to be caused by water entering the fuselage around the side
sections and was retained by the fire-retardant insulation.

Aircraft model M20J, serial number 240318;

Corrosion of tube 340155021 on left fuselage. It was revealed that the
fire-retardant insulation soaked with moisture from leaking windows
caused the corrosion.

Aircraft model M20J, serial number 240656;

Tubing part number 340155 was corroded through tubing wall and severely
pitted. Other tubing was also pitted as far back as left side of the
baggage bulk head. It was caused by deteriorated cabin window sealant.

Aircraft model M20J, serial number 240921;

Corrosion in the fuselage tubes was reported along with electrical
problems from the wires

and the connectors in this area. The fire-retardant insulation was
soaked with moisture and was the probable cause of corrosion.

Aircraft model M20J, serial number 240746;

Corrosion in the fuselage tubing. Water appeared to have entered side
panel areas through poor bonding of the sealer along the bottom of the
windows. This soaked the insulation and rusted the tubing.

Aircraft model M20K, serial number 250020;

Corrosion in tubings 350155009, 340177141, 350155061, 350155021, and
through the upper fuselage. It was found that corrosion was due to water
soaked fire-retardant insulation from a leak at angle P/N
320009-083+320013.

Aircraft model M20K, serial number 250047;

Corrosion in tube 340155067 in left hand side of the fuselage. Leaking
cabin side windows caused the corrosion of the tube structure.

**[CESSNA]{.underline}**

Aircraft model 337A, serial number 3370297;

There was a report of corrosion in the cabin roof interior from FS
135.45 to 165.09 and LBL 13.75 to RBL 13.75. The possible cause was that
three of the stiffeners were lying on the loose fire-retardant
insulation thus causing galvanic corrosion.

**[AEROSPATIAL]{.underline}**

Aircraft model ATR42300, serial number 37;

The frame in station 17319 was corroded. The fire-retardant insulation
blanket was found saturated with moisture and galley fluids which caused
the corrosion.

**[ROCKWELL]{.underline}**

Aircraft model NA26560, serial number 306131;

The main fuselage frame was found to have been corroded at fuselage
station 206. The frames are of 7178-T6 extrusion and the corrosion
appeared to be caused by moisture entering the fire-retardant insulation
around window area during manufacture.

**[3. SUMMARY OF SERVICE DIFFICULTY REPORTS.]{.underline}**

Figure 1 presents a histographic representation of various corrosion
cases from SDR\'s with respect to the aircraft manufacturers. Figure 2
presents the locations at which corrosion was reported in SDR\'s. This
graph illustrates that the most frequently observed corrosion was in the
fuselage, with especially high occurrences near windows and frames.

![](media/image1.emf){width="6.495833333333334in"
height="5.069444444444445in"}

![](media/image2.emf){width="6.495833333333334in"
height="4.407638888888889in"}

The following inferences and recommendations are made based on study of
the Service Difficulty Report data base.

Reports stated that most of the corrosion was due to the presence of
moisture in the fire-retardant insulation. In many of these cases the
presence of moisture was due to window leaks, saturation by galley
fluids, deterioration of cabin window sealant, and leaking door seals.
Following are a series of suggested practices based on review of the
SDR\'s:

1.  Windows should be leak proof and there should be no deterioration of
    window sealants.

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1.  Insulation should be contained in a plastic bag so that it does not
    rest directly against the aircraft skin or structure.

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```
1.  Interior of the aircraft should be coated with primer.

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```
1.  Regular visual inspections should be conducted of the insulation in
    areas that can retain water.

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```
1.  Insulation should be removed and dried if moisture gets in. It
    should not come in contact with metallic parts \[7,8\].

The Service Difficulty Report Data Base clearly raised the question
concerning the role of fire-retardant treated materials in accelerated
metal corrosion. The lack of pertinent data regarding fire-retardant
corrosion suggested the need of controlled laboratory experiments to
quantify the problem. To evaluate the corrosiveness of various fire
retardants, the following experimental program was designed.

**[4. LABORATORY CORROSION EXPERIMENTS.]{.underline}**

After thorough consideration and research of the existing interiors of
small planes, two aircraft structural aluminum alloys, Al 2024-T3 and Al
7075-T6 (bare and clad), were selected to represent the most common
materials for floor panels, seats, side wall, and floor tracks \[6\].
After consultation with local small aircraft manufacturers such as
Cessna and Beechcraft, and fire- retardant product manufacturers, three
fire-retardant aircraft interior materials were selected for
experiments: 1) Ultrasuede, 2) Glenlivit and 3) Highland Wool. In a
generic sense, most fire retardants in current use are halide based
(bromides, chlorides or fluorides). Ultrasuede and Glenlivit
fire-retardants were provided by the Tapis Corporation, and Highland
Wool was provided by Cessna Aircraft Company.

The several experimental approaches available \[9,10,20\] were
thoroughly investigated and the search for appropriate testing procedure
was narrowed down to the sandwich test. This test method was also
recommended by the Tapis Corporation and United States Testing Company,
Inc. for evaluating the corrosiveness of fire-retardant materials on
aluminum alloys. Alloys, specimen size and fire-retardant aircraft
interior materials used during experiments were:

Alloy: Al 2024-T3 & Al 7075-T6 bare and clad

Specimen size: 2 x 2 inch x 0.040 inch thick

(51 x 51 mm x 1.02 mm thick)

Fire-retardant aircraft materials: Ultrasuede, Glenlivit, Highland Wool

Surfaces of the specimens were cleaned using isopropyl alcohol before
the tests. Corrosion test articles consisted of the fire-retardant
material \"sandwiched\" between two aluminum specimens, with a masking
tape wrap to maintain uniform contact between the aluminum and the
fire-retardant material.(See Figure 3.) The sandwich was then placed in
the environmental chamber where the desired humidity and temperature
were accurately maintained with digital humidistat and thermostat.

Over 288 tests were performed at room temperature (70^o^F) and at
elevated temperatures (100^o^F and 130^o^F), with humidity varying from
50% to 90% for the purpose of accelerating the corrosion process. Time
periods used were: 7, 14, and 21 days. These tests included [Control
specimens]{.underline} for each aluminum alloy which were tested
[without]{.underline} fire-retardant material applied to determine basic
corrosion of the aluminum alloy as a function of temperature and
humidity.

![](media/image3.emf){width="6.5in" height="4.308333333333334in"}

FIGURE 3. ASSEMBLY OF SANDWICH TEST SPECIMEN

After the exposure period, the test and control specimens were removed
from the chamber and the fire-retardant material was carefully separated
from the aluminum test article. Specimen surfaces were cleaned with warm
tap water and wiped with a clean, soft cloth. Specimen panels were
photographed with an ordinary camera to record the appearance of the
corrosion to the un-aided eye. Later each specimen was examined using an
optical microscope and micrographs were prepared. Corrosion
characteristics such as uniformity of corrosion and severity of pitting
were recorded.

**[5. EVALUATION OF CORROSION]{.underline}**

In order to **grade** corrosion, **three corroded specimens** to be used
as references were selected from all the test specimens. The specimens
selected were judged to be examples of **severe**, **moderate** and
**minimal** corrosion. An arbitrary corrosion level value of 100 was
assigned to the specimen judged to have severe corrosion, a value of 50
was assigned to the specimen judged to have moderate corrosion, and a
value of 5 was assigned to the specimen judged to have minimal
corrosion. Table 1 details the specimens selected as references based on
an analysis of the specimen micrographs. Rating for all other specimens
was done by comparing the appearance of each specimen with these three
reference specimens and interpolating the number to be assigned.
Micrographs of the three reference specimens are shown in Figures 4, 5,
and 6.

TABLE 1. REFERENCE SPECIMENS

+--------------+------------+-------------+-------------+------------+
| Sample       | T          | Humidity    | Duration    | Rating     |
|              | emperature |             |             |            |
| Material     |            | (%)         | (Days)      |            |
|              | (Deg. F)   |             |             |            |
+--------------+------------+-------------+-------------+------------+
| FR7075-T6    | 100        | 90          | 21          | 100        |
|              |            |             |             |            |
| (Ultrasuede) |            |             |             |            |
+--------------+------------+-------------+-------------+------------+
| FR2024-T3    | 100        | 90          | 14          | 50         |
|              |            |             |             |            |
| (Glenlivit)  |            |             |             |            |
+--------------+------------+-------------+-------------+------------+
| FR7075-T6    | 70         | 50          | 7           | 5          |
|              |            |             |             |            |
| (Highland    |            |             |             |            |
| Wool)        |            |             |             |            |
+--------------+------------+-------------+-------------+------------+

Detailed results of these evaluations for 288 specimen sets are given in
Tables 2 through 5 in the following section. Each specimen rating listed
in the tables indicates the average value for three identical material
specimens tested at the same conditions.

![](media/image4.emf){width="6.497916666666667in"
height="3.9604166666666667in"}

![](media/image5.emf){width="6.497222222222222in"
height="9.073611111111111in"}

**[6. CORROSION RESULTS.]{.underline}**

Typical optical micrographs for specimens in each category are presented
in figures 7 through 16. Cross sections were cut from the samples and
optical micrography was performed where the depth of pitting was the
greatest. Figures 17 to 22 present selected cross-sectional micrographs.

The corrosion rating was averaged for each set of three specimens and
for the three time durations (average of a total of nine specimens).
GB-STAT and STORM \[11\] software systems were utilized for entry,
storage, editing, manipulation, graphics, and statistical analysis of
numeric data as they were gathered during corrosion experiments.

Corrosion ratings for each condition with different aluminum alloys,
cabin interior materials and various combinations of temperature and
humidity for the 288 specimen test sets are shown in Tables 2, 3, 4 and
5, and illustrated graphically in Figures 23 through 33. The rating for
each test condition shown is an average for three distinct specimens at
that condition. An average for the three different time periods (7, 14,
and 21 days) at each temperature and humidity condition is also shown in
these tables. In most test conditions, the data show that the intensity
of corrosion was increased in the presence of a fire-retardant product.
Figures 23 through 33 present data selected from Tables 2, 3, 4, and 5
to illustrate the relative corrosive behavior of the three fire
retardants at different test conditions of temperature and humidity. The
corrosion values presented in these tables are the average of the 7, 14,
and 21 day tests for each material at the temperature and humidity
conditions noted.

![](media/image6.emf){width="6.153472222222222in"
height="3.777083333333333in"}

![](media/image7.emf){width="6.497222222222222in"
height="9.073611111111111in"}

![](media/image8.emf){width="6.497222222222222in"
height="9.073611111111111in"}

![](media/image9.emf){width="6.497222222222222in"
height="9.073611111111111in"}

![](media/image10.emf){width="6.497222222222222in"
height="9.073611111111111in"}

![](media/image11.emf){width="6.497222222222222in"
height="9.073611111111111in"}

![](media/image12.emf){width="6.497222222222222in"
height="9.073611111111111in"}

![](media/image13.emf){width="6.497222222222222in"
height="9.073611111111111in"}

![](media/image14.emf){width="6.497222222222222in"
height="9.073611111111111in"}

TABLE 2. ALUMINUM CONTROL SPECIMENS WITHOUT FIRE RETARDANT

+-----------+----------+--------+-------+---------+--------+---------+
| Sample    | Tem      | Hu     | Rat   |         |        | Average |
|           | perature | midity | ing\* |         |        |         |
| Material  |          |        |       |         |        | Rating  |
|           | (Deg F)  | (%)    |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+
|           |          |        | 7     | 14 Days | 21     |         |
|           |          |        | Days  |         | Days   |         |
+-----------+----------+--------+-------+---------+--------+---------+
| AL2024‑T3 | 70       | 50     | 10    | 12      | 20     | 14      |
+-----------+----------+--------+-------+---------+--------+---------+
| +         | 70       | 90     | 14    | 15      | 22     | 17      |
| AL2024‑T3 |          |        |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+
| +         | 100      | 50     | 10    | 15      | 14     | 13      |
| AL2024‑T3 |          |        |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+
| AL2024‑T3 | 100      | 90     | 8     | 12      | 20     | 13.3    |
+-----------+----------+--------+-------+---------+--------+---------+
| +         | 130      | 50     | 10    | 12      | 15     | 12.3    |
| AL2024‑T3 |          |        |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+
| +         | 130      | 90     | 10    | 20      | 25     | 18.3    |
| AL2024‑T3 |          |        |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+
| A         | 70       | 50     | 6     | 5       | 7      | 6       |
| L2024A‑T3 |          |        |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+
| A         | 70       | 90     | 8     | 12      | 14     | 11.3    |
| L2024A‑T3 |          |        |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+
| A         | 100      | 50     | 6     | 10      | 10     | 8.7     |
| L2024A‑T3 |          |        |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+
| A         | 100      | 90     | 8     | 14      | 14     | 12      |
| L2024A‑T3 |          |        |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+
| +A        | 130      | 50     | 2     | 6       | 7      | 5       |
| L2024A‑T3 |          |        |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+
| +A        | 130      | 90     | 5     | 10      | 6      | 7       |
| L2024A‑T3 |          |        |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+
| +         | 70       | 50     | 2     | 5       | 5      | 4       |
| AL7075‑T6 |          |        |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+
| AL7075‑T6 | 70       | 90     | 10    | 17      | 25     | 17.3    |
+-----------+----------+--------+-------+---------+--------+---------+
| AL7075‑T6 | 100      | 50     | 15    | 22      | 30     | 22.3    |
+-----------+----------+--------+-------+---------+--------+---------+
| AL7075‑T6 | 100      | 90     | 10    | 18      | 15     | 14.3    |
+-----------+----------+--------+-------+---------+--------+---------+
| +         | 130      | 50     | 15    | 18      | 12     | 15      |
| AL7075‑T6 |          |        |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+
| +         | 130      | 90     | 12    | 13      | 20     | 15      |
| AL7075‑T6 |          |        |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+
| A         | 70       | 50     | 3     | 8       | 10     | 7       |
| L7075A‑T6 |          |        |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+
| A         | 70       | 90     | 8     | 12      | 15     | 11.7    |
| L7075A‑T6 |          |        |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+
| A         | 100      | 50     | 8     | 15      | 9      | 10.7    |
| L7075A‑T6 |          |        |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+
| A         | 100      | 90     | 9     | 15      | 14     | 12.67   |
| L7075A‑T6 |          |        |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+
| +A        | 130      | 50     | 10    | 18      | 17     | 15      |
| L7075A‑T6 |          |        |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+
| +A        | 130      | 90     | 2     | 5       | 5      | 4       |
| L7075A‑T6 |          |        |       |         |        |         |
+-----------+----------+--------+-------+---------+--------+---------+

\* Rating is the average of 3 specimens.

\+ Average rating for these conditions for all fire-retardant materials
are graphically displayed in figures 23 through 33.

NOTE: AL2024-T3 designates Al 2024-T3, AL2024A-T3 designates Al 2024-T3
Alclad, AL7075 designates Al 7075-T6, all tested in the absence of
fire-retardant material.

TABLE 3. AVERAGE CORROSION RATING FOR ALUMINUM SPECIMENS WITH ULTRASUEDE

+-----------+----------+---------+-------+---------+--------+--------+
| Sample    | Tem      | H       | Rat   |         |        | A      |
|           | perature | umidity | ing\* |         |        | verage |
| Material  |          |         |       |         |        | Rating |
|           | (Deg F)  | (%)     |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
|           |          |         | 7     | 14 Days | 21     |        |
|           |          |         | Days  |         | Days   |        |
+-----------+----------+---------+-------+---------+--------+--------+
| FR2024‑T3 | 70       | 50      | 8     | 10      | 16     | 11.3   |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 70       | 90      | 75    | 85      | 85     | 81.7   |
| FR2024‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 100      | 50      | 40    | 40      | 55     | 45     |
| FR2024‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| FR2024‑T3 | 100      | 90      | 65    | 70      | 50     | 61.7   |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 130      | 50      | 30    | 80      | 40     | 50     |
| FR2024‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 130      | 90      | 50    | 80      | 60     | 63.3   |
| FR2024‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 70       | 50      | 5     | 10      | 10     | 8.3    |
| R2024A‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 70       | 90      | 10    | 8       | 15     | 11     |
| R2024A‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 100      | 50      | 10    | 20      | 55     | 28.3   |
| R2024A‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 100      | 90      | 25    | 60      | 65     | 50     |
| R2024A‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +F        | 130      | 50      | 75    | 60      | 85     | 73.3   |
| R2024A‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +F        | 130      | 90      | 60    | 50      | 95     | 68.3   |
| R2024A‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 70       | 50      | 10    | 10      | 40     | 20     |
| FR7075‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| FR7075‑T6 | 70       | 90      | 80    | 65      | 80     | 75     |
+-----------+----------+---------+-------+---------+--------+--------+
| FR7075‑T6 | 100      | 50      | 10    | 30      | 65     | 35     |
+-----------+----------+---------+-------+---------+--------+--------+
| FR7075‑T6 | 100      | 90      | 70    | 70      | 75     | 71.7   |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 130      | 50      | 30    | 45      | 60     | 45     |
| FR7075‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 130      | 90      | 5     | 5       | 15     | 8.3    |
| FR7075‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 70       | 50      | 5     | 8       | 20     | 11     |
| R7075A‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 70       | 90      | 50    | 50      | 60     | 53.3   |
| R7075A‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 100      | 50      | 10    | 10      | 30     | 16.7   |
| R7075A‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 100      | 90      | 10    | 18      | 40     | 22.7   |
| R7075A‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +F        | 130      | 50      | 15    | 40      | 70     | 41.7   |
| R7075A‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +F        | 130      | 90      | 40    | 15      | 40     | 31.7   |
| R7075A‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+

\*Rating is the average of 3 specimens.

\+ Average rating for these conditions for all fire-retardant materials
are graphically displayed in figures 23 through 33.

NOTE: FR2024-T3 designates Al 2024-T3, FR2024A-T3 designates Al 2024-T3
Alclad, FR7075-T6 designates Al 7075-T6, and FR7075A-T6 designates Al
7075-T6 Alclad, all with Ultrasuede.

TABLE 4. AVERAGE CORROSION RATING FOR ALUMINUM SPECIMENS WITH GLENLIVIT

+-----------+----------+---------+-------+---------+--------+--------+
| Sample    | Tem      | H       | Rat   |         |        | A      |
|           | perature | umidity | ing\* |         |        | verage |
| Material  |          |         |       |         |        |        |
|           | (Deg F)  | (%)     |       |         |        | Rating |
+-----------+----------+---------+-------+---------+--------+--------+
|           |          |         | 7     | 14 Days | 21     |        |
|           |          |         | Days  |         | Days   |        |
+-----------+----------+---------+-------+---------+--------+--------+
| FR2024‑T3 | 70       | 50      | 12    | 15      | 20     | 15.7   |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 70       | 90      | 50    | 70      | 80     | 66.7   |
| FR2024‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 100      | 50      | 30    | 45      | 75     | 50     |
| FR2024‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| FR2024‑T3 | 100      | 90      | 65    | 75      | 80     | 73.3   |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 130      | 50      | 20    | 60      | 75     | 51.6   |
| FR2024‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 130      | 90      | 20    | 18      | 85     | 41     |
| FR2024‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 70       | 50      | 8     | 12      | 18     | 12.7   |
| R2024A‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 70       | 90      | 20    | 32      | 40     | 30.7   |
| R2024A‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 100      | 50      | 15    | 20      | 60     | 31.7   |
| R2024A‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 100      | 90      | 15    | 50      | 60     | 41.7   |
| R2024A‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +F        | 130      | 50      | 35    | 80      | 85     | 66.7   |
| R2024A‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +F        | 130      | 90      | 25    | 85      | 75     | 61.7   |
| R2024A‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 70       | 50      | 40    | 70      | 50     | 53.3   |
| FR7075‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| FR7075‑T6 | 70       | 90      | 25    | 85      | 80     | 63.3   |
+-----------+----------+---------+-------+---------+--------+--------+
| FR7075‑T6 | 100      | 50      | 20    | 30      | 85     | 45     |
+-----------+----------+---------+-------+---------+--------+--------+
| FR7075‑T6 | 100      | 90      | 65    | 70      | 85     | 73.3   |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 130      | 50      | 25    | 47      | 70     | 47.3   |
| FR7075‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 130      | 90      | 50    | 20      | 30     | 33.3   |
| FR7075‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 70       | 50      | 10    | 8       | 25     | 14.3   |
| R7075A‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 70       | 90      | 40    | 45      | 80     | 55     |
| R7075A‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 100      | 50      | 7     | 15      | 35     | 19     |
| R7075A‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 100      | 90      | 20    | 25      | 35     | 26.7   |
| R7075A‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +F        | 130      | 50      | 20    | 40      | 55     | 38.3   |
| R7075A‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +F        | 130      | 90      | 20    | 40      | 60     | 40     |
| R7075A‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+

\*Rating is the average of 3 specimens.

\+ Average rating for these conditions for all fire-retardant materials
are graphically displayed in figures 23 through 33.

NOTE: FR2024-T3 designates Al 2024-T3, FR2024A-T3 designates Al 2024-T3
Alclad, FR7075-T6 designates Al 7075-T6, and FR7075A-T6 designates Al
7075-T6 Alclad, all with Glenlivit.

TABLE 5. AVERAGE CORROSION RATING FOR ALUMINUM SPECIMENS WITH HIGHLAND
WOOL

+-----------+----------+---------+-------+---------+--------+--------+
| Sample    | Tem      | H       | Rat   |         |        | A      |
|           | perature | umidity | ing\* |         |        | verage |
| Material  |          |         |       |         |        | Rating |
|           | (Deg F)  | (%)     |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
|           |          |         | 7     | 14 Days | 21     |        |
|           |          |         | Days  |         | Days   |        |
+-----------+----------+---------+-------+---------+--------+--------+
| FR2024‑T3 | 70       | 50      | 8     | 40      | 15     | 21     |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 70       | 90      | 40    | 75      | 50     | 55     |
| FR2024‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 100      | 50      | 25    | 50      | 45     | 40     |
| FR2024‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| FR2024‑T3 | 100      | 90      | 30    | 70      | 35     | 45     |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 130      | 50      | 35    | 60      | 60     | 51.7   |
| FR2024‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 130      | 90      | 35    | 35      | 80     | 50     |
| FR2024‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 70       | 50      | 10    | 18      | 20     | 16     |
| R2024A‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 70       | 90      | 12    | 22      | 18     | 17.3   |
| R2024A‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 100      | 50      | 28    | 20      | 40     | 29.3   |
| R2024A‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 100      | 90      | 20    | 35      | 50     | 35     |
| R2024A‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +F        | 130      | 50      | 55    | 40      | 45     | 46.7   |
| R2024A‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +F        | 130      | 90      | 35    | 65      | 45     | 48.3   |
| R2024A‑T3 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 70       | 50      | 15    | 20      | 30     | 21.7   |
| FR7075‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| FR7075‑T6 | 70       | 90      | 50    | 90      | 65     | 68.3   |
+-----------+----------+---------+-------+---------+--------+--------+
| FR7075‑T6 | 100      | 50      | 25    | 35      | 65     | 41.7   |
+-----------+----------+---------+-------+---------+--------+--------+
| FR7075‑T6 | 100      | 90      | 30    | 65      | 75     | 56.7   |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 130      | 50      | 25    | 35      | 75     | 45     |
| FR7075‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +         | 130      | 90      | 45    | 80      | 50     | 58.3   |
| FR7075‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 70       | 50      | 5     | 8       | 10     | 7.7    |
| R7075A‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 70       | 90      | 8     | 15      | 12     | 11.7   |
| R7075A‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 100      | 50      | 45    | 55      | 35     | 45     |
| R7075A‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| F         | 100      | 90      | 10    | 20      | 18     | 16     |
| R7075A‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +F        | 130      | 50      | 50    | 20      | 45     | 38.3   |
| R7075A‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+
| +F        | 130      | 90      | 15    | 60      | 65     | 46.7   |
| R7075A‑T6 |          |         |       |         |        |        |
+-----------+----------+---------+-------+---------+--------+--------+

\*Rating is the average of 3 specimens.

\+ Average rating for these conditions for all fire-retardant materials
are graphically displayed in figures 23 through 33.

NOTE: FR2024-T3 designates Al 2024-T3, FR2024A-T3 designates Al 2024-T3
Alclad, FR7075-T6 designates Al 7075-T6, and FR7075A-T6 designates Al
7075-T6 Alclad, all with Highland Wool.

![](media/image15.emf){width="6.497222222222222in"
height="9.073611111111111in"}

![](media/image16.emf){width="6.497222222222222in"
height="9.073611111111111in"}

![](media/image17.emf){width="6.497222222222222in"
height="9.073611111111111in"}

![](media/image18.emf){width="6.497222222222222in"
height="9.073611111111111in"}

![](media/image19.emf){width="6.497222222222222in"
height="9.073611111111111in"}

![](media/image20.emf){width="6.497222222222222in"
height="4.664583333333334in"}

**[7. CHEMICAL COMPOSITION OF THE FIRE-RETARDANT
MATERIALS.]{.underline}**

Ultrasuede, Glenlivit and Highland Wool are fire-retardant materials
commonly used in aircraft seats and wall coverings. In order to identify
the specific corrosion-causing element, the chemical composition of the
fire-retardant must be known. Due to its proprietary nature, this
information is not generally released by the manufacturers. This
information was obtained by EDAX (Electron Dispersion Analysis of
X-rays) microanalysis. X-ray microanalysis graphs for the three aircraft
interior fire-retardant materials are given in Figures 34 to 36. The
tests were performed to exclude the majority content of hydrocarbons and
other materials usually present in interior fabrics and amplified the
ability to detect small levels of elements. Table 6 summarizes the
results of an EDAX analysis for elements usually associated with the
fire retardants. The result given is the mass percent of the given
element of the total mass of the elements selected for measurement.
Halogen peaks in the EDAX analysis of Ultrasuede show approximately 32%
bromine and 23% chlorine. In Glenlivit, negligible bromine and
approximately 21% chlorine was found. A negligible amount of bromine and
only 0.2% chlorine was found in Highland Wool. There was a significant
amount of sulfur present in Glenlivit (49.3%) and Highland Wool (46.7%),
but none was observed in the Ultrasuede material. The absence of
significant halogen content for Highland Wool and significant sulfur
content for Ultrasuede discounts the ideas that either halogens or
sulfur are unique causes of increased corrosion.

![](media/image21.emf){width="6.497222222222222in"
height="9.073611111111111in"}

![](media/image22.emf){width="6.497222222222222in"
height="9.073611111111111in"}

![](media/image23.emf){width="6.497222222222222in"
height="9.073611111111111in"}

TABLE 6. ELEMENTS ASSOCIATED WITH FIRE RETARDANTS PRESENT IN

ULTRASUEDE, GLENLIVIT, AND HIGHLAND WOOL.

  ----------------- ------------------ ----------------- -----------------
                    Mass Percentage of                   
                    Total Measurement                    

  Element           Ultrasuede         Glenlivit         Highland Wool

  Bromine           32.1               \-                \-

  Fluorine          \-                 3.6               \-

  Chlorine          23.0               21.6              0.2

  Zirconium         \-                 22.5              \-

  Sulfur            \-                 49.3              46.7

  Silicon           10.9               3.0               \-

  Phosphorus        \-                 \-                40.9

  Argon             \-                 \-                8.5

  Calcium           18.3               \-                3.7

  Potassium         15.7               \-                \-

  Totals            100.0              100.0             100.0
  ----------------- ------------------ ----------------- -----------------

**[8. CONCLUDING REMARKS.]{.underline}**

This research project evaluated the potential for fire-retardant
materials used in aircraft interiors to cause corrosion of aluminum
structural alloys. This work was initiated based on evidence of some
corrosion problems in general aviation, small business jets and commuter
aircraft, in areas near fire-retardant interior materials.

Service Difficulty Reports (SDR) data were studied to identify the
frequency of fire-retardant related corrosion. The most frequent
locations for corrosion were identified as fuselage and windows and
frames.

Laboratory experiments were designed and conducted for corrosion testing
of common aircraft structural alloys (Al 2024-T3 and Al 7075-T6) in the
presence of aircraft interior materials. Tests were conducted for
Ultrasuede, Glenlivit and Highland Wool, common interior materials.

Results of accelerated corrosion tests show that corrosion was increased
for all three fire-retardant materials under most test conditions
compared to baseline tests without fire retardants.

Chemical composition from EDAX studies of the fire-retardants reveal
substantial halogens in Ultrasuede and Glenlivit, but negligible
halogens in Highland Wool. Thus the corrosion results cannot be
attributed solely to halogens.

Sulfur, which is present in substantial amounts in both Glenlivit and
Highland Wool, could be another cause for corrosion observed with these
materials.

**[9. REFERENCES]{.underline}**.

1\. Federal Aviation Administration, \"Flammability Requirements for
Aircraft Seat Cushions, 25.853-1\", 1986.

2\. AGARD, \"Aircraft Fire Safety\", AGARD lectures series No. 123.

3\. G. A. Gehring, Jr. and C. W. George, \"Guidelines for Preventing
Fire Retardant Corrosion\", U.S. Government Printing Office, 1986.

4\. General Aviation, Airworthiness (FAA), \"ALERTS\", Alert No. 161,
1991.

5\. \"Service Difficulty Report Data\", Prepared by the operational
systems branch/AFS-620, Oklahoma City, FAA, 1980 to date.

6\. V. M. Bhatnagar, \"Advances in Fire Retardant Textiles\", Technomic
Publishing Co. Inc., 1975.

7\. L. K. Chew, \"Corrosion Experience On Inservice Airplanes\",
Singapore Airlines, 1991.

8\. M. Atkinson, \"Corrosion and its Control\", National Association of
Corrosion Engineers, 1982.

9\. S. V. Crume, \"A Corrosiveness Test for Fibrous Insulations\", ASTM
STP 866, p 215, 1985.

10\. ASTM Standards, G1-81, ASTM STP, 866, p 505.

11\. Emmons, \"STORM\", H. Holden-Day, Inc, 1993.

12\. ASM International, \"Metals HandBook\", 13, 1987.

13\. Hanes and Baboin, \"Laboratory Corrosion Tests and Standards\",
ASTM Special Technical Publication 866, 1985.

14\. M. G. Fontana, \"Corrosion Engineering\", Mc. Graw-Hill Inc., 1986.

15\. J. W. Lysons, \"The Chemistry and Use of Fire Retardants\", Wiley
and Sons Inc., 1970.

16\. AGARD, \"Fire Worthiness of Transport Aircraft Interior System\",
AGARD CP 166.

17\. H. Buchert, E. Koch, et al., \"Aircraft Interiors, Flammability
Impact Maintenance and Refurbishing Technology\", Third Conference for
NIAR, Wichita State University, 1991.

18\. F. D. Bogar and R. T. Foley, \"The Influence of Chloride Ion on the
Pitting of Aluminum\", J. Electrochem. Soc., 119, 462, 1972.

19\. ASTM, \"Standard Method of Salt Spray (Fog) Testing\", B117 Annual
Book of ASTM Standards, 1985.

20\. Sandwich Test Report, United States Testing Company Inc., No.
052281, 1992.

21\. R. S. Treseder, \"NACE Corrosion Engineer\'s Reference Book\",
National Association of Corrosion Engineers, 1980.