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DEPARTMENT OF MATERIALS ENGINEERING
MTRL 456:
ENVIRONMENTAL DEGRADATION IN MATERIALS ENGINEERING
Term Project:
Corrosion Prevention Technique Based on Aircraft Accident Report El Al Flight 1862
Boeing 747
Daniel Shim
Igor Vranjes
Muhammad Arshad Hasni
Muhammad Harith Mohd Fauzi
Vishal Sharma

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Abstract
As one may be aware, metals never stay in the same shape as they have an evitable
tendency to rust and degrade over time. If we look around the environment we live in, we
are surrounded by numerous applications of metals. These can be large buildings,
airplanes or even the cars we drive everyday as they all contain metal components that
are prone to corrosion. The issues that result from metals corroding is not as simple as
one may think. In fact, it may be one of the several complex problems that materials
engineers deal with in the industry today. For most instances, the majority of everyday
people cannot identify from the naked eye that a metal is undergoing corrosion. Even
though a certain metal may appear to be in great condition, an engineer must perform
diligent inspection to ensure that the fatigue or degradation of the metal be quantified and
understood.
Corrosion occurs when a reaction takes place between a metal and its environment.
Thermodynamics allows engineers to determine if a reaction is possible to occur. Then,
whether that reaction occurs fast enough to be a practical concern is defined by reaction
kinetics, as it takes into account heat and mass transfer as well as material properties.
There are 3 different behaviors a metal can behave in an environment: immune, active,
and passive. At certain environmental conditions, a metal can be considered having an
immune behavior and this is when the metal is safe or corrosion prevented. Passive
behavior is also a desirable trait, as a thin reaction product film is formed on the surface
of the metal, which greatly reduces the corrosion rate. Active behavior is when the metal
is corroding at a significant rate in a given environmental condition. This active behavior
can lead to degradation and eventual failure of a metal, putting the public in danger.
In this report, we will examine a case of corrosion-related engineering failure that
occurred in a Boeing 747 plane.

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Introduction
On October 1992, an EL AL 747 freighter crashed in the city of Amsterdam, The
Netherlands as a result of corrosion failure. The accident resulted in deaths of all four
people on board and over 50 people civilians on the ground. The main cause of the
accident was due to the corroded connection of the engines and the wings, resulting in an
uncontrollable separation of the No.3 and No.4 engines from the wing. The structural
component that makes this connection and holds the engine and strut to the wing are
called fuse pins. Under normal operating conditions, the role of the fuse pin is to cause
separation of the engine and the wing, in order to protect the fuselage from engine fire in
the event of a crash.
The No.3 and No.4 engines on the right side of the plane were torn apart from the
fuselage due to the failure of the fuse pin. It was determined that the inboard fuse pin of
the No.3 engine failed due to corrosion cracking and fatigue. The engine then became
unstable and vibrated to an extent where fuel began to leak. The leak led to a fire and the
other fuse pins failed by overload and heating, causing the No.3 and No.4 engines to tear
off from the plane. This corrosion failure in the fuse pin was the ultimate factor to the
tragic accident.
In order to avoid such tragedy or further accidents, engineers must ensure that
corrosion can be predicted and managed. In the following sections, we will propose three
solutions to this issue that will prevent corrosion-related failure. The solutions include
cathodic protection, electropolishing and application of stainless steel as the material for
the fuse pin
Solution 1: Cathodic Protection
Original Material: steel SAE 4330M
One simple way to prevent the corrosion pitting of the pylon pins would be to
coat the pins with Zn. Since Zn has a more negative reduction potential than Fe (-.763 V
vs. -.44 V respectively), the Zn will become oxidized (anode) and the steel will be
reduced (cathode) in the electrochemical reaction between the two metals. This will result

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in the Zn corroding on the outside of the base steel material while the steel remains
protected. This is termed cathodic protection.
The Zn coating will protect the steel in a number of different ways. First of all, as
mentioned previously, the Zn will serve as a sacrificial anode and reduce the underlying
steel to ensure corrosion of the steel does not occur. Secondly, the thin Zn layer applied
to the steel will present a physical barrier between the steel and the corrosive
environment. The Zn layer will effectively reduce/eliminate the mass transport of the
corrosive reactants to the steel. Finally, due to the fact that the Zn will be corroding, the
Zn will form a passive oxide layer on top of the steel which will further protect the steel.
The very nature of oxides are that they are generally stable, which is why we see most
metals in nature occurring in their oxide forms. This stability of oxides is what allows the
Zn oxide layer to protect the steel from a variety corrosion attacks.
In terms of technological feasibility, this should be a relatively simple procedure
to undertake due to the fact that using zinc to cathodically protect the steel has been
common practice for many years.
When looking at the economics of Zn cathodic protection, using reference graphs
(Rahrig, n.d.) we can say that for a plane to have a very conservative service life of 100
years the thickness of Zn coating required would be approximately 150 microns. In order
to coat all 16 of the pylon pins a layer of Zn 150 microns thick needs to be applied to the
each of the 5.5" long and 2.25" diameter pins. Again using reference material (Rahrig,
n.d.) we can say that it will cost $0.3838/sq. ft to coat a surface with Zn. Then doing a
calculation of the surface area of a cylinder with the aforementioned dimensions we
obtain 0.325 sq. ft per pin and multiplying by the 16 pins we obtain 5.203 sq. ft of pin
surface area to coat. Therefore, converting to $ we obtain $1.99 for the coating of all 16
pins on one B-747 airplane which is a tiny amount so we can safely assume that this
coating will be economically viable.
Finally, in terms of resource feasibility, Zn is a readily available metal across the
world so finding enough Zn to coat the pins should not be an issue.

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However, one issue that may be a problem could be that the Zn coating will melt
due to its relatively low melting temperature of 419. 5°C. This could be an issue because
the typical
Solution 2: Electro polishing
Electropolishing is an electrochemical process similar to, but the reverse of,
electroplating. The electropolishing process smooth and streamlines the microscopic
surface of a metal object. In electropolishing, the metal is removed ion by ion from the
surface of the metal object being polished. Electrochemistry and the fundamental
principles of electrolysis (Faraday's Law) replace traditional mechanical finishing
techniques, including grinding, milling, blasting and buffing as the final finish. In basic
terms, the metal object to be electropolished is immersed in an electrolyte and subjected
to a direct electrical current. The object is maintained anodic, with the cathodic
connection being made to a nearby metal conductor.
How it works?
The metal (to be electropolished) is immersed in an electrolyte and subjected to
direct current. The metal is made anodic (+) and another metal act as a cathode (-). The
direct current then flows from the anode, causing the formations of metal ions (Ionization
of the metal part) and then diffuses through the solution to the cathode. This allows the
removal of metal (through diffusion of metal ions) at a controlled rate. The amount of
metal removed depends on the specific bath, temperature, current density, and the alloy
being polished.
Technological feasibility
Conventional mechanical finishing systems tend to affect the surface structure
(smear, bend, stress, etc.) and even fracture the crystalline metal surface to achieve
smoothness. Electropolishing offers the advantages of removing metal from the surface
that is stress-free and microscopically smooth. Corrosion resistance and passivity can also
be improved on many ferrous and nonferrous alloys (To protect against corrosion pits). It

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is also based on a simple mechanism in which the concept of electroplating is applied in
the system.
Economic feasibility
In order to overcome the structural disadvantages, which result from mechanical work
and to obtain a deburring of the work piece. It has been proposed to conduct electro
polishing on alloys. In such operations, electrolytes comprising chromic and/or
phosphoric acid have generally been used. However, these materials are relatively
expensive and hence the electro polishing operation using such electrolyte baths, are not
appreciably more economical than mechanical buffing.
Benefits
 Stress relief of surface
Tensile stresses concentrated in the part surface reduce its fatigue. The stresses may be
induced in various fabrication stages: metalworking, heat treatment, electroplating, etc.
Electro polishing allows removing the stresses surface skin from the work piece due to
the smoothening of the surface, which then enhances the fatigue strength. The surface

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defects such as scratches and tool-produce notch effect decrease the fatigue limit. Defects
free electro polished surface provides an increased fatigue strength.
 Passivation of stainless steel, brass, and copper and superior corrosion resistance
Passivation is a chemical process of a restoration of the corrosion resistance of a
contaminated stainless steel part. The contaminant particles embedded into the surface
disturb the protecting layer of chromium oxide and allow oxidation of iron (rust
formation). In the conventional passivation process the contaminants are removed by a
treatment in 20% nitric acid. The contaminating particles (e.g. oxides) may also be
removed by electro polishing. Additionally, electro polishing produces higher surface
concentration of chromium due to the preferential dissolution of iron and nickel atoms. In
contrast to the treatment by nitric acid the passivation by electro polishing does not
produce distortion and does not cause hydrogen embrittlement.
Solutions 3: Application of stainless steel as the material for the fuse pin
Stress corrosion cracking and corrosion fatigue can be prevented through three
general ways: material selection, controlled stresses, and controlled environment. The
first proposed solution involves lowering large stress concentrations caused by cracks
through electro-polishing of the steel fuse pin. The second proposed solution involves
material selection through coating of the steel pin. By implementing a zinc coating on the
steel pin, it acts as cathodic protection as the zinc coating is corroded, leaving the steel
pin intact. Unfortunately, the third option for prevention of stress corrosion cracking and
corrosion fatigue - controlling the environment - is not a very feasible solution to this
specific problem. This is because the fuse pin is used to hold the engine and strut to the
wing, meaning the environment around the pin is essentially fixed and uncontrollable.
Therefore, we propose the third solution to be a switch in material used from regular steel
to stainless steel.
Contrary to regular steel, stainless steel has better corrosion resistance due to the
chromium content present within it. With a minimum 10.5wt% chromium, a passive layer
of chromium oxide forms on the surface of stainless steel, significantly lowering the rate

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of corrosion compared to that of regular steel. Therefore, from a material selection point
of view, it is seemingly beneficial to our application to switch from regular steel fuse pins
to stainless steel fuse pins. The switch is also very simple technically as stainless steel
can be manufactured into shape and machined the same way as regular steel; very little
changes in process would need to be made.
From an economic point of view, this solution may not be the best option. Steel
scrap and billet prices range from $200 USD per long ton whereas stainless steel scrap
currently costs approximately $1500 USD per long ton. However, the fuse pins used in
the airplane are not very large meaning that the cost increase from switching to stainless
steel may be worth accepting, taking into consideration the benefit it provides.
Resource-wise, stainless steel is an abundant material and a switch to this material
should prove to be no problem. As mentioned earlier, manufacturing methods would not
need to be changed; therefore, the same machinery would be used.
Lastly, the mechanical properties of steel and stainless steel are essentially the
same. However, a change to stainless steel still presents some problems. Even though
stainless steel has a form of corrosion protection via its passive surface layer, the
environment in which the fuse pin would function (temperatures up to 2000°C) are likely
to still cause some form of corrosion cracking and fatigue. High external forces and stress
concentration within the fuse pin are not taken into account.This problem may simply be
unavoidable from a material selection standpoint and would be more successfully solved
by taking geometry of the fuse pin into account as well.
Conclusion:

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Reference:
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Retrieved March 22, 2015, from
http://www.slideshare.net/RachelGamblin/when-technology-fails-
amsterdam-plan-crash
Hensel,K.B.(2002). Electropolishing.Metal Finishing,100, 425-433. doi:10.1016/S0026-
0576(02)82046-3
Materials Engineering. (n.d.). Retrieved March 19, 2015, from
http://www.substech.com/dokuwiki/doku.php?id=electropolishing
Rahrig, P. (n.d.). Analyzing true costs of galvanizing strctural steel. Retrieved March
22, 2015, from
http://www.galvanizeit.org/images/uploads/articles/costs_pe_1004.pdf
Terada, H., & Kobayashi, H. (n.d.). Case Details Crash of B-747 of El Al Israel Airlines
by Fatigue Failure of Engine Fuse Pin. Retrieved March 22, 2015, from
http://www.sozogaku.com/fkd/en/cfen/CB1071013.html
What is Electropolishing? (n.d.). Retrieved March 20, 2015,
http://www.delstar.com/electropolishing.html