Metallurgy/Ramshorn lifting hooks and corrosion
QUESTION: Dear Mr Sharma,
I am a long distance student of marine surveying. I have an assignment based on metals and corrosion. I have encountered that some months ago you have answered the exact following question to another student that was named Sam. My questions are the following:
Two (2) Lifting hooks on a very large floating crane ( I have made a research and I found out that belong to "YOSHIDA" that was built by Mitsubishi heavy industry division )
925 tons lift capacity each. What material and grade might be made from and explain why.
Describe in detail two processes of constructing such hooks and explain which method is most suitable, considering load transmission, concept of load paths and stress concentration.
Write analysis on three (3) corrosion processes and explain in detail how they affect structural integrity of parts in service, with particular emphasis on applied loads, stress concentrations and the materials response to them. How can these corrosion processes be avoided?
Could you please help me ?
Thank you in advance for your time and your help.
ANSWER: pl wait till 10th
---------- FOLLOW-UP ----------
QUESTION: Dear Mr Sharma,
I have waited till 10th May but I did not receive an answer yet. If for any reason whatsoever, you cannot help me in any way , please let me know because unfortunately I have a deadline on delivery date of my assignment.
Oh! You waited and your urgency became critical.Following bullet points will aid you to meet your requirement;
1) The material of hooks can be ideally DIN class V, super alloy steel, 34CrNiMo6-30CrNiMo8(Class-V), similar to SAE 4340/4337.
2) The steel must contain >= 0,020 Aluminium total or otherwise it has to be proved that the steel is free of nitrogen
3) The manufacturing process involves drop forging followed by subsequent heat treatment(Hardening and tempering, hardening at 850*C and tempering at 550*C.This will stabilize the strength and remove internal stresses)
4) Sub zero treatment below -20*C will further improve fatigue strength and impact strength.
5) Here suspension load matters and DIN 15402 B can prove best grade.
7) Zinc plating is one of the corrosion prevention method for its split nuts.
8) Ni coating or enamel coating can be alternative for hooks.
Why: Coating is must to withstand the attack by moisture and salts in sea water
9)You can check Lamet Sollvamenti company which is in such type of business.
10) Corrosion under stress are of three types;
a) Active path dissolution: This process involves accelerated corrosion along a path of
higher than normal corrosion susceptibility, with the bulk of
the material typically being passive. The most common active
path is the grain boundary, where segregation of impurity
elements can make it marginally more difficult for passivation
to occur. For example, when an austenitic stainless steel has
been sensitised by precipitation of chromium carbide along
the grain boundary, the local chromium concentration at the
grain boundary will be reduced, and this region will be slightly
less easily passivated. Consequently, a form of crevice
corrosion can occur, whereby the grain boundary corrodes,
with the specimen surface and the crack walls remaining
passive. This process can occur in the absence of stress,
giving rise to intergranular corrosion that is uniformly
distributed over the specimen. The effect of the applied stress
is probably mainly to open up the cracks, thereby allowing
easier diffusion of corrosion products away from the crack tip
and allowing the crack tip to corrode faster. Active path
corrosion processes are inherently limited by the rate of
corrosion of the metal at the crack tip, which limits the
maximum crack growth rate to around 10-2mm/s, and crack
growth rates are often much lower, down to around 10-8 mm/s
(about 1 mm in 3 years) or less
b) Hydrogen embitterment:Hydrogen dissolves in all metals to a moderate extent. It is a
very small atom, and fits in between the metal atoms in the
crystals of the metal.3 Consequently it can diffuse much more
rapidly than larger atoms. For example, the diffusion
coefficient for hydrogen in ferritic steel at room temperature is
similar to the diffusion coefficient for salt in water. Hydrogen
tends to be attracted to regions of high triaxial tensile stress
where the metal structure is dilated. Thus, it is drawn to the
regions ahead of cracks or notches that are under stress. The
dissolved hydrogen then assists in the fracture of the metal,
possibly by making cleavage easier or possibly by assisting in
the development of intense local plastic deformation. These
effects lead to embrittlement of the metal; cracking may be
either inter- or transgranular. Crack growth rates are typically
relatively rapid, up to 1 mm/s in the most extreme cases.
c) Film-induced cleavage:If a normally ductile material is coated with a brittle film, then
a crack initiated in that film can propagate into the ductile
material for a small distance (around 1m) before being
arrested by ductile blunting. If the brittle film has been formed
by a corrosion process then it can reform on the blunted crack
tip and the process can be repeated. The brittle films that are
best-established as causing film-induced cleavage are
de-alloyed layers (e.g. in brass). The film-induced cleavage
process would normally be expected to give a transgranular
I think your quarries remains answered and it is 1:30 am in India, going to sleep.Please feel free what more help you require to complete your project.