Preventive
Maintenance
Vol. 3
RUST ON BOOM SECTION
Anti-Corrosion just delays occurrence of rust!
Lattice Boom Crawler Crane (LBCC) has extendable (attachable) boom sections to extend
the working radius. The sections mainly consist of main chords and lacing pipes to
support the compression stress caused by lifting loads. These components usually covered
with 1 ) primer [anti-corrosion paint] and 2 ) top coat [to protect the anti-corrosion paint and
look it in fashion] to protect them from the ambient environment. Although they are protected
with paint coats, it can get rusty if maintenance and inspection is not done properly.
This document explains 1 ) what causes rust on boom sections, 2 ) how corrosion occurs on
them, 3 ) how to prevent rust.
1. Fault on Boom Section
The section which we introduce below is an example
of fault due to lack of maintenance. The crane owner
remained the sections exposing to ambient environment
without any maintenance, and as a result, the sections
got rusted. If a boom section is rusted and a crane
operator leaves the rusted section, the strength of boom
section dramatically decreases, and it results in a long
down-time for repair.
Pitting
Fig 1. Rust on Section
Fig 2. Blistering
Fig 3. Cracks of Paint
2. Mechanism how boom section gets rust
Rust on Section
Scars and Scratches
Inadequate Surface
Treatment
Fault on Boom Sections
Blistering
Penetration of water
and acid solution
Crack
Rust on boom sections is caused by, in most cases,
exposure of base metal to the ambient environment.
Once it is exposed to oxgen, moisture, salty wind and
etc, the spreading speed of rust is accelerated. In
addition, in some cases, those factors and causes above
are sometimes combined and occurred simultaneously.
Degradation
ex) Due to penetration of water, blistering is occurred.
When the blistering is occurred, if the blistering is
cruched by external factors such as hit of hook block,
the swelling gets cracked. From the crack, water gets
into the paint coat. If the water sneaks in upto the base
metal, the rust is occurred.
Preventive Maintenance Vol. 3
Mechanism to have fault for each case
General Steps to have fault
e-
O2
Water reaches to the surface of base metal, ionization of Fe and H2O
occurs due to ionization tendency.
1) 8Fe
8Fe3++24e- (Fe
Fe3++3e-)
2) 12H2O+6O2+24e
4OH-)
24OH (2H2O+O2+4e-
ee-
OH-
At the same time, chemical reaction occurs.
3) 8Fe3++24OH 4Fe2O3+12H2O (2Fe3++6OHFe2O3+3H2O)
Water remains
Rust does not stop as long as oxygen is present!
H2O
Fe
Base Metal
Rust on Section
From the scars, water (H₂O) and
oxigen (O₂) can get into the base
metal (Fe ).
* Fe2O3 = Iron (III) oxide = Red Rust
Blistering
Crack
The solutions and oxygen can penetrate the coats due to
microscopic holes in the paint and absorption of top coat.
Due to degradation, the surface
becomes hard.
Top Coat
Top Coat
Top Coat
Base Metal
Base Metal
Base Metal
Water (H2O)
Anticorrosive
Anticorrosive
Anticorrosive
Oxgen can contact with the base
metal directly with water, and
chemical reaction is occurred.
Water reaches to the surface of base metal, ionization and
chemical reaction occur. As a result, red rust occurs on the
surface of base metal, and it causes blistering of coat. Generally speaking, if acid solution stays on the base metal, the
speed of oxidation is much faster than normal.
The hardened surface creates
crack due to lack of flexibility.
Through the crack, water invades
to the base metal.
Top Coat
Top Coat
Top Coat
Base Metal
Base Metal
Base Metal
Red Rust (Fe2O3)
Anticorrosive
Anticorrosive
* Even if Surface treatment is inadequate, blistering occurs as well.
In addition, once the rust is occurred, the rust spreads
out in dramatical speed between the primer and base
metal. It means that rust occurs on the other spots and
Anticorrosive
locations when a rust is created. Therefore, in order to
stop the invisible rust, stop creating even a spot of rust by
maintenance and perform periodical maintenance.
3. Maintenance of Boom Section
As "facility" of customers, boom sections should be maintained properly and periodically.
Countermeasure
1. Keep the surface of boom sections as clean as
possible.
2. Avoid any damage or scratches on boom sections.
3. Once rust, blistering or crack is found, remove the rust
and measure the wall thickness of pipe.
4. If the depth of rusty portion on lacing pipes exceeds
Kobelco standard (10% of original thickness), replace
the lacing pipe.
(For more detail, consult with Kobelco Cranes
Distributors)
For further information, please contact...
Global Service Department
740, Yagi, Okubo-cho, Akashi-shi, Hyogo, 674-0063 JAPAN
TEL: +81-78-936-1408 FAX: +81-78-935-5240
PMV03_2014-R1