MEC
THERMAL SPRAY FACILITIES
COATING SYSTEMS FOR HVOF, PLASMA, FLAME SPRAY, ARC SPRAY & ROD SPRAY
Tech. Bulletin#06/102.00
In the recent years, there has been a growing
interest in the use of HVOF process to deposit
protective overlaycoatingsontothesurfacesof
engineering components to allow them to
functionunderextremeconditions.
COATING REQUIREMENT :
High hardness (to prevent erosion because
ofashandsilica).
Hot Corrosion resistance (that will react with
the environment to produce a slow growing
protective oxide scale, which should not
allow thecorrosivespeciestodiffuseinto the
coating )
Low porosity (Less area for erodent particle
BOILER TUBES being toimpactandabrade).
coated by HIPOJET
Small grain size (Small grains tend to be
stronger).
High temperature erosion-corrosion and
Absence of cracks (Ductile structure,
oxidation of heat transfer pipes and other
thermal stability,crackingleadstospalling).
structural materials in coal fired boilers are
recognized as being the main causes of Uniform coating structure (Homogenous
distribution of hard constituents & ductile
downtime at power generating plants,
behavior).
accounting for 50-75% of the total arrest time.
Maintenance costs for replacing broken pipes Smoothsurface.
in the same installations are also very high, and
HVOF Coating
can be estimated at up to 54% of the total
at SITE
production costs. Superalloys have been
developed for high temperature applications,
but they are not able to meet both the high-
t e m p e r a t u r e s t r e n g t h a n d the h i g h -
temperature erosion-corrosion resistance
simultaneously. One possible way to address
these problems is by applying a thin layer of
anti-wear and anti-oxidation coatings with
good thermal conductivity, such as thermally
sprayed nickel- or iron based alloyed coatings.
Coatings provide a way of extending the limits
of use of materials for higher temperature
applications.
Fromthecoatingrequirementsitisclearthatthe Criteria for Selecting Cr3C2-NiCr
coating should have sufficient erosion
resistance as well as should be corrosion CHROMIUMCARBIDE
a) Due to hard chromium carbide content,
resistance as well. Thecoating whichmeets the
said requirement is Chromium Carbide- Nickel itoffersmoreerosionresistance(Fig.1)
chrome.
NICKELCHROMIUM
a) Chromium is a corrosion resistant alloy
that binds the continuous skeleton of
erosion resistant chromium carbide
constituents.
b) Due to high binding energy and ductility,
nickel exhibit enhance erosionresistance
by their ability to dissipate the impact
force ofparticlesbyplasticdeformation.
Fig. 1 : Hardness Profile of Cr3C2-NiCr coated When these coatings were subjected rigorous
on various boiler grade steels testings they gave very excellent properties to
combatcorrosion. This isillustratedintheFig.2.
Boiler tubes are huge structures and considering
the down time involved in transporting the
same, best results are obtained if they are
coated with Cr3C2 -NiCr using HVOF system. MEC
offers this state of art technology that can be
carried to any site using a pick up truck and the
coating would be executed as the installation
canbedoneinreadtime.
a b c
Fig : 2 SEM back scattered images for the bare and HVOF coated Superni 600 superalloy
subjected to hot corrosion in Na2 SO4-60%V2 O5 environment at 900 Deg. C for 50 cycles
(a) Bare Superalloy (b) Cr3C2-NiCr coated (c) Ni-20%Cr coated
CertifiedISO9001by
ROBOT METALLIZING EQUIPMENT CO. PVT. LTD.
E-101, M.I.A., Phase-II, Basni, Jodhpur-342005 (India)
Ph. : +91 291 2747601 Fax : 2746359
E-Mail : mecpl@sancharnet.in / mecpl@vsnl.com
MEMBER OF Web : www.mecpl.com
Delhi Mumbai Bangalore Secunderabad
09312890541 022-24934370 09343861755 040-27813760
SPRAYWATCH mecdly@ndf.vsnl.net.in mecbby@bom5.vsnl.net.in mecpl.bgl@gmail.com mecsec@satyam.net.in
