Transcript Thermal Spray VS Galvanizing

Thermal Spray Coatings of Zinc and Aluminum
Zinc Metallizing
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Prepared byJim Weber - Sulzer Metco (US) Inc. – Westbury, NY
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Thermal Spray Materials Development
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Systems Engineering
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Equipment Research & Development
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Field Service Manager
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Training Manager
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Quality Assurance Manager
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Currently the Product Line Manager for industrial markets, focusing on
combustion (wires, powder, & HVOF) and arc equipment
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Latest industry focus - working with NACE International (National Association
of Corrosion Engineers) and the petrochemical industry to solve Corrosion Under
Insulation (CUI) problems with Thermal Spray Aluminum (TSA) coatings and with
the Gas Technology Institute (GTI) solving natural gas transmission and metering
station corrosion problems.
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Information
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A brief introduction to thermal sprayed coatings are of Zn (TSZ), Al
(TSA), and their alloys (85/15 Zn/Al), and how they provide long term
corrosion protection
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Some examples of where are these coatings are used and how they
have performed
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A brief introduction to galvanizing and its comparison to thermal spray
coatings
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An overview of the most popular types of equipment that apply these
coatings
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Question & answer session
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What is Thermal Spray?
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Thermal spray is NOT a welding process
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Thermal spray coatings are a melted, or softened ceramic, metallic, or
polymer materials are transported by a gas stream to a properly
prepared substrate
Substrate
Material Feedstock
Heat Source
Accelerated
Droplet
Or
Coating
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What is Thermal Spray?
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These coatings are typically mechanically bonded to a grit blasted
surface
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Metals that feed into the thermal spray gun are the actual coatings.
There are no solvents or VOC's.
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The coatings are similar to the metals being sprayed, however there are
some important differences
1.
There are metal oxide stringers and porosity in the coatings
2.
Metal particles in the coating create a layered effect within the coating
structure
3.
Due to the rapid cooling of the metal particles as they adhere to the
substrates, thermal sprayed coatings have unique crystalline structures
not normally found in wrought metals
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Almost any material can be thermal sprayed onto almost any substrate
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What is Thermal Spray?
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Thermal spray, especially with soft metals sprayed with the combustion
wire equipment, is a relatively cold process. Substrate temperatures
seldom reach >200F/95C.
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How thermally sprayed coatings of
Zn and Al, combat corrosion
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For atmospheric, buried, and marine environment corrosion protection, Zn (TSZ), Al
(TSA), and their alloys have proven that they provide long term corrosion protection
and outperform most all other methods.
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Anodic (TSZ/TSA) metal coatings applied to steel cathodes (more noble than Zn or
Al), are referred to as cathodic or sacrificial protection coating systems.
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These thermal spray coatings provide corrosion protection by excluding the
environment (or electrolyte) and acting as a barrier coating (like paints, polymers,
and epoxies), but unlike typical barrier coatings they also provide sacrificial anodic
protection.
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Typical thermal spray
applications or Zn, Al, and their alloys
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Hundreds of bridges have been thermal sprayed (metallized) over the past 100
years. There are many document cases of >50 years of corrosion protection
provided by thermal spray coatings.
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Zinc and zinc alloys are also sprayed directly onto concrete to protect the steel rebar
within.
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Typical thermal spray applications
for Zn, Al, and their alloys
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Typical thermal spray applications
for Zn, Al, and their alloys
 Carbon steel equipment (petrochemical facilities, power generation, Naval
ships, etc.) are coated with TSA, TSZ, and 85/15.
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Petrochemical users expect TSA coatings to provide >20 years with no
maintenance or corrosion inspections.
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A TSA coating has been operating in severe petrochemical vessel operating
conditions. One coating in particular has protecting carbon steel equipment
operating in cyclic service of ambient to 350F/175C, in contact with wet
insulation, for >50 years with no visible corrosion .
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TSA coatings are also specified as a solution to stress corrosion cracking
(SCC) of austenitic stainless steel.
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Offshore oil rigs operating in severe conditions rely on thermal spray
aluminum for corrosion protection. >20 service life with no maintenance has
been documented.
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These coating systems meet specifications from organizations such as
NACE, SSPC, AWS, US Navy, US Army Corps of Engineers, and many
others.
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Petrochemical applications
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Petrochemical applications
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Petrochemical applications
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Navy corrosion
applications
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The Navy has many documented uses for thermal spray coatings of all
types, including corrosion coatings
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High temperature (>900F/480C) steam valves and associated piping
have been protected by thermal sprayed aluminum on Naval ships. It is
documented that these coatings lasted longer than 5 years in areas
where paint coatings had lasted only months.
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Hot-Dip Galvanizing
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Hot-dip galvanizing is essentially a brazing process. Steel is cleaned
(mechanically and chemically) and then heated to >850°F in a molten
zinc bath. The molten zinc reacts with the surface of the steel and forms
a coating of various layers of zinc and iron alloys, depositing a layer of
material that is approximately 40% pure zinc.
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A. Degreasing in a hot, alkaline solution
B. Rinsing thoroughly in a water rinse
C. Pickling in a hot, acid bath
D. Rinsing thoroughly in a water rinse
E. Prefluxing in a zinc ammonium chloride solution
F. Immersing the article in the molten zinc through a molten flux cover
(usually zinc ammonium chloride)
G. Finishing (dusting with ammonium chloride to produce a smooth
finish).
H. Sometimes step F is followed by immersion of the zinc coated article
in a quench bath which may contain a dichromate solution.
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Hot-Dip Galvanizing
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Hot-Dip Galvanizing
Galvanized Coating
Thermal
Spray
Coating
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Galvanizing VS. Thermal Spray
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Pure aluminum (>99%), zinc (>99.9%), and zinc-aluminum alloys may be
sprayed, whereas galvanizing is never pure zinc, it is Zn/Fe matrix. Also,
the molten zinc bath is often contaminated with pickup from materials
that are dipped into it.
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Aluminum and the 85/15 zinc-aluminum alloy coatings are not available
by hot dip galvanizing.
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Aluminum and Zn/Al coatings protect steel better than pure zinc in
marine and industrial environments.
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When metalizing, the surface being coated is not preheated and it
remains at a low temperature, with local temperature never exceeding
about 250-300° F. Because metalizing is a "cold process" when
compared to galvanizing’s >850°F temperature, there is virtually no risk
of weld damage or distortion of the steel due to high temperatures or
overheating
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Galvanizing VS. Thermal Spray
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The acids, fumes, contaminated rinse water, and other byproducts of the
galvanizing process are considered hazardous. Thermal spray waste is
generally metal dust, which when applied in a shop environment, is
collected by specially designed dust collectors that remove up to 99.99%
of the generated dust, down to .12 microns, and may be recycled. Metal
dust generated while spraying onsite may be ignored, swept up, or
collected with grit blasting containment and collection systems
depending on local requirements and conditions.
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Due to environmental concerns, new galvanizing lines are no longer
permitted in many states, including NY state. The lines that are currently
running must be updated to current environmental regulations within a
set time frame, as dictated by local, state, and federal codes for
hazardous waste and emissions.
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Most paint and powder coating applicators can easily upgrade to thermal
spray coatings. It is difficult, or impossible to upgrade to a galvanizing
line, therefore fabricated parts must be shipped to approved galvanizers
and then shipped back to approved painters/powder coaters.
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Galvanizing VS. Thermal Spray
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Because galvanized coatings must be dipped in a tank, parts are limited
to the size of the molten zinc galvanizing tank.
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While galvanized coatings are difficult to top coat and may require
special surface preparations (acid etching, phosphating, etc.) to allow
topcoats to adhere to them, thermal spray coatings 5-15% porosity make
them a perfect surface for paints and powder coats. The coating soaks
up topcoats like a sponge, creating a tremendous bond between the
metal coating and the top coat.
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Thermal spray coatings are also less susceptible to out-gassing, a
phenomenon that causes bubbling and loss of adhesion of topcoats.
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Field repairs to galvanizing can only be done with paint, which does not
last nearly as long as the galvanized coating. Typical thermal spray
equipment is portable and easily used onsite in the field. An added
benefit to this equipment is it’s low cost, less than $12,000 for a complete
portable system.
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Galvanizing VS. Thermal Spray
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“The Use of Thermal Sprayed Zinc Alternative to Hot Dipped
Galvanizing” Joseph G. Radzik, Director of Engineering Research &
Development, Tyco Fire & Building Products
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Representative samples of Thermal Sprayed Zinc and Hot Dipped
Galvanized ductile iron castings conforming to ASTM2 A 536, Grade 6545-12, were subjected to a 5% salt spray fog test at 95 °F in accordance
with ASTM B 117. Coating thickness was measured in the range of 3.4 to
5.5 mils for all samples evaluated, which conforms to the industry
requirement for grooved piping products. An independent laboratory
NADCAP accredited in materials and nondestructive testing methods
performed the testing. After 120 hours exposure, the Hot Dipped
Galvanized samples exhibited red corrosion. The Thermal Sprayed Zinc
samples did not exhibit red rust corrosion. Testing was continued on the
Thermal Sprayed Zinc samples for an additional 72 hours for a total of
192 hours and examined for signs of red rust. None of the Thermal
Sprayed Zinc samples exhibited this condition and testing was stopped.
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“Ski-Lift Maintenance: Wire Arc Spray vs.Galvanizing,” M. Bhursari
and R. Mitchener, SSPC International Conference, 1998.
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This paper reviews the use of wire arc spray zinc vs. galvanizing on ski
lifts. The authors discuss a case study in which painted lifts required
repainting every 3 years, hot dipped lifts showed signs of corrosion in
fewer than 5 years and thermal sprayed ski lifts exhibited no corrosion
after 5 years. It was estimated that the wire arc-spray zinc coating,
depending upon the thickness, would have a life expectancy of 20 years
with minimal maintenance. The authors concluded that thermal spray
coatings were more resistant to abrasion and wear than thin galvanized
coatings.
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Combustion Wire System
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Combustion Wire System
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Combustion Wire System
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Combustion Wire System
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Combustion Wire System
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Combustion Wire System
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Combustion Wire System
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Twin Wire Arc System
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Twin Wire Arc System
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Twin Wire Arc System
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Twin Wire Arc System
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Twin Wire Arc System
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Twin Wire Arc System
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Twin Wire Arc System
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Twin Wire Arc System
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