chapter 8 other environments. mild corrosives can cause severe problem under certain conditions
TRANSCRIPT
CHAPTER 8
OTHER
ENVIRONMENTS
Mild corrosives can cause
severe problem under certain
conditions.
8.1 Organic acids.• Acetic acid Type 316, 304, Cu,
Bronzes, Duriron, 1100 Al, 3003 Al,
• Hastelloy C
• Durimet 20 – pumps
• Duriron pumps, lines, column
• Cu, Stainless – High Temp.
• Formic acid one of the strongest –
the most corrosive
8.2 Alkalines• common alkalines
– NaOH, KOH – steel
– Stress corrosion (certain conc. + temperature)
– Rubber base, coatings + linings prevent iron contamination
– Nickel, Nickel alloys for combating corrosion (all conditions of conc. + temp)
– Corrosion resistance to caustic is almost directly proportional to the nickel content of an
alloy
– Al – very poor material
8.2 Alkalines
• Steel, Cast Iron except high temp.
– 430, 304 stainless – high temp.
– Not to use Cu + alloy stress
corrosion
8.3 Atmospheric Corrosion
Various atmospheres
– Atmosphere
• Industrial
• Marine
• Rural
Corrosion
due to moisture + O2 accentuated by
contaminants Sulfur compounds, NaCl
**Corrosion of steel on
- the seacoast is 400 – 500 times >
a desert area
- Industrial atm. 50 – 100 > Desert
areas
• sulfur gases generated by the burning
of fuels (SO2)
• Small amount of Cu increase
resistance of steel to atm corrosion
• Nickel – insolubles sulfates
• Cu, lead, Al, - widely used for atm.
• Shelteced Corrosion causes much
damage. (inside surface of an
Automobile door)
8.4 Sea – Water
• 3.4% Salt + slightly alkaline, pH8 =
good electrolyte can cause galvanic
corrosion & service corrosion
• Corrosion is affected by O2 content,
velocity, temp and biological
organisms.
Fig. 8-1 Corrosion of ordinary steel in the sea.
• Corrosion by seawater at great
depths (i.e. 1 mile) is usually
decreased because of the lower
temp. (40F)
8.5 Fresh water
• Corrosivity depends on oxygen content,
hardness, chloride content sulfur
content, and many other [Local
Problem]
• Hard water, carbonates deposit on the
metal surface and protect it. But pitting
may occur if the coating is not complete
8.5 Fresh water
• Soft water are usually more corrosive
• Complete corrosive resistance requires
more expensive stainless steel.
Cast iron, steel and galvanized steel
8.6 High – purity water
• Atomic power plants, high – pressure
power units
• Corrosion decreases with increasing
purity of the water
• Intergranular attack and cracking
stainless steel + O2
• Zirconium, Zircalloys
8.7 Soils
• Factors affecting corrosiveness moisture,
alkalinity, acidity, permeability of water air,
oxygen, salts, stray currents, biological
organisms
• Pitting is a major problem
• Carbon steel and cast iron with without
organic coatings and cathodic protection
are most common for underground
structures. Other materials are generally
not economical.
8.8 Aerospace• hard vacuum of space does not cause
corrosion
• severe corrosion due to liquids such as oxidizers and fuels and also the
high temp. Encountered in blast nozzles and during reentry
• Tungsten
• Al, Mg, Ti, Fe – primary metallic materials for aircraft
8.9 Petroleum Industry1. Production
– Iron + steel pipe tubing, casing, pumps, valves
2. Transportation and storage
– Tankers, pipelines, railway tank cars, tank trucks
– Cathodic Protection
– Coating
– Inhibitor – Sodium chromate, amines, nitrites
– Inside + Outside
3. Refinery Operations
– Due to inorganics such H2O, H2S, CO2, H2SO4, NaCl,
– H2O – crude oils – acts as an electrolyte and cause corrosion
tends to hydrolyze forms an acid
– CO2 – most important corrosive agents
– Salt water – CaCl2, MgCl2, NaCl HCl
– H2S
3. Refinery Operations (continue)
– N2 NH3, cyanides will from
– O2 Shutdown periods, pumps
– H2SO4 Alkylation, polymerization
– NH3 control pH, reduce chloride
acidity damage copper
– HCl hydrolysis
3. Refinery Operations (continue)
–Caustic (NaOH) line – neutralization
–Naphthetic acid corrosive at 430 –
750F
1) low temperature corrosion
2) high – temperature corrosion
–Ordinary Carbon steel 98%
8.10 Biological Corrosion
1. Directly influencing anodic + cathodic
reactions
2. Influencing protective surface films
3. creating corrosive conditions
4. producing deposite
8.11 Human Body
Silver amalgams, gold,
cements, porcelain, stainless steel
plastics, Teflon, Dacron, nylon,
silicone polymers
8-12 Corrosion of Metals by Halogens.
In summary, boron, carbon, silicon,
germanium, titanium, vanadium, and
many of the second and third row
transition metals form low-melting
volatile halides : hence, these metals
are particularly subject to halogen
attack, even at low temperatures.
8-13 Corrosion of Automobiles.
This is a severe economic
problem, particularly in marine
atmospheres (seacoasts).
- touch – up paint when the car is
brand new.
- frequent washing (to remove salt).
- use a plastic body.
- galvanized steel, electroplated steels,
and complete immersion of the body
in a rust – preventing primer coat.
- use inhibitor in engine cooling system.
- avoid very short runs, like moving the
car from the driveway to the garage
(water condenses in the exhaust
system).
- keep the gasoline tank at least half
full. This minimizes condensation of
water when the temperature drops (at
night). Water in the tank corrodes the
steel, and corrosion products clog the
fuel filter and carburetor jets.
8-14 Nuclear Waste Isolation.
8.15 Liquid Metals and Fused Salts
Superior heat – transfer characteristics
1. Low vapor pressure
2. Low melting point
3. Low pumping power
4. Low neutron cross section (low
absorption coeff. For neutrons
Liquid Metals
- Na - K
- Na-K alloys - Al
- Li - Ga
- Mg - lead Bismuth
- Tin - Hg
Fused Salts
NaOH – Nickel and Nickel alloys
8-16 Solar Energy• There are thousands of small
installations for heating domestic hot water galvanized steel, stainless
steel, or glass–lined steel with a sacrificial anode mounted on a rooftop.
• molten salt (60% potassium nitrate, 40% sodium nitrate) producing steam at 1050F. Inconel 800 is the preferred
choice of material of construction.
8-17 Geothermal Energy.
8-18 Sewage and Plant - Waste Treatment.
The wet air – oxidation process.
Fig. 8-14 Performance data from several municipal
sewage plants constructed of types 304, 316 and 316L
stainless steels. Pilot plants and shaking autoclave
corrosion test results are also indicated.
- below about 300 to 400 ppm chlorides,
stainless steel types 304, 316 and
316L show excellent performance
without pitting and cracking.
- One titanium plant in Japan has been
operating for more than 8 years with
over 5000 ppm chlorides
8-19 Pollution Control.
Three common types of installations.
1. Incinerators for solid trash.
2. Scrubbers for flue gas desulfurization
(FGD) of power plants and
metallurgical plants.
3. Processes for treatment of municipal
sewage, wastewater and liquid plant
wastes.
• One coal-burning power plant cost $75
million and “attached” to it is a $25 –
million plant to remove sulfur
compounds from combustion gases
by scrubbing.
• Various wet and dry environments –
gases, liquids, and solids are involved
and temperatures vary from low to
very high.
• All 8 forms of corrosion.
• Table 8-14
• Figure 8-16
• Table 8-15
• Table 8-16
• Table 8-17
8-20 Coal Conversion.
The conversion of coal to gas and
oil has opened a new era in the field of
corrosion and materials of construction.
The problems are challenging and tough.
Examples are : valve that close at
2500F; erosion corrosion failure of a
type 347 stainless steel pipe within 4
hours : reactor vessels weighing up
to 4000 tons, 250 ft high/22 ft ID, with
walls 12 in thick.
• A troublesome and unique feature of
coal conversion processes is severe
erosion because of the presence of
solids (fly ash).
• highly reducing conditions often exist
in coal conversion processes.
• Table 8-18
• Table 8-19
• Figure 8-17
8-21 Pulp and Paper Industry
The most common method for
converting wood to fibres for paper
making is the Kraft pulping process.
(Figure 8-18).
• Figure 8-18
8-21 Pulp and Paper Industry
The batch digester is a welded,
thickwall, carbon steel pressure
vessel that is fully stress-relieved. A
rimmed steel of low silicon content
(0.02 wt%) = type 316L stainless steel
overlay is commonly used in region
subject to erosion corrosion.
8-22 Dew Point Corrosion.• FGD plants often reheat the treated
gases to avoid condensation.
• Water (dew) that condenses on the
metal surfaces is usually saturated
with oxygen and corrodes steel.
• Shaded or under surface not exposed
to sunlight could stay wet for along
time. (sheltered corrosion).
8-23 Corrosion Under Insulation.
• The attack under insulation also
includes general corrosion, pitting
and crevice corrosion.
• Visible wet spots are a sign of trouble
investigated.
• The best known way to control
corrosion under insulation is to paint
the metal with a good coating.
8-24 Electronic Equipment.
This equipment often contains a
conglomeration of different materials.
Gold – plated parts may be in contact
with aluminum or solder. The parts
are usually small in size, and a little
corrosion can cause shorts and
dysfunction.
Poor cleaning of solder flux,
moisture penetration of coatings, lack
of cleanliness, poor choice of
materials, and cleaning with halogen –
containing solutions are cited as
causes of failure.
8-25 Liquid Metal Embrittlement or Cracking.
Liquid-metal-assisted cracking (LMC).
- molten metals that react specifically
with the alloy system.
8-26 Hydrogen Peroxide
Molybdenum in stainless alloys and
other than high-purity aluminum alloys
can cause decomposition of the H2O2.
8-27 Rebar Corrosion
Corrosion of steel reinforcing
bars is a problem in many structures
(i.e., piers and buildings), but it is a
major problem in highway bridges.
8-28 Bolting
Many failures of bolts occur in
flanges, pumps, valves, and other
structures probably because not
enough attention is paid to bolts
when specifying materials.
8-28 Bolting
• Do review vendors’s bolting
specifications.
• Don’t use austenitic stainless
steels where there is a potential
of exposure to chloride ions.
8-29 Statue of Liberty
• the marine environment is naturally
corrosive.
• acid rain.