chapter 8 other environments. mild corrosives can cause severe problem under certain conditions

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.