Corrosion Damage Mechanisms in the Utility Industry

J. L. Blough, Supervisor Metallurgical ServicesJ. L. Blough, Supervisor Metallurgical Services

FirstEnergy BETA Labs FirstEnergy BETA Labs 6670 Beta Drive 6670 Beta Drive Mayfield Village, Ohio 44143Mayfield Village, Ohio 44143

jblough@firstenergycorp.comjblough@firstenergycorp.com440440--604604--98439843September 20, 2012September 20, 2012www.beta-lab.com

Corrosion Forum 2012

CORROSION

Destruction or deterioration of a material because of the reaction with its environment

Destruction of material by means other than straight mechanical

Extractive metallurgy in reverse (oxide to metal product to oxide).

total annual USA estimated direct cost of corrosion $276 billion—approximately 3.1% (GDP).

Indirect costs may equal the direct costs Controllable IF you understand

mechanisms and variables effecting them2

COST OF CORROSION

3

$4.2 Nuclear, $1.9 Fossil, $0.15 misc. power, $0.6 distribution1999-2001

BOILER

4

UTILITY ENVIRONMENT AND COMPONENTS

Utility Industry involves most Corrosion and Mechanical Damage Modes • Room Temperature to 2000 °F• Air, acidic, basic, microbiological to molten salts• brittle fracture, fatigue, creep and creep fatigue

Most metals and numerous non-metallic materials of construction• Ferritic steel• Austenitic, ferritic and martensitic stainless

steels• Nickel base alloys• Copper base alloys• Titanium alloys• Cast iron to high alloy castings• Weld overlays

Fabrication of all the above alloys 5

FOSSIL-FIRED POWER PLANTS

Boiler tube failures (BTF) primary cause of lost availability

3% lost availability 80% of all BTF result in an outage ~3 days 3 days ~$ 3 million for replacement power In summer 1000MW plant 12 million

6

2004 LEADING BTF MECHANISM

7

LEADING BTF MECHANISMS

8

MechanismConventional Boilers 2004 2001 1997

Flyash erosion 71% 75% 74%Corrosion fatigue 56% 77% 63%Longterm overheating/creep 79% 81% 80%Sootblower erosionHydrogen damage 50% 57% 37%Waterwall fireside corrosion 42% 49% 48%

HRSGsFlow-accelerated corrosion 35% 26%Thermal fatigue 20% 31%Corrosion fatigue 15% 42%Pitting 11%Hydrogen damage 5%Long term overheating/creep 0%

Percentage of Units Experiencing the Mechanism

Damage Modes in Water Touched Tubes

Corrosion fatigue Hydrogen damageAcid phosphate

corrosionCaustic gougingWaterwall fireside

corrosion

Thermal fatigue- water blower

Thermal-mechanical fatigue and vibration-induced fatigue

Flow-accelerated corrosion

Sootblower erosionFlyash erosion

9

DAMAGE MODES IN STEAM TOUCHED TUBES

• SH/RH fireside corrosion

• Stress Corrosion Cracking

• Pitting in steam- touched tubes

• Fireside Corrosion Fatigue

• Long-term overheating/creep

• Short-term overheating in SH/RH tubing

• Dissimilar metal weld failures

• Thermal-mechanical fatigue and vibration- induced fatigue in conventional units

• Creep fatigue• Flow-induced vibration

fatigue• Thermal quenching• Rubbing/fretting• SH/RH sootblower

erosion• Graphitization• Damage caused by

explosive cleaning

10

BASIC FORMS OF CORROSION IN BALANCE OF PLANT

Uniform or General AttackGalvanic or Two Metal CorrosionCrevice CorrosionPitting CorrosionIntergranular CorrosionSelective Leaching or DealloyingFlow Assisted CorrosionEnvironmental Cracking

11

DAMAGE MECHANISM TO ROOT CAUSE DETERMINATION

Determine the damage mechanism- Do Not Guess Know the variables that effect the damage

mechanism- do things add upWork with the plant to explain the mechanism and

variable effecting the mechanism• Operations, Maintenance, Design• Stress, temperature, cycles, pH, water treatment, oxygen,

down time, fabrication method, operating hours Root Cause determination must be determined to

avoid a repeat failure

EXAMPLES

FIGURE 11, TYPICAL CROSS SECTION MICROSTRUCTURES JUST BELOW THE FRACTURE FRONT. ABUNDANT “LIGHTENING-BOLT” CRACKING TYPICAL OF STRESS CORROSION STARTING ON THE OD,

USUALLY AT PITS, IS EVIDENT.