Process Corrosion

1.

PROCESS CORROSION
CONTINUOUSLY DEGRADING INTEGRITY

2.

GOLDOBIN
ALEKSANDR
Maintenance Engineer
https://dzen.ru/alexgold
[email protected]

3.

CORROSION PRINCIPLES
Corrosion rate is measured as weight loss per unit area and is expressed in mils per year (mpy) or mm/y.
Corrosion Rates can be affected by:
Passivity forming protective surface films (including corrosion inhibitors, paints and coatings)
Oxygen content
Flow velocity/rates
Temperature
pH effects (Low and High)
Contaminants/intermediates

4.

SOME CORROSIVES FOUND IN THE PROCESS INDUSTRY
Water
Deposits
Oxygen
Hydrogen Chloride
Naphthenic Acid
Sulfuric Acid
Polythionic Acid
Hydrogen
Chlorides
Phenols
Carbon Dioxide
Dimer and Trimer acids
Ammonia
Cyanides
Other

5.

LOW TEMPERATURE CORROSION
Below 500° F (<260’ C)
Occurrences:
Inorganic compounds such as water, hydrogen sulphide, hydrogen chloride, sulphuric acid, salts, etc.
Presence of water (even in very small amounts)
Electrolyte in hydrocarbon stream
Hydrocarbons in water streams creating acidic conditions
Solids.. Under deposit
Organic acids
Vapour Streams at water condensation points
Obeys electrochemical laws
Stable films can reduce or prevent corrosion

6.

LOW TEMPERATURE CORROSION
From Process chemicals
From Process contaminants
Not caused by clean hydrocarbons
Caused by inorganic compounds such as water, hydrogen sulphide, hydrogen chloride, sulphuric acid, salts, etc.

7.

HIGH TEMPERATURE CORROSION
Above 500° F (>260° C)
No water present
Result of a reaction between metal and process ions (such as oxygen O’, sulphur S, etc.)

8.

HIGH TEMPERATURE CORROSION
Important due to serious consequences
High temperatures usually involve high pressures
Dependent on the nature of the scale formed
General thinning
Localized thinning (pitting)
Inter-granular attack
Mixed phase flow
Metallurgical changes

9.

SITUATIONS LEADING TO DETERIORATION
Normal operation, upset, startup/shutdown conditions
Material/Environment condition interactions
Many combinations of corrosive process streams and temperature/pressure conditions.
In the absence of corrosion, mechanical and metallurgical deterioration can occur
Weather effects ....

10.

FORMS OF THE DAMAGE
General loss due to general or localized corrosion
Pitting attack 0 Stress Corrosion Cracking (SCC)
Metallurgical Changes d Mechanical damage
High Temperature Hydrogen Attack (HTHA)
Damage types occur with specific combinations of materials and environmental/ operating conditions

11.

STRESS CORROSION CRACKING DETECTION
SOH IC in soft base metal.
Stress-Oriented Hydrogen Induced Cracking
In contrast to general corrosion, SCC is very hard to
detect visually even when it has progressed to an
extreme condition.

12.

TYPES OF STRESS CORROSION CRACKING
Chloride stress corrosion cracking (CI-)
Nitrates 9 Caustic stress cracking (NaOH)
Polythionic acid stress corrosion cracking
Ammonia stress corrosion cracking (NH4)
Hydrogen effects (in steel)
Sulfide stress corrosion cracking SSC, hydrogen induced cracking HIC, stress oriented hydrogen
induced cracking SOHIC
Hydrogen cyanide HCN 9 Others

13.

HIGHT TEMPERATURE HYDROGEN ATTACK
Longitudinal Weld
Magnification: 500x
Etch: 2% Nital