http://www.search-document.com/pdf/1/nace-tm0374.htmlSour Corrosion Mechanism

These are not actual mathematical equations, rather chemical equations demonstrating the mechanism of sour corrosion. Metal components will eventually deteriorate in environments that contain liquid water, carbon dioxide and hydrogen sulphide. Hydrogen sulphide, in very small concentrations, drastically affects the corrosion processes and results in a very different corrosion mechanism known as sour corrosion in opposed to sweet corrosion (When there is no hydrogen sulphide).

Pitting Rate Calculation from Maximum Pit Depth on the Coupon

This equation helps to calculate the pitting rate, having the maximum pit depth on the coupon.

PCR = MPD/T

PCR is Pitting corrosion rate of coupon, mpy

PCR is Pitting corrosion rate, mpy

MPD is Maximum Pit depth, micron

T is Time of exposure, hr

Calculating the Inhibitor Efficiency

Inhibitors are applied to the pipeline to reduce corrosion. This parameter is calculated to assess the effectiveness of a particular corrosion inhibitor in the system.

einhibitor is Inhibitor efficiency of inhibitor, dimensionless

einhibitor is Inhibitor efficiency, dimensionless

CRuninhibited is Corrosion rate without applying the inhibitor, mpy

CRinhibited is Corrosion rate with applying the inhibitor, ppm

Remaining Life and Reassessment Interval Calculations

Remaining life is the time required to corrode away 80% of the metal at the current corrosion rate. Reassessment interval is half this time or 5 years (this value might be different depending on the application and the regulatory laws enforced) whichever is smaller.

RL is Remaining life of metal, years

k is Corrosion rate conversion factor, mpy*hr/micron

RL is Remaining life, years

CR is Corrosion rate, mpy

Th is Wall thickness, mm

Coating Surface Area

This equation is used to identify the amount of coating material required to cover the surface of a pipeline.

A is Surface area of the pipe covered with the coating, m2A is Surface area of the pipe, m2Vco is Volume of the coating, L

DFT is Dry wall thickness, microns

percentsolid is Percent Solids added, dimensionless