Corrosion techniques

Different corrosion techniques

Non Destructive Testing Analytical Chemistry • Ultrasonic testing • Radiography • Thermography • Eddy current/magnetic flux • Intelligent pigs

Analytical Chemistry • pH measurement • Dissolved gas (O2, CO2, H2S) • Metal ion count (Fe2+, Fe3+)• Microbiological analysis

Different corrosion techniques Corrosion Monitoring

• Weight loss coupons • Electrical resistance • Linear polarization • Hydrogen penetration • Galvanic current

Fluid Electrochemistry • Potential measurement • Potentiostatic measurements • Potentiodynamic measurements • A.C. impedance

Mostly used techniques

Corrosion coupons: • This is one of the effective and easy method for the

corrosion monitoring techniques.• It consists of the metal coupons connected to the

holder • The principle of this technique is measuring of the

weight loss of the coupon after the exposed to the environment

• It can record several type of corrosion which cant be done by most of the different methods

Mostly used techniques• From the corrosion couples we can obtain the

a. Corrosion rate

b. Pitting rate

c. Weight loss • Corrosion rate depends on the faraday law• Weight of metal dissolving (g) = K x I x t

K = (atomic weight of metal (g/mol))/ No. of electrons transferred * 96,500 Amp/Sec

where: I = current (amps), t = time(sec)• Pitting rate • Pit (mpy) = (pit depth(mils) x 365)/exposure time in days

Mostly used techniques Electrical resistivity (ER)• The principle of this technique is measuring the change in

the resistance

R= r*(L/A)

• Reduction in the element’s cross section due to corrosion will be accompanied by a proportionate increase in the element’s electrical resistance

• It consists of 3 parts they are working element, reference element, check element

• If the resistance difference between check element and the reference changes the probe is not working properly

Mostly used techniques

Mostly used techniques

• From ER we can obtain the metal loss and corrosion rate

• Metal loss(M)= (S*P)/1000

where S= linearized Signal

P= probe life

• Corrosion rate(C)=(P*365(S2-S1))/( T*1000)

Mostly used techniques

Linear Polarization Resistance(LPR)• In this we will measure the relation between the

electrochemical potential and current generated between the electrodes

• The electric conductivity of a fluid can be related to its corrosiveness

R= V/I• During this process only small current so we will

provide external potential of 20mVto the process

Mostly used techniques

Ultrasonic• This method is used to detect the general corrosion

and erosion • In this method the transmitter produces the sound

wave and these travel through the samples • If there is any defects or corrosion there is change in

the reflected sound wave• From the information we can know the hidden

corrosion and the depth

Mostly used techniques

• Eddy current• This technique is used only to the conductive

elements• We will pass the eddy currents through the metal • If there is any corrosion there is fluctuation in these

currents these are used to detect the hidden corrosion