TEST CORROSION AND CATHODIC PROTECTION Objective (15 Questions = 30 marks) 1) Corrosion reactions are a. chemical reaction b. electrochemical reaction c. electrical reaction d. combustion reaction 2) Choose the correct answer for sacrificial anode system a. The metal to be protected is made anode b. Only the more active metal will be corroded, protecting the parent metal c. Since the anodic metal is sacrificed, the method is also called galvanic cathodic protection d. Usually Platinum and Silver are used as sacrificial anodes 3) The corrosion current flow is due to a. Anaerobic environment b. A potential difference between anodes and cathodes. c. Low soil resistivities d. Electrical continuity 4) In Cathodic Protection system, the structure (pipe) to be protected should become as as. a. Anode b. Cathode c. Electrolyte d. Copper Sulphate 1
5) A galvanic cell is formed a. When two metals are immersed in solutions differencing in concentration b. When two different metals are immersed in one electrolyte c. When two different metals are exposed to dry air d. When two metals are brought close together and electrically insulated from one another 6) The corrosion current flows is due to a. Anaerobic environment b. A potential difference between anodes and cathodes c. Low soil resistivity d. Electrical continuity 7) Select the wrong power sources for impressed current cathodic protection a. 4-pin Wenner b. Solar cell c. Fuel cell d. Engine Generator 8) Select the right common anode material for impressed current cathodic protection a. graphite b. gold c. wood d. glass 2
9) What is the most common method to measure soil electrolyte resistivity a. 4 pin Wenner method b. 8 pin Wenner method c. Resistivity meter d. 4 pin Wendy method 10) Stray current sources are from the following except a. Cathodic protection system b. Direct current welding operations c. High voltage direct current transmission d. Galvanic corrosion 11) The three metals that are commonly used in cathodic protection as a sacrificial/galvanic anodes are a. magnesium b. aluminium c. silver d. zinc 12) Choose the correct answer a. Corrosion can be classified as low temperature corrosion and high temperature corrosion. b. Corrosion call must have electron. c. Wet corrosion and dry corrosion is not a type of corrosion. d. Sulphidation is a wet corrosion. 3
13) In Cathodic Protection system, the structure (pipe) to be protected should become as a.. a. Anode b. Cathode c. Electrolyte d. Copper sulphate 14) Choose the correct answer a. Painting is normally used to protect under ground or buried pipe. b. Coating is suitable to preventing on the above ground structure from corrosion. c. Coating is preventing structure from anodic and cathodic reaction. d. All above statement is correct. 15) The corrosion current flow is due to. a. Anaerobic environment b. A potential difference between anodes and cathodes. c. Low soil resistivities d. Electrical continuity 4
Subjective (3 Questions = 20 markah) Question 1 Explain what you understand on the following; a) Cathodic Protection b) Why all surface to be coated shall be clean by abrasive blasting following SSPC-SP 10 c) Impressed Current d) Consequences of corrosion 5
Question 2 a) Given the formula of resistivity as below, calculate soil resistivity from the following data given and give comment on the corrosivity of the soil. ρ = V on V off x spacing of pins x 191.5 Current Pin spacing = 3 ft Impressed voltage = 10V Current reading = 8 ma Voltage across the inside pins = 50mV with no current flowing Voltage across the inside pins = 500mV with current flowing b) Two gas pipelines, each 75 km long and 1 m diameter, are laid in different parts of Middle Eastern oil state at the same time. Pipeline A receives a very poorly applied coal tar epoxy coating, while pipeline B is given a high quality protective coat. Each line is further protected by a standard ICCP installation which uses a 100V, 100 A (10kW) rectifier/ground bed systems to cover the whole length of line. After several years it is found that pipeline A requires a current density of 1.72mAm -2 to achieve the protection potential, meanwhile B requires 86 µa. The recommended protection current density is 130 µa.m -2. For each pipeline: 1. Comment upon any excess or shortfall in the capacity of the protection system 2. Describe the effect of the corrosion protection system 6
Question 3 Corrosion occured in a buried oil pipeline 360 km long, which has a 200 mm external diameter. A wall thickness of 6.3 mm was adequate to cope with the stress levels imposed on the pipe, but to allow for corrosion it was increased to 8.3 mm. This corrosion allowance used an extra 3000 tonnes of steel and caused a loss of 4% carrying capacity in the line. Do the analysis and give your comment Analysis: Comment: 7