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16. Describe the cp application, by writing the following sentences in the correct order.

A. driving force for corrosion reaction is stopped.

B. metal surface becomes uniform potential

C. steel surface is polarized

D. current flow is driven by electrochemical potential

difference

17. Complete the following dialogue about corrosion patterns. Use the phrases, terms and photos.

A: Different corrosion types produce distinct corrosion patterns.

B: Corrosion is a result of low level and pitting corrosion that affects large areas.

A: However, the result is metal loss that compromises the integrity of the pipe.

B

corrosion patterns

uniform defects produce

pitted surfaces

striations (бороздчатость) include

channel defects

: ………….

Fig 1: An example of general deep pitting corrosion with some pits joining to form larger pits and interconnected pitting.

Fig 2: Image presenting the trend towards channel style corrosion. The channels were initially small pits that joined together and continued to grow. This type of corrosion pattern can result in defects with significant depth and length.

17. Describe the following type of corrosion- SCC. Use the terms and phrases and photos

Fig 5: Photomicrograph of a SCC crack in pipeline steel.

Fig 6: Photograph of a SCC crack at the weld fusion line (toe crack). Branching nature that may occur at the crack tip can clearly be seen in this profile.

Fig 7: Photomicrograph of a SCC in a weld. The two indications shown are located adjacent to one another and both occur within the weld material.

cracking residual stress

pipeline temperature

be influenced by load stress

environment stress bending

water local stress

come into contact high pH conditions

steel cause

create intergranular cracks

initial corrosion site low pH conditions

act on transgranular cracks

crack growth non-classic SCC

factors result in

18. Discuss these two problems and state your own ideas and solutions.

1. Consideration of defect initiation mechanisms and the ability to interpret defect styles should enable the NDT technician to choose the best inspection option for the conditions at hand. By providing background knowledge, sample defects, and appropriate calibration blocks the technician will be able to confidently address the requirements of the application.

2. The use of modern computers and automated scanning systems has enabled significant advancements in ultrasonic same side sizing techniques for corrosion and SCC sizing. Corrosion mapping and crack sizing using tip diffraction, angled longitudinal, or shear wave inspection techniques have the potential to offer cost savings by reducing inspection times and providing detailed information about the corrosion feature or crack profile.

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