Corrosion Control & Prevention Flashcards

What is the primary purpose of cathodic protection in corrosion control?

Answer: To make the metal surface the cathode of an electrochemical cell

Cathodic protection is a corrosion control technique that works by transforming the entire surface of the metal to be protected into a cathode. By supplying electrons to the metal, it prevents the anodic (corroding) reactions from occurring. This is achieved by connecting the protected metal to a more active sacrificial anode or by using an impressed current system.

Which type of corrosion occurs due to differences in metal composition?

Answer: Galvanic corrosion

Galvanic corrosion occurs when two dissimilar metals are in electrical contact and exposed to an electrolyte. The difference in their electrochemical potentials causes the less noble (more active) metal to act as an anode and corrode preferentially, while the more noble metal acts as a cathode and is protected. This phenomenon is a significant concern in material selection and design.

What is the minimum protective potential for steel in seawater according to NACE standards?

Answer: -0.80 V vs. CSE

According to NACE standards, the minimum protective potential for cathodically protected steel in seawater is generally accepted as -0.80 V vs. a Copper-Copper Sulfate Electrode (CSE). This potential ensures that the steel surface is sufficiently polarized to prevent corrosion. Maintaining this potential helps to achieve effective long-term corrosion control in marine environments.

Which coating defect appears as small, blister-like formations?

Answer: Blistering

Blistering is a common coating defect characterized by the formation of dome-shaped, localized swellings on the coating surface. These blisters occur when moisture, gas, or other fluids become trapped beneath the coating, causing a localized loss of adhesion and lifting the coating from the substrate. It indicates a failure in coating adhesion or permeability.

What is the purpose of an insulating flange in pipeline systems?

Answer: To prevent electrical continuity between pipeline sections

An insulating flange is a critical component in pipeline systems designed to prevent electrical continuity between different sections of the pipeline. This electrical isolation is essential for effective cathodic protection systems, as it ensures that the protective current is directed only to the intended pipe segment and prevents stray current interference with other structures.

Which NACE standard covers the selection of corrosion-resistant alloys?

Answer: NACE MR0175

NACE MR0175 (now ISO 15156) is a crucial NACE standard that specifies requirements for materials resistant to sulfide stress cracking (SSC) in H2S-containing environments. This standard is widely used in the oil and gas industry to select and qualify materials for equipment exposed to sour service, ensuring their integrity and preventing catastrophic failures due to SSC.

What is the primary cause of microbiologically influenced corrosion (MIC)?

Answer: Microbial activity producing corrosive metabolites

Microbiologically Influenced Corrosion (MIC) is primarily caused by the metabolic activities of microorganisms on material surfaces. These microbes can produce corrosive byproducts like acids or sulfides, create differential aeration cells, or alter the local chemistry, all of which accelerate the degradation of the material. MIC can lead to severe localized corrosion, such as pitting.

Which instrument measures coating thickness non-destructively?

Answer: Coating thickness gauge

A coating thickness gauge is a non-destructive instrument specifically designed to measure the dry film thickness of protective coatings on various substrates. This measurement is crucial for quality control, ensuring that the applied coating meets specifications and provides adequate corrosion protection without damaging the coating or the underlying material.

What is the recommended maximum anode utilization factor for magnesium anodes?

Answer: 85%

The recommended maximum anode utilization factor for magnesium anodes is typically 85%. This factor accounts for the fact that not all of the anode material is effectively consumed during its service life due to factors like uneven dissolution or residual material. Using 85% ensures a conservative and realistic estimate of the anode's operational lifespan.