Corrosion Mechanisms and Monitoring Flashcards
7 cards from real API 510 practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Corrosion Mechanisms and Monitoring flashcards as text
Which nondestructive examination (NDE) method is best suited for detecting hydrogen-induced cracking (HIC) in plate steel?
Answer: Automated ultrasonic testing (AUT) with phased array
AUT with phased array ultrasonics can detect the internal, planar HIC blisters and step-wise cracking that occur within the steel plate, which surface methods cannot find.
Naphthenic acid corrosion in refinery equipment is characterized by which distinctive feature?
Answer: Pitting and grooving at areas of high turbulence and velocity
Naphthenic acid corrosion produces characteristic pitting and grooving at high-turbulence locations because the corrosion product (iron naphthenate) is soluble and is swept away by flow.
What does the term 'short-term corrosion rate' mean in the context of API 510 remaining life calculations?
Answer: Corrosion rate measured over the last inspection interval only
The short-term corrosion rate in API 510 is calculated from the most recent inspection interval, reflecting current operating conditions more closely than the long-term rate.
Which condition is required for chloride stress corrosion cracking (Cl-SCC) to occur in austenitic stainless steel?
Answer: Tensile stress, chloride ions, and temperature typically above 140°F (60°C)
Cl-SCC requires the simultaneous presence of tensile stress, chloride ions, and elevated temperature (typically above 140°F/60°C) to initiate and propagate cracks.
In high-temperature service above 750°F (400°C), what corrosion mechanism causes carbon steel to lose strength and ductility through carbon removal from the steel matrix?
Answer: High-temperature hydrogen attack (HTHA)
HTHA occurs when hydrogen reacts with carbon in the steel to form methane gas, which decarburizes the steel and creates internal fissures, reducing mechanical properties.
A corrosion monitoring program uses electrical resistance (ER) probes and weight loss coupons. What is the primary advantage of ER probes over coupons?
Answer: ER probes provide continuous, real-time corrosion rate data without retrieval
ER probes provide continuous online monitoring without requiring retrieval and re-exposure periods, allowing real-time tracking of corrosion rate changes with process upsets.
Which corrosion mechanism is specifically associated with amine treating units in gas processing plants and is identified by thin-edged, sharp cracks typically in weld HAZ regions?
Answer: Amine stress corrosion cracking (amine SCC)
Amine SCC produces sharp, thin-edged cracks preferentially in the weld HAZ of carbon steel equipment due to residual tensile stresses combined with amine environment exposure.