Vessel Stability & Structural Integrity Flashcards

Stress corrosion cracking in marine structural steel most commonly occurs when:

Answer: Sustained tensile stress combines simultaneously with exposure to a corrosive environment

Stress corrosion cracking requires the simultaneous presence of sustained tensile stress, a susceptible material, and a corrosive environment; removing any one of these three factors prevents the mechanism.

What is the standard survey interval used by classification societies to maintain a vessel's class notation?

Answer: Annual surveys combined with a special survey (renewal survey) every 4–5 years

Classification societies maintain vessel class through annual surveys verifying ongoing compliance and comprehensive special surveys (typically every 4–5 years) that examine the hull structure, machinery, and equipment in detail.

In marine structural investigation, 'wasting' refers to which condition?

Answer: Reduction in metal plate or member thickness caused by corrosion or erosion

Wasting describes the measurable reduction in cross-sectional thickness of plating or structural members caused by corrosion, erosion, or mechanical wear over time, directly reducing the structural load-bearing capacity.

Fatigue cracks in a vessel's hull structure preferentially initiate at:

Answer: Stress concentration points such as cutouts, bracket toes, and weld terminations

Fatigue cracks initiate at geometric stress concentrations—holes, notches, bracket terminations, and weld toes—where local stress amplification significantly exceeds the nominal stress in the surrounding structure.

In vessel structural terminology, 'hogging' is best described as:

Answer: The midship section of the hull bending upward relative to the bow and stern

Hogging occurs when buoyancy is concentrated amidships (e.g., when a vessel rides a wave crest) causing the midship section to arch upward, placing the deck in compression and the keel in tension—resembling a hog's arched back.

During a marine structural failure investigation, which categories of documentary evidence should be collected as the highest priority?

Answer: Pre-existing defects, repair history, maintenance logs, and operational loading patterns

Structural failures are rarely sudden without prior contributing factors; pre-existing defects, repair history, maintenance records, and loading patterns together establish whether failure was progressive or precipitated by an operational cause.

Compared to conventional mild steel, high-tensile steel (HTS) used in modern ship construction:

Answer: Allows reduced plate thickness due to higher yield strength but requires careful welding procedures because of greater sensitivity to weld defects

HTS has higher yield strength than mild steel, enabling designers to reduce plating thickness and overall vessel weight, but this benefit is offset by greater sensitivity to weld quality—weld defects have a larger relative effect on HTS fatigue life.