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Lead sheath of cable may get damaged due to
Mechanical injury
Crystallization of lead through vibration
Chemical reaction with impurities present in a soil
Any of above
Any of above
The lead sheath of an underground cable is susceptible to damage from physical, mechanical, and chemical stressors due to its material properties and environment. Because lead is a relatively soft, malleable metal, it is prone to deformation and degradation when exposed to external pressures or harsh chemical environments.
The lead sheath of an underground cable is susceptible to damage from physical, mechanical, and chemical stressors due to its material properties and environment. Because lead is a relatively soft, malleable metal, it is prone to deformation and degradation when exposed to external pressures or harsh chemical environments.
VstressтАЛ=AFтАЛ тАФ representing the mechanical stress leading to sheath deformation
╬ФLтИЭ╬▒L╬ФT тАФ representing thermal expansion stresses that can crack brittle lead
Mechanical injury often results from excavation or shifting ground, while vibration induces metal fatigue, leading to 'crystallization'тАФa process where the grain structure of the lead changes, causing brittleness and eventual cracking. Chemically, if the surrounding soil contains salts, organic acids, or groundwater with specific minerals, the lead undergoes electrolysis or chemical corrosion, resulting in localized pitting and sheath failure.
Lead is used in cables to provide a moisture-proof seal and mechanical protection.
Crystallization is a long-term phenomenon primarily caused by cyclic loading and vibrations.
Chemical corrosion is accelerated in soils with high moisture and acidity.
Armoring is typically provided over the bedding to protect the lead sheath from mechanical injury.
Impermeability to moisture and gases
Good resistance to chemical attack in non-corrosive environments
High density/weight increases installation difficulty
Subject to fatigue cracking under vibration
High-voltage underground transmission
Submarine power cables
Modern cables often use extruded thermoplastic sheaths (like PVC or PE) instead of lead to avoid these specific vulnerabilities.
Option A, B, and C are all primary causes of sheath failure, making D the correct choice.
D is correct тАФ The lead sheath is vulnerable to mechanical, vibrational (crystallization), and chemical degradation in the underground environment.
Always remember that the lead sheath acts as both a moisture barrier and a ground path; its integrity is vital for cable insulation longevity.