Which part of the cargo tank motor vehicle's piping system must be inspected monthly?

The correct answer is based on the comprehensive requirements for maintaining the cargo tank motor vehicle's piping system to ensure safety and compliance with NFPA 58 standards. Regular inspections of the elements, bolts, and the entire piping system are crucial because these components are integral to the safe operation of the vehicle and the safe transport of liquefied petroleum gas (LPG).

Inspecting the entire piping system, including connections, fittings, and bolts, allows for the detection of any potential leaks, corrosion, or other failures that could lead to unsafe conditions. By thoroughly examining all elements of the system, operators can take early action to address any issues, thereby mitigating risks associated with LPG, which is highly flammable and poses significant hazards if not properly contained.

Other options, such as inspecting only valves, hoses, or pressure gauges, would not provide a complete safety assurance. Valves and hoses are important, but they form part of the broader system, and focusing solely on elements like pressure gauges ignores other critical components that could compromise safety if they are not regularly checked. Hence, the requirement for a holistic monthly inspection emerges from a proactive approach to LPG safety and regulatory compliance, emphasizing the importance of checking all related components together rather than in isolation.