What should be avoided at threaded socket welded joints?

The appropriate choice emphasizes that the use of uncoated materials should be avoided at threaded socket welded joints. Uncoated materials can lead to corrosion or chemical reactions over time, which may compromise the integrity of the joint. Corrosion can weaken the joint and lead to failures, leaks, or other hazardous situations, especially in environments where CNG is involved.

In addition, uncoated metal can react with the threaded connections, leading to galling or seizing, which would further jeopardize the reliability and safety of the joint. Proper coatings or finishes are essential to protect metal surfaces from environmental factors and ensure long-term durability.

The other options, while relevant in specific contexts, do not directly address the risks associated with uncoated materials in threaded socket welded joints. Using plastic connections might limit temperature and pressure withstand capabilities; flexible hoses are generally used in applications requiring movement and flexibility, which might not apply to welded joints; and insulation materials, while sometimes necessary, are not specified as critical issues for threaded welded joints in the context of this question. The focus clearly lies in the risks posed by uncoated materials.