What must the exposed surfaces of each fillet weld show?

The correct choice requires the exposed surfaces of each fillet weld to exhibit complete penetration and fusion. This ensures the weld properly bonds the two elements being joined, providing the necessary strength and durability to withstand operational conditions.

Complete penetration indicates that the weld metal has fused all the way through the joint, reaching the base metal on either side. This is critical in pipeline welding because it prevents the likelihood of voids or weak spots that can lead to failures, especially under high pressure or stress. Fusion ensures that the base metals and the weld metal interconnect effectively, resulting in a cohesive structure that can perform reliably.

In pipeline construction, adhering to the standards for weld quality as prescribed in API 1104 is paramount to ensure the integrity and safety of the pipeline system. Such quality controls are designed to mitigate risks associated with leaks or structural failures that could have significant consequences. Thus, emphasizing the importance of complete penetration and fusion in fillet welds directly correlates with meeting industry standards for safety and performance.