What are adjacent boiler tubes defined as when they are warped in such a way that they touch each other?

The correct choice is "Married." In the context of boiler tubes, when adjacent tubes warp and touch each other, they are said to be "married." This term is used to describe the phenomenon where two or more boiler tubes come into contact due to distortion or misalignment caused by heat stress, pressure, or age-related wear. This contact can lead to various operational issues, such as degradation of the tubes, restricted heat transfer, or even failure if not addressed.

Understanding the terminology is crucial for maintenance and operational discussions regarding boiler systems, as it highlights the potential problems that arise from tube interactions. The other terms do not accurately capture this specific condition and hence are not suitable descriptors in this context.