What is the maximum pipe size that may be welded or threaded?

The maximum pipe size that may be welded or threaded in many piping applications is typically determined by industry standards and specific regulations. In this context, 1-1/4" pipe size is often the limit for threaded connections, as threading can become less effective and more prone to failure in larger diameters due to the increased stress and reduced surface area for the thread engagement.

Welding can be performed on larger sizes, but threaded connections are usually restricted for practical application. Therefore, the choice of 1-1/4" pipe aligns with the commonly accepted practices in piping standards, making it the correct answer. This also reflects the understanding of how to achieve reliable connections based on the size and material of pipes used in high-pressure systems, ensuring safety and structural integrity.