The phrase "diameter pipes" refers to pipes that are measured and categorized based on their width or size. It is used to describe the dimension of a pipe, specifically referring to the distance across its circular shape. Full definition
Even moving hydrogen by pipeline has its problems, much larger diameter pipes would be needed than to transport a comparable amount (in terms of energy value) of natural gas. (ramblingsdc.net)
The standard dual mode exhaust system and larger - diameter pipes enable improved air flow. (topspeed.com)
The problem is finding a 5 - inch diameter pipe at the bottom of the seabed or below. (dotearth.blogs.nytimes.com)