Final answer:
HDPE pipes are commonly joined by welding, which leverages the material's high tensile strength and closely packed linear molecules for strong, durable connections.
Step-by-step explanation:
HDPE (High density polyethylene) pipe is most commonly joined by welding. The process typically involves heating the ends of the pipes to be joined, which causes the material to melt and fuse together as it cools, creating a strong, leak-proof joint. HDPE's superior characteristics, like its high tensile strength and the way its mostly linear molecules pack well together, make welding an effective method for joining these types of pipes. This is especially critical in applications such as water pipes, where a secure and durable connection is necessary.