The difference between pipes and tubes is simply in the way it is sized.
PVC pipe for plumbing applications and galvanized steel pipe for instance, are measured in IPS (iron pipe size).
Copper tube, CPVC, PeX and other tubing is measured nominally, which is basically an average diameter.
PeX and CPVC tubing also comes in rigid "joints" or flexible rolls.
Pipe wall thickness increases with schedule, and is available in schedules 20, 40, 80, and higher in special cases.The schedule is largely determined by the operating pressure of the system, with higher pressures commanding greater thickness. Copper tubing is available in four wall thicknesses: type DWV (thinnest wall; only allowed as drain pipe per UPC), type 'M' (thin; typically only allowed as drain pipe by IPC code), type 'L' (thicker, standard duty for water lines and water service), and type 'K' (thickest, typically used underground between the main and the meter). Because piping and tubing are commodities, having a greater wall thickness implies higher initial cost.
Thicker walled pipe generally implies greater durability and higher pressure tolerances.Źródło: https://en.wikipedia.org/wiki/Water_pipe#Difference_between_pipes_and_tubes
However, this should not affect their quality, and sometimes it turns out that the plumber running his own business applies doubly to perform the outsourced tasks themselves.They may rely on both the exchange of a faulty seal and at the connection of the new tap.
Plastic pipework is used for the conveyance of drinking water, waste water, chemicals, heating fluid and cooling fluids, foodstuffs, ultra-pure liquids, slurries, gases, compressed air and vacuum system applications. Plastic pipe systems fulfil a wide variety of service requirements.Product standards for plastics pipe systems are prepared within the standards committee known as CEN/TC155. These requirements are precisely described in a complete set of European Product Standards for each application alongside their specific characteristics. For example: Conveyance of drinking water: Hygienic requirements Conveyance of gas: Highest Safety requirements Plastic pipes for radiant heating and floor heating: Temperature resistance over decades Sewer applications: High chemical resistance. Plastic pipes are perfectly capable of fulfilling the specific requirement for each application. They do so with a high level of performance over a long lifetime and with reliability and safety. The key factor for success is achieved by maintaining consistently high quality levels. For plastic pipe products, these levels are closely defined by the different standards.Źródło: https://en.wikipedia.org/wiki/Plastic_pipework.