There is always a doubt among several marine engineers about the basic difference between pipes and tubes especially when it comes to spares order.
Pipes
- Pipes are classified by schedule and nominal diameter. For example, a 250mm nominal diameter and schedule 80 pipes.
- In pipes, all the fittings can be matched by nominal size and schedule.
- For example, a schedule 40 one inch pipe will have fittings specified by the same name. These pipe fittings would not fit a 1” tube.
- Pipes are always round or cylindrical.
Tubes
- Tubes are classified by outside diameter and thickness. For example 10mm copper tube 2 mm thickness.
- Tubes may be square, rectangular and cylindrical.
Nominal Diameter
- The nominal diameter is not internal diameter but similar to it.
- The nominal diameter is the approximate inner diameter of the pipe it is a rounded figure easier to use and remember
- By prescribing the nominal size of the pipe all the different fittings can be selected based on the same nominal diameter, without physically checking the dimensions and compatibility of each component.
Schedule of Pipes
- In ships, we generally use schedule 40 for light-duty and schedule 80 for heavy-duty.
- There are however many other schedules that have been incorporated due to improvement in metallurgy and increased pressure demands.
- As a general thumb rule, as the schedule increases the wall thickness increases and the ID deceases.