Pipes

Pipes and Pipe Sizing
Pipe sizing is a crucial aspect of steam system design. This tutorial offers detailed advice on standards, schedules, materials and sizing for various saturated and superheated steam duties.
Use the quick links below to take you to the main sections of this tutorial:
• The printable version of this page has now been replaced by The Steam and Condensate Loop Book
• Viewthe complete collection of Steam Engineering Tutorials
• Contact Us
Top
Standards and wall thickness
There are a number of piping standards in existence around the world, but arguably the most global are those derived by the American Petroleum Institute (API), where pipes are categorised in schedule numbers.

These schedule numbers bear a relation to the pressure rating of the piping. Thereare eleven Schedules ranging from the lowest at 5 through 10, 20, 30, 40, 60, 80, 100, 120, 140 to schedule No. 160. For nominal size piping 150 mm and smaller, Schedule 40 (sometimes called 'standard weight') is the lightest that would be specified for steam applications.

Regardless of schedule number, pipes of a particular size all have the same outside diameter (not withstandingmanufacturing tolerances). As the schedule number increases, the wall thickness increases, and the actual bore is reduced. For example:
• A 100 mm Schedule 40 pipe has an outside diameter of 114.30 mm, a wall thickness of 6.02 mm, giving a bore of 102.26 mm.
• A 100 mm Schedule 80 pipe has an outside diameter of 114.30 mm, a wall thickness of 8.56 mm, giving a bore of 97.18 mm.
Only Schedules 40 and 80cover the full range from 15 mm up to 600 mm nominal sizes and are the most commonly used schedule for steam pipe installations.

This Tutorial considers Schedule 40 pipework as covered in BS 1600.

Tables of schedule numbers can be obtained from BS 1600 which are used as a reference for the nominal pipe size and wall thickness in millimetres. Table 10.2.1 compares the actual bore sizes ofdifferent sized pipes, for different schedule numbers.

In mainland Europe, pipe is manufactured to DIN standards, and DIN 2448 pipe is included in Table 10.2.1.
Table 10.2.1 Comparison of pipe standards and actual bore diameters.
In the United Kingdom, piping to EN 10255, (steel tubes and tubulars suitable for screwing to BS 21 threads) is also used in applications where the pipe is screwedrather than flanged. They are commonly referred to as 'Blue Band' and 'Red Band'; this being due to their banded identification marks. The different colours refer to particular grades of pipe:
• Red Band, being heavy grade, is commonly used for steam pipe applications.
• Blue Band, being medium grade, is commonly used for air distribution systems, although it is sometimes used for low-pressure steamsystems.
The coloured bands are 50 mm wide, and their positions on the pipe denote its length. Pipes less than 4 metres in length only have a coloured band at one end, while pipes of 4 to 7 metres in length have a coloured band at either end.
Fig. 10.2.1 Red band, branded pipe, - heavy grade
Fig. 10.2.2 Blue band, branded pipe, - medium grade, between 4-7 metres in length
Top
Pipematerial
Pipes for steam systems are commonly manufactured from carbon steel to ASME B 16.9 A106. The same material may be used for condensate lines, although copper tubing is preferred in some industries.

For high temperature superheated steam mains, additional alloying elements, such as chromium and molybdenum, are included to improve tensile strength and creep resistance at high temperatures.Typically, pipes are supplied in 6 metre lengths.
Top
Pipeline sizing
The objective of the steam distribution system is to supply steam at the correct pressure to the point of use. It follows, therefore, that pressure drop through the distribution system is an important feature.
Liquids
Bernoulli's Theorem (Daniel Bernoulli 1700 - 1782) is discussed in Block 4 - Flowmetering. D'Arcy (D'Arcy...