Table 5.1 Recommended maximum velocities on pump delivery side for guidance
Max velocity [m/s]
Pipe material
Piping
3
Stainless steel
LNG piping
20
Stainless steel / Carbon steel
Fuel gas piping
1.0
Black steel
Fuel oil piping (MDF and HFO)
1.5
Black steel
Lubricating oil piping
2.5
Black steel
Fresh water piping
2.5
Galvanized steel
Sea water piping
2.5
Aluminum brass
3.0
10/90 copper-nickel-iron
4.5
70/30 copper-nickel
4.5
Rubber lined pipes
NOTE!
The diameter of gas fuel piping depends only on the allowed pressure loss in the piping, which
has to be calculated project specifically.
Compressed air pipe sizing has to be calculated project specifically. The pipe sizes may be chosen on the
basis of air velocity or pressure drop. In each pipeline case it is advised to check the pipe sizes using both
methods, this to ensure that the alternative limits are not being exceeded.
Pipeline sizing on air velocity:
For dry air, practical experience shows that reasonable velocities are 25...30
m/s, but these should be regarded as the maximum above which noise and erosion will take place, partic-
ularly if air is not dry. Even these velocities can be high in terms of their effect on pressure drop. In longer
supply lines, it is often necessary to restrict velocities to 15 m/s to limit the pressure drop.
Pipeline sizing on pressure drop:
As a rule of thumb the pressure drop from the starting air vessel to the
inlet of the engine should be max. 0.1 MPa (1 bar) when the bottle pressure is 3 MPa (30 bar).
It is essential that the instrument air pressure, feeding to some critical control instrumentation, is not allowed
to fall below the nominal pressure stated in chapter "Compressed air system" due to pressure drop in the
pipeline.
5.2
Trace heating
The following pipes shall be equipped with trace heating (steam, thermal oil or electrical). It shall be possible
to shut off the trace heating.
•
All heavy fuel pipes
•
All leak fuel and filter flushing pipes carrying heavy fuel
5.3
Pressure class
The pressure class of the piping should be higher than or equal to the design pressure, which should be
higher than or equal to the highest operating (working) pressure. The highest operating (working) pressure
is equal to the setting of the safety valve in a system.
The pressure in the system can:
•
Originate from a positive displacement pump
•
Be a combination of the static pressure and the pressure on the highest point of the pump curve for
a centrifugal pump
•
Rise in an isolated system if the liquid is heated
Within this publication there are tables attached to drawings, which specify pressure classes of connections.
The pressure class of a connection can be higher than the pressure class required for the pipe.
Example 1:
The fuel pressure before the engine should be 0.7 MPa (7 bar). The safety filter in dirty condition may cause
a pressure loss of 0.1 MPa (1.0 bar). The viscosimeter, automatic filter, preheater and piping may cause a
30
Product Guide Wärtsilä 34DF - 3/2012
Product Guide
5. Piping Design, Treatment and Installation
