Wartsila ?31DF Series Product Manual page 159

Wärtsilä 31DF Product Guide
11.2.4 Piping
The piping should be as short and straight as possible. Pipe bends and expansions should
be smooth to minimise the backpressure. The diameter of the exhaust pipe should be increased
directly after the bellows on the turbocharger. Pipe bends should be made with the largest
possible bending radius; the bending radius should not be smaller than 1.5 x D.
The recommended flow velocity in the pipe is maximum 35...40 m/s at full output. If there are
many resistance factors in the piping, or the pipe is very long, then the flow velocity needs to
be lower. The exhaust gas mass flow given in chapter Technical data can be translated to
velocity using the formula:
where:
The exhaust pipe must be insulated with insulation material approved for concerned operation
conditions, minimum thickness 30 mm considering the shape of engine mounted insulation.
Insulation has to be continuous and protected by a covering plate or similar to keep the
insulation intact.
Closest to the turbocharger the insulation should consist of a hook on padding to facilitate
maintenance. It is especially important to prevent the airstream to the turbocharger from
detaching insulation, which will clog the filters.
After the insulation work has been finished, it has to be verified that it fulfils SOLAS-regulations.
Surface temperatures must be below 220°C on whole engine operating range.
11.2.5 Supporting
It is very important that the exhaust pipe is properly fixed to a support that is rigid in all
directions directly after the bellows on the turbocharger. There should be a fixing point on
both sides of the pipe at the support. The bellows on the turbocharger may not be used to
absorb thermal expansion from the exhaust pipe. The first fixing point must direct the thermal
expansion away from the engine. The following support must prevent the pipe from pivoting
around the first fixing point.
Absolutely rigid mounting between the pipe and the support is recommended at the first fixing
point after the turbocharger. Resilient mounts can be accepted for resiliently mounted engines
with "double" variant bellows (bellow capable of handling the additional movement), provided
that the mounts are self-captive; maximum deflection at total failure being less than 2 mm
radial and 4 mm axial with regards to the bellows. The natural frequencies of the mounting
should be on a safe distance from the running speed, the firing frequency of the engine and
the blade passing frequency of the propeller. The resilient mounts can be rubber mounts of
conical type, or high damping stainless steel wire pads. Adequate thermal insulation must be
provided to protect rubber mounts from high temperatures. When using resilient mounting,
the alignment of the exhaust bellows must be checked on a regular basis and corrected when
necessary.
DBAE248994
v = gas velocity [m/s]
m' = exhaust gas mass flow [kg/s]
T = exhaust gas temperature [°C]
D = exhaust gas pipe diameter [m]
11. Exhaust Gas System
11-5