WÄRTSILÄ WARTSILA 20, Product Manual

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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.
11.3.2 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 long bellows, 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.
After the first fixing point resilient mounts are recommended. The mounting supports should
be positioned at stiffened locations within the ship’s structure, e.g. deck levels, frame webs
or specially constructed supports.
The supporting must allow thermal expansion and ship’s structural deflections.
11.3.3 Back pressure
The maximum permissible exhaust gas back pressure is stated in chapter Technical Data. The
back pressure in the system must be calculated by the shipyard based on the actual piping
design and the resistance of the components in the exhaust system. The exhaust gas mass
flow and temperature given in chapter Technical Data may be used for the calculation.
Each exhaust pipe should be provided with a connection for measurement of the back pressure.
The back pressure must be measured by the shipyard during the sea trial.
11.3.4 Exhaust gas bellows (5H01, 5H03)
Bellows must be used in the exhaust gas piping where thermal expansion or ship’s structural
deflections have to be segregated. The flexible bellows mounted directly on the turbocharger
outlet serves to minimise the external forces on the turbocharger and thus prevent excessive
vibrations and possible damage. All exhaust gas bellows must be of an approved type.
11.3.5 SCR-unit (11N14)
The SCR-unit requires special arrangement on the engine in order to keep the exhaust gas
temperature and backpressure into SCR-unit working range. The exhaust gas piping must be
straight at least 3...5 meters in front of the SCR unit. If both an exhaust gas boiler and a SCR
unit will be installed, then the exhaust gas boiler shall be installed after the SCR. Arrangements
11-4 Wärtsilä 20 Product Guide - a13 - 6 September 2016
Wärtsilä 20 Product Guide 11. Exhaust Gas System