Special Bellows for Marine Exhaust Systems

By: Frank Caprio | On: November 26, 2019

The rapid improvement in marine propulsion technologies has given rise to a whole generation of new equipment designed to move vessels as efficiently and safely as possible while also reducing both airborne and marine exhaust. New emissions regulations – IMO 2020 – are due to go into effect in January 2020 that drastically reduce the allowable sulfur content of marine fuels from 3.5% by weight to 0.5%. Newer vessels are increasingly choosing Liquefied Natural Gas (LNG) as a low-sulfur fuel to meet the IMO requirements. Older vessels may opt to install scrubbers to remove excess sulfur from non-compliant fuels. Because IMO 2020 is right around the corner, most carriers have already made the necessary changes in order to comply with the mandate, and are now looking towards the next big thing: ESG.

What is ESG?

ESG is short for “Environmental, Social, and Governance”. It is a term used to describe the global shipping industry’s commitment to sustainability. As part of this plan, the industry has vowed to reduce shipping emissions 50% by the year 2050, which will require introducing new propulsion technologies by 2030. That means the companies designing these new engines have a lot of work to do in the next ten years. Whether new engine designs or retrofits of existing engines, the components on these engines must work safely, reliably, and economically.

Marine Economics and the Great Recession

Prior to the global recession in 2008, the global economy was humming along, and shippers ordered many new vessels to keep up with the demand for global shipping capacity. These large shipping vessels typically take 2 to 3 years to build, and the global recession hit before these vessels could be delivered. This perfect storm of overcapacity during a global slowdown decimated shipping rates for years, and the industry has only recently started to recover.

These economics also affected the way the vessels are built and serviced. Ship builders had to find ways to trim costs wherever possible, as long as safety was not sacrificed. These cost-saving measures reduce the up-front cost of the vessel, but often end up costing more for the vessel owner over time. A small but not insignificant example of this is exhaust system components.

Pay now or pay more later…

Most large shipping vessels use internal combustion engines or gas turbines for propulsion. These reciprocating engines generate large amounts of vibration, which must be controlled in order to prevent damage to the engine and exhaust system. The best way to prevent vibration-induced damage is to incorporate one or more metal bellows expansion joints into the exhaust piping, to provide a flexible connection that dampens the vibration in the system. These metal exhaust bellows are often covered with some type of insulation, to prevent the excess heat in the exhaust gases from radiating into the engine room (see photo).

Typical marine engine exhaust. Note the insulation covering the bellows

As a cost-saving measure, these exhaust bellows are often made from a single ply of convoluted stainless steel tubing. This single-ply design is typically used to accommodate higher pressures and gradual movements, such as those encountered due to thermal expansion in a steam system. Unfortunately, their design is not optimal for dampening vibration from the engines, and two things happen as a result. First, the vibration is transferred through the piping system where it can damage piping anchors, dampers, or bearings. Secondly, the associated stresses quickly fatigue the metal bellows. Soon, cracks will begin to appear in the bellows, and the exhaust will begin to leak into the engine room. Operators must then act quickly to replace the bellows, which can be troublesome if the vessel is at sea.

To prevent this problem, a different bellows construction should be considered; instead of a single ply of material, the bellows can be fabricated from two or more plies of thinner-walled tubing, which are nested inside of each other prior to the bellows forming process. This multi-plied bellows may cost a little more than the single-ply OEM replacement bellows, but offers much better value. The multiple layers of metal in the bellows work to dampen the vibration much more effectively while maintaining the pressure rating of the single, heaver ply used originally. That means that the bellows will last longer, and protect the engine and exhaust from costly repairs resulting from excess vibration.

Hose Master has the experience needed to design engine exhaust bellows that will provide years of trouble-free operation, and we offer full Product Type Approval by ABS and other maritime classification societies. Whether installing a new exhaust bellows or refurbishing an old one, we have the expertise to ensure maximum service life. If improving safety and reliability while reducing overall costs are important to you, contact us today so we can provide engineered solutions for your toughest applications.

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