Dave Gerr - Boat Mechanical Systems Handbook-How to Design, Install, and Recognize Proper Systems in Boats

Chapter 9:Dry Exhaust Systems

Figure 9-11. Flanged flexible bellows

(Courtesy Volvo Penta)

Figure 9-12.

Flexible bellows

failure from stress

corrosion

(Courtesy

Applegate

Industrial

Materials, Inc.)

Babying Flexible Bellows

and Bellows with Turbo

Liners

The stainless flexible bellows need careful
attention during layout and installation
(Figure 9-11). Remember, once installed
and hidden behind their removable lagging
boots, they are seldom inspected again—
and almost never from their inside. Simple

corrosion and stress corrosion (Figure 9-12)

can result in spectacular failures, which can

essentially stop you dead in the water. Weld

spatter or even grease on the bellows can

result in failure. Keep in mind that flexible

bellows are of thin metal parts that are con-

stantly moving, at temperatures around

1,000°F (540°C). The local temperature dif-

ferential resulting from grease or weld spat-

ter on their surface can result in a severe

local breakdown.

The bellows need to be carefully installed

at half their designated expansion, and they

must not be twisted or torqued during instal-

lation. Twisting the bellows when tightening

the flange bolts or welding them in place

(Figure 9-13) will result in stress that will

Figure 9-13.

Welded-in flexible

bellows (Courtesy

Applegate

Industrial

Materials, Inc.)