A welded tubesheet to shell joint, as shown below, is typically used for any material that can be welded together. The biggest advantage of a welded joint is that it eliminates potential air leaks on the shellside. Since the joint is welded together and tested by the manufacturer, there should be no air leaks at this joint. Some of the most common materials for this type of joint are carbon steel shell with stainless steel tubesheets. Another common option for material is a clad tubesheet. A clad tubesheet is typically explosion bonded and can vary in materials and sizes. Depending on material costs it may be more economical to use clad tubesheets for larger diameters. Another advantage for clad is you can have a dissimilar higher alloy metal such as a brass alloy on the tube side with carbon steel on the shell side and still have a welded joint.

The disadvantage of having a welded joint is that it’s harder to replace the tubesheet if needed, since it’s welded. This is less of a concern when this joint is used in a clean shell side service, which is typically the case for turbine exhaust steam surface condensers. Also, the tubesheet is not likely required to be replaced very often, if ever.

A bolted and flanged tubesheet to shell joint, as shown below, is typically used for materials that are not able to be welded together. This joint is most common with brass alloy materials for the tubesheet as the shell is typically made with carbon steel material. It’s important to note that even though this is a gasketed joint, that it is still considered a fixed tubesheet design. The reason is the gasket is more of a permanent seal. The most common type used is a canvas gasket soaked in a sealant to insure a tight seal at this joint. This type of joint can be compromised by improper maintenance activities.

The way the bolted design works is stake studs are typically installed at every third hole, holding the tapped tubesheet to the shell flange. These stake studs are identified with a double nut or are marked with a rounded end. Therefore, the channel or bonnet on the tube side can be removed without disturbing the tubesheet to shell joint. This should be noted in any maintenance or turnaround activities due to the untypical nature of the joint. If the stake studs are removed or the double nuts removed, the joint is no longer held in place. This can lead to a failure at that joint between the tubesheet and shell. If the joint is compromised the canvas gasket soaked in sealant will need to be replaced and will require re-tubing of the condenser.

Replacement of this canvas gasket soaked in sealant is done when a tubesheet is being replaced or the condenser is being re-bundled. A quote for replacement gaskets and sealant, along with the installation procedure can be provided upon request.