The experienced and certified Belman on-site service team has recently completed a project at a German steel plant. The project involved the installation of clamshell bellows, with two units in size DN 2400 and one DN 2500.

Benefits of Clamshell bellows
Clamshell bellows provide a very effective solution when a quick and unplanned replacement of the bellows is needed. Clamshell bellows are two-piece expansion joints that are welded together on-site. They can be introduced retrospectively when the existing bellows lose their ability to contain pressure. The purpose of clamshell bellows is to provide a very quick remedial solution with the least disruption to the operation of the pipe system. The use of clamshell bellows invariably yields huge cost savings when compared with the cost of manufacturing and fitting a completely new expansion joint. They can be designed as an over-sized or in the same-size and for either a temporary or permanent solution. We design and manufacture this type of bellows up to DN 12.000 in size, utilising all kinds of materials and in both round and rectangular shapes.

Comparison of Over-sized Clamshell bellows vs. Same-size Clamshell bellows
These are mounted on packing rings and welded to the outer surface of the pipe or pressure vessel on either side of the existing bellows. These rings are sized so that the clamshell bellow is installed over the original bellow. The clamshell bellow is welded to the packing rings and the pressure is finally sealed by a longitudinal butt-weld joining the bellow convolutions. Provided that the system temperature or any leakage from the original bellows does not constitute a safety hazard, the oversized clamshell bellow can be fitted while the system is still fully operational. This has the critical benefit that no system downtime is required. The original bellows together with any inner sleeves or insulating materials are left in place and are not directly affected by the installation of the clamshell bellow. Fitting an oversize clamshell bellow will inevitably result in an increase in the bellows deflection forces with a small increase in the effective area. This aspect has to be considered by the system designer as part of the change-management process and our project engineers will be pleased to provide information in respect of this.

Installation of same-size clamshell bellows requires a shutdown of the pipe system. The existing bellows are
stripped from the pipe system or pressure vessel and replaced by new bellows sized to match and mounted directly onto the original pipe system. The tangents on the bellows are welded to the outer surface of the pipe system, as with an over-sized clamshell and the convolution halves are connected using a longitudinal butt-weld at each joint. Same-size clamshells can usually be designed so that the stiffness and effective area exactly or very closely, match the original bellows. The result is zero or negligible changes to the performance characteristics.

On-site installation of clamshell bellows
Installation of metallic expansion joints and in particular clamshell bellows requires skilled and experienced installation professionals. In many instances, customers prefer the manufacturer to perform such installation work to minimise the risks from an incorrect installation. In such cases, our on-site service team of skilled and certified welders can deliver the required expert assistance to our customers.
Belman is highly experienced and through the years has installed many clamshell bellows in steel plants, oil refineries and chemical plants.

Design parameters
Dimension: DN 2400, DN 2500 • Installation length: 400, 650 mm • Design pressure: 3,5 barg • Design temperature: 240°C • AX: Up to +/-22 mm • Bellow: 1.4571 • Mounting rings: 1.0425

Belman on-site installation


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