We have recently supplied a very special compensator for installation in the hot blast main at a steel plant in the United Kingdom.

Complex and special design

The compensator is shown in the photograph and it is basically a single-bellows compensator to accept axial movement, it is fitted into a 2 700mm duct and is flanged for installation. What makes the compensator complex and special is the very high temperature of the gas which necessities the inclusion of refractory lining of the main. This lining has a total thickness of just over 350mm and is made from layers of insulating bricks; these were fitted into the compensator by a refractory lining specialist after the compensator was built in our Esbjerg facility and delivered to site.

Working closely with insulation specialist

We worked closely with the insulation specialist to establish the requirements for the work he was to carry out and incorporated them into the design. The lining is made with expansion gaps which allow the unit to compress, these gaps are staggered through the length of the unit and are packed with flexible insulating materials which are retained by packing rope. Additionally for added security the convolutions in the bellows are packed with flexible insulation. The mains ductwork itself is fabricated from carbon steel, this possible because the internal insulation in the pipework reduces the temperature dramatically at the surface of the pipework. Piping components and the flow liner in the compensator are fabricated from 1,4841 (310 stainless steel) with the flanged manufactured in 1,0425 (EN 10028 P265 GH), the bellows is single-ply and is 4mm thick.

Heavy flow liner

An important feature of the compensator fabrication is the inclusion of a very heavy flow liner to carry the weight of the refractory lining in the unit and a stop ring up onto which the insulating materials are carried. The design conditions at the bellows are 6,5 Bar / 300°C and the unit was hydrostatically tested, in works, at 9,75 Bar, the flexible insulation was introduced into the convolutions with the unit dried out after testing.

Careful handling

A major consideration in the design process was handling, the unit is heavy and cumbersome, careful handling to avoid damage to the bellows element or the insulation is essential. To assist with this the unit was fitted with transit bars to fix the length and lifting points were included to enable the compensator to be correctly lifted into position for handling and fitting. The lifting points are placed at several positions around the flanges to allow the unit to be tilted from the vertical position adopted for addition of the refractory into the horizontal orientation when it is lifted to install it in the pipework.

Comprehensive testing

As would be expected with such a critical piece of equipment a good deal of non-destructive testing was undertaken during manufacture, this included radiographic and ultrasonic  examination of the welds in the bellows and pipe seams together with dye-penetrant examination of the bellows seam and assembly fillet welds.
Supporting documentation included material certification, works pressure test certificate together with weld procedures and welder qualifications.

Expansion joint for high temperature gas