The shells are easy to install around each reformer tube (at pigtail connection) on top of the steel roof area. The upper set of 2 half shells (fixed around tube), moves like a telescope over the lower set, which is fixed on roof casing plate. This results in a perfect seal that can absorb axial movements of more then 250 mm. The Wearflex® telescopic seals are maintenance free, easy and quick to install and removable for maintenance to the reformer tubes.