Tube support methods vary in steam/methane-reforming heaters. Some designs require full support from the top. In these designs the pigtail may be below the tube and unable to take any load from the catalyst-filled tube. Counterweights are often used and may support two or more tubes. The lever or pulley system must work as designed. Interference from tube flange bolts, slipping of supports off tube flanges, and other similar problems have led to pigtail failures.
Inadequate support also allows tube bending, which puts a bending moment on a pigtail that exits the tube from the side, thus causing localized high stress at the fitting on the tube or the outlet headers.
Outlet headers grow, usually from a center anchor point. Bottom tube supports on short pigtailed tubes must allow movement of the tube bottom to minimize stress on the pigtail. If the tube is designed for bottom movement, the upper tube supports must allow the tube to move at the bottom end. To prevent a pigtail bending moment, the heater lining must not press on the tube. Loose bricks are often used to help close openings. The bricks must move freely if the tube presses on them.
If support springs are used, those that have been stretched should be replaced. A stretched spring cannot support a tube. When the tube is heated up after shutdown, the spring will no longer support it as designed.