plastic or castable refractory. If the lane cannot be plugged, the firing rate of the boiler must be restricted to avoid overheating the superheater tubes next to the gas lane.

When a sidewall tube needs to be plugged, cut the tube 3 to 4 inches above the sidewall heater and 3 to 4 inches below the steam drum. The space left exposed after removal of the tube should be packed with plastic refractory to protect the pressure parts previously cooled by the plugged tube. Do not plug more than two tubes next to each other, since an exposed area wider than this cannot be effectively protected for an extended operation. Sidewall tubes that have been plugged should be replaced at the earliest opportunity.

When a rear wall tube needs to be plugged, cut the tube 3 to 4 inches from the headers or at other cutoff points specified in the manufacturer's technical manual. Use a plastic refractory to plug casing openings, to cover exposed areas not protected by firebrick or high-temperature castable refractory, and to cover the exposed pressure parts previously cooled by the plugged tube. Rear wall tubes that have been plugged should be replaced at the earliest opportunity.

Superheater screen 1 1/2 and 2 inches in outside diameter should, in general, be replaced, rather than plugged, when tube failure occurs. In plugging generating tubes 1 inch and 1 1/4 inches in outside diameter behind the superheater tube bank (in single-furnace boilers) and behind the 2-inch tubes (in double-furnace boilers), consider gas laning and drum protection. Any complete lane through the tube bank more than three tube rows wide should be retubed, especially if such a lane is bounded by the boiler casing. Any drum area greater than 4 inches square should have refractory protection over the drum or, if this is not practicable, have blind nipples replace the failed tubes instead of just plugging the failed tubes. The blind nipples give greater protection to the drum than plugged tubes.

If an economizer element develops a leak, the ends of the element should be plugged at the inlet header and at the outlet header. To install a tapered plug in an economizer element, screw the plug extractor into the plug and insert the plug into the tube. Unscrew and remove the extractor from the plug. Drive the plug securely into position by holding one end of a piece of pipe against the plug and striking the pipe on the other end.

Figure 2-14. - Removing plug from economizer element.

plug. Place the handhole plate binder in position over the extractor, and then thread on the handhole fitting nut. As you tighten the handhole fitting nut, the plug pulls out. Some activities, using boilers of recent design, are furnished with expandable gasketed plugs for plugging economizer elements. One of these plugs is shown in figure 2-15. The installation of the expandable plug is shown in figure 2-16. After inserting the plug assembly into the tube, hold a screwdriver in the slot of the retainer stem to keep the

Figure 2-15. - Expandable gasketed plug for economizer element.

Figure 2-16. - Installing expandable plug in economizer element.

Figure 2-14 shows how to remove a plug from an economizer element. Screw the plug extractor into the