Inspection of Stacks
Visually inspect the outside surface of welded steel stacks with telescope or binoculars from the ground to determine the general stack condition. Look for evidence of overheating and heavy scaling, rusting of the external surfaces or cracks.
Steel stacks may be gaged ultrasonically, using crane and basket or staging. Each course should be gaged, usually on two or more quadrants. An alternate method of ultrasonically gaging a stack is through the use of the magnetic tank gaging crawler.
On self-supporting stacks, check the anchor bolts, brackets, and the condition of the concrete around the anchor bolts. On guyed steel stacks, note the condition of the cables and the cable anchors. Guy wires should be checked for proper tensioning. Engineering should be consulted for determining proper tension.
Where steel stacks have external insulation, either part or in full, note the condition of the insulation. Suspect the possibility of external corrosion under the insulation if defects exist. Remove insulation and gage it, if necessary.
In unlined steel stacks, inspect the interior surfaces for scaling, overheating, distortion, and corrosion. Examine the steel under any ash deposits, particularly at the base of the stack. Ultrasonically gage any thin areas that may be found.
In refractory lined stacks, look for failure of the lining which may be evidenced by sagging, bulging, buckling, or loosened bricks or insulation material. Note the condition of the support rings and arches over the flue inlets to the stack.
Inspect concrete and brick stacks for cracks and settling, and for disintegration or spalling of the masonry or bond. If necessary, use field glasses or the telescope to check the condition at the upper levels and for loose brick at the top. Pay particular attention to the breech inlet openings for possible cracking. Note the size and extent of any cracking, and watch for progress or growth of the cracks.
Where settling or deterioration of any stack or foundation is noted, the stack shall be checked for plumb.
In all stacks, look for any evidence of cracking or leakage. Pay particular attention to clean-out or access doors and breaching connections. Where the base of the stack is drained through a sewer connection, inspect the condition of the seal around the connection.