Sec.29-232-56. Age limit of lap joint fire tube boilers

The age limit of a tubular, flue or cylinder boiler having a longitudinal lap joint and operating at a pressure in excess of fifty psig shall be thirty years. A reasonable time for replacement shall be given by the commissioner. All lap seam boilers in this state 30 years or older shall have the long seam exposed for annual examination for detection of a possible lap seam crack. A typical lap seam crack extends approximately parallel to the line of the rivet hold of a longitudinal seam, and near the edge of the rivet heads as shown in figure 1.

Figure 1.

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To determine the existing condition of the riveted lap joint type seam, the seam should be notched and slotted. Figure 2-A illustrates a slot approximately 3/16 inch inside, extending 2/3 of the thickness of the plate in depth and about 1-1/2 inches in length, cut from the outer surface and so located that its center will be on a line with the edges of the rivet heads of the inner row. One quarter inch diameter holes drilled 2/3 through the plate, so a hole will be at each end of a slot, with the material between the holes removed with 3/16 inch cape chisel, forms a satisfactory procedure of cutting the slot, which, it will be noted upon referring to figures 1 and 2 will cross the path of a lap seam crack if one exists adjacent to that line of rivet holes. Generally, three slots per course are sufficient. One slot is cut at the center of the course and one on each side, midway between the center and the girth seams.

The application of a hydrostatic test not exceeding one hundred fifty percent (150%) of the safe working pressure will be sufficient to cause leakage at the slot if a lap seam crack has extended through 1/2 of the thickness of the plate. If there is a lap seam crack present, which has not developed through 1/3 the thickness of the plate, leakage will appear when the crack finally reaches the bottom of the slot; Therefore, the slot should not be closed or covered after the test.

The outside surface of the inside plate of the seam should be exposed for examination by cutting a "V" notch, as illustrated in figure 2-B. The removal of the small section of the outer plate at the caulking edge uncovers the plate underneath.

The notch should have an angle of 90°, or as near thereto as possible, while retaining the normal lap between the edge of rivet hole and the caulking edge of the plate. Care should be taken when cutting the V-notch to avoid tool marking the under plate of the seam, as that plate must be clean and polished to some extent for a thorough examination. A magnifying glass should be used for this purpose.

The boiler may be returned to service if no defect is found.

(Effective August 25, 1987)