Each handhole and handhole plate seat should be examined for erosion, steam cutting, tool marks, and other damage that might permit leakage. If the plate has leaked previously, it should be checked for trueness and possible deformation. Seating surfaces and faces of handholes should be examined for cracks. It may be necessary to use a hand mirror to inspect the handhole seats.

The inside surface of the headers should be inspected for corrosion and erosion. The location and amount of scale buildup should be noted, and the tube ends should be checked for pits, scale, cutting or other damage from tube cleaners, and deposit buildup. If there is considerable scale or deposit buildup, the flow may be restricted to the point that tubes become overheated because of insufficient circulation. Deposits and scale should be removed with a scraper and the depth of coating determined. Lower waterwall headers are particularly susceptible to heavy deposit buildup.

Downcomers and risers should also be inspected for this type of deposit. Thickness readings of headers should be obtained periodically by ultrasonic technique. The headers should be calipered whenever tubes are removed.

External surfaces of headers should be examined either directly or indirectly with mirrors, and particular attention should be paid to the points where tubes enter the header for indications of leakage from the tube roll. The header surfaces adjacent to tube rolls and handholes should be inspected for cracks. If external inspection of headers reveals pitting, thickness measurements should be made using ultrasonic techniques.

No comments: