ASME CRTD-103:2014 pdf free download.CONSENSUS ON BEST TUBE SAMPLING PRACTICES FOR BOILERS & NONNUCLEAR STEAM GENERATORS.
In boilers with a drum-type generation bank (tubes between a mud drum and a steam drum). the downcomer tubes also can be subject to localized deposition. In this design. the water passes through these tubes before reaching other areas of the furnace. Therefore, the composition of deposits in the downcomer will be more reflective of feedwater contamination. In industrial boilers with hardness in the feedwater, the proportion of hardness compounds (e.g., calcium hydroxyapatite [calcium phosphate]. serpentine [magnesium silicatel, and munsonite [magnesium phosphatcj) in the generation bank can be quite high.
Because of the relative ease of hydrojetting generation bank tubes and the difficulty of removing a tube sample from this location, generation bank tubes generally are not collected. Most facilities elect to hydrojel these tubes if they appear to be dirtier than the waterwall tubes. If dispersants are routinely added during operation, precipitation in the drums and generation bank tubes may be inhibited and heavier deposit accumulations may be found elsewhere in the boiler.
Gravity Settling. — Areas susceptible to settling are obvious by looking at a side view diagram of the unit. Areas closer to horizontal are expected to experience settling during shutdown periods, when the boiler or [IRS(i is drained, and during operation if there is heat flux on the lower surface. Such areas include nose tubes, roof tubes. sloped screen tubes, and bent tubes around port.s in the walls. Sludge also can be left on sloped tubes following chemical cleanings. Residual solids can bake on tube surfaces during subsequent operation and lead to excessive deposit accumulations. Sometimes rapid drains of the boiler can eftectively remove loose solids. Occasionally. flushing of individual tubes is required atler a cleaning. but flushing can be impractical for many units.
ASME CRTD-103:2014 pdf free download
