Selective plugging of broken fibers in tubesheet-hollow fiber assemblies

The method of treating a tubesheet/hollow fiber assembly to ensure that any defective fibers and/or tubesheet channels included therein will be selectively plugged, said method comprising

• A. providing as said assembly one which comprises a bundle of gas-filled, hollow fiber lengths passing through and sealingly engaged with a rigid, relatively thin wall-member of tubesheet having first and second generally parallel faces, each of said lengths having an open end terminating in or protruding from said first face and at least a majority of said lengths having portions depending from said second face which have closed ends or are generally U-shaped loops having second open ends terminating in or protruding from said first face,
• B. covering said first face with a body of a flowable, curable sealant and developing a pressure differential between said body and the exteriors of said dependent fiber portions, thereby
• (1) causing said sealant to flow into the defective fibers and/or tubesheet channels and to displace therefrom at least a portion of the gas contained therein, and
• (2) causing said sealant to flow into the open ends of the non-defective fibers to a limited extent determined by the resistance to compression of the gas they contain,
• C. diluting the sealant external to the fibers,
• D. subjecting the exteriors of said dependent fiber portions and the diluted sealant body to essentially the same reduced pressure, with the results that:
• the gas in the non-defective fibers expands until the pressure inside them is the same as the pressure outside them,
• the undiluted sealant in the non-defective fibers is expelled and the diluted sealant intrudes slightly into them,
• the column of sealant in each defective fiber and tubesheet channel remains in place and no more than a small terminal portion of it is diluted,
• E. While maintaining the pressure equilibrium established in step D, removing the main body of the diluted sealant from contact with the tubesheet,
• F. optionally, rinsing said first face and open fiber ends with a diluent, and
• G. curing the sealant in the defective fibers and/or tubesheet channels, thereby plugging them,
• said sealant being so composed as to be convertible, in-situ in said defective fiber lengths or channels and at a temperature below the distortion temperature of said fibers, to plugs of a solid, non-porous material sealingly bonded to the fiber or channel walls and having a coefficient of expansion substantially matching that of the fiber material.