End lid on spray pipe is made of short glass fiber/ barium phenolic resin, some end lids cracked after five years under naturally store. By examination,test and analysis, it is considered that the end lids cracked by the reason of that, mass ratio of resin of local part in end lid is relatively low that resulted in lower intensity. There was internal stress in the end lid at the same time and intensity of material fell gradually during naturally store, then the end lids cracked when intensity fell lower than internal stress.