[建] cleaning of pipe with steel grit

yòng gāng shā lì qīng jìng guǎn zǐ ㄩㄥˋ ㄍㄤ ㄕㄚ ㄌㄧˋ ㄑㄧㄥ ㄐㄧㄥˋ ㄍㄨㄢˇ ㄗˇ