... resisting pipe of conveying coal powder,fly ash,mine dust,metallurgy slag ,sand,and concrete,etc. wear ... frequency and heat treatment process makes the inner wall to be high intensity(HRC 55-62) ... resistant layer(1.8mm), and leaves the outer wall with high plasticity and strength to avoid bursting ... 30,000 cubic meter of concrete3. Dual wall pipe thoroughly resolves the problem that hardening layer ...