DN mm≤ 60065090010001100120013001400150016001700180019002000 S< 5mm 0 ≤ 4 ≤ 5 ≤ 6S≥ 5mm 0 ≤ 3 ≤ 4 S< 5mm 0 ≤ 4 ≤ 5 ≤ 6 ≤ 7S≥ 5mm 0 ≤ 4 ≤ 5 U Ω C U U 1 ——— 50℃ σ c σ t q 2 3