Table. 2 Temperatures at the inner edge. T_i with temperatures at outer edge, T₀ in case of pipe diameter; 32 A (sch 80)

　

Table. 3 Temperatures at inner edge, T_i with temperatures at outer edge, T₀ in case of pipe diameter; 40A (sch 80)

　

Circumferential stress on large thickness pipe corresponding to boiler drum with feed water inlet pipe according to temperatures shown in Table. 1 was calculated. The result is shown in Fig. 3. Maximum stress of about 160 Mpa is observed at the inner edge of the pipe, and the stress decreases immediately as the length from the edge increases. Moreover, minus stress is observed at a point located in r = 3 r₁. In Fig. 3, the value of the inner radius is 12.5 mm, 37.5 mm is located in r = 3 r₁.

By the way, steam pressures are respectively 0.62 Mpa, 0.85 Mpa, 1.0 Mpa, 1.26 Mpa, 1.56 Mpa, 1.91 Mpa and 2.32 Mpa corresponding to saturated steam temperatures of 160℃, 170℃, 180℃, 190℃, 200℃, 210℃ and 220℃.

　

Fig. 3 Thermal stress distiribution irl case of feed water inlet pipe diameter of 25A (sch80)

　

Fig. 4 shows the result of calculation of circumferential stress distribution in case of feed water inlet pipe diameter of 32A (sch80). The inner radius and a point located in r = 3 r₁ are 16.5 mm and 49.4 mm respectively in Fig. 4. Maximum stress of about 160 Mpa (N/mm²) is observed at the inner edge in the case of saturated boiler water temperature of 220℃ as same as the result shown in Fig. 3

　

Fig. 4 Thermal stress distribution in case of feed water inlet pipe diameter of 32A (sch80)

　

Fig. 5 shows the result of calculation of circumferential stress distribution in case of feed water inlet pipe diameter of 40A (sch80). The inner radius and a point located in r = 3 r₁ are 19.2 mm and 57.6 mm respectively in Fig.5. Maximum stress of about 150 Mpa is observed at the inner edge of the pipe.

　

Fig. 5 Thermal stress distribution in case of feed water inlet pipe diameter of 40A (sch80)

　

(2) When α is calculated by Von Karman's formula

α was calculated respectively according to feed water inlet pipe diameter of 25A, 32A, 40A (sch 80) as follows;

α = 10542 in case of diameter of 25A (sch80)

α = 6398 in case of diameter of 32A (sch80)

α = 4830 in case of diameter of 40A (sch80)

Using above heat transfer coefficient α of feed water, temperature at inner edge was calculated under the condition of feed water temperature of 50℃ and temperatures at outer edge corresponding to saturated boiler water pressure of 0.63 Mpa to 2.3 Mpa as same as above (1).

BACK　　　CONTENTS　　　NEXT