... = 20 ,000 5 = 23 ,300in. in. psig psig1XS 0.179 5 ,27 02Std 0.154 2, 380 —2XS 0 .21 8 3,440 —2XXS 0.436 7,340 8,5602J4Std 0 .20 3 2, 600 — 2! 4XS 0 .27 6 3,610 —2I4XXS 0.5 52 7,770 ... —2I4XXS 0.5 52 7,770 9,050 2 1A 0.750 10, 720 12, 490 2 1A 0.875 12, 530 14,6003Std 0 .21 6 2, 260 —3XS 0.300 3 ,20 0 —3XXS 0.600 6, 820 7,9404Std 0 .23 7 1, 920 —4XS 0.337 2, 770 —4XXS 0.674 ... of the fire tube is normally calculated based on a heat fluxrate of 10,000 Btu/hr-ft 2 . The fire-tube length can be determined from: 124 Design of GAS-HANDLING Systems and ...