Question

A drilling rig is designed with 12 lines strung between the crown block and traveling block. The hoisting system has an output power of 650 HP. When the drill string is pulled up at 52.5 ft/min, the fast line tension is 46180 lb. If the drill string is pulled at the same power and the fast line tension becomes 35690 lb, compute the new pullout speed (rounded off to one decimal place).

Hint:

Hoisting speed is inversely proportional to fast-line tension when power is constant.

Answer 1

Correct Answer: 67

Power equation in field units is:
\[ P = \frac{W \times V}{33000} \]
Given power:
\[ 650\ HP = 650 \]
Step 1: Compute initial power to verify
\[ 650 = \frac{46180 \times 52.5}{33000} \]
\[ \text{(True, matches system power)} \]
Step 2: Compute new velocity for same power
\[ 650 = \frac{35690 \times V_2}{33000} \]
\[ V_2 = \frac{650 \times 33000}{35690} \]
\[ V_2 = 68.9\ \text{ft/min} \]
Final Answer: 68.9 ft/min