Drawworks

1 FUNCTION
2 TYPES AND CHARACTERISTICS
3 MAIN SYSTEMS
- Main Drum
- Catheads
- Stationary Brake (Main brake)
- Auxiliary brake
4 POWER CALCULATION
5 INSPECTIONS
- Manufacture specifications
The Drawworks is built in according to specifications in API 7K or related ISO (International
Organization for Standardization) 14693.
2 TYPES AND CHARACTERISTICS
Depending on the engines on the rig, the drawworks can be either:
- MECHANICAL
- ELECTRICAL
- MECHANICAL
Diesel engines are directly connected (compounded) to the drawwork by chain.
This system is still in use for small Drilling Rigs (under 1500 HP), but is no longer used on medium-Hi powered rigs( 1500 & 3000 HP).
- ELECTRICAL
Electrical system are normally used today on land rigs and is the only system in use on offshore rigs. The drawworks are generally connected to 1000 HP D.C. engines, although A.C. engines are
now being used as well
- Connection Drawworks-Engines
The connection between the drawworks and the engines can be either:
- CHAIN DRIVEN
- GEAR DRIVEN
3 MAIN SYSTEMS
a- Main Drum b- Catheads
c - Stationary Brake (Main brake)
d - Auxiliary brake
a - Main Drum
- Main Drum Diameter
The diameter of the main drum is a function of the diameter of the drilling line being used.
It is preferable to have the drum as large as possible to reduce the number of wraps and the bending of the cable.
- Drum Length
The length of the drum is a function of the distance D between Crown block and Drawworks.
- Fleet Angle
To reduce the wear on the drilling line, it is good practice to keep the angle alpha under 2 degrees.
b - Catheads
- Spinning line and Breakout Cathead
Catheads are winches with pneumatic clutch and are mounted on the extremity of the secondary drum of
the drawworks.
The make up cathead is located beside the driller's console and the break-out cathead is located on the opposite side of the driller's console.
The catheads apply the pulling force on the hand tongs connections.
- Model 16 Spinning line Cathead
- Model 16 Breakout Cathead
- Employment scheme
For safety reasons and convenience their employment comes supplanted from the dedicated equipments.
c - Stationary Brake
- Band Brake
- Disk Brake
- Regenerative Brake System
- Band Brake
- Description (parts)
- BRAKE HANDLE
- LEFT BAND
- RIGHT BAND
- BALANCE BAR
- Braking action
Braking action is activated by pushing the D  Brake handle down towards the floor.
Through a strength multiplier system, the braking force is transmitted on the D balance bar, then to the brake bands, and finally to the two drums on either side of main drum.
Heat produced by the braking action is dissipated through the circulating water cooling system.
- Disk Brake
Depending of the size the drawworks, there are 2 to 4 hydraulically-actuated calipers.
In addition to these main calipers, each disc brake system has 2 dedicated calipers (normally closed) that are used as the emergency and parking brake.
These calipers are actuated by an independent hydraulic system.
Disk brakes can be mounted on Drawworks that was originally equipped with band brake.
- Advantages
The advantages are:
- Greater braking capability
- Emergency braking system
- Possibility of Remote control
- Significant noise reduction during drilling
- Use
Disk Brake is a development of the band brake, due to the necessity to handle heavier loads
- Regenerative Brake System
- New generation of drawworks
The newest generation of drawworks (4000-5000 HP), mounted on ultradeep offshore rigs, have a direct drive transmission system, permanently connecting the drawworks to the motors.
When the travelling block descends in the derrick, the motors turns in the opposite direction, producing an opposite current and hence a braking action.
- NOTE: This braking system, is not able to hold, when the motors are rest, hence the need for emergency and parking the disk brake system.
d - Auxiliary brake / dynamic brake

The function of the auxiliary brake is to assist the main braking system during rapid descent of the blocks with heavy string weights. The auxiliary brake prevents the overheating and premature wear of main brakes.

Types:

- Hydrodynamic Brake
- Elettromagnetic Brake
- Hydrodynamic Brake
That system is still in use on small drawworks. However, on medium-Hi powered drawworks, this system has been replaced by the Electromagnetic brake.
- Description
The Hydrodynamic brake consisting of two box with a rotor pressed onto the main drive shaft and two stators.
When the main shaft rotates the rotor drags water against the two stators, producing a braking action.
Braking capability can be regulated by increasing or decreasing the water levels in the "Hydraulic Brake box".
- Hydrodynamic Brake
The electromagnetic brake consists of a stator with coil, two magnetic poles and a rotor pressed onto the main drive shaft.
When the driller activates the brake control, a magnetic field is produced by 4 electromagnetic coils mounted concentrically inside the drum.
By varying the amount of current to these stationery coils, the driller can control the amount of braking torque applied to the rotating drum.
- "Baylor" brakes
The use of electromagnetic brake began with diesel-electric rigs. Almost all drawworks today are equipped with "Baylor" brakes.
Baylor Brakes are manufactured in 5 standard sizes for nominal drilling depths up to 30.000feet.
- Braking force
The diagram shows the values of braking force as a function of rpm of the drawworks shaft.
Notice how the electromagnetic brake is also effective at low speeds.

4 POWER CALCULATION
WORK = Force x Step
POWER= Force x Pooh velocity

- Hook Power Ph = P xVe / 75
Where Ph = Hook Power (HP) Ve = Pooh velocity (m/s)
P = Weight on Hook (kg)

- Drawwork Power = pa = F x Vf/75 x E    
where F = Pull to Fast line equal to:
        P = (Weigh on Hook) / N (Number of lines)
        Vf = fast line velocity equal to:
        Ve * = 2 R n (rpm drawwork shaft)
E= Efficiency of sheaves. This value (empiric)
provided by API in function of number of lines.
6.5 INSPECTIONS
- Periodic inspections
The API applicable references are:
API RP 7L and API RP 54 (chapt. 9.4 and 9.5). and the Manufacturer's recommendations.
inspection (as per API RP 7L) every 5 years.