CONTENT
CONTENT...............................................................................................1 Cap 1 Function........................................................................................2 Cap 2 Types and characteristics............................................................3 Cap 3 Main systems................................................................................8 a) Main drum.........................................................................9 b) Catheads..........................................................................10 c) Stationary brake (main brake).....................................12 d) Auxiliary brake...............................................................17 Cap 4 Power calculation.......................................................................23 Cap 5 Inspection....................................................................................24 Cap 6 Drawworks brake band.............................................................25
REFERENCES......................................................................................36 APPENDIX 1
1
Drawworks 1 FUNCTION - Drawworks Functions The Drawworks is one of most important equipment on drilling rig. The unit supplies the hoisting power, the drawworks spools the drilling line as pipe is run into and pulled out from the well. The drilling line spools out under gravity and is reeled in by an electrical or diesel engine.
Figure 1.1 Schematic Draw 2
1. MAST & SUBSTRUCTURE 2. CROWN BLOCK 3. TRAVELLING BLOCK 4. TOP DRIVE 5. ROTARY TABLE 6. DRAWWORKS 7. DRILLING LINE 8. DEADLINE ANCHOR
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).
3
Figure 2.1 Schematic draw
4
- 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.
Figure 2.2 Schematic draw
5
- Connection Drawworks-Engines The connection between the drawworks and the engines can be either: - CHAIN DRIVEN - GEAR DRIVEN Electric type(chain driven)
Figure 2.3 Chain driven
6
ELECTRIC TYPE (Gear-Driven)
Figure 2.4
7
3 MAIN SYSTEMS a - Main Drum b - Catheads c - Stationary Brake (Main brake) d - Auxiliary brake
Figure 3.1 Drawworks main systems
8
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 _ 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 degrees. (see pictures)
Figure 3.2 Fleet angle
9
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
Figure 3.3 Cathead
10
- Employment scheme For safety reasons and convenience their employment comes supplanted from the dedicated equipments.
Figure 3.4
11
c - Stationary Brake - Band Brake - Disk Brake - Regenerative Brake System
Figure 3.5 Band brake 12
- Band Brake - Description (parts) - BRAKE HANDLE - LEFT BAND - RIGHT BAND - BALANCE BAR - Braking action Braking action is activated by pushing the _ Brake handle down towards the floor. Through a strength multiplier system, the braking force is transmitted on the _ 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 hydraulicallyactuated 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.
13
Figure 3.6 Disk 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
14
Figure 3.7 Disk brake
15
- Performance Comparison diagram of 3 brake combinations
Figure 3.8 Performance diagram
16
- 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.
Figure 3.9 Regenerative 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.
17
Types: - Hydrodynamic Brake - Elettromagnetic Brake - Hydrodynamic Brake That system is still in use on small drawworks. However, on mediumHi powered drawworks, this system has been replaced by the Electromagnetic brake.
Figure 3.10 Hydrodinamic 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".
18
Figure 3.11 Hydrodinamic brake schematic
19
- Electromagnetic 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.
Figure 3.12 Electromagnetic brake schematic
20
- "Baylor" brakes The use of electromagnetic brake began with diesel-electric rigs. Almost all drawworks today a equipped with "Baylor" brakes. Baylor Brakes are manufactured in 5 standard sizes for nominal drilling depths up to 30.000feet.
Figure 3.13 Baylor brakes
21
- 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.
Figure 3.14 Braking Force Diagram
22
4 POWER CALCULATION WORK = Force x Step POWER= Force x Pooh velocity
Figure 4.1 Power calculation - Hook Power
Ph = Hook Power (HP) Ve = Pooh velocity (m/s) P = Weight on Hook (kg)
- Drawwork Power
23
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.
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. ENI policy requires the API Category IV inspection (as per API RP 7L) every 5 years.
Figure 5.1 Drawwork Inspection 24
6 DRAWWORKS BRAKE BAND
• The drawworks brake system uses coolant from the brake water cooling tank to cool the brakes. • As shown in Figure 6.1, the coolant enters the water union on the end of the drumshaft, passes through both brake rims The coolant then returns to the drumshaft. • The heated coolant will then flow back to the coolant reservoir where it is allowed to cool again. • Use the protection of antifreeze, Inhibitor and water to best meet the unit‟s requirements for its ambient operating temperature. • The use of inhibitor will help prevent corrosion of the system pipework and brake rims. • Do not use 100% Inhibitor (Nalcool or equivalent) as this will increase the concentration of antifreeze in the cooling system which will then increase the concentration of dissolved solids and non-dissolved chemical inhibitors.
Figure 6.1 Brake Cooling Schematic • Support roller and jack screws (item # “2” in Figure 6.2), located behind the brake bands assist in the rolling action of the brake bands when band lift-off occurs. • When the brake handle is in the applied position, clearance between the rollers, jack screws, and bands should be approximately ¼” (6 mm).
25
Brake Adjustment; • Adjust the brake handle (item # „1” in Figure 6.4) height using the main brake anchor eyebolts located at the front of the brake bands (item # “1” in Figure 6.2) • Ensure an even gap is maintained between the stopping blocks and the brake equalizer beam (item # “11” in Figure 6.2) to enable even break band application. • Adjust the main brake anchor eyebolts with the brake handle in the up position. • Gauging of the gap between the stopper blocks and the equalizer beam must be done with the brake handle down and the brake applied. • Ensure the centerline of the keyway on the brake linkage shaft is 30° from the horizontal when the brakes are engaged. • Rollers should be adjusted to give proper band clearance. The proper clearance is 1/8” between the roller and with the band brakes engaged.
Figure 6.2
26
Figure 6.2 Band Brake Assembly
27
Table 6.1
28
Table 6.2
Brake Band Maintenance Replace brake flanges when they are worn to the extent displayed in Figure 6.3.
29
Figure 6.3 Brake Band Flanges Worn-out
30
Figure 6.4
31
Figure 6.4 Remote Brake Linkage Assembly
32
Table 6.3
33
Figure 6.5 Band brake components 34
REFERENCES
1. Wheatherford mechanic - Drawworks 2. Drilling engeneering manual 3. IADC - Drilling manual 4. Saipem 23533775-RIG-BOOK 5. API specification 7K 《Drilling equipment criterion》 6. API recommended practice 7L 《Procedures for Inspection, Maintenance, Repair, and Remanufacture of Drilling Equipment》
35
