Crown block

Crown block assembly The stationary sheave or block assembly installed at the top of a derrick or mast. 

Height of derrick and mast without guy lines The minimum clear vertical distance from the top of the working floor to the bottom of the crown block support beams. 

D — Tha imallait claar dimaniion at tha top of tha darrick that would raitrict patiaga of crown block. 

API Standard 4A (superseded by Standard 4F) provides rating of derrick capacities in terms of maximum safe load. This is simply the load capacity of a single leg multiplied by four. It does not account for pipe setback, wind loads, the number of lines between the crown block and the traveling block, the location of the dead line, or vibratory and impact loads. Thus, it is recommended that the maximum safe static load of derricks designed under Standard 4A exceed the derrick load as follows ... 

In general, = W n if the deadline is attached to one of the derrick legs, and F = W 2n if the deadline is attached between two derrick legs, n is the number of lines between the crown block and traveling block. The formula for F assumes that no single leg shares the deadline and fastline loads. 

A hoisting system, as shown in Figure 4-8, is composed of the drawworks, traveling block, crown block, extra line storage spool, various clamps, hooks, and wire rope. 

Normally, a hoisting system has an even number of working lines between the traveling block and the crown block. The fast line is spooled onto the drawworks hoisting drum. The dead line is anchored to the rig floor across from the drawworks. The weight indicator is a load cell incorporated in the dead line anchor. 

The mechanical advantage of the hoisting system is determined by the block and tackle and the number of working lines between the crown block and the traveling block [7]. 

When the hook load is lifted, friction losses in crown block and traveling block sheaves occur. It is normally assumed that these losses are approximately 2% deduction per working line. Under dynamic conditions, there will be an efficiency factor for the block and tackle system to reflect these losses. The efficiency will be denoted as the hook-to-drawwork efficiency (e, ). The force in the fast line under dynamic conditions (i.e., hook is moving) will be... 

It is required that the drawworks input power be able to lift 600,000 lb at a rate of 50 ft/min. There are eight working lines between the traveling block and the crown block. Three input power systems are available 1,100, 1,400, and 1,800 hp. Which of the three will be the most appropriate The value of e is... 

Crown block sheaves and bearings The stationary pulley system at the top of the derrick or mast. 

Traveling blocks A heavy duty pulley system that hangs in the derrick and travels up and down with the hoisted tools. It is connected to the crown block with a wire rope that ultimately runs to the hoisting drum. 

Maximum Load Rating Bases. The maximum load rating will be based on the design safety factor and the yield strength of the material. Crown block beams are an exception and shall be rated and tested in accordance with API Spec 4E Specification for Drilling and Well Servicing Structures. ... 

Crown Blocks. For crown block design, see API Specification 4F. Crown block sheaves and bearings shall be designed in accordance with API Specification 8A. 

Figure 4-75. Typical reeving diagram for 14-line string-up with eight-sheave crown block and seven-sheave traveling block left-hand reeving [11],...

Minimum fleet angle from the drawworks drum to the first sheave of the crown block, and from the crown block sheaves to the traveling block sheaves. 

Recommended Reeving Arrangements for 12-, 10-, 8-, and 6-Line String-ups Using 7-Sheave Crown Blocks with 6-Sheave Traveling Blocks and 6-Sheave Crown Blocks with 5-Sheave Travelina Blocks 1111... 

Wo Tt t. Block (Reod From Left to Right Starting wiili Crown Block and Going Allenuttly From Crown to Traveling lo Crown) ... 

Right Hanc a Crown Block Trav Block 6 b n c B H ... 

Schematic diagram of a drill ship equipped with crown block heave compensator and seabed clamp. (After Richards, A.F., and Zuidberg, H.M., Sampling and in situ geotechnical investigations offehore. In Marine Geotechnology and Nearshore/Offshore Structures, ASTM STP 923, Chaney, R.C., and Fang, H.Y., eds., American Society for Testing and Materials, Philadelphia, PA, 51-73,1986. Reprinted with permission. Copyright ASTM.)...

Is the Crown-Block access ladder fitted with safety hoops and or a fall-arrestor (If so, is it in date for test )... 

---