subsea - page 8

RamPreventers

Subsea Engineers Handbook Section 8

In-Spec Inc. 1999 Ram Preventers

Table Of Contents Section 8

Page

1. Rams, How They Operate 1 2. Cameron TL Pipe Rams 3

3. Cameron TL Shearing Blind Rams 4

4. Packer Pressure, The Secret to Maintaining a Drip Tight Seal5 5. Closing Ratio 6

6. Manufacturers 7

7. Cameron U-II Blowout Preventers 8

8. Hydril 18 3/4 15,000 Blowout Preventers 10

9. Ram Cavity to Ram Block Allowable Clearance 11

10. Hydril Engineering Bulletin #92002 12

11. Hydril 18 /4 15,000 Shear Ram Capability 13

12. Shaffer 18 10,000 psi SL Ram 14

13. Shaffer Poslock Operation 15

14. Shaffer Ultralock II Operation 17

15. Typical Ram Problems 19

16. Ram Preventer Operation and Inspection Points 19


In-Spec Inc. 1999 1 Ram Preventers

1) Rams, How They Operate

a) Blocks of steel push into the wellbore around drill pipe by hydraulic cylinders.Elastomer seals on the ram blocks are made of nitrile and form the seal betweenthe ram blocks, pipe and preventer body. Due to the inflexible design of the ramblocks, each set of ram blocks is designed to perform a specific function ;

Closing on : Ram Block Name pipe of one specific size fixed pipe ramsrange of pipe sizes variable, flexible, or multi-size ramsclose open hole or cut the drill pipeshear/blind rams, or SBRopen hole (no pipe in the hole) blind rams or CSO rams (surface

stacks)

b) Hydraulic operators use 1,500 psi for normal operation to close and open thepreventers, but operating chambers are rated for up to 3,000 psi WP .

c) Ram rubbers seal around the drill pipe and the annulus between pipe and bore.

d) Wellbore pressure assists closing action by energizing the rams closed.

e) Shear/blind rams (SBRs) are used to seal the wellbore with no pipe in the hole.

f) Shear/Blind Rams are also used to shear pipe in an emergency.

g) Drill pipe usually requires 2,000 to 3,000+ psi to shear depending on pipestrength, ram operating piston diameter, and ram manufacturer.

h) Super shears with 28 diameter pistons vs. the 14 or 15 standard size pistons(4x larger area) allow shearing of drill collars with the preventers.

i) Typical stack arrangement is shear rams on top (1 or 2 cavities) with 3 sets ofpipe rams below the shears - upper, middle, and lower pipe rams.

j) What is an emergency: in order of most likely occurrence, loss of DP, (loss ofpositioning reference, loss of station keeping power), loop current, or blowout.

k) While disconnected no hydraulic power is applied to the rams, so we need alocking mechanism on the rams to maintain them in the closed position.

l) Hanging off a tool joint on a closed set of rams (Now see why shear rams areabove pipe rams), also tends to open pipe rams.



2) Cameron TL Pipe Rams



3) Cameron TL Shearing Blind Rams



4) Closing Ratio The ram blocks are forced into the wellbore by ram shafts connected to hydraulicallydriven pistons. Closing hydraulic pressure behind the piston areas forces thepistons closed with a force equal to the hydraulic closing pressure times piston area.

Closing Force on ram shaft = Closing pressure (psi) X Piston Area (pD2/4, in.)

When closing the preventer with pressure in the wellbore, the pressure is acting onthe ram shaft area attempting to force the ram shaft into the open position. Becausethe piston area is much larger than the ram shaft area, a lower hydraulic operatingpressure will over come a larger wellbore pressure to force the ram blocks into theclosed position. The ration of piston closing area to ram shaft area gives us theclosing ratio.

In the example above 1,428 psi of hydraulic closing pressure is required to close theram with 10,000 psi wellbore pressure inside it. Ram preventers from differentmanufactures have different piston and ram shaft diameters and therefore differentclosing ratio. For example, a Cameron 18 15,000 U-II has a closing ratio of 9.3 to one. Thismeans that for every 9.3 psi of wellbore pressure it requires only 1 psi of hydraulicpressure to over come that wellbore pressure. If the preventer had 15,000 psi in thewellbore it would require 15,000 psi / 9.3 = 1,612 psi of hydraulic closing pressure toclose the preventer.



5) Packer Pressure, the secret to maintaining a drip tight seal

Ram rubbers, or sometimes called ram packers, are squeezed and forced intocompression when the ram blocks move into the closed position. The compressiveforce placed on the ram packers is called packer pressure. Only when the pressure generated inside the rubber packers (the packer pressure)is greater than the pressure trying to separate the packers (the well bore pressure)

can a pressure tight seal be achieved. This is a basic concept for all seals. It canbe applied to elastomer O-rings in electrical enclosures as well as steel ring gasketsin well control equipment Typically, when closing the ram BOP with 1,500 psi closing hydraulic pressure wegenerate 1,000 to 2,000 psi of compression inside the ram rubbers. This isadequate to form a low pressure seal, but you may ask, what happens as wellborepressures are raised. Ram blocks are designed to be self energizing. That is, aswellbore pressure is raised, the pressure behind the blocks forces the blocks toclose even more tightly. This self-sealing effect raises the packer pressure so that itis always greater than the wellbore pressure.



Wellbore pressure should always be bled off the BOP before attempting to open aset of rams. When wellbore pressure is under a set of closed rams, you should notattempt to open the rams. Opening the rams with 1,500 psi operating pressure mayblow the ram rubbers off the ram block. Attempting to open the preventer with 3,000psi hydraulic opening pressure may shear the ram shaft attachment with the ramblock.

6) Manufacturers

There are 3 major manufacturers of ram preventers, Cameron, Hydril, and Shaffer.The majority of rams on Transocean rigs are Cameron and Hydril. Only the D-534has Shaffer rams.

Cameron rams used on subsea stacks are the Model U, U-II, T, and the model TL Hydril rams used on subsea stacks are the standard 18-10 and 15k psi models andthe light weight (LW) models. Shaffer rams used on subsea stacks are the model SL and SLX. They are equippedwith Poslock or Ultralock II hydraulic operators.



7) Cameron U-II Blowout Preventer

a) Hydraulic System



b) Ram Shaft Packing

c) Wedgelocks



In the event of loss of hydraulic closing pressure on the ram closing chamber,the wedgelock after having been activated on a closed preventer, will retain thepacker pressure in the ram rubbers and allow the preventer to continue to sealwith no closing hydraulic pressure.

Above left is the hydraulic hook-up for the sequence cap which is show in crosssection on the right. In this arrangement hydraulic opening fluid can not passthrough the sequence valve to the rams opening port until the whistle pistonhas traveled to the fully open position.



8) Hydril 18 15,000 PSI Blowout Preventer

9) Multiple Position Lock (MPL) Components



9) Ram Cavity to Ram Block Allowable Clearance



10) Hydril Engineering Bulletin #92002



11) Hydril 183/4 - 15,000 Shear Ram CapabilityHydril Shear Rams are capable of shearing andsealing wellbore pressure in one continuousmotion as required by API Specification 16 A.This is necessary because shear rams act as thelast line of defence during wild well controlsituations for preservation of life, limb, expensivedrilling equipment, and avoidance of pollution.

The Hydril 18 3/4 - 15,000 Ram BOP has beensupplied with three optional operator sizes forthe shear rams - 15 1/2 - inch, 19 - inch, or 22-inch. The Hydril 18 3/4 - 15,000 Shear Ramshave demonstrated shearing and sealingcapability, as a minimum, on the following list oftubulars. The shear rams have also demonstrated fatigue life in excess of 1 1/2 yearsof service in fatigue testing per API Specification 16 A.

Hydril welcomes customer contracts to demonstrate shear capability and providestatistical analysis of shear reliability on customer specified tubulars.

Description Shear Pressures (psi) TestReport22-inch 19-inch 15 1/2-inch

Drill Pipe5 inch 19.5 lb/ft S- 135 TBA 1355 HO 920405 inch 25.6 lb/ft G-105 2250 HO 930275 1/2 inch 21.9 lb/ft S- 135 2524 HO 920406 5/8 inch 25.2 lb/ft S- 135 TBA 1251 HO 95043 Casing7 inch 29.0 lb/ft N-80 1090 HO 960389 5/8 inch 49.0 lb/ft N-80 1250 HO 96038

Tubing1 3/4 inch 0. 175 wall 450 HO 950432 7/8 inch 0. 190 wall 512 HO 950434 1/2 inch 26.5 Ib/ft C,95 2646 HO 930275 1/2 inch 29.7 Ib/ft c-90 2839 HO 92008

Production Tubulars5 1/2 inch All Metal Composite Screens 1616 HO 950195 1/2 inch Prepacked Dual Screens 2046 HO 950196 /8 inch Prepacked Slotted Screens 1871 HO 930537 Inch Prepacked Slotted Screens 2236 HO 930537 5/8 in. 29.7 lb/ft, three 2-in. Coiled Tubes, 16Cnd lines

TBA 3114 HO 96026

Dual string 5 112 inch 17 lb/ft + 2 3/8 inch 1-80 2127 HO 93030 Fatigue Life Tests 104 Wellbore Pressure Cycles at 15,000 psi(728 Closure Cycles)

HO 95037



12) Shaffer 18 10,000 psi SL

Both the Shaffer SL and SLX rams use SL and SL-D ram blocks.

Shaffer ram assemblies1 are different from the Cameron and Hydril ram blocks inthat the blocks are fabricated from 2 pieces of steel. The 2 pieces are called the ramblock and the holder which fits around the outside of the ram block and ram rubber.The holder and ram block are held together by retracting screws. Retaining screwsare used to secure the ram rubber on to the ram block.

Shaffer Ram Assemblies

The SL and SL-D blocks are identical except for the addition of the hard inlay aroundthe drill pipe cut out in the SL-D ram block. This hard inlay allows the ram blocks toreliably hang-off drill pipe with up to 600,000 lb. of string weight. The hard inlay cutsinto the 18o tapered shoulder on the drill pipe box upset to form a supporting ledge.

1 Shaffer uses the term ram assembly to refer to the block, holder and rubber as a unit. It takes 2assemblies to close the wellbore.

Insert



13) Shaffer Poslock Operation

The Poslock operator allows the ram to move into a fully closed position and lockinto place when hydraulic closing pressure is applied. No additional hydraulic linesor operations are required to lock the preventer in the closed position. Then, in theevent of hydraulic pressure failure, the rams will remain in the closed position. Toopen the rams, hydraulic opening pressure is applied to the opening chamber, andthis automatically releases the locking mechanism, allowing the preventer to open only upon command. The poslock operator will only lock in one closed position therefor it can only be used with shear rams and fixed pipe rams. Ultralock IIoperators are used to lock the preventer closed in multiple positions as required bymulti rams.

Generally, a low closing pressure2 will close the rams inward until the ram rubbercontacts the pipe. At this point, the locking segments are near the locking shoulderon the cylinder wall. As additional pressure is applied, the ram rubber iscompressed and the locking segments move out to engage behind the lockingshoulder. The locking segments move outward because they are forced by thetaper on the locking cone. Actually, the locking cone is a piston inside the mainpiston and is forced inward by the same closing hydraulic pressure which moves themain piston forward. After the locking segments have moved radially outward, thelocking cone moves forward, blocking the segments from retracting and thus lockingthe rams in the closed position. The spring behind the locking cone prevents thelocking cone from vibrating out of position.

When opening, the rams the operation is reversed. Opening pressure forces thelocking cone backwards against the spring which in turn allows the locking segmentsto move inward, unlocking the ram and allowing the piston to open the ram.

The poslocks have to be properly adjusted to insure that the locking segments areengaged when there will be sufficient sealing compression at the face and the topram seals. If hydraulic closing fluid is slowly throttled into the preventer, pressuredrops will be observed as the locking cones suddenly move into the locked position.The pressure at which these fluctuations occur indicates the amount of ram rubbercompression. Poslock operation should be verified each time routine maintenanceis done on the stack to insure that they are properly adjusted, particularly afterchanging rams. This can be performed by installing a valve and gauge in ahydraulic hot line at the closing port on the preventer. An alternative method is toclose the preventer with 1500 psi and then, after the preventer has closed andlocked, perform a wellbore low pressure test with the closing hydraulic pressureremove. This will demonstrate the locking action of the poslocks.

2 This closing pressure will be typically around 200 psi



Shaffer Poslock Operation



14) Shaffer Ultralock II Operation

In a similar manner to the Shaffer Poslock, the Ultralock II closes and locks thepreventer closed with only the aplication of closing hydraulic pressure. Theapplication of opening pressure unlocks the preventer and moves the preventer tothe open position.

Shaffer Ultralock IIin Closed & Locked Position

LockPiston Piston

PoppetValve

Spring LockWedge

LockRod



a) Closing and Locking

When closing pressure is applied to the preventer the entire piston assemblymoves inward toward the closed position. Closing pressure attempts to drive thelock piston toward the lock position as well. The lock piston can not move inwarddue to opening hydraulic fluid trapped behind the lock piston by the poppet valve.As the rams contact the pipe and begin to generate packer pressure, the poppetvalve is unseated as the poppet end hits the door casting. The lock piston canthen begin to move inward as well. The inward movement of the lock pistonsimultaneously drives 4 lock wedges outwards into contact with the taperedsurfaces on the 4 lock rods.

Now, if closing hydraulic pressure is lost with the preventer in the closed position,the wedge of the lock piston forcing the lock wedges out to the lock rods will holdthe preventer in the closed position. The 5o taper of the lock wedges is a lockingtaper, meaning that the ram rubber compression or drill pipe hang-off forces willnot drive the wedges back wards to unlock the preventer.

b) Unlocking and Opening

When opening pressure is applied to the opening chamber, the pressureattempts to shift the piston assembly towards the open position. The piston willnot move outwards since it is in the locked position. Opening pressure alsotravels through the poppet valve and forces the lock piston outwards to theunlocked position. This releases engagement of the locking wedge with the lockrod and allows the piston assembly to travel outwards toward the open position.

After the piston assembly has traveled back a sufficient amount the spring loadedpoppet valve returns to the closed position. This will once again hold thepreventer in the unlocked position until the rams are later closed enough toengage the lock wedges with the lock rods.



15) Typical Ram Problems :

Hydraulic operating chamber leak. Bonnet or ram shaft packing leak Outlet ring gasket leak Ram packer leaking

16) Ram Preventer Operation and Inspection Points

i) All Ram preventers in general Never close pipe rams on a open hole. Maximum operating chamber pressure is 3,000 psi. Perform hydraulic operating chamber pressure test on OPEN and

CLOSE ports. Check for leaks across seals and at weep hole (leak intocavity at ram shaft indicates weep hole is plugged).

During well bore pressure testing, check for wellbore leaks at weep hole. Function test and pressure test wedgelocks and / or MPL locks. Ram cavity inspection Bonnet groove and seal carrier, bonnet sealing

surface on ram body, ram blocks (look for damage such as closing ontool shoulder), and ram cavity sealing surfaces.

Check ram block to cavity clearance limits per manufactures tolerances.

ii) Cameron 18-3/4-10m Type U Ram Preventer Check 4 bonnet bolts and hydraulic stud tensioning system for hydraulic

leaks. Hydraulic ram change piston Close pressure Opens the bonnets and

Open pressure Closes the bonnets, use only 200-500 psi to openbonnets. Requiring excessive pressure indicates a problem.

Hydraulic operated wedgelocks, operating procedure:

Closing -X Close with 1,500 psi closing pressureX Apply 1,500 psi locking pressure to activate wedgelocksX Pressure can be released from both chambers to perform pressure test.Note: Never close a 2nd ram while locking pressure is still applied to the

wedgelock

Opening X Apply 1,500 psi closing pressure (reduces force of tail rod on wedge

piston)X Apply unlocking pressure to wedgelocksX Only after locks are completely open can opening pressure be applied

to the preventer



Sequence Caps are to ensure wedgelocks are fully unlocked beforepressure can be applied to the preventer Open port and the preventerfully closed before locking pressure can be applied to the wedgelocks..

Dismantle and inspect both sequence cap assemblies every time therams are on the surface to ensure the mechanism and seals are in goodcondition.

Cameron state that when the clearance between top of block and ramcavity exceeds 0.060, low pressure sealing performance of thepreventer may be compromised.3

iii) Hydril Compact 18-3/4-15m Ram Preventer Swing out bonnet design requires that rams be in open position prior to

swinging open Ram cavity seal seat and ram cavity wear plates. Inspect seat seal to

ensure that it is fully seated - on 10 and 15k rams the gap at the borefrom top of seat seal to preventer body is approximately .011".

Operating hydraulics are circuited through the hinge assembly. Duringoperator testing, check the fluid hinge assembly for leakage.

Multiple position locking (MPL) check periodically and replace thebearings annually. A ram block attempting to rise and buck whileopening & closing the preventer with the bonnets open will be anindicator that the bearings are going bad.

Never perform a lock out test of the MPL system without having thebonnet bolted closed. The ram block & ram shaft will attempt to rotatewhile performing this test.

For an 18-3/4 15k ram BOP Hydril state that when the clearancebetween top of block and ram cavity exceeds 0.113, low pressuresealing performance of the preventer may be compromised.4

i) Shaffer 18-3/4-10m Ram Preventer Swing out door design requires that rams be in open position prior to

swinging open the door. Operating hydraulics are circuited through the hinge assembly. During

operator testing, check the hinge assembly for leakage. Poslock check locking pressure periodically and after replacing ram

blocks. Whenever pipe rams are exchanged with shear rams, theposlock settings must be adjusted.

Ultralock II Periodically verify proper operation by performing awellbore pressure test with hydraulic closing pressure bleed to zero. Asuccessful pressure test indicates the locks are properly maintaining thepreventer in the locked and closed position.

3 From Cameron Periodic Inspection of Cameron U & U-II BOPs. 4 From Hydril 18-3/4 15,000 psi Ram BOP Operators Manual



For an 18-3/4 10k ram BOP, Shaffer state that when the clearancebetween top of block and ram cavity exceeds 0.095 for pipe rams tohang-off drill pipe5 and .089 for shear rams, low pressure sealingperformance of the preventer may be compromised.6

5 or 0.125 for pipe rams not required to hang-off drill pipe 6 From Shaffer Engineering Report #124-A

BACK TO E-MANUALS TRAININGCoverTable of ContentsForewordSection 1 Overview of Drilling a WellSection 2 Basic ConceptsSection 3 Flange Hub ConnectionsSection 4 BOP Hydraulic Control SystemsSection 5 BOP Multiplex Control SystemsSection 6 Surface Well Control EquipmentSection 7 ConnectorsSection 8 Ram PreventersSection 9 AnnularsSection 10 Gate ValvesSection 11 LMRP ComponentsSection 12 Subsea BOP Stack ArrangementsSection 13 Riser EquipmentSection 14 Riser TensionersSection 15 BOP Pressure TestingSection 16 Codes and StandardsSection 17 Typical Operations ProceduresSection 18 Subsea Resources

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