Displacing End of Job
15. SURFACE WELLHEAD
15.2. BASE FLANGE INSTALLATION 1. Welding Procedure
1) Cut the 30” CP at cellar deck level (Jack-up) or at cellar bottom (land rig).
2) Cut the 20” casing at about 50cm above the cellar deck or cellar bottom
3) Empty the casing of mud bringing the fluid level down to 50 cm below the cellar deck or cellar bottom.
4) Pre-heat the casing in the proximity of the final cut line up to the same temperature required for welding.
5) Cut the casing at about 200-400mm from cellar deck or cellar bottom according to the Drilling Programme, with a 30-35o internal bevel, using a guide frame to ensure the cut is horizontal.
6) Thoroughly clean the surfaces to be welded and ensure they are free from paint, grease, rust or dirt.
7) Install the base flange, checking it is horizontal and that the lateral outlets are aligned according to Company Drilling and Completion Supervisor’ s requirements.
8) During welding operations ensure that all parts are protected against rain, wind, oil, mud or water.
9) Heat the outside of the base flange and the inside of the casing with an oxyacetylene torch until the surface reach the required pre-heated temperature. For carbon steels, refer to Table, for chromium molybdenum steels refer to table 15.b.
10) During this operation care shall be given to ensure the uniform expansion of the parts to be welded, as there may be significant differences in their wall thickness.
11) Perform internal welding first. Start welding two sections of 5-10cm length diametrically
opposite. Continue and repeat this step at 900. Continue and repeat for subsequent sections until the first weld bead is completed.
12) Subsequent passes should be performed continuously to complete the fill up the joint.
Care should be given to avoid overlapping or causing any discontinuity of the weld bead during the same pass.
13) The external weld should be performed using the same procedure.
14) Once started, welding should be finished without interruption. Slow cooling should be carried out by using appropriate insulating systems.
15) Pressure test the welding after complete cooling of the base flange.
16) Check the base flange horizontal alignment and the inside alignment of the welded area.
17) Seal the CP-casing annulus with two semicircular steel plates, leaving a test port for pressure checking.
% Carbon Thickness (mm)
8 12 25 40 and more
0.2 C 20°C 50°C 100°C 150°C
0.3 C 50°C 70°C 150°C 200°C
0.4 C 100°C 200°C 250°C 300°C
0.5 C 200°C 300°C 300°C 300°C
0.6 C 300°C 350°C 350°C 350°C
0.7 C 300°C 400°C 400°C 400°C
Table 15.A - Required Pre-Heating Temperature Carbon Steels
Chemical Analysis Preheating
% Cr % Mo Temperature
0.5 0.5 100 - 150°C
1.0 0.5 100 - 150°C
2.0 0.5 150 - 200 °C
2.25 1.0 200 - 280°C
5.0 0.5 200 - 280°C
Table 15.B - Required Pre-Heating Temperature Chromium/Molybdenum Steel
15.2.2. Safety
a) During the time of operation to prepare and carry out the welding of the base flange, it is absolutely forbidden to work on the drilling floor or in proximity of the wellhead.
b) Make sure that the welder has efficient ground and safety switches conforming to CEI standards or other international/local regulations.
c) The welder and his assistant must wear protective clothing.
d) The welder must never be left by himself.
e) The work area must be protected from any falling objects. For this reason a protective system with scaffolding must be built in order to guarantee safety during the base flange welding operations.
15.2.3. Pressure Testing
a) A pressure test must be carried out using hydraulic oil after cooling of the base flange.
Do not exceed 70% of API casing collapse pressure rating although the pressure values should be stated in the Drilling Programme.
b) During this test, no sweating should occur. Upon completion of the test, install a wellhead protection cap to prevent objects accidentally falling into the wellbore.
c) Re-install the 3/4” NPT plug in the test port.
15.2.4. Slips Installation
1) All slips, packing elements and ring joints and their seats should be thoroughly cleaned and lubricated.
2) Make sure the hinged slips and spring retaining rings are unlatched.
3) Pick-up the BOP
4) Be sure that the correct tension is applied to the casing string.
5) Clean and inspect the ID of the base flange, polishing out any burrs or scratchers.
6) Place two wooden boards of equal thickness across the base flange so that they straddle the casing.
7) Wrap the casing slips around the casing. Latch the hinged slips and spring retaining ring.
8) Lower the slips into the base flange bowl until they shoulder on the casing-spool, checking the correct alignment of the slip segments and the correct position.
9) Slowly release the casing tension permitting the slips to set. Slippage between slips and casing must be prevented.
15.2.5. Casing Preparation
1) Cut a drain hole in the casing approximately 12” (30cm) from the top of the base flange.
2) Allow the casing to drain and cut it off at 12” (30cm) above the base flange.
3) Remove the casing reminant and prepare for the final cut.
4) Remove the fluid inside the casing to below the top of the base flange using a cup or a bucket.
5) Cut the casing again at 4” (101.6mm) to 41/4” (108mm) from the top of the base flange.
Make sure the cut surface is level.
15.2.6. Primary And Secondary Packing Installation
1) Remove any burrs from the cut edges of the casing.
2) Install the first primary support. Place the primary support over the casing with the bevelled side up. Lower the packing support until it shoulders on the body counterbore.
3) Install the primary packing by:
a) Clean and oil the casing and packing thoroughly.
b) Fit one side of the packing lip over the casing.
c) Insert a clean welding rod (with the flux removed) or screw driver between the ID of the base flange and the OD of the packing. This will facilitate installation of the primary packing.
4) Tap around the packing with a hammer until the packing is completely installed on the casing.
Caution: Make sure that the packing is not cut or gouged during the installation.
5) Continue to tap the packing down until it is flush with the body flange and the outer lips have fully entered the bevel of the counterbore. Drive the packing down until it contacts the first primary support.
Note: If the body outlet valve is open, entrapped gas will not hinder seating of packing.
6) Install the second primary support by placing the upper packing support, with the lip receiving face down, over the casing and dropping it into place.
Note: When properly installed, the back face of the second primary support shall not protrude past the base flange face.
7) Install the first secondary support by placing the secondary support over the casing with bevelled side up. Lower the support until it rests on top of primary packing group.
8) Install the secondary packing by:
a) Thoroughly grease the packing and fit one side of the packing lip over the casing.
b) Install the packing with a hammer as in step (4).
c) Drive the packing down until it contacts the first secondary support.
d) Install the second secondary support by: placing the secondary support over the casing with bevel facing down. Lower support until it contacts the secondary packing.
15.2.7. Casing Spool Installation
1) Clean the ring grooves on the bottom flange of casing spool and on the base flange, as well as the restricted packing bore of the casing spool.
2) Oil the secondary packing and the restricted packing bore of the casing spool.
3) Fill the void area with oil around the primary and secondary packing group.
4) Place the metal ring joint in its groove.
5) Align the bolt holes on the casing spool with the bolt holes on the base flange.
6) Lower the casing spool over the secondary packing assembly (being careful not to roll or tear the secondary packing), until the casing spool comes to rest on the ring gasket.
The use of a torque wrench is recommended.
7) Assemble nuts to bolts and tighten. Wherever possible use a ‘hydraulic studs tensioning system’. This system allows tightening of all studs together at once with a reduced make-up time.
Otherwise tighten them conventionally with the correct torque (Refer to 15.3) to ensure a proper seal, tighten the bolts using the following method:
8) Tighten the first bolt.
9) Tighten the bolt at 180° from the 1st bolt.
10) Tighten the bolt 90° from the 1st bolt.
11) Tighten the bolt 180° from the 3rd bolt.
12) Continue this alternating procedure until all bolts have been tightened.
Checking the torque of the stud bolts must be done during drilling and after each BOP test due to the vibration and weight that they have to bear.
15.3. RECOMMENDED FLANGE BOLT TORQUE