1. Scope This procedure covers inspection and repair of Tk-7 bottom plate and annular plate to shell (including critical zone). The repair carry out during Tk-7 out of service are covered:1.1 The replacement of annular plate to shell including critical zone (3” int & ext distance from tank shell) is to address an extensive damage of existing area detected during on-stream inspection. 1.2
The bottom plate weld patch repair is to address the minimum thickness as found during tank floor scanning.
2. Definition Annular plate - an approximate 2 feet of bottom plate area from outer rim are consider annular plate. 3. Consideration All new material used for repair, alteration shall meet applicable of tank standard API Standard 653/650. 4. Safety Consideration 4.1
Prior to proceed with tank repair, Tk-7 shall be clean and gas free compliance.
4.2
If product suspected under floor plate, prior to any hot work special procedure shall be developed by the repair contractor and review with respective PDR personnel.
4.3
If existing material where repair require was confirm contaminated with other hazardous material e.g lead, special procedure shall be developed by repair contractor and review with respective PDR personnel.
5. Reference 5.1
ExxonMobil Global Practice
5.2
API Std 653
5.3
API Std 650
6. Repair Procedure 6.1
Welding 6.1.1
Welding procedure shall be in accordance with API Std 653.
6.1.2
When necessary to weld new annular to existing shell plate:6.1.2a Clean to SSPC SP-7 brush off cleaning from rust, mill scale and/or old coating. 6.1.2b Assemble the annular plate and shell plate. All assembly to be witnessed by contractor QC and reviewed with ESSO personnel. 6.1.2c Using low Hydrogen electrode (E-7018/E7016) to deposit a fillet weld. As per design 1st pass weld deposit should be on vertical leg against shell plate and for 2nd pass weld deposit should be on horizontal leg against annular plate. Refer to below sketch-1 for details: Shell plate
3rd
1st
1st
2nd
3rd 2nd
Bottom plate
Sketch-1 6.1.2d Perform visual inspection on root to be sure all welds area free from notches and undercut, grind remove any finding is recommended. Perform magnetic particle inspection prior to proceed with 2nd and 3rd pass. 6.1.2e Visually inspect final weld, also inspect using Dye penetrant testing. 6.1.3
All other bottom plate to bottom plate fillet weld shall made using 2 passes with low hydrogen electrode.(E-7018/E-7016) 6.1.3a Visually inspect final weld, random DPT shall be performed and 100% vacuum box testing.
6.2
Replacement of annular to shell plate including critical zone.
6.2.1
Unless otherwise specify during construction, all plate shall be uniformly cut in parallel to tank bottom. Details dimension and number of annular plate to shell replacement will be refer to drawing no Tk-7-001/09.
6.2.2
Site verification and marking on removal annular plate and shell to annular plate weld seam should be carry out before any hot work activity start.
6.2.3
Mobilize of equipment and tools to site for inspection by PDR personnel
6.2.4
All fabrications on new annular plate should be carry out in fabrication yard. Traceability should be recorded as per API Std 653.
6.2.5
Temporary square nut (100mm X 100mm X 25mm) shall be use as a part of component to wedge the shell plate up. Refer to sketch-2 AND Drawing Tk-7 004/09 for details.
6.2.6
Weld vertically the square nut at 25mm elevation from tank bottom outside of Tk-7 shell with approximate spacing between 2.3m surrounding the tank perimeter where wedges are required. Refer to sketch-2(a) & (b) for details. Refer Attachment 1.0, Drawing Tk-7001/09, Tk-7002/09, Tk-7 004/09, Tk-7 003/09 SHT 1, Tk-7 003/09 SHT 2,
C-Channel as stiffener ring
Shell Plate Square Nut 100mm X 100mm X 25mm
Square Nut 100mm X 100mm X 20mm
166.7 mm elevation
Wedges
Annular Plate
Skecth-2(a) Side View
6.2.7
50mm
25 mm elevation
Max 15mm gap
250mm Skecth-2(b) Front View
Visually inspect final weld, also inspect using dye penetrates testing.
6.2.8
Tack weld temporary stiffener rings (C-channel 100mm x 50mm x 6mm) to shell according to ID. The stiffener shall be attached 166.7 mm from tank bottom around the tank shell. Refer to sketch-2(a) for details.
6.2.9
Temporary back up jack (support) install internally (4 locations) to assist during wedging the square nut. Refer to sketch-3 for details.
Square Plate 210mm X 210mm X 20mm
Square Nut 100mm X 100mm X 20mm
266.7 mm elevation
25 mm elevation
Annular Plate
Skecth-3 Side View
6.2.10 Gouge shell to annular plate weld seam with approximate of 80m length on internal and external of the Tk-7 except the length of weldment around marine line noozle. 6.2.11 Clean the gouging area from scale or other foreign material and ensure all remaining welding are completely removed between shell and annular. 6.2.12 Lay the wedges in between the square nut and bottom plate with slight force by hammer. 6.2.13 Standby 20 workers to raise up the half round tank to the height of 15mm by wedging. 6.2.14 Raise up the other half round of the tank to 15mm as item 6.2.13 6.2.15 Gouge and cut the annular plate as mark in drawing Tk-7-001/09. 6.2.16 To prevent shell distortion at Marine Suction Line, attached related bottom plate will be gouged.
6.2.17 After complete gouging, pull out the 1st 2 pieces of the existing annular plate in sequence (Refer Drawing 05/09 SHT 1) Grind off all gouging plate to smooth and clean edges of shell or annular plates. 6.2.18 To prevent from galvanic corrosion, ensure old bottom plate and other foreign materials are completely removed prior to install new annular plate. 6.2.19 Install the 1st new annular plate from tank outside by the method as per Drawing 05/09 SHT 1 after inspection of tank pad. Any voids on the foundation below the old bottom plate should be filled with material such as oil sand and premix. (temporary platform may require to prevent further damage on tank pad) 6.2.20 Install the 2nd new annular plate from tank outside after 3rd piece of existing annular plate is removed .Tack welding 1st to 2nd new annular plate after installation as per Drawing 05/09 SHT 2. Fit up the new plate with existing bottom plate as per drawing Tk-7-001/09 and ensure it meet API Std 650 for critical zone and outer rim. 6.2.21 Repeat the removal and installation of annular plates in sequence as item 6.2.19 and 6.2.20. 6.2.22 Remove few wedges at nearest to fit up plate and let Tk-7 shell plate laying down on it. 6.2.23 Once shell plate was completely settle down on new annular plate tack weld should be carry out. The tack weld shall be remove prior to actual welding of the annular to shell plate weld seam. 6.2.24 An alternate welding at approximate 1m length as per 6.1 shall be carry out in sequence to minimize distortion on shell and annular plate. 6.2.25 All square nuts shall be remove by grinding. Also inspect the area using penetrant testing (DPT). Any defect on the shell course shall be repair. 6.2.26 All grinded area are to be touch up paint. 6.3 Patching of bottom plate. 6.3.1
Site verification and marking on bottom plate should be carry out before any hot work activity started.
6.3.2
Mobilize of equipment and tools to site for inspection by PDR personnel
6.3.3
Patch plate shall be size to allow welding to the bottom with remaining thickness at least 0.20” (5.08mm)
6.3.4
Individual weld patch plate should be limited to an area of 10 ft square or less. The min. requirement of patch plate should be refer to API Std 653.
6.3.5
All weld patch plate may be circular, oblong, or polygonal with rounded corners.
6.3.6
All weld patch shall be examine with DPT and vacuum tested.
