Section 9 — Storage Tanks

Atmospheric Storage Tank Lifting, Shell Relieving and Floating

IPE Engineering Practice IPE-EP-9-1-6

Document number: IPE-EP-9-1-6 · Section: 9 — Storage Tanks

SCOPE

This Practice covers mandatory requirements for lifting, shell relevelling, and floating atmospheric storage tanks. Tanks covered by this Practice include those built in accordance with APl Standard 650 and its predecessor 12C.
Shell relevelling requirements are given in this Practice. For tank bottom relevelling requirements, refer to EP 4-2-10.
The requirements of this Practice apply to tanks of both welded and rivetted construction. However, a contractor experienced in lifting rivetted tanks shall be consulted prior to lifting, relevelling or floating a rivetted tank.
Any deviation from this Practice must be approved by the procedure described in EP 1-1-3.
An asterisk (*) indicates that a decision or approval by the Owner or Owner's Engineer is required, or that additional information is furnished by the Purchaser.

2.0 REFERENCES

The latest edition of the following standards and publications are referred to herein.

STANDARDS AND PUBLICATIONS

Engineering Practices
EP 1-1-3 Deviations to Engineering Practices EP 4-2-1 Foundations Types and Selection Criteria EP 4-2-? Foundations for Atmospheric Storage Tanks EP 4-2-10 Atmospheric Storage Tank Foundation Monitoring, Repair and Retrofit EP 4-5-1 Structural Steel EP 4-5-2 Structural Steel Construction EP ?-1-? Pressure Vessel Details EP 9-1-1 Atmospheric Storage Tanks EP 9-1-2 Welding Requirements for Atmospheric Storage Tanks EP 9-1-5 Repair, Alteration, and Reconstruction of Atmospheric Storage Tanks
APl Standards
Std 650 Welded Steel Tanks for Oil Storage
Std 653 Tank Inspection, Repair, Alteration and Reconstruction
ASTM Standards
D693 Crushed Stone, Crushed Slag, and Crushed Gravel for Bituminous Macadam Base and Surface Courses of Pavements D4253 Maximum Index Density of Soils using a Vibratory Table D4254 Minimum Index Density of Soils and Calculation of Relative Density

STANDARDS AND PUBLICATIONS (Cont.)

DEFINITIONS

Contractor - Company or business that agrees to furnish materials or perform specified services at a specified price and/or rate to the Owner.
Earth Pad - The soil used to elevate tank above surface grade.
Inspector - A Refining Company appointed engineer or inspector.
Jacking - Procedure whereby a portion of or an entire tank shell is lifted to a height sufficient to permit relevelling of the tank shell or minor repairs to the foundation. Typically, hydraulic jacks are used, and lift points are lugs welded to the external surface of the tank shell near the bottom.
Owner - Refining Company.
Owner's Engineer - A Refining Company appointed engineer.
Pile - Structural member of timber, concrete, and/or steel, used to transmit surface loads to lower levels in the soil mass.
Relevelling - Procedure whereby a portion of or an entire tank shell and/or bottom is/are brought to a prescribed elevation using jacking and placement of fill, or using pressure injection of Portland cement grout.
Ringwall - Foundation provided under the shell to minimize settlement caused by the shell cutting into the soil.
Tank Lifting - Procedure whereby an above ground storage tank is lifted to a sufficient height for human access to the entire tank bottom and foundation for repairs or retrofit. Typically, the tank will be lifted to a height of seven feet or more above grade.

TANK LIFTING

General
(*)Unless otherwise approved by the Owner's Engineer, tanks shall be lifted either by hydraulic jacks with lifting lugs attached to lower portions of the shell and, if necessary, internal structures built to support the roof, or by crane with lines attached to lifting lugs on the upper portions of the shell.
(*)The Owner's Engineer shall approve all lifting of tanks that are not braced internally, based on calculations provided by the Contractor.
(*)Unless otherwise specified by the Owner's Engineer, tanks shall be lifted to a height that results in a minimum of ? feet clear access after accounting for foundation build-up and tank bottom sag.

The tank shall be cleaned and gas freed prior to starting work.
Prior to attachment of lifting lugs or other support structures a survey of shell thickness shall be performed.
As a minimum, shell thickness readings shall be taken every 20 feet along the circumference of the tank at three elevations, including one within two feet of the tank bottom, one within two feet of the top of the shell and one at the approximate mid-height of the tank shell.
Bottom thickness readings shall be taken at a minimum of two points along four equal spaced diameter axes, including one within two feet of the shell and one at mid-radius.
(*)A minimum of two soil borings shall be taken at the tank site to determine the soil bearing capacity. The results of the soils investigation shall be used to determine allowable loads on jack pads or crane wheels and supports. Alternatively, when approved by the Owner's Engineer, the values for soil bearing capacity given in EP 4-2-1 can be used.
(*)Jacks and cranes shall bear on pads of well-graded gravel per ASTM D693, size number 6 or ?, compacted to ?0% relative density in accordance with ASTM D4253 and ASTM D4254. Unless otherwise specified, compaction of pads within 6 feet of the periphery of the tank shall be by hand-held compaction tools.
(*)Structures required to brace the tank and/or support the roof during a tank lift shall be designed and constructed per EP 4-5-1 and EP 4-5-2. The Owner's Engineer shall approve the final design of such structures.
After the completion of the tank lift and repairs, all lifting equipment shall be removed from the site in an expeditious manner.
Hydraulic Jacking
(*)Unless otherwise specified by the Owner's Engineer, hydraulic jacks shall be used to jack against shells. The total jack capacity shall be a minimum of two times the weight of the tank being lifted.
(*)Lugs for jacking shall be designed as stiffened seat connections in accordance with the procedures given in Salmon and Johnson, see Section 2.0. In addition, localized stresses in the shell resulting from the loads on the lug attachments shall be evaluated. Calculations for the lug design and localized shell stresses shall be submitted to the Owner's Engineer for approval.
Welding procedures for tank lugs shall be in accordance with EP 9-1-2.
(*)Jack spacing and associated calculations shall be submitted to the Owner's Engineer for approval. As a rule of thumb, a minimum of two jacks per bottom shell course sheet is required.
All jacks shall operate simultaneously and shall be connected to a single hydraulic supply. A safety system shall be in place to prevent jack failure in case of pump or hydraulic line failures.
(*)The general tank jacking procedure shall be in accordance with the following requirements. The actual jacking procedure shall be submitted to the Owner's Engineer for review and approval prior to the initiation of any work.
The tank shall be raised gradually to minimize stresses.

The tank shall be temporarily supported on cribbing consisting of 6 inch x 6 inch or greater timbers placed at jacking points while foundation and tank work is being performed.
While the tank is in the air, tank repairs or retrofits shall be performed in accordance with EP 4- 2-10 and EP 9-1-5.
The tank shall be lowered gradually in a procedure reviewed and approved by the Owner's Engineer.
Temporary support structures shall be removed.
Liner and tank bottom patches shall be made at any internal jacking points.
Exterior areas where jacks and shims were located shall be filled after all other fill material has been placed and compacted.
Fill materials shall be placed and compacted using hand-held compaction tools.
Asphalt covering shall be applied to the fill immediately surrounding the tank per the appropriate figure in EP 4-2-?. The grade around the tank shall be sloped away from the tank for proper drainage.
Crane Lifts
The total crane capacity shall be 125% of the weight of the tank and rigging being lifted.
Lifting lugs for crane lifts shall designed per EP ?-1-?.
(*)The tank shall be supported on timber cribbing while foundation and tank repairs are being performed. The Owner's Engineer shall approve the number of equal-spaced locations of timbers.
(*)Crane lifting and lowering procedures shall be submitted to the Owner's Engineer for review and approval.
Air Bags

(*)Inflatable air bags may be used under the shell and bottom to lift a tank, if approved by the Owner's Engineer.

TANK SHELL RELEVELLING

General Requirements
Tank shell relevelling shall be performed by jacking against lugs welded to the tank shell. Jacking from beneath annular plates is not permitted.
The tank shall be cleaned and gas freed prior to starting work.
Prior to shell relevelling, a survey of shell and bottom thickness shall be performed per Paragraph 4.1.
Preparations for Tank Jacking
(*)Lugs for jacking shall be designed in accordance with the requirements of Paragraph 4.2.
Jack pads shall comply with Paragraph 4.1.

(*)The design of jack pads for use with tanks on concrete ringwalls, mats or pilecaps shall be submitted to the Owner's Engineer for approval.
(*)Hydraulic jacks shall be used, unless otherwise approved by the Owner's Engineer. The requirements for hydraulic jacks are given in Paragraph 4.2.
Jacking Procedure
The jacking procedure shall comply with requirements in Paragraph 4.2 and the following:
Localized sections of differential settlement shall be jacked first to bring the shell to a planar position.
The tank shall be jacked a height sufficient to add a course of timber beams or metal shims.
Jacks shall be repositioned and additional jacking, as may be required to bring the tank to the proper elevation can then be performed.
Fill shall be placed to obtain the required elevation. The elevation of placed fill materials shall take into account an estimate of the compaction that will take place upon lowering the tank.
Areas where jacks and shims were located shall be filled after all other fill material has been placed and compacted and as jacks are removed, sequentially.
For tanks on earth pads and gravel ringwalls, fill materials shall comply with Note 1, Figure 28 of EP 4-2-?. For tanks on concrete ringwalls, mats or pilecaps, the shell shall be relevelled by forming and placing concrete per the appropriate Figure(s) in EP 4-2-?.
Fill material placement and grading shall comply with Paragraph 4.2.
After the completion of the shell relevelling, all lifting equipment shall be removed from the site in an expeditious manner.

6.0 TANK FLOATING

(*)Air and water flotation methods may be used to temporarily or permanently relocate storage tanks only if approved by the Owner.
Relocation of a tank shall comply with the requirements of this Practice and APl 653.
A survey of shell and bottom thickness shall be taken prior to evaluating flotation methods per Paragraph 4.1.
(*)The height of water required to float a tank shall be determined taking into consideration the deformation that will occur when the tank is buoyant. The method of analysis to determine the deflected shape of the tank and distribution of buoyant forces shall be reviewed and approved by the Owner's Engineer.
Membrane stresses in the tank generated by water or air flotation, particularly at the shell to bottom junction, shall be determined. Tensile stresses shall be less than the yield strength of the material.
Local buckling at the shell to bottom junction shall be examined and bracing added or the method of relocation modified if buoyant forces create a buckling problem.

The tank shall be enclosed in a diked area for water flotation. The flooded dike area shall be provided with a means of rapid raising and lowering of the water level, and thus, raising or grounding the tank should problems arise.
A minimum of four anchor lines shall be attached to a tank being air or water floated, including at least one towing and tailing line and two side anchor lines.
(*)The actual flotation procedure shall be reviewed and approved by the Owner's Engineer.
The new foundation for the relocated tank shall comply with EP 4-2-?.
After the completion of the tank relocation, all lifting equipment shall be removed from the site in an expeditious manner.

7.0 HYDROTESTING

All tanks that have been lifted, relocated or jacked for shell relevelling shall be hydrotested after all tank repairs and retrofits have been made.
Hydrotesting shall be performed per EP 9-1-1 and EP 4-2-10

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