investigated for buckling, local circumferential bending and shear stresses per GP 5-1-1.
3. In addition, reinforced concrete retaining walls have been used to confine the earth mound. Reinforced concrete walls shall have adequate drainage and the concrete shall not touch the drum or it can cause accelerated corrosion. See also GP 4-9-1 “Site Preparation/Earthwork.”
It is recommended that soils investigation and assessments be completed prior to determining the most suitable type of foundation. The primary objective of these investigations should be to reduce to an absolute minimum the potential for differential
settlement. The foundation design shall be based on the weight of the drum full of
water (needed for pressure test).
If these settlements are not kept to a practical minimum, they may introduce
service failures. The sensitivity to such settlements is due to the large length to diameter ratios and the relatively thin shells in these drums. Also the piping connecting to the drum must be kept free floating and not embedded into concrete or other fixations. It is important that connecting piping is not subjected to any stress from earth movement etc. In view of the above considerations, a maximum differential settlement of 25 mm on a
16.5 m long drum has been used at one facility.
Where groundwater or possible flooding makes it advisable, anchorage shall be provided to prevent flotation. Underground pipes and services, such as steam, water, electricity and sewer, shall be at least 1.5 m horizontally from the mounded tank. Above ground horizontal LPG tanks of more than 7.6 m3 water capacity shall be provided with structural steel saddles designed to be mounted on flat-topped concrete foundations by means of anchor bolts or other adequate devices. Lifting lugs for LPG horizontal tank, where provided, shall be designed for taking 1.5 times of the total weight of an empty tank. LPG horizontal tanks’ supports shall be of reinforced concrete, masonry or fireproofed structural steelworks. Design of the supports and foundations shall take into consideration:
1. Ground conditions, including allowable bearing pressure and differential settlement.
2. Possibility of flotation.
3. Expansion and contraction of the tank shell.
4. The greatest combination of static loading due to weight of the tank, its contents, weight of water used for testing, wind loading, vibration, thermal effects and seismic conditions.
3.2.4 Testing Requirements
NDE and testing of LPG horizontal tanks shall be per ASME Code Section VIII, Division 1.
For a tank which has a wall thickness of:
More than 38 mm, the minimum Non-Destructive Examination (NDE) shall be per the following sequence:
1. 100% X-ray on all seams.
2. Post Weld Heat Treatment (PWHT). Hardness test after PWHT shall not be more than 225 HB unless waived by EMRE Engineering.
3. 100% ultrasonic test on all seams.
4. 100% Magnetic Particle Test (MT) on all seams.
5. Hydrostatic test at 1.3 times of the design pressure. (The 1999 ASME Section VIII, Div.1 specify 1.3 times of MAWP as Hydrostatic testing pressure, since ASME has lowered the safety factor for materials from 4 to 3.5. For any alteration of a tank built prior to 1999, EMRE Engineering shall be consulted.) Also refer to GP 5-3-1 "Pressure Testing of Unfired Pressure Vessels", which has a clearer description for hydrostatic testing. It states: In the hydrostatic test condition, the maximum membrane stress in the tank in the un-corroded or corroded condition shall not exceed 90% of the specified minimum yield strength for ferritic steels, nor 100% of the specified minimum yield strength for austenitic steels or non-ferrous materials.
6. 100% MT on all seams.
1. If a service condition permits (e.g. H2S concentration under 50 ppm), PWHT
can be waived provided that the Metal is preheated prior to welding. Otherwise, follow the procedures as above.
2. 100% X-ray on all seams.
3. Hydrostatic test at 1.3 times of the design pressure. 4. 100% MT on all seams.
Less than 32 mm, the minimum NDE shall be per the following sequence:
1. If a service condition permits (e.g. H2S concentration under 50 ppm), PWHT
can be waived. Otherwise, follow the procedures as above. 2. 100% X-ray on all seams.
3. Hydrostatic test at 1.3 times of the design pressure. 4. 100% MT on all seams.
NDE and testing of LPG sphere tanks shall be per ASME Code Section VIII, Division 2. For a tank which has a wall thickness of:
More than 38 mm, the minimum Non-Destructive Examination (NDE) shall be per the following sequence:
1. 100% X-ray on all seams
2. Post Weld Heat Treatment (PWHT). Hardness test after PWHT shall not be more than 225 HB unless waived by EMRE Engineering.
3. 100% ultrasonic test on all seams.
4. 100% Magnetic Particle Test (MT) on all seams. 5. Hydrostatic test at 1.25 times of the design pressure. 6. 100% MT on all seams.
Between 32 mm to 38 mm, the minimum NDE shall be per the following sequence: 1. If a service condition permits (e.g. H2S concentration under 50 ppm), PWHT
can be waived provided that the Material is preheated prior to welding. Otherwise, follow the procedures as above.
2. 100% X-ray on all seams.
3. Hydrostatic test at 1.25 times of the design pressure. 4. 100% MT on all seams.
Less than 32 mm, the minimum NDE shall be per the following sequence:
1. If a service condition permits (e.g. H2S concentration under 50 ppm), PWHT
can be waived. Otherwise, follow the procedures as above. 2. 100% X-ray on all seams.
3. Hydrostatic test at 1.25 times of the design pressure. 4. 100% MT on all seams.
Documentation from fabricator shall include MDR (manufacturer's data report) and all test recordings according to ASME VIII requirement.
3.2.5 Horizontal “Bullets” and Spherical Tanks
Design procedures for horizontal “bullet” tanks and spheres are similar to those described above for mounded drums except those items that are specific to mounded drums. All connections shall be flanged. Existing screw type connections in older Marketing tanks need not be retrofitted to flange connections. Older Marketing bullets also may have 3 meters from the edge of the bullet to the water drain discharge point
compared with the latest 4.5 meter recommendation in DP XXII-C. Existing drain points do not need to be retrofitted.
For aboveground bullets the bottom nozzles should be positioned at the two ends and not between foundations. This is to facilitate access of valves and better firewater coverage if needed. If possible the bottom nozzles may be reduced in favor of top nozzles. This may avoid the potential for liquid leaks. Top spray filling is desired for bullets and spheres since it lowers the pressure during filling. Typical sphere and bullet designs are shown in Figure “Typical horizontal bullet tank” and Figure “Typical spherical tank.” Tanks used in loading and unloading service would normally have a vapor balancing line, which is not shown in these figures.
3 LHA (INDEPENDENT) P I CSO BLEED (GUSSETED) DRAIN WITH ELL SAFETY
VALVE 7
PI
3
1 PLATFORM ACCESSVIA LADDERS 7
INSTRUMENTS 1 3
(IF LARGE BULLET) 4
OUTSIDE TOE WALL
EBV(D) (FIREPROOFED OR FIRE SAFE ACTUATOR) SAMPLE CONNECTION H TO SEWER OR DRAINAGE SYSTEM 2 HYDRANTS (PREFERABLY WITH MONITORS) 4 TOE WALL 2 WATER CATCH BASIN 2 THROTTLING 5 30 m MIN. FILL WATER FLOOD LHA AND LHHA FOR
ALL BULLETS LHCO IF FILLED BY RUNDOWN, PIPELINE OR SHIP. 5 5 DRAW-OFF NC 1 2 3 4 5 6 7 GP9-1-1 GP15-1-3 GP3-2-3 GP3-5-1 GP14-3-1 GP3-2-4 DPM XV-J REFERENCES GENERAL GP9-2-1 GP9-2-1 NO GAGE GLASSES SUPPORTS FIREPROOFED FIRE-SAFE QUICK CLOSING 5 NON-FREEZE DRAIN (IF COLD CLIMATE) 1
6
NOTES:
1 IF POSSIBLE ALL CONNECTIONS SHOULD BE AT ONE END OF VESSEL AND THE CATCH BASIN SHOULD BE LOCATED NEARBY.
1 5 FILL & DISCHARGE
SLOPE SLOPE SLOPE GROUNDED DR, 3/2001 LI PdI LHA PI 4 m MIN. RELIABLE GAUGE BULLET IN OPERATION MAINTAINABLE WITH
Figure 3.2.5-a: Typical horizontal bullet tank (from DP XXII-C)
2
TO SEWER OR DRAINAGE SYSTEM
2 2 OR MORE FIRE HYDRANTS (PREFERARLY WITH MONITORS)
4 COATED OR SLEEVED 5 H NC 1 2 3 4 5 6 7 8 GP9-2-1 GP9-1-1 GP15-1-3 GP3-2-3 GP3-5-1 GP14-3-1 GP4-2-1 GP3-2-4 GP9-2-1 DPM XV-J REFERENCES GENERAL TYPICAL AREA LAYOUT
LHA IF FILLED BY RUNDOWN, PIPELINE, OR SHIP 3 NO GAGE GLASSES STAIRWAY & PLATFORM 1 7 (INDEPANDENT) CSO PI 3 1 LHA DELUGE SYSTEM 4 INSTRUMENTS 1 3 PdI LI 4 FILL & DISCHARGE 5 1 CATCH BASIN 2 2 SUPPORTS FIREPROOFED DIKE WATER DELUGE INSTRUCTION SIGN 4 SUCTION CONNECTION 1 TI 1 3 4 m MIN 5 SAMPLE CONNECTION FIRE-SAFE QUICK CLOSING THROTTLING 1 6 5 5 1 WATER DRAW-OFF NON-FREEZE DRAIN
(IF IN COLD CLIMATE) 1
WATER 4 OUTSIDE DIKED AREA 5 MIN 30 m OR FIRE-SAFE ACTUATOR) 5 EBV(D) (FIREPROOFED FLOOD FILL
GREATER OF 30 m OR ONE DIAMETER RELIABLE GAGE
MAINTAINABLE WITH
SPHERE IN OPERATION BLEED (GUSSETED)
DRAIN WITH ELL SAFETY VALVE 8 GROUNDED 1 SLOPE 2 SLOPE DR 1999 FIREWATER SPRAY SYSTEM BELOW SPHERE
Figure 3.2.5-b: Typical spherical tanks (from DP XXII-C)
Note: GP 15-1-3 referenced in the both figures further refers to GP 9-7-1 for details on installing level devices. GP 9-7-1 shows welding to an atmospheric tank. Welding shall not be done to pressure tanks and an alternate means of level device support is necessary.
Aboveground pressurized LPG tanks need certain considerations as to siting and location. These are explained under section 2.2.2.4 “Siting of Aboveground Tanks and Equipment.” Horizontal bullets and spheres are more vulnerable to fire exposure than mounded drums. Therefore, codes recommend installation of some kind of fixed fire protection. Depending on risk, fire resistant coatings may be needed for bullets and spheres that are normally equipped with fixed water spray or water deluge systems. These requirements are discussed in depth in Chapter 8 under “Firewater Sprays,” “Firewater Deluge for Spheres,” and “Fire Resistant Coatings.” Storage at refineries and Upstream Gas Plants shall be provided with water flooding facilities to inject water and displace LPG in the lower parts of tanks, in the event of a tank leak.
Spheres shall be built in accordance with GP 9-2-1. They are normally equipped with top and bottom manholes. The filling and withdrawal connections for spheres are normally at the bottom. LPG Sphere tanks shall be provided with steel support columns and wind (earthquake) girders. Columns shall be mounted on concrete foundation with anchor bolts. The columns shall be fireproofed from ground level to intersection of the support with the tank shell (see also drawing in Chapter 8).
3.2.6 Spill Containment
Spill containment shall be considered for all locations and shall be provided in locations in which either of the following would result in a significant hazard to important nearby facilities, nearby properties, or public areas, per API 2510:
1. The physical properties of the stored LPG make it likely that liquid material will collect on the ground. The more hydrocarbons like Butane (or Pentane) is contained in the LPG the more it will spill as a liquid.
2. Climatic conditions during portions of the year make it likely that liquid LPG will collect on the ground.
The ground beneath aboveground LPG tanks shall be of impervious construction and graded to be sloping away from the tanks at minimum 1 percent gradient, to drain any liquid spills to a safe area away from the tanks and piping. Diversion kerbs with a height not exceeding 380 mm to avoid formation of gas traps may be permitted if necessary for directing possible spillage away from bullet tanks.
If spill containment is to be provided, it shall be either remote impoundment or diking of the area surrounding the spherical tank. If diking around the tank is to be used for spill containment, the diked area shall be designed according to GP 9-1-1.
Remote impoundment collects any spill at a location away from the tank. This may be
of significant importance shall the vaporizing LPG ignite during the spill. However, installation of remote impoundment may need more land. In any case, all materials for components of spill containment shall be capable of withstanding the effects of a thermal shock associated with spilling LPG. Furthermore, spill containment shall allow for adequate venting of the vapor generated during an LPG spill.
If remote impoundment is to be used for spill containment, the remote impoundment facility shall be designed as follows:
1. Grading of the area under and surrounding the tanks shall direct any leaks or spills to the remote impoundment area. Grading shall be at a minimum of 1 percent slope.
2. Walls, dikes, trenches, or channels may be used to assist in draining the area. 3. The remote impoundment area shall be located at least 15 m from the tanks
draining to it and from any piping or other equipment.
4. The holdup of the remote impoundment area shall be not less than 25 percent of the volume of the largest tank draining to it. If the material stored in the
tank has a vapor pressure less than 690 kPa at 38 °C, the holdup for the remote impoundment facility shall be not less than 50 percent of the volume of the largest tank draining to it. Larger holdups shall be provided in the remote impoundment facility at locations where the expected vaporization is less than that specified above because of climatic conditions or the physical properties of the material.
5. The electrical classification is to be the same as a diked area.
Whether spill containment is provided or not, the ground under and surrounding a tank used to store LPG shall be graded to drain any spills to a safer area away from the tank. The drainage system shall be designed to prevent liquid spilled from one tank from flowing under any other tank. The spill drainage area shall not contain equipment like pumps or LPG piping not associated with the tank.
3.2.7 Vacuum Conditions
An additional design consideration shall be addressed where commercial Butanes are stored in cold climates in horizontal “bullet” tanks and spheres. If the temperature of the stored liquid can fall below boiling point of Butane (approximately –7 °C, for the typical commercial Butane/Butene mixture and 0 °C for pure normal Butane), the pressure in the tank can drop below atmospheric pressure. There are several options to handle this low pressure situation.