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Lightning protection of a vertical stainless steel tank 20000 m3 in Kazakhstan

  • 19.03.2019

There had been many fires at the storages of oil and gas products (tank storages) in the result of lightning strike, that is why approach to the development of lightning protecton systems and grounding for such objects should be on a very high level.

 

ZANDZ Technical Center received a request for the development of lightning protection of a vertical steel tank 20 000 m3 in volume (VST-20000). Below we will study the solution we prepared.

 

Initial data:

  • VST volume: 20000 m3;
  • VST diameter: 39.9;
  • VST height: 18m;
  • upper wall ring thickness: 10 mm;
  • bottom wall ring thickness: 16 mm:
  • number of wall rings: 12 rings;
  • breathe valve: present;
  • soil resistivity: 100 Ohm * m.

Task: calculate lightning protection and grounding system.

 

The arrangements were fulfilled in compliance with:

 

The object refers to "special, dangerous for immediate surrounding" in accordance with IS and to the II category according to AD.

 

According to AD p.2.6 and 2.18 - space around the breathe valve in the hemisphere shape is being protected R=5 m, Н=5 m.

 

Protection of buildings and structures against lightning discharges is ensured by lightning rods. A lightning rod is a device rising above the facility that diverts lightning current into the ground without entering the facility. It comprises a lightning rod that directly receives the lightning discharge, a down conductor and a ground electrode.

 

The set of measures to provide the required lightning protection to VST-20000 is offered by the following solutions:

  1. Air terminal masts are used as lightning rods, they are being welded to the metal structure 14 m high (fixation to 2 m from the top mark).
  2. VST bodyframe is used as a down conductor.
  3. VST bodyframe is connected to the groundign device in places of lightning rods fixation.
  4. Stainless steel pins 3 m long are used as a vertical ground electrodes.
  5. Copper-bonded steel tape with the cross-section of 40x4 mm uniting all ground electrodes is used as a horizontal ground electrode. Deepening - 0,5- 0.7 m. The distance to the bodyframe/VST foundation is at least 1 m.
  6. Connection to the grounding device is carried out with the help of clamps ZZ-005-064.

 

Grounding device resistance calculation:

Vertical electrode resistance:

where ρэкв - equivalent soil resistivity - 100 Ohm*m;

L – vertical electrode length - 3 m;

d – vertical electrode diameter - 0,016 m;

T – deepening - the distance from the ground surface to the ground electrode system - 2 m;

where t  is the deepening of the electrode top - 0,5 m

 

Horizontal electrode resistance:

where ρэкв - equivalent soil resistivity - 100 Ohm*m;

b - width of the horizontal electrode tape - 0.04 m;

h - horizontal electrode laying depth -0.5 m;

Lгор – horizontal electrode length - 132 m.

 

Impedance of the grounding device:

where n-number of kits, vertical ground electrodes -4 pc., horizontal ground electrode - 1 pc.;

Kисп – utilization ratio, 0.75;

 

The design resistance of the grounding device is 1,92 Ohm.

 

Results of calculations for the protection zone in compliance with the IS:

Air terminal mast № 1- 4 (ZZ-201-014-3):

h = 30 m;

Height of the cone according to the IS chart. 3.4:

h0 = 0.8*h = 24 m;

The radius of the cone according to the IS chart. 3.4:

r0 = 0.8*h = 24 m;

Distance between the lightning rods:

L = 28,2 m;

The ultimate distance between the lightning rods, according to the IS chart.3.6:

Lmax = 4,75*h = 142,5 m;

L0 = 2,25*h = 67,5 m;

There is no vertical clearance.

For a protection zone with the required reliability, the radius rx at the height hx = 18 m is determined as:

For a protection zone with the required reliability, the radius rx at the height hx = 23 m is determined as:

 

Location of equipment and protection zone are shown in figure 1.

 

The list of equipment and required materials is given in Table 1.

Молниезащита РВС

условные обозначения Type Codes
молниеприемник мачта высотой 14 м air terminal mast 14 m high
полоса стальная оцинкованная сечением  40*4 мм galvanized steel tape with the cross-section of 40*4mm
пространство над дыхательным клапаном space over the vent valve
вертикальный заземлитель 3 м vertical ground electrode 3 m
зона защиты protection zone

Figure 1 - Arrangement of equipment and protection zone.

 

Table 1 - Materials requirement list.

№ Product item Name Quantity, pcs. Unit weight, kg Note
1. ZZ-201-014-3 ZANDZ Vertical air-terminal mast 14 m (galvanized steel; for welding) 4    
2. ZZ-502-404-38 ZANDZ galvanized steel tape (40*4 mm; coil of 38,5 m) 4 1,26 In meters
3. ZZ-001-165 ZANDZ Stainless steel threaded ground pin (D16; 1.5 m; 5/8 UNC) 8 2,35  
4. ZZ-002-161 ZANDZ Stainless steel threaded coupler (5/8 UNC) 5 0,082  
5. ZZ-003-061 ZANDZ Starting tip 4 0,05  
6. ZZ-004-060 ZANDZ Driving head for a jackhammer 2 0,09  
7. ZZ-005-064 ZANDZ Clamp for connecting conductor (up to 40 mm) 12 0,16  
8. ZZ-006-000 ZANDZ Conductive grease 1 0,10  
9. ZZ-007-030 ZANDZ Waterproof tape 3 0,40  
10. ZZ-008-000 ZANDZ Header for a jackhammer (SDS max) 1 0,50  

 

Do you have any questions on grounding and lightning protection of VST-20000? Please contact our ZANDZ Technical center!

 

 

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