Cargo Tank Vacuum Damage Jack Rademacher Chief Engineer

Transcription

1 Cargo Tank Vacuum Damage Jack Rademacher Chief Engineer

2 2014 WALKER GROUP EXPO SUCK-IN EVENT A BAD WAY TO START YOUR DAY!!!

3 2014 WALKER GROUP EXPO SUCK-IN EVENT The concluding event of the 2014 Walker Group Expo. A Controlled Demonstration of a Tank Trailer Vacuum Collapse

4 2014 WALKER GROUP EXPO SUCK-IN EVENT Why Destroy a Cargo Tank by Vacuum Implosion? Verification of engineering structural integrity vacuum design calculations and FEA. Educate our customers tank operators to potential catastrophic damage caused when a cargo tank is not properly vented during unload. Educate the industry to the importance of proper training.

5 2014 WALKER GROUP EXPO SUCK-IN EVENT Continuing Test Program. 3 round, stainless tanks imploded. 5 aluminum, elliptical implosions.

6 2014 WALKER GROUP EXPO SUCK-IN EVENT The Specimen for Destruction.

7 TEST VESSEL DIMENSIONS 63 ⁷/₈ I.D min thickness 54 max ring space

8 The Math Behind Cargo Tank Vacuum Collapse What s your prediction? What vacuum pressure would you expect collapse? Where would you expect the collapse to first initiate?

9 The Math Behind Cargo Tank Vacuum Collapse ASME UG-28 Thickness of Shells and Tubes Under External Pressure Pa = Maximum Allowable External Pressure = 3.0 psi (6.11 Hg) ASME safety factor for vacuum is approximately 3⅟₂:1.

10 The Math Behind Cargo Tank Vacuum Collapse From Roark s Formulas for Stress & Strain Assumes a perfectly round vessel with no dents or distortion from welding. Pa = 4.48 psi (9.12 Hg) *** With Safety Factor = 2:1 Accounts for welding distortion and other factors.

11 Suck-In Video And now the video. Controlled Demonstration of a Tank Trailer Vacuum Collapse

12 The Math Behind Cargo Tank Vacuum Collapse The video is available on YouTube for you to use in your training programs

13 More Math Behind Cargo Tank Vacuum Collapse Boyle s Law Pressure exerted on the vessel is inversely proportional to the volume if temperature remains the same. p₁v₁ = p₂v₂ Or: p₂ = p₁v₁/v₂ (p = absolute pressure) Where

14 More Math Behind Cargo Tank Vacuum Collapse Example: Assume 60 gal of vapor space at 0 psig (14.7 psia) and pumping off 100 gal with no venting. p₂ = p₁v₁/v₂ = 14.7psia*60 gal/160gal = 5.5 psia = -9.2 psig (18.74 Hg) *** Does not consider compressive load created by product weight.***

15 More Math Behind Cargo Tank Vacuum Collapse Ideal gas law. Pressure exerted on the vessel is proportional to temperature if volume remains the same. p₁ T₁ = p₂ T₂ Or: p₂ = p₁t₂/t₁ (T = absolute Temperature = Rankine or Kelvin)

16 More Math Behind Cargo Tank Vacuum Collapse Example: Assume an empty tank that has just been steam cleaned with inside temp. of 200 F (660 R) that is closed up tight with no available venting and cools to 30 F (490 R). p₂ = p₁t₂/t₁ = 14.7psia* 490 R/ 660 R = 10.9 psia = -3.8 psig (7.74 Hg) *** Does not consider steam vapor condensing to water. Condensation could more than double the pressure.

17 More Math Behind Cargo Tank Vacuum Collapse Where might lower vacuum pressures be a factor? Single bulkhead design? Wide ring/baffle spacing?

18 The Math Behind Cargo Tank Vacuum Collapse The video is available on YouTube for you to use in your training programs