Tank Tie off Report for Pipes Albuquerque 1/3

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1 Tank Tie off Report for Pipes Albuquerque 1/3 Summary: The following report contains an analysis created by Core Engineering LLC for NuStar Energy. This report was commissioned to analyze anchor points on the roofs of storage tanks at the NuStar Albuquerque location. All pipes with supplied information were checked for their ability to function as tie off points. All pipes checked have some capability of use as a tie off point. Table 1 shows the data for each pipe tested and the amount of people it can support at a given time. Introduction: Storage tanks have pipes and protrusions on their roof. These protrusions can be used as an anchor so that they can serve as fall protection. In order for them to be used as anchors, they must meet the requirements laid out by OSHA. Figure 1: Pipe Nozzle Pictures [1] 1

2 Figure 2: Nozzle Locations [2] The piping is attached to the tank via a solid weld around the circumference in contact with the tank. Figure 2 shows an example of a nozzle attached to the tank roof and its relative location on the roof. Failure Modes: There are two failure modes that may affect the anchor points. The anchor points may fail in shear from the applied load or they may fail due to bending stress where the pipe is welded to the tank. Both of these failure modes will be examined to determine the loading necessary to cause failure to the pipe. The lowest force found to cause failure in either mode will then be compared to the OSHA standards to determine the tie off feasibility of the pipes. The pipes will also be checked for deflection according to OSHA standard. Analysis: The first step in the analysis will be to check for failure due to deflection caused by a 2,250 pound load. The nozzle can be treated as a cantilever anchored at one end. We will assume that the 2,250 pound load is applied at the maximum distance from the anchor such that it will cause the greatest deflection. Figure 3 shows an equivalent free body diagram of the analysis. Figure 3: Free Body Diagram 2

3 The governing equation for deflection is of a cantilever beam with a load applied at the maximum distance is: Displacement = Force Length3 3EI (1) The next test will be for shear failure of the pipe. Shear failure can occur in single and double shear. In the case of these anchors, single shear would be the method of failure and therefore it will be analyzed. For shear failure to occur, the load applied to the pipe must create a stress greater than the yield stress of the pipe (35 ksi). Since the cross sectional area is known for all anchors, simply multiplying the yield stress by the cross sectional area will give the required load to cause shear failure. Comparing this to the OSHA requirements of 5,000 pounds per person and using a safety factor of two leads to the number of people that can be supported by the anchor. The final method of failure would be at the weld due to bending stresses. A force applied at a distance from the anchor will cause a moment at the anchor point. This moment can cause the anchor to tear off the tank. The governing equation for bending stress of a cantilever beam with a load applied at the maximum distance is: σ = Force Length Z (2) Where Z is the section modulus of a pipe: Z = 0.78(R O 4 R I 4 ) R O (3) Now that the governing equations are known along with the necessary input data, an excel spreadsheet can be created to achieve the answers. The maximum bending stress and shear stress will be calculated after applying a factor of safety to the applied force. The higher of the two stresses will then be compared to the yield stress. The ratio between the higher of the two stresses and the yield stress will determine the number of people that can be supported by each anchor. 3

4 Figure 4: Excel Sheet for data output Results: The pipe was tested for multiple failure modes and the requirements set forth by OSHA standards. The table below lists the Tank, support description and viability of each pipe based on the calculated data. A factor of safety of two was used in the calculations. Name Table 1: Results 3M1 5M1 5M1 10M1 10M1 55M1 55M2 Center Vent- Manway Vent- Manway Center Center Post Flange Flange Post Post Diameter Height # of people supportable Conclusion: In conclusion, all pipes tested to be used as fall protection anchors are able to support workers. Only the pipes shown in table 1 were tested in the analysis. Failure within the roof panels is analyzed in a separate report. The number of people supportable by each anchor does not take into account the possibility of stress concentrations caused by multiple restraints on the same anchor point or corrosion damage. Multiple people attached to the same anchor point can also cause a hazardous work environment if the anchor ropes become tangled during work procedures. 4

5 References: [1] 3m-1_5m-1_10m-1 PowerPoint provided by NuStar [2] TK-3M1 Final PDF provided by NuStar and created by ROSEN USA [3] R.C. Hibbeler, Mechanics of Materials 8th Edition, January 11, 2011 [4] OSHA Regulations Standards 29 CFR, Standard Number App C 5