Mahendra D. Rana

Prediction of Fracture Stresses of High Pressure Gas Cylinders Containing Cracklike Flaws

Full scale tests were conducted on high pressure gas cylinders containing cracklike flaws. The cylinders were then pressurized to destruction, and the membrane hoop stress at failure in the cylinder wall was calculated from the failure pressure. Mechanical properties, including tensile and fracture data, were obtained on specimens representing the heats of the tested cylinders. Analyses were performed to predict the failure stresses using several methods available in the open literature. This paper presents the results of the predicted and measured fracture stresses.

Development of ASME Section X Code Rules for High Pressure Composite Hydrogen Pressure Vessels With Nonload Sharing Liners

The Boiler and Pressure Vessel Project Team on Hydrogen Tanks was formed in 2004 to develop Code rules to address the various needs that had been identified for the design and construction of up to 15000 psi hydrogen storage vessel. One of these needs was the development of Code rules for high pressure composite vessels with non-load sharing liners for stationary applications. In 2009, ASME approved new Appendix 8, for Section X Code which contains the rules for these vessels. These vessels are designated as Class III vessels with design pressure ranging from 20.7 MPa (3,000 ps)i to 103.4 MPa (15,000 psi) and maximum allowable outside liner diameter of 2.54 m (100 inches). The maximum design life of these vessels is limited to 20 years. Design, fabrication, and examination requirements have been specified, included Acoustic Emission testing at time of manufacture. The Code rules include the design qualification testing of prototype vessels. Qualification includes proof, expansion, burst, cyclic fatigue, creep, flaw, permeability, torque, penetration, and environmental testing.

Technical Basis and Application of New Rules on Fracture Control of High Pressure Hydrogen Vessel in ASME Section VIII, Division 3 Code

As a part of an ongoing activity to develop ASME Code rules for the hydrogen infrastructure, the ASME Boiler and Pressure Vessel Code Committee approved new fracture control rules for Sec. VIII, Division 3 vessels in 2006. These rules have been incorporated into new Article KD-10 in Division 3. The new rules require determining fatigue-crack-growth rate and fracture resistance properties of materials in high pressure hydrogen gas. Test methods have been specified to measure these fracture properties, which are required to be used in establishing the vessel fatigue life. An example has been given to demonstrate the application of these new rules.

Fatigue Assessment of a Weld Joint of a Pressure Vessel

A full-penetration weld on both sides between a shell and a flat head is evaluated for fatigue strength by four methods, two based on structural stress and two on notch stress. Internal pressure is cycled with constant amplitude. The allowable cycles are calculated by each method. The number of cycles for the same geometry and loading varies widely, ranging from 4,835 to 137,000.Copyright

Technical Basis for ASME Section VIII Code Case 2235 on Ultrasonic Examination of Welds in Lieu of Radiography

In 1996, Code Case 2235, which allows ultrasonic examination of welds in lieu of radiography for ASME Section VIII Division 1 and Division 2 vessels, was approved by the ASME B&PV Code Committee. This Code Case has been revised to incorporate: I) a reduction in minimum usable thickness from 4 (107.6 mm) to 0.5 (12.7 mm), and 2) flaw acceptance criteria including rules on multiple flaws. A linear elastic fracture mechanics procedure has been used in developing the flaw acceptance criteria. This paper presents the technical basis for Code Case 2235.

DEVELOPMENT OF ASME SECTION X CODE RULES FOR HIGH PRESSURE COMPOSITE HYDROGEN PRESSURE VESSELS WITH NON-LOAD SHARING LINERS

The Boiler and Pressure Vessel Project Team on Hydrogen Tanks was formed in 2004 to develop Code rules to address the various needs that had been identified for the design and construction of up to 15,000 psi hydrogen storage vessel. One of these needs was the development of Code rules for high pressure composite vessels with non-load sharing liners for stationary applications. In 2009, ASME approved new Appendix 8, for Section X Code which contains the rules for these vessels. These vessels are designated as Class III vessels with design pressure ranging from 20.7 MPa (3,000 psi) to 103.4 MPa (15,000 psi) and maximum allowable outside liner diameter of 2.54 m (100 inches). The maximum design life of these vessels is limited to 20 years. Design, fabrication, and examination requirements have been specified, included Acoustic Emission testing at time of manufacture. The Code rules include the design qualification testing of prototype vessels. Qualification includes proof, expansion, burst, cyclic fatigue, creep, flaw, permeability, torque, penetration, and environmental testing.Copyright

Prediction of Fracture Stresses of High Pressure Gas Cylinders Containing Crack Like Flaws

Full scale tests were conducted on high pressure gas cylinders containing crack-like flaws. The cylinders were then pressurized to destruction and the membrane hoop stress at failure in the cylinder wall was calculated from the failure pressure. Mechanical properties including tensile and fracture data were obtained on specimens representing the heats of the tested cylinders. Analyses were performed to predict the failure stresses using several methods available in the open literature. This paper presents the results of the predicted and measured fracture stresses.Copyright

The Use of “Fitness for Service” Assessment Procedures to Establish Allowable Flaw Sizes in Steel Cylinders

As part of the U.S. Department of Transportation safety regulations, seamless steel cylinders that are used to transport high-pressure gases are required to be periodically retested during their lifetime [I]. The safety regulations have recently been revised to permit the use of ultrasonic methods for retesting steel cylinders. These ultrasonic test methods permit the quantitative determination of the size ofany flaws that are detected in the cylinders. Therefore, to use these ultrasonic test methods it is required that quantitative, allowable flaw sizes be established to set acceptance/rejection limits for the cylinders at the time of retesting. Typical flaws that can occur in seamless steel cylinders during service are line corrosion, gouges, local thin areas of corrosion, notches, and cracks. To establish allowable flaw sizes for seamless steel cylinders, an assessment of typical flaws that occur in seamless cylinders was first carried out to establish the critical flaw sizes (e.g., depth and length or area) for selected types of flaws. The critical flaw size is the size ofthe flaw that will cause the cylinders to fail at either the designated test pressure or at the marked service pressure. The API Recommended Practice 579 Fitness-for-Service was used to calculate the critical flaw sizes for a range of cylinder sizes and strength levels [2]. Several hundred monotonic hydrostatic, flawed-cylinder burst tests were conducted as part of an International Standards Organization (ISO) test program to evaluate the fracture performance of a wide range of steel cylinders [3]. The results of these tests were used to verify the calculated critical flaw sizes that were calculated using the API 579 procedures. These results showed that the analysis conducted according to API 579 always underestimated the actual flaw sizes to cause failure at test pressure or at service pressure. Therefore, the Fitness for Service assessment procedures can be used reliably to establish the critical flaw sizes for cylinders of all sizes and strength levels. After the critical flaw sizes to cause failure of the cylinders at both the test pressure and the service were established, the allowable flaw sizes were calculated for a wide range of the cylinder types and strength levels. This was done modifying (reducing) the size of the critical flaw sizes for each cylinder by adjusting for fatigue crack growth that may occur during the use of the cylinder. This results in the final allowable flaw size criteria that are used for defining the acceptance or rejection of the cylinders during retesting. This paper presents the results of the analytical and experimental work that was performed to establish the critical flaw sizes and allowable flaw sizes for a wide range of high-pressure gas cylinders.

The Use of “Fitness for Service” Assessment Procedures to Establish Critical Flaw Sizes in High-Pressure Gas Cylinders

Typical flaws that can occur in high-pressure seamless gas cylinders during service are: corrosion pits, line corrosion, gouges, local thin areas of corrosion, and cracks. The required periodic inspection of seamless cylinders requires that critical flaw sizes be established. To establish critical flaw sizes an assessment of typical flaws that occur in seamless cylinders was carried out using the analytical procedures described in the API Recommended Practice 579 Fitness-for-Service. To verify the API 579 analysis procedures, a number of hydrostatic tests were conducted on selected cylinders with various sizes of flaws to determine the burst pressure of cylinder containing flaws. These results showed that the analysis conducted according to API 579 reliably estimated the actual measured burst pressure of the cylinders for all flaw sizes and types. After the API 579 analysis procedures were verified by these experiments to reliably estimate the burst pressure of cylinders with various types of flaws, the critical flaw sizes to cause failure of the cylinders at selected pressures were determined by analysis. This paper presents the results of the analytical and experimental work that was performed on the assessment procedures to establish the critical flaw sizes in high-pressure gas cylinders.

Failure Investigation of a 500 Gallon Liquid Nitrogen Storage Tank

A 500-gallon liquid nitrogen (LN2 ) storage tank failed while being filled by a pump truck. The failure of the tank was the first of its kind and quite unusual. The cryogenic storage tank was a typical double-wall construction. The inner and outer vessels were made of 5083-O aluminum and low-carbon ferritic steel, respectively. The inner liquid container was an ASME Section VIII, Div. 1 Code stamped vessel. The outer vessel was not Code stamped since it was designed for vacuum service. The outer vessel was made to support the inner vessel and insulation material and maintain this vacuum for thermal insulation purposes. The heads on both the outer carbon steel and the inner aluminum vessel were fractured at a girth weld resulting in a rocketing of the vessel. A detailed investigation was conducted to find the root cause. This investigation showed that a failure of a nozzle in the annular area between the two tanks caused LN2 to pour into that area. The warmer carbon steel outer shell caused the LN2 to vaporize and rapidly pressurize the annular area. This pressurization of the annular region caused the inner aluminum tank to buckle and resulted in the head separating from the main (inner) cylinder during the buckling process. The liquid LN2 from the inner tank flowed into the outer tank (along with possible flow from the truck) and the pressure continued to increase as the LN2 level increased. The pressure in the annular space reached critical level to cause the failure of the weld in the carbon steel tank. This paper describes the analyses that were carried out for this investigation which involved determining the crack-driving force from the combined weld residual stresses, thermal stresses from the LN2 liquid level, and pressure.Copyright