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

2003 ◽  
Vol 125 (2) ◽  
pp. 177-181 ◽  
Author(s):  
John H. Smith ◽  
Mahendra D. Rana ◽  
Clark Hall
Keyword(s):  
High Pressure ◽  
Experimental Work ◽  
Burst Pressure ◽  
Periodic Inspection ◽  
Critical Flaw ◽  
Analytical Procedures ◽  
Corrosion Pits ◽  
Assessment Procedures ◽  
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.

scholarly journals Correction for Longitudinal Stress in the Assessment of Corroded Line Pipe

1998 ◽  
Author(s):  
K. Andrew Roberts ◽  
Roy J. Pick
Keyword(s):  
Finite Element ◽  
Finite Element Modeling ◽  
Correction Factor ◽  
Circumferential Stress ◽  
Burst Pressure ◽  
Longitudinal Stress ◽  
Line Pipe ◽  
Element Modeling ◽  
Corrosion Pits ◽  
Assessment Procedures

It is common to assess corroded line pipe using ASME B31-G, its Canadian equivalent CSA Z662 Clause 10.8.2, or more recently RSTRENG. These techniques consider only the circumferential stress in the pipe in predicting the burst pressure of corroded pipe. This paper describes the results of experiments and finite element modeling to investigate the effect of longitudinal stress on the burst pressure of pipe with isolated corrosion pits. The results are used to develop a correction factor applicable to the assessment procedures listed above.

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

2004 ◽  
Vol 126 (2) ◽  
pp. 202-207 ◽  
Author(s):  
Mahendra D. Rana ◽  
John H. Smith
Keyword(s):  
High Pressure ◽  
Test Methods ◽  
Ultrasonic Test ◽  
Flaw Size ◽  
Safety Regulations ◽  
Wide Range ◽  
Critical Flaw ◽  
Test Pressure ◽  
Assessment Procedures ◽  
Seamless Steel

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 [1]. 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 of any 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 of the 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.

Experimental Verification of Fracture Toughness Requirement for Leak-Before-Break Performance for 155–175 ksi Strength Level Gas Cylinders

1987 ◽  
Vol 109 (4) ◽  
pp. 435-439 ◽  
Author(s):  
M. D. Rana
Keyword(s):  
Fracture Toughness ◽  
High Pressure ◽  
Plane Stress ◽  
Experimental Work ◽  
Strength Level ◽  
State Problem ◽  
Gas Cylinder ◽  
Gas Cylinders ◽  
Leak Before Break

This paper deals with a determination of the fracture toughness requirement to obtain leak-before-break performance for a 155–175 ksi strength level high-pressure gas cylinder. Analytical LEFM methods along with Irwin’s KIc-Kc equation related by the parameter βIc were used to predict the fracture toughness requirement for the plane-stress fracture state problem. Experimental work was conducted on flawed cylinders to quantify the fracture toughness requirement for leak-before-break performance. The results indicated that the analytically predicted toughness requirement is 4 to 25 percent higher than that established experimentally. The results also indicated that the minimum specified KIc(J) value of 85 ksi in. (93.5 MPam) for the gas cylinder is sufficiently higher than the analytically and experimentally established toughness values to provide the desired leak-before-break performance.

Technical Basis for Acceptance/Rejection Criteria for Flaws in High Pressure Gas Cylinder

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Mahendra D. Rana ◽  
John H. Smith ◽  
Henry Holroyd
Keyword(s):  
High Pressure ◽  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Operating Conditions ◽  
Flaw Size ◽  
Technical Report ◽  
Critical Flaw ◽  
Technical Basis ◽  
Gas Cylinders

The objective of this paper is to present the technical basis used for developing acceptance/rejection limits for seamless, high pressure gas cylinders that can be used at the time of retesting the cylinders. The development of acceptance/rejection limits for cylinders is done in three steps. First, the “critical flaw sizes” (e.g., depth and length or area) for selected types of flaws are established by an analysis procedure that has been verified by experimental tests. Next the “allowable flaw sizes” are calculated by 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. Finally, the “acceptance/rejection criteria” is established to take into account other factors, such as all the expected operating conditions that the cylinders may see in service, and the reliability and detectability of the specific inspection equipment to be used and to adjust the allowable flaw sizes to provide an additional margin of safety. This acceptance/rejection limits have been incorporated in a recently published ISO Technical Report No. TR 22694:2008 (2007, “Gas Cylinders—Methods for Establishing Acceptance/Rejection Criteria for Flaws in Seamless Steel and Aluminum Alloy Cylinders at Time of Periodic Inspection and Requalification,” The International Standards Organization, Geneva, Switzerland, Technical Report No. 22694). In this work, the API 579 “Recommended Practice for Fitness-for-Service” (2000, API 579: Recommended Practice for Fitness-for-Service, 1st ed., American Petroleum Institute, Washington, DC) was used to calculate the critical flaw sizes for a range of cylinder sizes and strength levels. For this study, the critical flaw size is defined as the size of the flaw that will cause the cylinders to fail at the test pressure of the cylinder. The results of flawed-cylinder burst tests were used to experimentally verify the calculated critical flaw sizes. The allowable flaw sizes were then calculated by using well established fatigue crack growth rate data for steel and aluminum alloys to allow for the expected amount of fatigue crack growth that may occur during the specified retesting intervals. A limited number of tests was conducted to verify the allowable flaw size calculations. Further adjustments are made to the allowable flaw sizes to define the acceptance/rejection criteria to be used during cylinder retesting.

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

2002 ◽  
Author(s):  
John H. Smith ◽  
Mahendra D. Rana
Keyword(s):  
High Pressure ◽  
Test Methods ◽  
Ultrasonic Test ◽  
Flaw Size ◽  
Safety Regulations ◽  
Wide Range ◽  
Critical Flaw ◽  
Test Pressure ◽  
Assessment Procedures ◽  
Seamless Steel

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 [1]. 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 of any 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 of the 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.

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