1、STP-PT-006DESIGNGUIDELINES FORHYDROGEN PIPINGAND PIPELINESSTP-PT-006 DESIGN GUIDELINES FOR HYDROGEN PIPING AND PIPELINES Prepared by: Louis E. Hayden Jr., PE President, Louis Hayden Consultants Adjunct Professor, Mechanical Engineering Lafayette College M. Erol Ulucakli, Ph.D. Associate Professor, M
2、echanical Engineering Lafayette College Date of Issuance: December 7, 2007 This report was prepared as an account of work sponsored by ASME Pressure Technology Codes design life considerations; nondestructive examination (NDE) recommendations; in-service inspection (integrity management) recommendat
3、ions; research needs and recommendations. The scope of this report includes all common metallic piping and pipeline materials used in the construction of piping and pipeline systems, of seamless and welded construction; composite reinforced welded or seamless metallic-lined piping and pipelines that
4、 are currently commercially manufactured and for which technical design data is available; composite reinforced plastic-lined piping and pipelines that are currently commercially manufactured and for which technical design data are available. Design factors are developed considering the operating co
5、nditions, internal hydrogen environment within the piping and pipeline systems and the effect of dry hydrogen gas on the material of construction. Composite piping and pipeline line pipe are considered as hoop-wrapped construction with liners capable of withstanding longitudinal loads. Other examina
6、tion and inspection recommendations are made using similar considerations. Research recommendations are made based on lack or vagueness of existing data or where the research results were not readily adaptable to engineering use. Design Guidelines for Hydrogen Piping and Pipelines STP-PT-006 1 1 INT
7、RODUCTION Depletion of fossil fuels and the search for other sources of energy has been a current endeavor of mankind. Gaseous hydrogen is believed to play an important role in this endeavor and a “hydrogen economy” is a strong possibility within the next 50 years. In such a scenario, large scale pr
8、oduction, storage, and transportation of hydrogen gas will become necessary. The objective of this work is to provide design guidelines for piping and pipelines transporting hydrogen gas under pressure. It is well documented that the hydrogen has no beneficial effects on steels but only detrimental
9、effects. The term “hydrogen damage” represents a number of processes by which the load-carrying properties of metals, often in combination with applied and residual stresses, are reduced due to the presence of hydrogen. Hydrogen damage occurs most frequently in carbon and low-alloy steels while many
10、 metals and alloys are susceptible to it. Hydrogen damage can severely restrict the use of certain materials. The containment and pressurization of hydrogen gas within metallic pipes is not a new concept or process. Hydrogen has been used in chemical processes for many years and industrial gas compa
11、nies have produced, stored and transported hydrogen in its gaseous and liquid forms in the United States, Europe, and in other parts of the world. It is believed that piping and pipeline systems will need to be operated at pressures with possible cyclic pressure loading in excess of our current oper
12、ating regimes. It is expected that hydrogen piping systems will have to be operated up to 15,000 psig (100 MPa) and that transport pipelines will operate up to 3000 psig (20 MPa) and both piping and pipeline systems will be operating at or below 300F (150C). In doing so, the metallic pipe materials
13、in use today could be placed in an operating environment for which we have little or no data on their mechanical properties and behavior in a dry hydrogen environment. This report deals primarily with the bulk properties of the material, however localized properties have been considered. Components
14、mechanical strength may be reduced for materials susceptible to hydrogen embrittlement in the presence of stress concentrations, such as weld reinforcements, threads, etc. 29. This report provides recommendations to the ASME B31.12 Hydrogen Piping and Pipelines Section Committee for design factors f
15、or commonly used metallic piping materials. The use of nonmetallic materials has also been considered and where design information is available, guidance has been provided. These factors are to be applied to the design process information contained within ASME B31.12 Hydrogen Piping and Pipeline Cod
16、e. In developing design factors industry standards, technical references, research reports and technical presentations were reviewed. A discussion is presented to establish the major concerns with hydrogen gas embrittlement of currently used pipe materials and how the material properties of these al
17、loys are affected. With these effects in mind the rationale for the design factors and the method used to derive them is provided. STP-PT-006 Design Guidelines for Hydrogen Piping and Pipelines 2 2 DEFINITIONS A Cross-sectional area Ao Initial cross-sectional area C Hydrogen concentration E Modulus
18、of elasticity da/dn Fatigue crack propagation speed e Engineering strain, (l lo) / lo , equal to for small strains less than 2% f Design factor FRP Fiber-reinforced plastic l Length of test bar P Axial force, pressure r Radius R Universal gas constant S Nominal engineering stress, P/Ao SMYS Specifie
19、d minimum yield strength SYYield strength SUUltimate strength, Pmax/Ao T Temperature (absolute) t Thickness True stress, P/A, S(1 + e) , equal to S for small strains less than 2% dDesign stress f True fracture stress, Pf/Af kkHydrostatic (average stress) hHoop stress rrRadial stress TAn alternative
20、symbol for ultimate tensile strength YAn alternative symbol for the yield stress zzAxial stress True or natural strain, d = dl/l, = ln (l/lo) = ln (A/Ao ) fTrue fracture strain or ductility = ln (Ao/Af) = ln 100/(100 % RA) %EL Percent elongation, 100 (lf lo)/lo%RA Percent reduction in area, 100 (Ao
21、Af)/Ao VHPartial molar volume Subscripts d design f fracture g gage k kilo o initial T ultimate tensile x, y, z coordinates Y yield Unit Conversions 1 psi = 6.894757 kPa 1 ksi = 1000 psi Design Guidelines for Hydrogen Piping and Pipelines STP-PT-006 3 3 REVIEW OF HYDROGEN EFFECTS ON PIPING AND PIPEL
22、INE MATERIALS 3.1 Overview of Metallic Pipe Materials 3.1.1 Hydrogen Damage and the Influence of Pressure Hydrogen Damage: A major concern in designing piping and pipeline systems for use in hydrogen service is the hydrogen damage. There are many ways in which hydrogen can be retained in steels to c
23、ause damage and pure hydrogen gas is one of them. Hydrogen gas (atomic) enters the metals by surface absorption and diffuses through the metal and eventually causes damage. Damages (also called attacks) are categorized and cover many industries. This report is focused on the effects of processes gro
24、uped under “hydrogen embrittlement.” These are (1) hydrogen environment embrittlement, (2) hydrogen stress cracking, and (3) the loss in tensile ductility. These phenomena occur at temperatures approximately below 200C. Hydrogen-induced embrittlement depends on factors such as material strength, com
25、position and heat treatment/microstructure, gas pressure and concentration, temperature, and the type of mechanical loading (e.g., strain rate). Hydrogen environment embrittlement (HEE) occurs during the plastic deformation of alloys in contact with hydrogen gas. It is dependent on strain rate. The
26、degradation of the mechanical properties is greatest when the strain rate is low and the hydrogen gas pressure is high 5, 19. Hydrogen stress cracking, also known as hydrogen-induced cracking or static fatigue, occurs when a steel containing hydrogen fails at a stress that is below its yield strengt
27、h (or much below its tensile strength 32). This phenomenon is characterized by a delayed brittle fracture of a normally ductile alloy under sustained load in the presence of hydrogen. Hydrogen stress cracking is related to the absorption of hydrogen and a delayed time to failure during which hydroge
28、n diffuses into the regions of high triaxial stress. The third mode of hydrogen damage in this category is the “loss in tensile ductility,” in which large decreases in elongation and ductility is observed often in lower strength alloys that are exposed to hydrogen. The loss in tensile ductility is s
29、ensitive to strain rate and increases as the strain rate decreases. High-strength steels were found to be susceptible to both brittle and delayed fracture at very low hydrogen concentrations. Also, delayed failures have been observed at applied stresses less than one-tenth of the yield strength in n
30、otched specimens of high strength steels 31. It was found that substantially greater hydrogen concentrations were necessary to induce brittleness in lower- strength quenched and tempered steels. HEE will be further discussed section 3.1.2 below. High-temperature hydrogen attack is another form of hy
31、drogen damage that occurs in steels exposed to high-temperature and high-pressure hydrogen. At temperatures approximately above 200C (400F), a form of decarburization occurs in the metal. It is due to the formation of methane bubbles in the grain boundaries by chemical reaction between carbon and hy
32、drogen. The discussion in this report will be restricted to temperatures below 200C. API 941 should be consulted for hydrogen service temperatures above this threshold 5. The Influence of Pressure: Pressure of hydrogen clearly is one of the important independent variable in pipeline design and opera
33、tion. First, it contributes to the state of stress in the pipe. Second, absorption of hydrogen gas on the metal surface is a function of pressure and amount of gas absorbed increases as the pressure increases. Third, pressure controls the diffusion process of hydrogen into the metal since the diffus
34、ion coefficient is a function of pressure. The influence of elevated hydrogen pressure on the strength of steels has been experimentally investigated 24, 33, 34. Walter and Chandler 24 tested AISI 310 stainless steel and ASTM STP-PT-006 Design Guidelines for Hydrogen Piping and Pipelines 4 A-302 at
35、hydrogen test pressures ranging between 1 atm and 10,000 psi (69 MPa). They found that the degree of hydrogen environment embrittlement to be more severe at higher hydrogen pressures but could be considerable at lower pressures extending down to 1 atm pressure. The reduction of tensile properties in
36、 hydrogen was found to be a linear function of the square root of hydrogen pressure. The influence of hydrogen pressure, from 1 atm to 2200 psi (15 MPa), on the embrittlement of unnotched 0.22% carbon steel specimens was determined 32. The results showed that ductility, as measured by percent elonga
37、tion, decreased by increasing hydrogen pressure, but even at 10 atm there was a significant decrease in ductility. A pipeline steel similar to X-42 was tested 33 under high pressure hydrogen from 1 atm to 2000 psi (14 MPa) and high susceptibility to hydrogen was found. Approximately above 1000 psi (
38、7 MPa) 40% change in reduction of area was observed. Reduction In Tensile Properties01020304050602040608010120Square Root of Hydrogen Pressure (psia)PrecentReductionfromHeilumReduction in Notch StrengthUnnotched Ductility (R.A)Figure 1 Reduction of Tensile Properties in Hydrogen from those in Helium
39、 as a Function of Hydrogen Pressure for ASTM A-302 Adapted from 24 The reduction of tensile properties in hydrogen was found to be a linear function of the square root of hydrogen pressure as shown in Figure 1. The notch strength and unnotched specimen ductility reductions extrapolate to zero effect
40、s at zero hydrogen pressure 24. The reduction in notched specimen ductility, as in area reduction, also shows linear relationship with the square root of hydrogen pressure on Figure 1 between zero and 30 psia. It may also be noted that the crack growth rate of 4130 steel in hydrogen was a linear fun
41、ction of the square root of hydrogen pressure 35. Hydrogen embrittlement (HE) as introduced above includes all of the effects that piping and pipeline alloys might experience in dry hydrogen gas at ambient temperature. These effects vary from very slight to very severe. Proper design and selection o
42、f materials can minimize the effects of HE. In Design Guidelines for Hydrogen Piping and Pipelines STP-PT-006 5 general, the effects of HE which amount to the degradation of mechanical properties are the greatest when the strain rate is low and the hydrogen pressure and purity is high 5, 19. These a
43、re the exact operating conditions expected for piping and pipeline systems in the new hydrogen infrastructure. Loss of Ductility due to Embrittlement: The effects of hydrogen on yield and tensile properties of metals and alloys have been investigated for many years. Tests have been performed using n
44、otched and unnotched specimens with high and low rates of strain. The results of investigations indicate that while there are changes in tensile properties, the most sensitive indicators of these tests are the reduction in area (%RA) and reduced elongation (%EL) at the fracture. Furthermore, percent
45、 reduction in area at fracture is preferred by investigators in reporting their data. It is well known that the decrease in tensile ductility is sensitive to strain rate and becomes more pronounced as strain rate decreases 5. Many materials showed significant change in RA when tested in hydrogen gas
46、 while others were not affected and showed no loss. Those alloys most affected were high nickel- or nickel-based alloys, high strength steels, high-strength stainless steels and titanium alloys. Those least affected were aluminum alloys, stable austenitic stainless steels and Oxygen-Free High Conduc
47、tivity (OFHC) copper. Carbon steels as used in many piping and pipeline systems have shown a loss of RA as high as 40% when tested in hydrogen compared to tests in air. In comparison, 316 stainless steel and 6061-T6 aluminum show no change or a modest gain in RA when tested in hydrogen 18. 3.1.2 Hyd
48、rogen Stress Cracking In the presence of hydrogen gas the resistance to cracking of some materials is reduced. The failure manifests itself as cracking at sustained stress levels below materials yield strength. This phenomenon was referred to as hydrogen stress cracking (HSC) above. It usually occur
49、s at room temperature for susceptible materials (e.g., carbon steel). HSC effects do not occur at cryogenic temperatures or above 150C (302F) 5. The susceptibility of steels to HSC increases with increasing yield and tensile strength. This mode of failure has been observed in the HAZ of welds and other areas of high residual stress. The term “sustained load cracking” has been used to describe hydrogen-assisted slow crack growth in pipeline steels 17. 3.2 Overview of Nonmetallic Pipe Materials Currently very little
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