BS 7910:2005:2007 Edition
$215.11
Guide to methods for assessing the acceptability of flaws in metallic structures
| Published By | Publication Date | Number of Pages |
| BSI | 2007 | 306 |
PDF Catalog
| PDF Pages | PDF Title |
|---|---|
| 1 | BRITISH STANDARD |
| 2 | Committees responsible for this British Standard |
| 3 | Contents |
| 9 | Introduction |
| 10 | 1 Scope 2 Normative references |
| 11 | 3 Symbols and definitions |
| 21 | 4 Types of flaw |
| 22 | 5 Modes of failure and material damage mechanisms 5.1 The influence of the flaws listed in Clause 4 may be assessed, using this document, for the modes of failure and damage mechanisms listed below: |
| 23 | 5.2 The following is the recommended sequence of operations for carrying out an assessment for a known flaw. 5.3 Several levels of treatment of flaws are possible, depending on the application and materials data available. Three levels of dealing with fracture are included in Clause 7. Level 1 is a conservative preliminary procedure which is simple to employ. 6 Information required for assessment 6.1 General |
| 24 | 6.2 Essential data 6.3 Non-destructive testing |
| 25 | 6.4 Stresses to be considered |
| 26 | Linearization of stress distributions |
| 29 | Schematic representation of stress distribution across section |
| 30 | Procedure for resolving flaws normal to principal stress |
| 31 | 7 Assessment for fracture resistance 7.1 Background |
| 32 | Flow charts – General methods |
| 33 | Flowchart – Level 1 |
| 34 | Flowchart – Level 2 |
| 35 | Flowchart – Level 3 |
| 36 | Flaw dimensions |
| 37 | Planar flaw interactions |
| 38 | Planar flaw interactions |
| 39 | Planar flaw interactions (continued) |
| 40 | Planar flaw interactions |
| 43 | 7.2 Level 1 – Simplified assessment |
| 44 | Level 1A FAD |
| 46 | 7.3 Level 2 – Normal assessment |
| 48 | Level 2 FADs |
| 52 | 7.4 Level 3 – Ductile tearing assessment |
| 55 | Level 3A FAD with assessment locus for a known flaw 7.5 Further points |
| 56 | Example of non-unique solutions (schematic) Limits for slag inclusions and porosity |
| 57 | 8 Assessment for fatigue 8.1 Assessment procedures |
| 58 | Procedure for assessment of known flaws |
| 60 | 8.2 Data required for assessment |
| 61 | Stress ranges used in fatigue assessments |
| 63 | Schematic crack growth relationships |
| 64 | Recommended fatigue crack growth laws Recommended fatigue crack growth laws for steels in air |
| 65 | Recommended fatigue crack growth laws for steels in a marine environmenta |
| 66 | Recommended fatigue crack growth threshold, |
| 67 | 8.3 Probability of survival 8.4 General procedure for fracture mechanics assessment of planar flaws |
| 68 | 8.5 Basis of procedure for assessing flaws using quality categories Details of quality category |
| 69 | Quality category S-N curves for use in simplified fatigue assessments |
| 71 | 8.6 Assessment of planar flaws using quality categories |
| 73 | Assessment of surface flaws in axially-loaded material for simplified procedure |
| 74 | Assessment of surface flaws in axially-loaded material for simplified procedure |
| 75 | Assessment of surface flaws in flat material (no weld toe or other stress raiser) in bending for simplified procedure |
| 76 | Assessment of surface flaws in flat material (no weld toe or other stress raiser) in bending for simplified procedure |
| 77 | Assessment of embedded flaws in axially-loaded joints for simplified procedure |
| 78 | Assessment of embedded flaws in axially-loaded joints for simplified procedure |
| 79 | Assessment of weld toe flaws in axially-loaded joints for simplified procedure |
| 80 | Assessment of weld toe flaws in axially-loaded joints for simplified procedure |
| 81 | Assessment of weld toe flaws in axially-loaded joints for simplified procedure |
| 82 | Assessment of weld toe flaws in axially-loaded joints for simplified procedure |
| 83 | Assessment of weld toe flaws in axially-loaded joints for simplified procedure |
| 84 | Assessment of weld toe flaws in axially-loaded joints for simplified procedure |
| 85 | Assessment of weld toe flaws in joints loaded in bending for simplified procedure |
| 86 | Assessment of weld toe flaws in joints loaded in bending for simplified procedure |
| 87 | Assessment of weld toe flaws in joints loaded in bending for simplified procedure |
| 88 | 8.7 Assessment of embedded non-planar flaws using quality categories |
| 89 | Minimum values of |
| 90 | Limits for non-planar flaws in as-welded steel and aluminium alloy weldments Limits for non-planar flaws in steel weldments stress relieved by PWHT 8.8 Assessment of shape imperfections using quality categories |
| 91 | Acceptance levels for misalignment expressed in terms of stress magnification factor, km Acceptance levels for weld toe undercut in material thicknesses from 10 mm to 40 mm |
| 92 | 8.9 Estimation of tolerable sizes of flaws 9 Assessment of flaws under creep conditions 9.1 General |
| 93 | 9.2 Creep exemption criteria |
| 94 | Determination of the temperature T Temperature below which creep is negligible in 200 000 h |
| 95 | Determination of the time t(T) to achieve an accumulated creep strain of 0.2 % at a stress level equal to the proof strength 9.3 General restrictions and information requirements |
| 96 | 9.4 Crack beheaviour at high temperature Schematic behaviour of crack subjected to steady loading at elevated temperature |
| 97 | Schematic representation of crack propagation and failure conditions |
| 98 | 9.5 Assessment procedures |
| 99 | Procedure for creep assessment |
| 100 | Procedure for creep assessment |
| 104 | 10 Assessment for other modes of failure 10.1 Yielding due to overloading of remaining cross section 10.2 Leakage in pressure, liquid or vacuum containing equipment |
| 105 | 10.3 Environmental effects |
| 106 | Schematic diagrams of typical relationships between crack velocity and stress intensity factor during stress corrosion cracking |
| 108 | Types of corrosion fatigue crack growth behaviour |
| 109 | 10.4 Instability (buckling) |
| 110 | (normative) Evaluation under combined direct and shear stresses or mode I, II and III loads (normative) Evaluation under combined direct and shear stresses or mode I, II and III loads Introduction Outline of methodology Determination of Kr General Linear elastic stress intensity factor |
| 111 | The effective stress intensity factor Determination of K Procedure for determining ‘ Determination of L |
| 112 | (informative) Assessment procedures for tubular joints in offshore structures (informative) Assessment procedures for tubular joints in offshore structures Overview Introduction General procedure Stress analysis General |
| 113 | Assessment methodology for fatigue crack growth in tubular joints |
| 114 | Global structural analysis Local joint stress analysis Stress intensity factor solutions Evaluation methods Numerical solutions for tubular joints |
| 115 | Plate solutions Fatigue assessment Stress range Stress intensity factor range Initial flaw dimensions Limit to fatigue crack propagation |
| 116 | Fracture assessment Introduction Primary stresses Residual stresses Determination of Kr or Collapse parameter L |
| 118 | Flaw assessment (informative) Fracture assessment procedures for pressure vessels and pipelines (informative) Fracture assessment procedures for pressure vessels and pipelines General Suggested methodology for the fitness for purpose assessment of flaws in pressure vessels and pipelines Pressure vessels |
| 119 | Algorithm for pressure vessel flaw assessment |
| 120 | Pipelines Guidance for pressure vessels General Toughness data |
| 121 | Flaw size data Flaw type Stress analysis Guidance for oil and gas transmission pipelines |
| 122 | (normative) Stress due to misalignment (normative) Stress due to misalignment Calculation of stress magnification factor |
| 124 | Formulae for calculating the bending stress due to misalignment in butt joints |
| 125 | Formulae for calculating the bending stress due to misalignment in butt joints |
| 126 | Formulae for calculating the bending stress due to misalignment in butt joints |
| 127 | Formulae for calculating the bending stress due to misalignment in cruciform joints |
| 129 | (normative) Flaw recharacterization (normative) Flaw recharacterization Rules for recharacterization of flaws |
| 130 | (informative) A procedure for leak-before-break assessment (informative) A procedure for leak-before-break assessment General The leak-before-break diagram |
| 132 | Guidance on selection of assessment sites around a pipe system Detectable leakage procedure |
| 133 | Leak-before-break procedure |
| 134 | Leak-before-break procedure |
| 135 | Full leak-before-break procedure |
| 137 | Background notes and guidance on using the procedure General Flaw characterization |
| 138 | Detailed leak-before-break diagram |
| 139 | Example characterization of a complex flaw |
| 140 | Calculation of limiting crack lengths Calculation of flaw length at breakthrough (only required for the full leak-before-break procedure) |
| 141 | Schematic crack profiles at breakthrough |
| 142 | Recommended re-characterization of flaws at breakthrough for predominantly tensile loading |
| 143 | Recommended re-characterization of flaws at breakthrough for predominantly through-wall bend |
| 144 | Calculation of crack-opening areas |
| 145 | Crack opening area methods for simple geometrics and loadings |
| 146 | Leak rate calculations |
| 147 | Summary of surface roughness values from Wilkowski et al [124] Leak detection and crack stability following breakthrough |
| 148 | Assessment of results |
| 149 | Inclusion of creep effects General Limiting length of through-wall crack, Crack length at breakthrough, |
| 150 | Time required to detect leak, Time, |
| 151 | Calculate times to creep rupture at crack sizes Assess results |
| 152 | Unstable crack growth before creep rupture Rupture before unstable crack growth |
| 153 | Sensitivity studies (normative) The assessment of corrosion in pipes and pressure vessels (normative) The assessment of corrosion in pipes and pressure vessels Background Applicability General |
| 154 | Applicable flaws Exclusions |
| 155 | Factors of safety Assessment Procedure Terminology |
| 156 | Flow chart of assessment procedure |
| 157 | Safe working pressure estimate for a single flaw Single flaw dimensions |
| 158 | Interaction rules |
| 159 | Interacting flaw dimensions Interacting flaws General Safe working pressure estimate |
| 161 | Corrosion depth adjustment for flaws with background corrosion Projection of circumferentially interacting flaws |
| 162 | Projection of overlapping sites onto a single projection line Combining interacting flaws |
| 163 | Example of the grouping of adjacent flaws for interaction to find the grouping which gives the lowest estimated failure pressure |
| 164 | Circular locally thinned areas in uncracked spherical shells (Sims et al [136]) |
| 165 | Cross section of locally thinned area geometry on spherical shell Further assessment Recommendations for conducting non-linear finite element analysis of corrosion flaws in pipes and pressure vessels General |
| 166 | Modelling |
| 167 | Finite element stress analysis Assessment of analysis results Prediction of failure pressure |
| 168 | (normative) Reporting of fracture, fatigue or creep assessments (normative) Reporting of fracture, fatigue or creep assessments General Fracture assessments Analysis details Input data Results Sensitivity analysis |
| 169 | Fatigue assessments Method and criterion of acceptance Input data Results Sensitivity analysis Creep assessments Analysis details |
| 170 | Input data Results Sensitivity analysis (informative) The significance of weld strength mismatch on the fracture behaviour of welded joints (informative) The significance of weld strength mismatch on the fracture behaviour of welded joints General |
| 171 | Effect of mismatch on fracture toughness measurement General K CTOD and CTOD and J measurements in HAZs (see also Annex L) Effect of mismatch on flaw assessment procedures General aspects Effect of crack size and material work hardening rate Assessment of butt welds perpendicular to the applied tensile stress |
| 172 | Assessment of butt welds parallel to the applied tensile stresses Assessment of fillet welds Specific procedures for assessing effects of mismatch |
| 173 | (informative) Use of Charpy V-notch impact tests to estimate fracture toughness (informative) Use of Charpy V-notch impact tests to estimate fracture toughness Introduction Charpy/fracture toughness correlations Lower shelf and transitional behaviour |
| 174 | Flowchart for selecting an appropriate correlation for estimating fracture toughness from Charpy data |
| 175 | Lower shelf transitional behaviour based on the master curve Lower shelf transitional behaviour based on the master curve |
| 176 | Validity limits Upper limit for |
| 177 | Treatment of sub-size Charpy data (normative) Reliability, partial safety factors, number of tests and reserve factors (normative) Reliability, partial safety factors, number of tests and reserve factors General |
| 178 | Use of partial safety factors for fracture assessment Partial safety factors – General Partial safety factors on stress, flaw size, toughness and yield strength Target probability of failure (events/year) |
| 180 | Recommended partial factors for different target probabilities of failure Fracture toughness values: number of tests |
| 181 | Equivalent fracture toughness values to the minimum of three results [152] |
| 182 | Sensitivity analyses for fracture assessments General Reserve factors Evaluation of FL for a single primary stress |
| 183 | Three scenarios for the graphical determination of FL in the presence of |
| 184 | Level 2 assessments – Sensitivity analysis using reserve load factors Level 3 assessment – Sensitivity analysis using reserve load factors |
| 185 | Typical load factor variation graphs |
| 186 | Load factor variation with flaw size Level 3 analysis |
| 187 | Sensitivity analyses Guidance on determination of safe loading conditions |
| 188 | Preferred sensitivity curves |
| 189 | (normative) Fracture toughness determination for welds (normative) Fracture toughness determination for welds General Test philosophy |
| 190 | Microstructures in steel weldments Heat affected zones Weld metals Test requirements Materials Welding |
| 191 | Specimen geometry Test procedure Metallographic validation Number of tests required Analysis of test results |
| 192 | (normative) Stress intensity factor solutions (normative) Stress intensity factor solutions General |
| 193 | Net area, misalignment, stress concentration and bulging effects Flat plates Through-thickness flaws in plates Surface flaws in plates (Raju and Newman [165]) |
| 194 | Through-thickness flaw geometry Surface flaw |
| 196 | Elliptical integral Õ as a function of a/2c used for the calculation of |
| 197 | Stress intensity magnification factor |
| 198 | Stress intensity magnification factor Mm for surface flaws in tension (continued) |
| 200 | Stress intensity magnification factor |
| 201 | Stress intensity magnification factor, |
| 202 | Long surface flaws in plates [39] Embedded flaws in plates [165] Long surface flaw geometry Embedded flaw |
| 204 | Stress intensity magnification factor Mm for embedded flaws in tension (at point nearest material surface) |
| 206 | Stress intensity magnification factor |
| 207 | Edge flaws in plates [165] Edge flaw geometry |
| 208 | Corner flaw geometry Corner flaws in plates [165] |
| 209 | Corner flaws at hole [164] Corner flaw at hole geometry |
| 211 | Single corner crack at hole Curved shells General Curved shells under internal pressure |
| 212 | Curved shells under internal pressure and mechanical loads Through-thickness flaw in cylinder oriented axially |
| 213 | M |
| 214 | M |
| 215 | M |
| 216 | M |
| 217 | Through-thickness flaw in cylinder oriented cicumferentially |
| 218 | M |
| 219 | M |
| 220 | M |
| 221 | M |
| 222 | M Through-thickness flaw in spherical shell |
| 223 | M |
| 224 | Internal surface flaw in cylinder oriented axially Internal surface flaw in cylinder oriented circumferentially |
| 225 | M M |
| 226 | Long internal surface flaw in cylinder oriented axially Long internal surface flaw in cylinder oriented circumferentially |
| 227 | M External surface flaw in cylinder oriented axially |
| 228 | Mm and Mb for axial external surface flaw in cylinder |
| 229 | Long axial external surface flaw in cylinder Long circumferential external surface flaw in cylinder |
| 230 | Embedded flaws in shells Flaws in nozzles Welded joints Surface cracks at weld toes [see Figure 23a) to Figure 23c)] |
| 231 | Crack and welded joint geometries |
| 232 | Transverse load-carrying cruciform joint Values of v and w for axial and bending loading |
| 236 | Weld root flaws in cruciform joints [181] |
| 237 | Round bars/bolts Straight-fronted flaws in round bars [182] Semi-circular surface flaws in round bars [182] |
| 238 | Surface flaw Semi-circular surface flaws in bolts |
| 239 | Circumferential flaws in round bars [40] Tubular joints (not nozzles) Circumferential flaw in bolt |
| 240 | (normative) Simplified procedures for determining the acceptability of a known flaw or estimating the acceptable flaw size using Level 1 fracture procedures (normative) Simplified procedures for determining the acceptability of a known flaw or estimating the acceptable flaw size using Level 1 fracture procedures Estimation of acceptable flaw sizes General Calculation of Calculation of |
| 241 | Finite width correction Estimation of the acceptability of a known flaw |
| 242 | Relationship between actual flaw dimensions and the parameter |
| 243 | Relationship between actual flaw dimensions and the parameter |
| 244 | (informative) Consideration of proof testing and warm prestressing (informative) Consideration of proof testing and warm prestressing General Proof or overload testing Warm prestressing |
| 245 | Typical warm pre-stress cycles |
| 246 | Simplified WPS argument Full WPS procedure |
| 247 | (normative) Calculation of reference stress (normative) Calculation of reference stress Purpose |
| 248 | General Formulae for flat plates [166] Through-thickness flaw (see Figure M.1) Surface flaw (see Figure M.2) Long surface flaws in plates (see Figure M.6) |
| 249 | Embedded flaw (see Figure M.7) Edge flaw (see Figure M.10) Corner flaws in plates (see Figure M.11) Corner flaws at hole (see Figure M.12) |
| 250 | Single corner flaw at hole Other geometries |
| 251 | Formulae for curved shells General Through-thickness flaws |
| 252 | Surface flaws in cylinders |
| 254 | Embedded flaws in shells Formulae for weld toe cracks [see Figure M.23a) to c)] Formulae for round bars and bolts [195] Semi-elliptical surface flaws in bolts/chordal surface flaws in bolts (see Figure M.25) Values of · |
| 255 | Circumferential flaw in round bar (see Figure M.26) Plastic collapse of tubular joints Plastic collapse from volumetric flaws Global collapse Conditions for which a check on global collapse should be made Methods |
| 256 | (informative) Residual stress distributions in as-welded joints (informative) Residual stress distributions in as-welded joints General Parametric ranges for recommended residual stress distributions |
| 257 | Typical residual stress distribution in welded joints |
| 258 | Plate butt welds – Figure Q.1a) Longitudinal residual stresses (i.e. parallel to the weld length) Transverse residual stresses (i.e. perpendicular to the weld length) Pipe circumferential butt welds Longitudinal residual stresses (i.e. parallel to the weld length and circumferential to the pipe) |
| 259 | Transverse residual stresses (i.e. perpendicular to the weld length and parallel to the axis of the pipe) Pipe axial seam welds T-butt and fillet welds – Figure Q.1c) General Electrical energy (heat input) based |
| 260 | Parametric formulae based on experimental data Repair welds – Figure Q.1d) |
| 261 | (normative) Determination of plasticity interaction effects with combined primary and secondary loading (normative) Determination of plasticity interaction effects with combined primary and secondary loading General Simplified procedure for the determination of ‘ when KIs/(KIp/ |
| 262 | Values of Detailed procedure for the determination of ‘ |
| 263 | Tabulation of |
| 264 | Tabulation of Advice on calculating Kps General Determination of |
| 265 | Linear elastic calculation of |
| 266 | Alternative approaches for assessing combined primary and secondary stresses The finite element method The EPRI-GE J-estimation scheme Through-thickness cracks with completely self-balancing residual stress fields |
| 267 | Stress intensity factor for through-thickness cracks with through-wall self-balancing stress distributions (normative) Approximate numerical integration methods for fatigue life estimation (normative) Approximate numerical integration methods for fatigue life estimation The use of finite crack growth increments |
| 269 | The use of blocks of stress cycles (informative) Information for making high temperature crack growth assessments (informative) Information for making high temperature crack growth assessments Materials data Tensile properties Creep strain versus time curves |
| 270 | Derivation of strain versus time curves from iso-strain curves |
| 271 | Derivation of incremental creep strains Strain hardening construction to obtain incremental strains Stress to rupture |
| 272 | Construction to estimate creep damage in block Fatigue crack propagation rate |
| 273 | Creep crack propagation rate Constants used to derive creep crack propagation rates in mm/h |
| 274 | Fracture toughness Typical values of fracture toughness (based on the value of Incubation period |
| 275 | Calculation procedure Step 1: Plot past operating history and future operating requirements |
| 276 | Division of operating history into blocks of constant stress and constant temperature Step 2: Calculate margin against fracture |
| 277 | Step 3: Calculate the effect of previous history Step 4: Assess future performance in block 6 |
| 279 | Step 5: Assess performance during future life Modifications to allow for incubation period The assessment of flaws in weldments General |
| 280 | Plant experience Advice on structural calculations for weldments |
| 281 | Residual stresses Assessment to include creep-fatigue loading General |
| 282 | Crack growth due to creep Crack growth due to fatigue Total crack growth in block Incubation period |
| 283 | (informative) Worked example to demonstrate high temperature failure assessment procedure (informative) Worked example to demonstrate high temperature failure assessment procedure General Problem specification Operating conditions |
| 284 | Flaw dimensions Thermal stress distribution in the region of the flaw |
| 285 | Selected materials data Assessment procedure Step 1: General (see 9.5.1) Step 2: Initial investigations to establish cause of cracking (see 9.5.2) Step 3: Define previous plant history and future operational requirements (see 9.5.3) Step 4: Establish stresses (see 9.5.4) Stress category Step 5: Characterize flaws (see 9.5.5) |
| 286 | Step 6: Establish material properties (see 9.5.6) Step 7: Check on fatigue (see 9.5.7) |
| 287 | Step 8: Perform flaw assessment |
| 288 | Margin against fracture for high pressure start up |
| 289 | Data at beginning of each month for deepest point of crack |
| 290 | Data at beginning of each month for crack growth along surface Creep crack growth for period August 1990 to July 2005 Step 9: Special considerations for welds (see 9.5.9) |
| 291 | Increase in creep damage from start of operation in April 1985 to July 2005 Step 10: Sensitivity analysis (see 9.5.10) |
| 292 | Step 11: Remedial action (see 9.5.11) |
