overview of api 579
DESCRIPTION
Overview of API 579TRANSCRIPT
Overview of API 579
API 579 Recommended Practice for Fitness-For-Service Goal for publication is end-1999 Contents
Assessment of Equipment for Brittle Fracture
Assessment of General Metal Loss Assessment of Local Metal Loss Assessment of Pitting Corrosion Assessment of Blisters and
Laminations
API RP 579 Contents (continued)
Assessment of Weld Misalignment and Shell Distortions
Assessment of Crack-Like Flaws Assessment of Components Operating
in the Creep Regime Assessment of Fire Damage
API RP 579 Appendices Include
Methods for calculating required thickness and guidelines on stress analysis
Compendium of Stress Intensity Factor Solutions
Compendium of Limit Load Solutions Residual Stresses for a FFS Assessment Material Properties Deterioration and Failure Modes
API RP 579 Covers equipment constructed to
Section VIII, Div 1 Section VIII, Div 2 B31.3, Process Piping B31.1, Power Piping API 650 API 620
It can also be used with equipment constructed to other recognized standards
Three Levels of Evaluation Provided for each flaw Level 1 - Evaluation simplified to
charts and simple formulae, generally simplified by conservative assumptions
Level 2 - Generally requires more detailed evaluation; more accurate
Level 3 - Allows for flaw assessment by more sophisticated methods
Typical Level 1 Limitations Original design in accordance with a
recognized code or standard Equipment is not operating in the creep
range Equipment is not in cyclic service
(check) Thickness governed by pressure Equation relates required thickness to
pressure
Level 2 Assessment Includes components requiring
more complex calculations such as nozzles and flanges
Includes consideration of supplemental loads
Includes evaluation of piping systems
Assessment of Equipment for Brittle Fracture Possible reasons for assessment
Change in operating conditions HAZOP identifies possibility of lower
temperature condition than considered in design
Equipment rerated using lower design margin
Brittle Fracture Level 1 - compliance with new
construction code exemption curves or impact test requirements
Level 2 include consideration of low stress-
based temperature reduction rules exemption based on hydrotest exemption based on service experience
Local Thin Areas Based on RSF=0.9 Also considers groove-like flaws Level 1 based on charts Level 2 based on equations
uses Folias factor method essentially must be computerized
due to large numbers of repetitive calculations
permits consideration of supplemental loads
General Corrosion Based on local thin area assessment
rules Point thickness readings may be used if
metal loss is confirmed to be general e.g. COV<10%
Level 1 using point thickness readings tam-FCA$tmin
tmin-FCA $max [0.5 tmin,2.5mm (0.10 inch)]
Level 1 (cont.) Based on CTP
L=Q(Dtmin)1/2
If s#L, OK for meridional corrosion, check longitudinal corrosion using LTA Level 1 chart
If s>L, use point thickness readings with tam=tmm, or
determine average and minimum thickness for circumferential and meridional directions
determine tam over length L centered on tmm
Point thickness readings, same as Level 1, may be used
Level 2 Evaluation methods for shells the
same as level 1, but considers supplemental loads
Evaluation methods provided for components with thickness interdependencies, such as nozzles, using average thickness measurements over prescribed lengths
Assement of Pitting Methods provided based on
ligament efficiency Pit couples evaluated Consider at least ten pit-couples
Level 1 Thickness partitioned into pitted
thickness based on average pit depth, and remaining thickness
Strength of pitted thickness adjusted based on ligament efficiency
Region of local pitting may be evaluated as LTA with equivalent thickness
Level 2 Orientation of pits relative to
direction of stress can be considered
Thickness may be subdivided into a number of thickness layers
Pitting on both sides can be considered
Blisters and Laminations Laminations not generally considered
to be detrimental (if not adjacent to major structural discontinuity)
Blisters caused by hydrogen accumulation at imperfections in the steel
Level 1 & 2 limited to low temperature hydrogen attack (<204C/400F)
Blisters Closely spaced blisters combined
based on LTA rules, and distance between two adjacent
blisters # 2tnom
Blisters generally drilled, if not already cracked, to relieve accumulation of pressure
Level 1 Blisters are accepted based on
diameter # 50.8mm (2 inch) and blister is vented or unvented or diameter# 0.6(Dtnom)1/2 and blister is vented
blister projection # 10% blister diameter tmm for unbulged side is $50% tnom
no periphery cracks towards inside or outside surface
distance to weld seam $25mm (1 inch) distance from major struct disc $ 1.8(Dtnom)1/2
Level 2 Permits consideration of blisters
that exceeds limits of Level 1 as LTAs
Permits consideration of peripheral cracking
Permits evaluation of blisters adjacent to weld seams
Permits evaluation of laminations in hydrogen charging service
Weld Misalignment and Shell Distortions Permits consideration of general
shell distortion, out-of-roundness, bulges and dents
Level 1 based on comparison to limits of new construction code
Level 2 based on stress analysis; equations are provided
Fatigue analysis may be required
Fire Damage Methods provided to determine fire
zone (maximum temperature) Level 1 acceptance based on fire
zone, depending on material of construction
Level 2 acceptance based on evaluation of fire exposed material properties