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