-
8/13/2019 Section 10 - Assessment of Pitting Metal Loss
1/6
Copyright 2005, TWI Ltd World Centre for Materials Joining TechnologyWorld Centre for Materials Joining Technology
Pitting Metal LossPitting Metal Loss
Copyright 2005, TWI Ltd World Centre for Materials Joining TechnologyWorld Centre for Materials Joining Technology
Primary published procedure:Primary published procedure:
API Section 6:API Section 6:
The theory is based on pit coupling andThe theory is based on pit coupling and
limit load analysislimit load analysis
Main challenge is the quality of theMain challenge is the quality of the
inspection datainspection data
Pitting Metal Loss
-
8/13/2019 Section 10 - Assessment of Pitting Metal Loss
2/6
Copyright 2005, TWI Ltd World Centre for Materials Joining TechnologyWorld Centre for Materials Joining Technology
Pitting Metal LossPitting Metal Loss
d d d
w w w
P
Copyright 2005, TWI Ltd World Centre for Materials Joining TechnologyWorld Centre for Materials Joining Technology
Pitting Metal LossPitting Metal Loss
Four pitting cases can be assessed:Four pitting cases can be assessed:
Widespread pittingWidespread pitting
Localised pittingLocalised pitting
Locally thinned area in widespreadLocally thinned area in widespread
pittingpitting
Pitting within a locally thinned areaPitting within a locally thinned area
-
8/13/2019 Section 10 - Assessment of Pitting Metal Loss
3/6
Copyright 2005, TWI Ltd World Centre for Materials Joining TechnologyWorld Centre for Materials Joining Technology
Pitting Metal LossPitting Metal Loss
Widespread pitting:Widespread pitting:
Assessments based on representativeAssessments based on representativesamples of pittingsamples of pitting
For example:For example:
Uniform 10 to 20 sample pit couplesUniform 10 to 20 sample pit couples
NonNon--uniform greater than 50uniform greater than 50
samplessamples
Copyright 2005, TWI Ltd World Centre for Materials Joining TechnologyWorld Centre for Materials Joining Technology
Pitting Metal LossPitting Metal Loss
Localised pitting:Localised pitting:
Assessments based on equivalent locallyAssessments based on equivalent locally
thinned area (then use Section 5)thinned area (then use Section 5)
Pitting within a LTA & LTA withinPitting within a LTA & LTA within
widespread pittingwidespread pitting
Assessment based on combined RSF forAssessment based on combined RSF for
locally thinned area and pittinglocally thinned area and pitting
-
8/13/2019 Section 10 - Assessment of Pitting Metal Loss
4/6
Copyright 2005, TWI Ltd World Centre for Materials Joining TechnologyWorld Centre for Materials Joining Technology
Pitting Metal LossPitting Metal Loss
Level 1 assessment:Level 1 assessment:
RSF calculated on pitRSF calculated on pit--couplecouple
Level 2 assessment:Level 2 assessment:
RSF calculated on pitRSF calculated on pit--couple withcouple with
respect to stress orientationrespect to stress orientation
Copyright 2005, TWI Ltd World Centre for Materials Joining TechnologyWorld Centre for Materials Joining Technology
Pitting Metal LossPitting Metal Loss
Level 3 assessment:Level 3 assessment:
Finite element analysis of individualFinite element analysis of individual
pitspits
Finite element analysis of effectiveFinite element analysis of effective
material properties e.g. elasticmaterial properties e.g. elastic
modulusmodulus
-
8/13/2019 Section 10 - Assessment of Pitting Metal Loss
5/6
Copyright 2005, TWI Ltd World Centre for Materials Joining TechnologyWorld Centre for Materials Joining Technology
Pitting Metal LossPitting Metal Loss
Possible futurePossible future
assessmentassessment
procedure to useprocedure to usecomparator chartscomparator charts
of pit densityof pit density
Copyright 2005, TWI Ltd World Centre for Materials Joining TechnologyWorld Centre for Materials Joining Technology
Metal lossMetal loss
Remediation
& Remaining life
Remediation
& Remaining life
-
8/13/2019 Section 10 - Assessment of Pitting Metal Loss
6/6
Copyright 2005, TWI Ltd World Centre for Materials Joining TechnologyWorld Centre for Materials Joining Technology
Remediation & Remaining lifeRemediation & Remaining life
Remediation actions:Remediation actions:
Weld repairWeld repair
Coatings and lining systemsCoatings and lining systems
Change operating environmentChange operating environment
ReRe--rate equipmentrate equipment
Inhibitors, etcInhibitors, etc
Copyright 2005, TWI Ltd World Centre for Materials Joining TechnologyWorld Centre for Materials Joining Technology
Remediation & Remaining lifeRemediation & Remaining life
Remaining life:Remaining life:
Thickness approach based on metalThickness approach based on metal
loss rate with timeloss rate with time Maximum allowable workingMaximum allowable workingpressure (MAWP) approachpressure (MAWP) approach
Use depends on design equationUse depends on design equationrelates pressure to wall thicknessrelates pressure to wall thickness