3.0 best practice - corrosion under insulation
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CHT INTEGRATED REFINERY BUSINESS IMPROVEMENT PROGRAM
HPCL Mumbai
Corrosion Under Insulation
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FACTORS CONTRIBUTING TO CORROSION UNDER INSULATION
Cladding and insulation condition
Insulation type
Water source
� External environment
� Presence of steam tracing
Temperature
Coating status, surface preparation, lifetime, coating type
Equipment shape: line size, nozzle, attachment
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CLADDING
Role of Cladding and Vapour Barriers:
Contain Isolation Material
To keep insulation dry.
Mechanical Protection
Mastics and sealants are used to close openings.
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Aluminised steel
Aluminium
Stainless steel
Polyester etc.
GRE wrap
Tapes
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DAMAGED CLADDING
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INSULATION MATERIAL
Water leachable salt content.
� chlorides, sulphate, acidic materials in fire retardants
Water retention, permeability, wettability.
Insulation foams that react with water to form acids
�
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RockwoolRockwool
FoamFoam--glassglass
PU FoamPU Foam
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MOIST INSULATION MATERIAL
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WATER SOURCES
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1. Condensation
2. External
3. Internal
Damaged steam tracing
Rainfall
Steam discharge,
Spillage
Deluge/sprinkler system,
Drift from cooling towers
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WATER SOURCES
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TEMPERATURE
Higher temperature:
Increased corrosion rate
High salt concentration
Reduced life coatings
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Cyclic temperatures, Temperature gradients
increase risk for Corrosion Under Insulation.
Lower temperature:
• Condensation
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TEMPERATURE
Carbon Steel
-5 to 60°C Moderate
50-120°C Severe
120-150°C Moderate
150-250°C Cold spots
>250°C No risk
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Stainless steel:Stress Corrosion
Cracking
<50°C no SCC
50-120°C High
120-150°C Moderate
>150°C no SCC
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COATING STATUS, TYPE, APPLICATION, AGE
Coating type
� Primer only
� Full coat
� Immersion coat
� Thermal Al spray
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Application
• Surface preparation
• Cold/Hot
• Maintenance
• No coating
Coating life varies between 0 and 10 years (approx)
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COATING STATUS
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EQUIPMENT SHAPE: LINE SIZE, NOZZLE, ATTACHMENT
Tees
Valves
Instruments
(Steam) Tracing
Equipment Nozzles
Stiffeners
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Difficult to seal
Cold spots (Hot spots)
Maintenance e.g. valves
Watertraps
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EQUIPMENT SHAPE
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CORROSION UNDER INSULATION
Prevention and mitigation of CUI is largely
a maintenance issue, whereby the corrosion is prevented
in case the insulation and underlying coating is
maintained where and when needed.
If no maintenance is executed, the coating and insulation
will deteriorate and corrosion will start.
The actual need for insulation has always to be challenged.
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CUI ASSESSMENT PROGRAMME
Assessment of susceptibility to CUI
Detection methods [and reliability]
Determination of corrosion severity
Criticality
Repair procedures
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CUI INSPECTION GUIDELINE
The CUI Inspection Guideline is used during the S-RBI process to
determine the Criticality Class, the Confidence Rating and the
corresponding Inspection/Maintenance Strategy for Corrosion Under
Insulation.
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CUI INSPECTION GUIDELINE
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THE CUI INSPECTION GUIDELINE CONSISTS OF TWO STEPS:
Step 1: A criticality ranking requiring limited input data.
Step 2: A detailed assessment and inspection plan for the high ranking items.
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STEP 1: CUI CRITICALITY RANKING
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The Susceptibility to CUI is determined with the dedicated questions in the Criticality Matrix for CUI.
This provides a worst case assessment.
The Consequence of Failure is copied from the internal corrosion failure.
The Criticality Matrix gives the Criticality Ranking for CUI.
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STEP 2: CUI INSPECTION PLAN
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1. Determine the Probability based on the cumulative score from the Susceptibility table.
2. Re-address the Criticality based on this Probability rating.
3. Determine the Confidence Rating for CUI using the dedicated Confidence Rating questionnaire.
4. Establish the Inspection/Maintenance Strategy for CUI based on the Criticality and Confidence Rating.
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THE SCHEMATICALLY REPRESENTATION OF THE S-RBI PROCESS FOR CUI.
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Susceptibility
Consequence
Confidence
Factor
Inspection
Strategies
Criticality
Rating
IS1
IS2
IS3
IS4
IS5
Susceptibility
Consequence
Confidence
Factor
Inspection
Strategies
Criticality
Rating
IS1
IS2
IS3
IS4
IS5
IS1
IS2
IS3
IS4
IS5
IS0
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SUSCEPTIBILITY TO CUI FAILUREFOR CS/LOW ALLOY STEEL (1)
DETERMINE THE PROBABILITY SCORE BY ADDING POINTS FROM THE
INDIVIDUAL COLUMNS IN THE TABLE (NEXT SLIDES).
NOTE:
Remember to challenge the requirement for insulation - it may be
possible to permanently remove it.
For Personal Protection perforated sheeting is preferred.
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CUI PREVENTION
Only insulate where necessary
Use screens for personnel protection
Use insulating coatings
Use waterproof cladding (plastics, laminates)
Use immersion coating or TSA
Use non-contacting insulation
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* In cyclic service (or temporarily temperature changes), the range of the most critical temperature reached shall be taken.
OperatingTemperature*
Initial coatingstatus
Insulationtype
Points
constantly >175 °Cor < −5 °C
Full QA paintprotection
- 0
150 - 175°C Expanded Perlite, Foamglass, Closed Cell Foam (right type)
1
−5 - 50 °Cor
120 -150 °C
Conventional QA
Paint protection; field welds
at construction
3
50 - 120 °Cunpainted
orunknown
5-
Fiberglass, Cal Sil,Asbestos, Regular Perlite, Mineral/Rock Wool
-
SUSCEPTIBILITY TO CUI FAILUREFOR CS/LOW ALLOY STEEL (2)
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* The most susceptible area of the equipment determines the rating.**Can be taken from RBI study for internal corrosion.
Wall Thickness &Surface Features*
Internalcorrosion / erosion
rate**
Externalcoil / steamtracing
Externalenvironment
Points
-Negligible
Not present inside building 0
Low (or < 0.1 mm/yr)rarely wetted
(<10% of the time)1
4 – 7.1 mm or Surface at Location of
Penetrationsthrough Insulation
Medium (or 0.1 - 0.4 mm/yr)Medium IntegrityDesign
frequentlywetted
(~40% of the time)3
≤ 4 orSurface at Location ofReinforcement Rings& Other Water Traps
High (or > 0.4 mm/yr)Low
IntegrityDesign
permanentlywetted (e.g.cooling tower,dripping water,condensation)
5
≥ 7.1 mmHigh Integrity Design
SUSCEPTIBILITY TO CUI FAILUREFOR CS/LOW ALLOY STEEL (3)
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SUSCEPTIBILITY TO CUI FAILUREFOR STAINLESS STEEL (1)
DETERMINE THE PROBABILITY SCORE BY ADDING POINTS
FROM THE INDIVIDUAL COLUMNS IN THE TABLE (NEXT SLIDES).
NOTE:
Remember to challenge the requirement for insulation - it may be
possible to permanently remove it.
For Personal Protection use perforated sheeting.
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OperatingTemperature*
Initialcoating status
External coil /steam tracing
Externalenvironment
Points
Not present 0
2
120 - 150 °C Medium IntegrityDesign
4
50 - 120 °C
LowIntegrityDesign
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* In cyclic service (or temporarily temperature changes), the range of the most criticaltemperature reached shall be taken.
Constantly>150 °C
or < 50 °C
-
Full QA paintprotection
Conventional QA paintProtection;field welds
at construction
Unpaintedor
unknown
-
Insulation type
Low chlorideinsulationmaterial
(<10ppm Cl-)
-
higher chlorideinsulationmaterial
(≥10ppm Cl-)
-
High IntegrityDesign
Inside building
Rarely wetted(<10% of the time)
frequentlywetted
(~40% of the time)
Permanently wetted (e.g. cooling tower,dripping water,condensation)
SUSCEPTIBILITY TO CUI FAILUREFOR STAINLESS STEEL (2)
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MH= Medium High E = ExtremeH = High M = MediumL = Low N = Negligible
N LL MM
H
MH
E
HMH
MHMM
MMLL
LL
N
N
EEHMHLL
M
L
N
H
PROBA
BILITY C
LASS
MULTIPLEFATALITIES
EXT. DAMAGE( >10M)
NO/SLIGHTINJURY
NO/SLIGHTDAMAGE (<10K)
NO/SLIGHTEFFECT
MINOR INJURY
MINOR DAMAGE(10-100K)
MINOREFFECT
MAJOR INJURY
LOCAL DAMAGE(0.1-1M)
LOCALISEDEFFECT
SINGLE FATALITY
MAJOR DAMAGE(1-10M)
MAJOREFFECT
MASSIVEEFFECT
HEALTH & SAFETY
ECONOMICS (USD)
ENVIRONMENTCONSEQUEN
CE
CATEGORY
CONSEQUENCE CLASS NEGLIGIBLE LOW MEDIUM HIGH EXTREME
TOTAL SCORE > 20
SUSCEPTIBILITY TOCUI FAILURE
TOTAL SCORE 14 - 20
TOTAL SCORE 7 - 13
TOTAL SCORE 0 - 6
CUI RRM CRITICALITY CLASS
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For Confidence Rating add scores; minimum: -0.2, maximum: +0.2Confidence Rating: -0.2 = very low, - 0.1 = low, 0 = medium, +0.1 = high, +0.2 = very high*In case of new equipment or piping, a 0 (zero) score shall be given for this aspect
CUI CONFIDENCE QUESTIONS Yes Intermediate No
+0.1 0 -0.1
+0.1 0 -0.1
+0.1 0
Cladding and insulation conditionCladding/insulation fully maintained: YESCladding/insulation normal: IntermediateCladding/insulation in poor condition: NO
Multiple reliable inspections for CUI have been carried out*Frequent inspection and selective delagging, followed by appropriateremedial action: YESInspection irregular/not to standard: IntermediateNo proper inspections: NO
-0.1
CONFIDENCE RATING FOR CUI
Monitoring CUI promoting conditionsThe presence of ALL possible CUI promoting conditions (see susceptibility categories) has been established and quantified: YESThe operating temperature is monitored and constantly in identified range AND the coating condition is known/established: IntermediateThe operating temperature is not established AND/OR the coatingcondition is not known/established: NO
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COATING/PAINT PROTECTION CREDIT
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Coverage and Quality of Applied Coating/PaintYears of protection
100% coverage (including field welds);according to the appropriate engineering standards
8
100% coverage (including field welds);not completely in accordance with the appropriate engineering standards
4
No 100% coverage or unknown;poor or unknown quality
0
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CUI MONITORING CS/LOW ALLOY STEELDETERMINING INSPECTION/MAINTENANCE STRATEGIES
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CONFIDENCE RATING
VERY LOW LOW MEDIUM HIGH VERY HIGH CRITICALITY
HIGH
MEDIUM HIGH
MEDIUM
LOW
STRATEGY 2 STRATEGY 3
NEGLIGIBLE (review only)
EXTREME
NO INSPECTIONS
STRATEGY 1
CONFIDENCE RATING
VERY LOW LOW MEDIUM HIGH VERY HIGH CRITICALITY
MEDIUM
LOW
STRATEGY 3
NEGLIGIBLE (review only)
STRATEGY 0 STRATEGY
1 STRATEGY 2 STRATEGY
3 STRATEGY 4 NO
INSPECTIONS
CONFIDENCE RATING
VERY LOW LOW MEDIUM HIGH VERY HIGH CRITICALITY
MEDIUM
LOW
STRATEGY 2 STRATEGY 3
NEGLIGIBLE (review only)
NO INSPECTIONS
STRATEGY 1
CONFIDENCE RATING
VERY LOW LOW MEDIUM HIGH VERY HIGH CRITICALITY
MEDIUM
LOW
STRATEGY 3
NEGLIGIBLE (review only)
STRATEGY 0
STRATEGY 1
STRATEGY 2
STRATEGY 3
STRATEGY 4
NO INSPECTIONS
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CUI INSPECTION/MAINTENANCE STRATEGIESCS/LOW ALLOY STEEL STRATEGY 0
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Initial Action*Initial Result
1st Following Action*
Further Results
2nd Following Action*
Reduce Criticality !
Analyse in detailConsider corrective action
Meanwhile follow strategy 1
- - - -
* Recommended maximum timing; an analysis should be performed to determine if the work should be completed within a shorter time frame.
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CUI INSPECTION/MAINTENANCE STRATEGIESCS/LOW ALLOY STEEL STRATEGY 1
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Initial ActionInitial Result**
1st Following ActionFurther Results**
2nd Following Action
Equipment shell& nozzles/piping ≥≥≥≥ 8":100% NDE combined with 100% delagging of ALL possible wet and susceptible areas:
⇒ within 1 year*
Piping & equipmentnozzles ≤≤≤≤ 8":100% delagging:
⇒ within 1 year*(proceed according to column "Further Results")
Significant
CUI found
Delag 100%:⇒ within 6 months
MoresignificantCUI found Repair & paint;
repeat Initial Action:⇒ every 3 years*No more
significant
CUI found
Nosignifican
t
CUI found
100% delagging of ALL wet and susceptible areas:
⇒ within 3 years
SignificantCUI found
100% delagging within 6 months; repair & paint; repeat Initial Action:
⇒ every 3 years*
Nosignificant
CUI found
Adjust confidence rating with +0.1; repeat Initial Action:
⇒ within 3 years
* 50% of coating/paint protection credit can be applied, Inspection interval starting at the moment the coating/paint protection has ended ** ”Significant CUI” means corrosion damage that requires remedial action.
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CUI INSPECTION/MAINTENANCE STRATEGIESCS/LOW ALLOY STEEL STRATEGY 2
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Initial ActionInitial Result**
1st Following ActionFurther Results**
2nd Following Action
Equipment shell& nozzles/piping ≥≥≥≥ 8": 100% NDE combined with selective delagging of possible wet and susceptible areas:
⇒ every 6 years*
Piping & equipmentnozzles ≤≤≤≤ 8": 100% delagging of ALL possible wet and susceptible areas :
⇒ every 6 years*
Significant
CUI found
Delag 100%:⇒ within 1 year
MoresignificantCUI found Repair & paint;
repeat Initial Action:⇒ every 6 years*No more
significant
CUI found
Nosignifican
t
CUI found
Delag more selective areas:⇒ within 1 year
SignificantCUI found
100% delagging within 1 year; repair & paint; repeat Initial Action:
⇒ every 6 years*
Nosignificant
CUI found
Adjust confidence rating with +0.1; repeat Initial Action:
⇒ within 6 years
* Inspection interval starting at the moment the coating/paint protection has ended** ”Significant CUI” means corrosion damage that requires remedial action.
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CUI MONITORING FOR STAINLESS STEELDETERMINING INSPECTION/MAINTENANCE STRATEGIES
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CONFIDENCE RATING
VERY LOW LOW MEDIUM HIGH VERY HIGH CRITICALITY
HIGH
MEDIUM HIGH
MEDIUM
LOW
STRATEGY 2
NEGLIGIBLE
(review only)
EXTREME
NO INSPECTIONS
STRATEGY 1
CONFIDENCE RATING
VERY LOW LOW MEDIUM HIGH VERY HIGH CRITICALITY
MEDIUM
LOW
NEGLIGIBLE
(review only)
STRATEGY 0
STRATEGY 1
STRATEGY 2
NO INSPECTIONS
CONFIDENCE RATING
VERY LOW LOW MEDIUM HIGH VERY HIGH CRITICALITY
MEDIUM
LOW
STRATEGY 2
NEGLIGIBLE
(review only)
NO INSPECTIONS
STRATEGY 1
CONFIDENCE RATING
VERY LOW LOW MEDIUM HIGH VERY HIGH CRITICALITY
MEDIUM
LOW
NEGLIGIBLE
(review only)
STRATEGY 0
STRATEGY 1
STRATEGY 2
NO INSPECTIONS
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CUI INSPECTION/MAINTENANCE STRATEGIESSTAINLESS STEEL STRATEGY 0
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Initial Action*Initial Result
1st Following Action*
Further Results
2nd Following Action*
Reduce Criticality !
Analyse in detailConsider corrective action
Meanwhile follow strategy 1
- - - -
* Recommended maximum timing; an analysis should be performed to determine if the work should be completed within a shorter time frame.
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CUI INSPECTION/MAINTENANCE STRATEGIESSTAINLESS STEEL STRATEGY 1
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Initial ActionInitial Result
1st Following ActionFurther Results
2nd Following Action
100% delagging of ALL possible wet and susceptible areas;check coating and perform Eddy Current testing:
⇒ within 3 months*
Cracking found
Delag 100%;check coating and perform DPI:
⇒ within 3 months
Morecracking found Repair & paint;
repeat Initial Action:⇒ every 5 years*No more
cracking found
Nocracking found
100% delagging of ALL wet and susceptible areas;check coating and perform DPI:
⇒ within 2 years
Cracking found
100% delagging within 3 months; repair & paint; repeat Initial Action:
⇒ every 5 years*
Nocracking found
Adjust confidence rating with +0.1; repeat Initial Action:
⇒ within 3 years
* 50% of coating/paint protection credit can be applied, Inspection interval starting at the moment the coating/paint protection has ended . CONFIDENTIAL
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CUI PREVENTION
Only insulate where necessary
Use screens for personnel protection
Use insulating coatings
Use waterproof cladding (plastics, laminates)
Use immersion coating or TSA
Use non-contacting insulation
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