3. Leader
Patiphon Suksawat
Consultant
Wasan Cheeppensuk Atip Nualnet
CUI team
Komsan Bangkrut Nawa Bunsayang Narong Sakulprasitsiri
4. What is CUI (Corrosion Under Insulation) ?
- CUI is a particularly severe form of localized corrosion
that has been plaguing chemical process industries since the
energy crisis of the s forced plant designers to include much
more insulation in their designs
- Intruding water is the key problem in CUI Special care
must be taken during design not to promote corrosion by
permitting water to enter a system either directly or indirectly by
capillary action
5. What is CUI (Corrosion Under Insulation) ?
External damage
Carbon steels or Stainless
low alloy steels steels
Subject to stress
Subject to thinning
corrosion cracking
6. • CUI is the mainly problem in petrochemical
plant.
• Current Inspection Program is not consider
corrosion under insulation problem.
• Increase Reliability of Plant.
Reference TPE
7. Conclusion and Future action Plan
Inspection ( Visual and Ultrasonic Testing)
Risk Evaluation and Identification
List up EQ and Collection Data
Make Inspection Guide Line (Check Sheet)
Select Loop To Implement CUI
Study CUI Theory From API 581, 570
9. Insulated Piping Systems
Susceptible to CUI
1. Carbon steel piping systems, including those insulated
operating between (– C to C).
2. Austenitic stainless steel piping systems operating
between ( C– C).
20. Consequence of failure rating
Consequence
1 2 3 4 5
class
No / Slight Minor Local Major Extensive
Economics Damage Damage Damage Damage Damage
< 0.4 M 0.4 – 4 M 4 – 40 M 40 – 400 M > 400 M
No / Slight Multiple
Health & Safe Minor Injury Major Injury Single Injury
Injury Injury
No / Slight Minor Localized Major Massive
Environment
effect effect effect effect effect
Select 3
Example
- 20 -
21. Probability Score Table of Carbon Steel
Initial
Operating Wall thickness Internal corrosion External coil / External
Point Coating Insulation Type
Temperature surface feature / erosion rate Steam tracing environment
Status
> 175 0C
Full QA paint
0 Or Negligible Not present Inside Building
protection
< -5 0C
Perlite
Foamglass Rarely wetted
Low High Integrity
1 150 – 175 0C Closed cell >7.1 mm (<10% of the
( < 0.1 mm/y) design
Foam (right time)
type)
Normal QA Fiberglass 4 – 7.1 mm or
-5 – 500C paint Cal Sil, surface location Intermittently
Medium Medium Integrity
3 or protection Asbestos of penetrations wetted (~40% of
(0.1-0.4 mm/y) design
120 – 150 0C field weld at Mineral Rock through the time)
construction wool insulation
< 4 mm or
Permanently
surface at
wetted (e.g.
Unpainted or location of High Low Integrity
5 50 – 120 0C condensation,
Unknown reinforcement ( >0.4 mm/y) design
cooling tower
ring & other
dripping water
5+5+1+1+1+0+1 = 14 water traps
score Example
22. Probability Score Table of Stainless Steel
Operating Initial Coating External coil / External
Points Insulation Type
Temperature Status Steam tracing environment
Constantly > 150 Low chloride
0C or Constantly Full QA paint
0 insulation material Not present Inside Building
protection
< 50 0C (<10 ppm Cl-)
Rarely wetted
High Integrity
2 (<10% of the
design
time)
Permanently
Normal QA paint
protection field
wetted (e.g.
Medium Integrity
4 120 – 150 0C weld at condensation,
design
construction cooling tower
dripping water
Higher chloride Intermittently
Unpainted or Low Integrity
7 50 – 120 0C insulation material wetted (~40% of
Unknown design
(>10 ppm Cl-) the time)
score
- 22 -
24. CUI Confidence rating
CUI Confidence Questions Yes Interm NO
Cladding and Insulation conditions
-Cladding/Insulation fully maintained : Yes
+1 0 -1
0 -1 + 0 = - 1
-Cladding/Insulation normal : Interm
-Cladding/Insulation in poor condition : NO
Multiple reliable inspections for CUI have been carried been
carried out
-Frequent inspection and selective delagly fallowed by
+1 0 -1
appropriate remedial action : Yes
-Inspection irregular / not standard : Interm
- No proper inspections : No
Monitoring CUI promoting condition
- The pressure of all possible CUI promoting condition
(see susceptibility categories) has been established and
quantified : Yes
- The operating temperature is monitored and constantly +1 0 -1
in identified rouge and coating condition is know /
established : Interm
- The operating temperature is not established or the
coating condition is not know : No
score Example
- 24 -
30. Strategy flowchart
Strategy 3
Yes No
Piping > 8 in
100 % NDE and delegging of all Delegging of
susceptible area within 6 years susceptible within 6
years
Yes No
Significant
CUI found
Every Delag 100% Delag more selective area
6 years within 1 year Within 1 year Every
6 years
Significant
CUI found No
Repair and Paint Yes
100 % delegging , repair and paint Adjust confidence
within 1 year with +1
42. Strategy flowchart
Strategy 3
Yes No
Piping > 8 in
100 % NDE and delegging of all Delegging of
susceptible area within 6 years susceptible within 6
years
Yes No
Significant
CUI found
Every Delag 100% Delag more selective area
6 years within 1 year Within 1 year Every
6 years
Significant
CUI found No
Repair and Paint Yes
100 % delegging , repair and paint Adjust confidence
within 1 year with +1
