Corrosion Under Insulation

Inspection in Ammonia

Urea Plant

Work Preparation & Planning

KhandakerAsirul Hoque

Asirul.Hoque@outlook.com

Definition of CUI

“Corrosion of piping, pressure

vessels and structural

components resulting from water

or moisture trapped under

insulation or fireproofing.”

Affected Materials:

Carbon steel, low alloy steels, 300

Series SS and duplex stainless

steels.

Ammonia jetty area pipeline CUI, 2009

Corrosion Under Insulation (CUI)

As per Giel Notten, widely known corrosion expert

“Corrosion Under Insulation (CUI) is the number-1

problem in Chemical Process plant after 20 years of

operation”

The plant is getting older and the insulation cover

sheeting is deteriorating. Near lugs, attachments,

instrumentation nozzles and inlet & outlet lines, the

insulation cover sheeting is not properly installed.

Rainwater can penetrate into the insulation and

cause CUI.

Susceptible temperature range

As per API 510- 9th Edition susceptable temperature range

for CUI is

• 10°F (–12°C) and 350°F (175°C) for carbon

and low alloy steels

140ºF (60ºC) and 400ºF (205ºC) for austenitic

stainless steels.

CUI Mechanism

Corrosion Under Insulation caused by:

� Ingress of water through-insulation

� Water vapors condensation

Corrosion promoted by:

� Trapping of water

� Elevated temperatures (around 100º C)

� Temperature gradient

� Temperature cycling (Intermediate Service)

� Absence or poor condition of coating

� Poor/broken insulation

� Marine Environment (Chloride Deposition)

Ammonia jetty area pipeline CUI, 2009

Influence of relative Humidity on Atmospheric

Corrosion of Carbon Steel

Susceptible Locations� Insulation support or stiffening rings

• Nozzles and man-ways

CO2 absorber

CUI near

bottom skirt,

2010

Susceptible Locations� Other penetrations, e.g. Ladder clips, pipe supports

� Damaged insulation areas

Susceptible Locations

� Un-insulated Lifting Lugs

� Near Bottom Drain Lines

� Saddle Support of

Horizontal Heat Exchangers

Morphology of CUI

� After insulation is removed from carbon

and low alloy steels, CUI damage often

appears as loose, flaky scale covering the

corroded component.

� In some localized cases, the corrosion can

appear to be carbuncle type pitting

� Austenitic SS often shows Cl-SCC

Damage Mechanisms

CUI

Carbon Steel

Uniform Corrosion &

uniform wall loss

Localized pitting

(below painting)

Stainless Steel

Stress Corrosion Cracking

CUI Inspection: Work Organization

Manager

Inspection

Supervisor from

Production for

permit and process

related support

(To be nominated

for each plant)

Visual Inspectors

From Inspection

Section

Insulation Removal

& Re-insulation

work

supervisor

(To be nominated)

Maintenance

Support

supervisor

(To be nominated

from each plant)

Civil Supervisor

For re-painting

job

(To be

nominated)

Operator from

NH3/ Urea &

Utility Plant

Insulation

Technician for

Insulation

removal

Mechanical

Technician for

scaffolding,

surface

preparation for

NDT

Civil contactor

for repainting

Production Inspection Workshop Maintenance Civil

Work Organization (cont.)

� CUI inspection is a multi disciplinary work. Good

communication & understanding is required between group

members.

� Best time to execute such inspection is during plant shut

down period and dry season.

� Insulation is hazardous material so proper safety

supervision is also important.

Work Schedule

Date April 2013 May 2013 June 2013

Job Tasks Week 1 Week 2 Week 3 Week 4 Week 1 Week 2 Week 3 Week 4 Week 1 Week 2

Study CUI as per API 510, 571 & RBI

recommendation

Preparation of CUI Job volume

Assessment of material and Job by

maintenance

Inspection Checklist preparation

CUI inspection work of Ammonia Plant

Repainting and reinsulation job in Ammonia

Plant

CUI inspection work of Utility Plant

Repainting and reinsulation job in Utility

Plant

CUI inspection work of Urea Plant

Repainting and reinsulation job in Urea

Plant

Report Preparation

Update information into RBI Software

Inspection Type

Stainless Steel

Uniform Oxidation & ThinningUltrasonic Thickness

Measurement (UT)

Localized Metal Loss Pit Depth Measurement

Carbon Steel

Cl stress Corrosion Cracking Dye Penetration Testing (DPT)

Ammonia Plant EquipmentSl Equipment

Number

Equipment Name Shell Material Probable

CUI Locations

1 1-S-202 PROCESS CONDENSATE

SEPARATOR

Carbon Steel Bottom Skirt,

Manhole, Lifting

Lug

2 1-S-302 MIST SEPARATOR Carbon Steel Bottom Skirt,

Manhole, Lugs

3 1-S-304 HOT CONDENSATE

SEPARATOR

Carbon Steel Bottom Skirt,

Manhole, Lugs

4 1-S-412 INTER SEPARATOR FOR 1-K-

401

Carbon Steel Bottom Skirt,

Ladder Supports,

Lugs

5 1-S-502 Let Down Vessel Carbon Steel Ladder, Manhole

cover support

6 1-S-503 Flash Vessel Carbon Steel Ladder, Level

Gauge, Lugs

7 1-V-102 Blow Down Vessel Carbon Steel Lugs, Manhole,

Ladder supports

Ammonia Plant Equipment

Ammonia Plant Equipment

Sometimes insulation is used at locations where only

personal protection (PP) is required. This increases the

risk for CUI considerably. When installing personal

protection instead of insulation, the structural integrity

will be improved.

� 1-E-421 1st intercooler (air) no insulation required, only personal

protection

� 1-E-504 NH3 water cooler no insulation required on inlet line

(only PP).

� 1-E-510A/B NH3 condensers no insulation required, only

personal protection

� 1-V-601 A/B Adsorber A & B

Utility Plant Equipment

Sl Equipment

Number

Equipment Name Shell Material Probable CUI

Locations

1 3-V-201 Continuous Blow Down

Flash Tank

Carbon Steel Near bottom support,

flange connection

2 3-V-203 Drain Flash Tank Carbon Steel Near bottom support,

flange connection

3 3-V-901 A Adsorber A Carbon Steel Around Insulation Support

Ring, Lugs

4 3-V-901B Adsorber B Carbon Steel Around Insulation Support

Ring, Lugs

5 3-S-901 MOISTURE SEPARATOR Carbon Steel Around Insulation Support

Ring, nameplate

6 3-E-701 Mixing Station Heat

Exchanger

Carbon Steel Insulation support ring,

nameplate, base

7 3-E-901 Air Cooler Carbon Steel Near nameplate & base

8 3-E-903 Regenaration Gas Heater Carbon Steel Near nameplate & base

Utility Plant Equipment

Urea Plant Equipment

Sl Equipment

Number

Equipment Name Shell Material Probable CUI

Locations

1 2-V-903 Boiler Feed water

Collecting Drum

Carbon Steel Lifting lug- 2 nos & Ladder

support

2 2-V-905 HP STEAM SATURATOR Carbon Steel Support- 2 nos & Level gauge

support

3 2-E-303 LP CARBAMATE

CONDENSER

Stainless Steel Lifting lug- 2 nos., Bottom

insulated part

4 2-E-202 HPCC Carbon Steel Saddle Support & inlet from

2-E-201

5 2-X-901 Steam Vent Stack Carbon Steel Bottom Insulated part where

damage occurred

6 2-E-803 A/B Hydrolizer Heat Exchanger Stainless Steel Partially remove insulation

near saddle support and

perform thickness monitoring

7 2-E-802 Desorber Heat Exchanger Stainless Steel Thickness check near saddle

support and perform

thickness monitoring

Urea Plant Equipment

RBI Approach of Pipeline CUI Inspection

Critical Areas for Pipeline CUI

Common Locations of pipeline CUI

1. Pipes those are in intermittent service

2. Steam tracing pipe lines

(sometimes in Urea plant SS pipe is steam traced by CS tracing

line- Introduce risk of external Cl-SCC)

3. Termination of insulation in a vertical pipe.

4. Bulges or staining of the insulation or jacketing system or

missing bands.

5. Low points in piping systems that have a known breach in the insulation system

Pipeline CUI

Vertical run pipeline partially

insulated are very prone for

CUI at the lower portion of

the pipe.

Several Pipelines in Boil Off Gas

and Ammonia Loading pump

area were found continually

wet and cold insulation

lifetime exhausted. Immediate

insulation replacement is

recommended

Pipeline CUI

� 4”-LA-60007-A2-C55

� 4”-LA-60020-A2-C55

12”-GA-60009-A2-C55

To 6-K-201 B inlet line

Conclusion

� Atmospheric corrosion is a serious threat to the safe

operation of older, petro-chemical process plant.

� CUI detection is a challenging job; it is highly

unpredictable

� Reduce use of insulation as much as possible

� Avoid insulation where it is not a process requirements

� Design modification, apply suitable coating, surface

preparation, use suitable aluminum cover sheet etc.

� Prepare painting surface and apply coating as per

internationally acceptable codes & standard.

Q&A Session