A Refinery Approach to Address Corrosion Under Insulation & External Corrosion

7/28/2019 A Refinery Approach to Address Corrosion Under Insulation & External Corrosion

1/35

A REFINERY APPROACH TO ADDRESS CORROSION UNDER INSULATION

& EXTERNAL CORROSION

Rob Scanlan, Ricardo Valbuena and Ian Harrison

ConocoPhillips,

Humber Refinery

South Killingholme, North Lincolnshire

United Kingdom DN40 3DW

Rafael Rengifo

ConocoPhillips

Trainer Refinery

4101 Post Road

Trainer, PA, 19061, USA

ABSTRACT

Corrosion under Insulation (CUI) and External Corrosion continue to be a major issue for all

Petrochemical facilities throughout the world. Over many years, refineries and petrochemical plants

have experienced extensive damage due to these mechanisms. As a result, several of the company

refineries have been investing in a CUI and External Corrosion inspection program. This paper details

the methodology used by two refineries for addressing this damage and lessons learned throughout the

implementation.

The methodologies used by the two refineries differed at first in that one approach involved an

initial cursory inspection of all areas in the refinery and history review of all fixed equipment items

followed by a thorough inspection and maintenance refurbishment of equipment selected by this initial

inspection. The second approach involved a software based desk top study with no initial inspection.

The programs are being managed as a total refurbishment project, which include the identification of

lines and vessels operating below 350 degrees F; inspection of vessels and lines, including insulated and

painted lines; 100% removal of insulation in areas ranked High and Medium High based on theassessment above; repair where necessary; repaint and finally re-insulate if necessary.

1

Paper No.

08558


2/35

The paperalso describes the findings from the work carried out so far. At Refinery A which

followed the initial cursory inspection approach, 18 vessels have had 100% insulation removal, 200

miles of piping have been visually inspected and 16 miles of piping refurbished. For vessels, 89 areas

had lost part or all of the corrosion allowance, 26 areas had undergone weld repairs, 2 tower top heads

have been replaced and a further nozzle replaced. On piping, 137 areas were found to have gone through

part or all of the corrosion allowance and 61 further pipe sections required replacement. At Refinery B,

the areas for inspection were selected using a desk top study. The selection did not include an initial

inspection of the entire refinery. The desk top study directed the efforts to discrete areas of the refinerywhere external conditions of insulation and long range NDEs were then used to decide whether further

insulation removal was necessary. The approach at Refinery B has resulted in fewer inspection finds and

it is now adjusting the CUI/External Corrosion program based on these finds and the lessons from

Refinery A.

Keywords: Refining, Corrosion under Insulation, External Corrosion.

INTRODUCTION

External corrosion and CUI continues to be a major issue for all refineries and petrochemical

plants throughout the world. CUI was brought to the awareness of the industry as a damage mechanism

in the early 1980s(1,2)

. Over many years, refineries and petrochemical plants have experienced extensive

damage due to these mechanisms and as the refineries and petrochemical sites age, this external damage

become more prevalent. To mitigate this damage, most refineries and petrochemical sites are instigating

a CUI/External Corrosion Program. This paper details the methodology used by two of these refineries

to address this damage.

Most CUI/External Corrosion programs follow the same basic steps as noted below:

Development of Corrosion Loops or areas with emphasis on CUI and External Corrosion.

Completion of an initial inspection of all areas in the refineries to establish scope.A thorough review of the equipment history.

Criticality and risk ranking of pieces of equipment based on initial inspection and

equipment history review.

Amount of insulation removal and inspection coverage in line with the initial inspection

and risk ranking.

Project approach to assure sustainability for the CUI and External Corrosion Program.

This paper also covers several case studies resulting from the work undertaken in the last three

years. Novel techniques to prevent CUI and external corrosion such as the use of non-metallic insulation

for sealing and cages for personal protection in lieu of insulation are also discussed.

Site description

Refinery Ais located on the south bank of the estuary of the River Humber on the east coast of

England, approximately 1.5 km northwest of the town of Immingham and 0.5 km east of the village of

Killingholme, See Figure 1. The refinery was constructed between 1966 and 1969 and commissioned in

1970. The current capacity of the refinery is about 225,000 bpd (11.4 million metric tons per year). The

2


3/35

exports are the full range of refinery products, including LPG, dimethyl ether, gasoline (petrol), aviation

kerosene, fuel oil, heating oil and petroleum coke.

An aerial picture of the refinery is provided in Figure 2, with an arrow showing north, the

prevailing winds are from the south west. The photo indicates the critical processing units of concern

due to the cooling tower drift area as shown by the shaded area in the schematic. The refinery location is

deemed as a mix of marine and rural due to its location.

Refinery B is located in Trainer, Pennsylvania, approximately 10 miles south of the Philadelphiaairport on the Delaware River, and 3 miles north of the Delaware State line. The refinery currently has a

crude oil processing capacity of 185 MBPD (9.4 million metric tons per year) and started operations in

1910. The Refinery has been operated by several owners in the last 97 years and has undergone several

major revamps.

Refinery B makes a large range of products which include reformulated gasoline and low-sulfur

diesel for the local markets. Refined products are distributed to customers in Pennsylvania, New York

and New Jersey via pipelines. An aerial picture of the refinery is provided in Figure 3.

METHODOLOGY

As part of corporate efforts to improve mechanical integrity, a set of required standards has been

under implementation since 2002 throughout the downstream organization. One of the key standards

developed was a CUI and External Corrosion Required Standard. Each refinery was required to

developed and execute its own CUI and External Corrosion program for piping and vessels following

this standard.

Piping Assessment Methodology

At Refinery A, the external condition of the piping was not known in sufficient detail to allow

the effective use of RBI software tools. Piping and painting/insulation condition and history over the 30-

year life of the plant were questionable. As a result, the refinery prioritized the areas of the refinery

using the consequence model from the API580 document (A-E). The likelihood of failure was based on

the following sources of data:

An initial cursory inspection of all the areas in the refinery looking for evidence of external

corrosion or CUI or areas potentially affected by CUI following the API RP 574 (Inspection

Practices for Piping System Components) section 6.3.3 (e.g. areas exposed to mist over-

spray from cooling water towers; areas exposed to steam vents; areas with damaged or

missing insulation; damaged paint; caulking which has hardened, separated or is missing;

etc.).

An External Visual Inspection (EVI) from grade of all the Oil Movement and Storage(OM&S) piping grouped and prioritised by consequence. This survey included bunds (tank

restraining walls), bridges and ground level piperack. Specialist techniques like

Electromagnetic Acoustic Transducer (EMAT) and Guided Wave Ultrasonic were used as

screening tools for pipe supports, bund penetrations and bridges.

An extensive initial inspection of pipe racks was performed using a Rope Access (Rope

Climbing) technique, further details of the rope access process can be found in Appendix 1.

3


4/35

EMAT was again used as a screening tool for pipe supports where excessive corrosion was

found by the rope access survey.

Areas of concern selected by the Inspectors, senior operators and maintenance leaders as

identified from years of walk rounds in their units.

History and assessments from the painting and insulation specialist and the corrosion

engineer.

Armed with this input, the corrosion engineer and inspectors at Refinery A selected and ranked

the piping most susceptible to CUI and External Corrosion, see Table 1. The piping selected included

whole or sections of process units and pipe-rack sections within a unit or between units as well as

bridges requiring lifting and bunds requiring excavation.

Vessel Assessment Methodology

Again the external condition of the vessels was not known in sufficient detail to allow the

effective use of RBI software tools. The likelihood of failure was based on the following sources of

data:

All insulated vessels or sections of vessels or towers operating below 350 degrees

Fahrenheit were selected for an initial review.

A review of inspection data for these vessels was performed to determine potential

susceptibility.

Further information provided by the unit Inspectors, senior operators and maintenance

leaders about their vessels of concern as identified from years of walk rounds in their units.

Using this information the corrosion engineer and inspectors again ranked the vessels on its

susceptibility to CUI, see Table 2.

Refinery B based its CUI and External Corrosion implementation program on a desktop study

process flow with no initial inspection to verify the general assumptions. The process involved selectingsome insulated vessels and piping with an operating temperature under 350F. The selection did not

include an initial inspection of the entire refinery. The desk top study directed the efforts to discrete areas

of the refinery where external conditions of insulation and long range NDEs were then used to decide

whether further insulation removal was necessary. This initial desk study proved not to be successful in

finding CUI/External corrosion damage and midway through the program, a field based approach similar

to Refinery A was adopted. Refinery B is now in the initial stages of this new approach.

Refurbishment Methodology

A total refurbishment is being applied to the piping and vessels ranked as High and Medium

High based on the above assessment methodology. On insulated piping this involves 100% insulationremoval. Painted lines are also inspected in piperacks, especially at pipe supports. Lines are lifted to

inspect contact points at supports, following operational contingency plans in case of any loss of

containment. Any repairs where necessary are performed and the lines repainted and finally re-insulated

if necessary. For painted lines at pipe supports, bonded pads (See figure 5) are installed to extend the

life of the piping.

4


5/35


6/35

circumferential bands up to 60% around the tower circumference, the band was 6-8" in height. It is

recommended to remove all transportation attachments at commissioning. These two bands were not

evident on the original construction drawings and were only found by a full insulation strip.

Refinery A Case Study 6 - H.D.A Purge Tower

The top of the tower operates at approximately 320F (160C). CUI on the top surface of the manway was

not noticeable with the insulation in place using external inspection. Nozzle UT inspection gave a

thickness of 9.7mm. Internal UT scan from internal surface of manway to external flange found CUI andgave a minimum thickness of 5.8mm. Nozzle inspection using UT scanning from the ID is more

effective at finding CUI.

Refinery A Case Study 7 - 3 Benzene Export Line

A digital radiography inspection point noted some thinning, this was followed up by partial removal of

asbestos insulation, the pipe was found to be suffering from CUI at the 12 oclock position with a

remaining wall thickness of 1mm. The area was prone to flooding and therefore insulated lines should

not sit in water.

Refinery A Case Study 8Vent on 12Naptha Line

An insulated unused vent line with a pressure gauge was found during the EVI program. The insulation

was removed to reveal severe CUI with a remaining thickness down to 0.56mm. Always remove

unnecessary insulation.

Refinery A Case Study 9 - 3 Hydrogen High Pressure Line

This high pressure hydrogen line sat on structural support and was partially buried by fireproofing.

Contact point corrosion was down to 1.75mm; the line was lifted and radiographed. It is prudent not to

let process lines sit in fireproofing, which is a moisture trap and only allows limited visual inspection.

Refinery A Case Study 1014 RefineryNitrogen Supply

EVI survey indicated major external corrosion at a water run off point from a road bridge. Corrosion

products were removed to give a minimum thickness remaining of 2.7mm at the contact point.

Considerations need to be given to water run off locations from bridges and to provide protection to

inaccessible lines.

Refinery A Case Study 11 - Virgin Distillate Run Down Lines

Severe corrosion was found at contact supports within a ground level piperack which is subject toflooding. The Naptha feed line failed with several other lines subject to severe external corrosion.

Areas of flooding need to be controlled and access for underside inspection needs to be provided.

Refinery A Case Study 12 - 1 Instrument Analyzer for 6 Sour Vent Gas

Severe CUI of the analyzer piping was found to have a minimum thickness of 0.74mm. Prior to the find,

new insulation had been installed over the old insulation without refurbishment, therefore hiding the area

6


7/35

of concern to visual inspection. Inspection of instrument piping should be included in any inspection

plan and old insulation should not have new installed over the existing.

Refinery A Case Study 13 - LPG Jetty Flushing Line

External corrosion occurred at a pipe support contact point on the Jetty on the LPG flushing line. Heavy

corrosion at the support contact point had resulted in completely corroding through the wear pad (3mm

thick). The measured pipe wall thickness remaining next to the wear pad was 2.9mm. Previously welded

supports added to the line were not re-painted leading to excessive corrosion.

Refinery A Case Study 146 Hydrogen Export Line

Heavy external corrosion down to 1.5mm was found at a contact point where the line was sat in

fireproofing, which acted as a moisture trap. This example was found by Guided Wave Ultrasonics.

Extra protection is required at all line support contact points, do not fireproof support contact points.

Refinery A Case Study 15 - 12 Blending Storage Diesel Line in Bund

External corrosion found within wrapped area that was buried in the soil bund. An initial partial dig

gave a UT thickness of 5.7mm; however wrapping was in poor condition. Complete bund excavation

and wrapping removal indicated a remaining wall thickness of 2mm. The section of line was replaced

prior to the bund replacement. Underground wrap systems breakdown over time. At this location the

wrap not reinstated and an underground paint was used.

Refinery B Case Study 16 - Diesel Treater Tank PV-1407

A small leak was detected at the bottom of the Diesel Treater Tank PV-1407. The metal jacket or

cladding was new. The insulation was in extremely poor condition when the cladding was removed. This

revealed a general corrosion attack with a thick corrosion products scale. The vessel was replaced and a

Root Cause Analysis initiated. Poor coating application and cladding over damaged insulation werenoted as potential causes.

Refinery B Case Study 17 - FCC Fractionator Top Reflux Out of Overhead Accumulator Piping

Circuit

A pinhole leak was detected at a support contact point, where a pack of cables created an environment

for debris and rust to accumulate. The corrosion attack observed was local and very severe at the 6

oclock position contact point. The piping section was replaced and a contact point bonded pad was

installed.

Refinery B Case Study 18 - Tank Farm Distillate Line

A pinhole leak was detected at a soil to air interface adjacent to a road crossing. The corrosion attack

observed was severe and local to the soil to air interface on both sides of the road crossing where the

coating/wrapping was in poor condition. The piping was replaced and the soil to air wrapped to current

refinery standards. Visual inspection of soil to air interface should always include some soil removal to

assess the coating/wrapping condition.

7


8/35

DISCUSSION

Refinery A has been undertaking its CUI/External Corrosion Program for the past 3 years; the

findings from the program are detailed in Table 3. At the time of writing this paper, Refinery A had

inspected and refurbished 18 vessels involving 100% insulation removal, refurbished 16 miles of piping

in 5 piperack systems and inspected and assessed approximately 200 miles of piping. The refinery has

classed a find as where part or all of the corrosion allowance has been lost due to CUI or external

corrosion.

The assessment process undertaken for vessels proved to be accurate at Refinery A. Of the 18

vessels inspected, CUI to some degree was found on 16 vessels, i.e. an 89% hit rate. On these 16

vessels, 89 areas have lost part or all of the corrosion allowance, 26 further areas have undergone weld

repairs, 2 tower top heads and a nozzle have also been replaced.

The CUI/External Corrosion Program on piping was less accurate. The total number of pipes

inspected/refurbished as part of the CUI/External Corrosion Control program is approximately 1800.

This has yielded 137 finds and 61 pipe replacements for an inspection hit rate of 11% for the High and

Medium High risk ranked piping systems. The finding hit rate was less than expected for piping ranked

Medium High and High. The piping of concern was 37 years old and exposed to the mist from the

cooling towers. More damage at the 6 oclock position was expected between supports. However, 48%

of these finds occurred at contact points on pipe supports, 14% at field welds where the coating had

broken down and 34% at other locations e.g. through earth bunds, bridges etc.

The desk top methodology used by Refinery B did not find any significant CUI/External

corrosion. The corrosion found them as it manifested in the form of leaks. Since the start of the

program, Refinery B experienced 5 CUI/External failures. Each failure instigated a Root Cause

Analyses (RCA) investigation, these RCA findings revealed coating damage and design flaws as a major

contributor to the failure. The failures experienced reinforced the need for a revised CUI/Program with

more initial inspections to validate assumptions (similar to Refinery A) and with 100% insulation

removals on critical piping systems and vessels deemed High or Medium High following the initialinspection.

Some of the major findings and lessons from the CUI/External Corrosion Program from Refinery

A and Refinery B regarding the assessment procedures and site work are detailed below; a section of

novel repair methods is also included.

Lessons Learned - Assessment Procedures:

Desk top RBI software assessments based on assumptions are not effective in prioritizing for

CUI or external corrosion. The CUI prioritization and ranking requires detailed field data and

knowledge of inspection and maintenance history.Visual inspection of the external condition of insulated equipment alone and without

consideration of operational and maintenance history is not effective. (See Case Study 12).

Effective CUI and External Corrosion management requires the development and implementation

of work processes to assure sustainability.

Large site implementations such as the ones described in this paper require the full backing of

management to again ensure sustainability and continued funding.

8


9/35

CUI/External Corrosion finds and leaks should be documented, tracked and trended to determine

the need and pace of new inspections and refurbishments.

Lessons Learned - Site work

100% insulation removal was required when inspecting vessels deemed as having a High or

Medium High susceptibility to CUI since damage was not always at the expected locations. One

vessel had transportation rings hidden beneath the insulation that formed a water trap causing

CUI. On another vessel CUI was found underneath the Fireproofing. See Case Studies 3 and 5.

Vessel inspection found that 90% of the CUI damage occurred at attachments and breaks in the

metal cladding. Severe CUI leading to replacement was also found around the top heads on two

vessels. See Case Studies 2 and 4.

During the visual inspection of piperacks using rope access, the corrosion found at Refinery A

was around pipe supports where debris and water was able to collect. EMAT was implemented

using rope access trained personnel as a follow up to evaluate the worst support contact points.

The accuracy of this technique was validated several times in the field by physically lifting the

pipes and inspecting visually and with pit gages.

The rope access inspection had other benefits in that it was able to highlight areas of immediate

concern needing immediate refurbishment or repair.The rope access technique also provided a further safety benefit by having the opportunity to

remove unattached debris within the pipe rack such as loose nuts and bolts, gaskets, and scaffold

clips.

Quality control of all the steps in the refurbishment program is critical for the future integrity of

the vessels or piping. Some of these steps include the quality assurance of blasting, inspection,

painting, insulation and addition of support pads.

Novel Repair Methods

Whilst undertaking full inspection of the vessel, the opportunity to blast and paint should be

undertaken. Current best practice is a thermally sprayed aluminum coating (TSA) (3).One development undertaken at Refinery A is that all attachments and the top head of vessels are

sealed using non-metallic cladding to reduce the possibility of water ingress. See Figure 4.

When the pipes were lifted for blasting and painting as part of the pipe refurbishment project,

support pads were fitted to increase the future life of the piping system, See Figure 5.

At the initial stages of the CUI/External Corrosion Program, a survey was performed on piping

with Insulation for Personnel Protection (Ip) at Refinery A. Initial results indicated that 6% of Ip

locations had CUI. As a result, all Ip is being replaced with perforated cladding See Figure 6.

CONCLUSIONS

The CUI risk ranking process of vessels and piping requires detailed field data and knowledge of

their inspection and maintenance history.

Full vessel insulation removal using the vessel assessment process produced a CUI hit rate of

89% for the 18 vessels inspected, with 89 areas having lost part or all of the corrosion allowance,

26 further areas have undergone weld repairs, 2 tower top heads and a nozzle have also been

replaced.

9


10/35

The CUI/External Corrosion Control program produced 61 pipe replacements and a hit rate of

11% for the High and Medium High risk ranked piping systems. The finding hit rate was less

than expected for piping ranked Medium High and High. The piping of concern was 37 years old

and exposed to the mist from the cooling tower. More damage at the 6 oclock position was

expected between supports. However, the majority of these finds occurred at contact points on

pipe supports or at field welds.

Close visual inspection of the piperacks via rope access provided many benefits, these included;

Quick collection of field data on which the piping refurbishment priority of the piperackswas based.

It also highlighted areas of immediate concern which could not be performed with a visualinspection from the ground. These allowed for their immediate refurbishment or repair.

Provided an added safety benefit of having the opportunity to identify and remove potentialfalling objects from piperacks.

EMAT was found to be very good for screening and evaluating pipe support contact points, but

the technique is very operator dependant.

Trials with the latest Guided Wave Ultrasonic Techniques are looking promising, especially for

screening of pipelines with limited access i.e. bunds, bridges etc. The accuracy of the techniqueshould improve after more field experience.

10


11/35

Figure 1A Schematic Locating Refinery A and its Crude import via the Monobouy .

Figure 2An aerial photo of refinery A indicating the areas of concern from the cooling tower drift due

to the prevailing winds from the south west.

N

Prevailing Wind

From South West

11


12/35

Figure 3An aerial photo of Refinery B.

Div UnitCUI

Priority

Year

Planned

A PR Coke Drums Piperack - Trial Section 1 2006

D UP IPC piping 1 2006

C UP LPG Bullet Piping 1 2006

BB PR HAD-AEU Piperack 1 2007

BE PR ALKY Piperack - All Sections 1 2007

C PR CTU-FCC Piperack - Cooling Towers Section 1 2007

BB PR No.2 CRU Unit Piperack 1 2008BB PR Sulphur & SWS Piperack 1 2008

BE UP ALKY Unit Piping 1 2008

BB UP HAD-AEU Unit Piping 1 2008

BE PR PRU Unit Piperack 2 2008

A PR Coke Drums Piperack - Section 2 2 2008

A PR Coke Drums Piperack - Section 3 & 4 2 2009

C PR CTU-FCC Piperack - FCC to Utilities Section 2 2009

BB UP CAT POLY & Merox Unit Piping 2 2009

B UP Sulphur & SWS Unit Piping 2 2009

BB PR CPU Piperack 2 2009

C PR Piperack Utilitiies 2 2009

BB PR Piperack Ave B Aromatics 3 2009

BE UP Butamer Unit Piping 3 2009

C UP Utilities Area 51 3 2009

C UP Tank Farm Piping - LPG 3 2009A UP Rail Loading 3 2009

B UP NO 1 CRU 3 2009

BB UP NO 2 CRU Unit Piping 3 2009

B UP VRU 3 2009

BE UP PRU Unit Piping 3 2009

BE PR Butamer Piperack 3 2009

C/BB PR Piperack Ave C - Utilities to AEU 3 2009

Refinery A - CUI Piping Project

Table 1A listing of the piping systems requiring refurbishment following the risk analysis performed.

12


13/35

Vessel Vessel Name RankYear

Planned

W7050 New SWS 1 2005

W3631 Alky Isostripper 1 2005

W574 Benzene Tower 1 2005

D3309 W305 Ovhd Drum 1 2005

D7402 Amine knockout Drum 1 2005

D5423 CPU Reactor 1 2007

W534 Stripper Column 2 2006

W533 Raffinate Splitter 2 2006

W531 Extractor 2 2006

W-573 2 2006

D-3622 SGP Butane Drier 2 2006

D-3623 SGP Butane Drier 2 2006

W4701 Aromatics Extr 2 2006

W308 2 2006

W-575 2 2006

W6301 No 2 Reformer Stab. 2 2007

D421A Butane Drier 3 2007

D454 Propane Drier 3 2007D455 Propane Drier 3 2007

D583 W575 Ovhd Accum. 3 2007

W4441 3 2007

W535 Recovery column 3 2007

D306 4 2008

D308 4 2008

D5402 4 2008

D5408 4 2008

Refinery A - CUI Vessel Work Scope

Table 2A listing of the vessels requiring refurbishment following the risk analysis performed.

Program Grit Blast & Paint Weld Repairs Replacement Total

Piping 137 0 61 198

Vessels 89 26 3 118

316

External Corrosion/Corrosion Under Insulation Find

Note: Finds Are Defined As Where The Corrosion Allowance (3mm) Has Been Lost

Table 3A listing of the corrosion finds from the CUI / External Corrosion project being undertaken at

Refinery A.

13


14/35

Figure 4Non metal cladding used to seal the top head and attachments to prevent future water

ingress

Figure 5The figures indicate piping in a piperack that has been refurbished, with pads added.

Figure 6. Perforated cladding which has been used to replace insulation for personnel protection.

14


15/35

Table 4 - Refinery A Case Study 1 - FCC Feed Drum

Duty: FCC Feed Drum Material: Carbon Steel

Wall Thickness: 12.7mm Damage mechanism: Crack

Commissioning Date: 1985 Period of Metal Loss: 21 years

Photograph:

Description of Corrosion Mechanism or Detail

The FCC feed drum operates at 193C (380F) which is above the temperature for CUI. The lifting lugs had been left on

the vessel at installation and not totally encapsulated in cladding. Severe corrosion was experienced behind the lifting

lug which acted as a heat sink, lowering the temperature locally to below 300F (149C). The CUI products forced the

lifting lug away from the vessel causing a through wall crack on the top head.

Action Taken

Lifting lugs were removed and the vessel repaired. Full paint coating and insulation re-instated.

Lessons Learned / Design Change

Remove lifting lugs at installation. If you do have to keep them, then fully encapsulate the lifting lugs in cladding.

15


16/35

Table 5 - Refinery A Case Study 2 - Sour Water Stripper Tower

Duty: Sour Water Stripper Tower Material: CS with SS cladding

Wall Thickness: 12.7mm Damage mechanism: Thinning


Photograph:

Description of Corrosion Mechanism or DetailSour Water Stripper Tower - Tower operates at 255F (107C) at the bottom and 180F (82C) at the top. Picture 1 -

Section of lower support ring which has virtually corroded through (22mm), shell was also showing losses of 3-4mm.

Picture 2 - Section of tower just below top head experienced severe CUI. Picture indicates 2-3 inches of corrosion

products (10mm thick). On the left hand side of the picture is the exposed internal SS cladding.

Action Taken

Support ring cut out and replaced, Shell of tower overlayed. Top of tower replaced.


Regular inspection of Cladding integrity is required. Top head cladding was in an extremely poor condition.

16


17/35

Table 6 - Refinery A Case Study 3 - Amine Knockout Drum

Duty: Amine Knockout Drum Material: Carbon Steel

Wall Thickness: 10mm Damage mechanism: 10mm


Photograph:

Description of Corrosion Mechanism or DetailKnock out drum operates at about 80F (27C). Severe corrosion of skirt, up to 10mm loss, full wall thickness metal loss.

Action Taken

Vessel was repaired, overplated and re-fireproofed.


Continued inspection of Fireproofing is required.

17


18/35

Table 7 - Refinery A Case Study 4 - AEU Recovery Column

Duty: AEURecovery Column Material: Carbon Steel

Wall Thickness: 11.1mm Damage mechanism: CUI


Photograph:


The recovery column operates at 180F (82C) at the top of the tower. Picture 1 indicates 40mm of scale above the 3rd

vacuum ring from the top of the tower. The rings were not water shedding. The second picture shows the metal loss

with the scale removed. The remaining thickness was as low as 2mm at various locations.

Action Taken

Temporary plates were bonded around the shell above the stiffening ring. New top section for tower ordered for

replacement in April 08.


Consideration for vacuum ring supports should be made during design stage, these supports should be drilled where

possible.

18


19/35

Table 8 - Refinery A Case Study 5 - AEU Extractor Tower

Duty: AEU Extractor Tower Material: Carbon steel



Photograph:


The Extractor Tower operates at approximately 180F (82C). Severe CUI was found at the transportation support bands.Support bands discovered during full insulation strip. Up to 10mm loss at two circumferential bands, 60% around the

tower circumference, bands were 6-8" in height.

Action Taken

Weld overlayed the tower back to 19mm at first opportunity.


Remove all transportation attachments at commissioning. These two bands were hidden by insulation and were not

evident on the original construction drawings and were only found by a full insulation strip.

19


20/35

Table 9 - Refinery A Case Study 6 - H.D.A Purge Tower

Duty: H.D.A Material: Carbon steel

Wall Thickness: 10mm Damage mechanism: CUI


Photograph:


Top of tower operates at approximately 320F (160C). CUI on top surface of top manway not noticeable with insulationin place from external inspection. Nozzle UT inspection gave a thickness of 9.7mm. Internal UT inspection of manway

(i.e. scan from internal surface to external flange) found CUI and gave a minimum thickness of 5.8mm. Pictures show

CUI with an approximate loss of 4mm.

Action Taken

Insulation removed and area grit blasted. Inspected indicated loss on shell up to 1.5mm. Area painted and insulation

replaced.


Nozzle inspection using UT scanning from the ID is more effective at finding CUI.

20


21/35

Table 10 - Refinery A Case Study 7 - 3 Benzene Export Line

Duty: 3 Benzene Export Line Material: Carbon Steel


Commissioning Date: 1969 Assumed Period of Metal Loss: 38 years

Photograph:


Thinning found while conducting digital radiography of nearby bend, this was followed up by partial removal ofasbestos insulation, the pipe was found to be suffering from CUI at the 12 oclock position with a remaining wall

thickness of 1mm. The area was prone to flooding.

Action Taken

The line was Furmanite clamped; Guided wave inspection of line back to pump was performed. Awaiting asbestos

insulation removal for full inspection.


Do not allow insulated lines to sit in water.

21


22/35

Table 11 - Refinery A Case Study 8Vent on 12 Naptha Line

Duty: Vent on 12 Naptha line Material: Carbon Steel



Photograph:


An insulated unused vent line with a pressure gauge was found during the EVI program. The insulation was removed to

reveal severe CUI with a remaining thickness down to 0.56mm.

Action Taken

Vent and pressure gauge replaced.


Remove unnecessary insulation.

22


23/35


24/35

Table 13 - Refinery A Case Study 1014 RefineryNitrogen Supply

Duty: 14 RefineryNitrogen

Supply

Material: Carbon Steel

Wall Thickness: 7.9mm Damage mechanism: Contact point

Commissioning Date: 1969 Assumed Period of Metal Loss: 38 years

Photograph:


EVI survey indicated major external corrosion at a water run off point from a road bridge. Corrosion products were

removed to give a minimum thickness remaining of 2.7mm at the contact point.

Action Taken

Line has been replaced. All lines under bridge refurbished and painted with underground spec paint, and pipe contact

support pads added.


Change water run off from bridge and provide better protection to inaccessible lines.

24


25/35

Table 14 - Refinery A Case Study 11 - Virgin Distillate Run Down Lines

Duty: Distillate rundown Material: Carbon steel

Wall Thickness: 6mm Damage mechanism: Contact point


Photograph:


Severe corrosion found at contact supports within a ground level piperack which is subject to flooding. The Napthafeed line failed with several other lines subject to severe external corrosion.

Action Taken

Failed line replaced, one other line clamped and three other lines underwent guided wave UT and were found to be

acceptable until next opportunity, when they will be replaced.


Control areas of flooding and provide access for underside inspection.

25


26/35


27/35

Table 16 - Refinery A Case Study 13 - LPG Jetty Flushing Line

Duty: LPG Jetty Flushing Line Material: Carbon Steel

Wall Thickness: 6mm Damage mechanism: Contact point


Photograph:


External corrosion occurred at a pipe support contact point on the Jetty on the LPG flushing line. Heavy corrosion at

the support contact point had resulted in completely corroding through the wear pad (3mm thick), the measured pipe

wall thickness remaining was 2.9mm.

Action Taken.

Line depressured and corrosion products removed to assess support location. Severely corroded section was replaced.

Full line was lifted, blasted and painted. Nine more wear pad areas required remedial work.


Previously welded supports added to line were not re-painted leading to excessive corrosion.

27


28/35

Table 18- Refinery A Case Study 146 Hydrogen Export Line

Duty: 6 Hydrogen Export Line Material: Carbon steel

Wall Thickness: 7.1mm Damage mechanism: Contact point


Photograph:

Description of Corrosion Mechanism or Detail.

Heavy external corrosion down to 1.5mm was found, worst location at contact point where the line was sat infireproofing, which acted as a moisture trap. Found by Guided wave Ultrasonics.

Action Taken.

Line taken out of service and replaced with a contact point bonded pad.

Lessons Learned / Design Change.

Extra protection is required at all line support contact points, do not fireproof lines.

28


29/35

Table 17- Refinery A Case Study 15 - 12 Blending Storage Diesel Line in Bund

Duty: 12 Blending storage

Diesel Line in Bund

Material: Carbon Steel



Photograph:

Description of Corrosion Mechanism or DetailExternal corrosion found within wrapped area that was buried in the soil bund. Initial partial dig gave a UT thickness of

5.7mm; however wrapping was in poor condition. Complete bund excavation and wrapping removal indicated a

remaining wall thickness of 2mm.

Action Taken.

Replaced the section of line prior to the bund replacement. .


Underground wrap systems breakdown over time. Wrap not reinstated, an underground paint specification was used.

29


30/35

Table 19 - Refinery B Case Study 16Diesel Treater Tank PV-1407

Duty: Diesel Treater Tank PV-

1407

Material: Carbon steel

Wall Thickness: X.X mm Damage mechanism: CUI


Photograph:


Severe corrosion detected at the bottom of the vessel, no sign of insulation deterioration was observed in the vessel and

the insulation metal jacket looked in very good condition. Corrosion attack observed was generalized severe corrosion

with thick corrosion product scale. The insulation under the metal jacket was in poor condition.

Action Taken.

Vessel replacement, Root Cause Analysis.


The metal jacket or cladding was new. The insulation was in extremely poor condition when the cladding was removed.

This revealed a general corrosion attack with a thick corrosion products scale. The vessel was replaced and a Root

Cause Analysis initiated. Poor coating application and cladding over damaged insulation were noted as potential causes.

30


31/35

Table 19 - Refinery B Case Study 17FCC Fractionator Top Reflux Out of Overhead Accumulator

Piping Circuit

Duty: FCC Fractionator Top

Reflux

Material: Carbon steel

Wall Thickness: X.X mm Damage mechanism: Contact Point


Photograph:


A pinhole leak was detected at a support contact point, where a pack of cables created room for debris and rust

accumulation. Corrosion attack observed was severe with very localized pitting corrosion at the contact point (6:00)

Action Taken.

Piping section replaced with a contact point bonded pad.


GUL is not always the best technique for contact point inspection because of the very localized nature of this attack.

31


32/35

Table 20 - Refinery B Case Study 18Tank Farm Distillate Line

Duty: Tank Farm Distillate Line Material: Carbon steel

Wall Thickness: X.X mm Damage mechanism: Soil to Air Interface


Photograph:


A pinhole leak was detected at a soil to air interface at the sides of a road crossing. The corrosion observed was severe

with very localized pitting corrosion at the soil to air interface on both the sides of the road crossing, where the

coating/wrapping was in poor condition.

Action Taken.

Piping section replaced and coating repaired as per ConocoPhillips Refining Engineering Practices


GUL is not the best technique for soil to air interfaces inspection because of the very localized nature of this attack and

attenuation produced by the coating and buried conditions

REFERENCES

1. Meeting on Corrosion underInsulation November 1980.2. James Richardson A review of the European meeting on Corrosion under Lagging held in

England, November 1980, ASTM 880 Corrosion of Metals under Thermal Insulation Ed.

Pollock/Barnhart, pp42-59

3. EFC WP13 and WP15Corrosion under Insulation (CUI) GuidelinesEuropean Federation ofCorrosion (EFC) 2007.

32


33/35

APPENDICES

Visual Inspection of Pipe work located within the Unit Piperacks

Introduction

An external Visual Inspection was carried out on the piping systems within the Unit pipe racks by

ConocoPhillips and Oceaneering Inspection personnel.Objectives

The objective of the inspection was to inspect all the piping systems within the unit to determine the

external integrity of the piping and to address any immediate problems with a view to making any

recommendations for any further inspections, which may be required.

Method

Fall arrest trained inspection personnel were used to visually inspect all the pipe work within the

confines of the pipe rack. Any areas of concern were assigned a severity rating, reported and

photographed. The adopted system to identify the pipe work and its position is explained further in theGuidelines for Inspection of Pipe racks.

The inspection addressed the following items:

Insulation Pipe Supports Corrosion Mechanical Damage Paint Work

The method used to apply a severity rating system is explained in the Guidelines for Inspection of

Pipe racks.

Results

Any areas of immediate concern were followed up at the time of the inspection. Photographs were

taken of any areas that were rated 4 or above. Any item with a severity rating of 3 or above was assigned

a tag number which is referenced on the report and has been tagged on-site to help identification. Areas

of concern at pipe supports and were pipes sit on concrete support beams were identified to allow further

inspection using the Emat Inspection System, the results of which were reported separately.

Recommendations

Insulation - Any area with a severity rating of 3 or above indicates that the insulation has been

compromised and may allow water ingress, which may lead to corrosion (CUI). Therefore, the

insulation in these areas needs to be removed to allow further inspection.

33


34/35

Pipe Supports - Areas of concern which have been identified have now been scheduled for further

inspection by Emat.

Paintwork- Any area with a severity rating of 3 or above indicates that the paintwork has broken down

sufficiently so that it does not provide the protection that was intended. Therefore, the pipe work needs

cleaning and preparing to carry out remedial paintwork.

Corrosion or Mechanical DamageAny Corrosion or Mechanical damage with a severity rating of 4

or above will require further inspection. These areas will need access providing.

In order to assist with the identification of the areas recommended for further work each item of concernhas been assigned a tag number which is included in the report and a yellow tag has been attached to the

area of the pipe on site.

For guidance examples of severity 4 and 5 ratings for each category are provided below;

Assessment Examples

Insulation

Severity 4 Severity 5

Pipe Supports


34


35/35

Paintwork


Corrosion or Mechanical Damage


Date post:	03-Apr-2018
Category:	Documents
Upload:	ishan-shah
View:	233 times
Download:	0 times

A Refinery Approach to Address Corrosion Under Insulation & External Corrosion

Documents