INTERNAL AXIAL CORROSION IN OFFSHORE … · DNV-RP-F101 NDT Global involved in testing & reviewing of algorithms DNV method gives guidance on extraction of RBPs from UT ILI data

INTERNAL AXIAL CORROSION

IN OFFSHORE PIPELINES:

INSPECTION & ASSESSMENT

Dr. Christoph Jäger & Abdullahi Atto

PPSA Seminar 2014

19th November 2014, Aberdeen, UK

12/5/2014Copyright © 2013 | NDT Global 1

AGENDATopics

19.11.2014Copyright © 2014 | NDT Global 2

1. Introduction: Long Axial Corrosion

2. Impacts of Long Axial Corrosion on ILI and FFP

3. DNV Method: Assessment of Long Axial Corrosion Defects

4. Summary & Conclusions

LONG AXIAL CORROSION


typical type of corrosion in crude oil and water injection pipelines:

internal corrosion along six o’clock position

coherent corrosion areas of up to several kilometers length

often high corrosion growth rates (> 1 mm/year)

synonyms: channeling, channeling corrosion, six o’clock corrosion,

bottom-line corrosion

different shape of corrosion anomalies:

smooth and uniform WT reduction (e.g. corrosion/erosion)

rough surface, irregular and complex shaped geometry (e.g. MIC)

Characteristic Observations

LONG AXIAL CORROSION: EXAMPLE 1


Smooth and Regular Shape, Groove-like



Rough Surface, Irregular and Complex Shape



Chain of Corrosion Pits (Early Stage of Channeling)

IMPACTS OF LONG AXIAL CORROSION…


characteristics of channeling corrosion

impacts on ILI and assessment:

ILI technology

UT

cleaning

modification of standard procedures

re-processing/filtering of ILI data

eliminate outliers

reporting & assessment

next slides

… on ILI and Assessment

IMPACTS OF LONG AXIAL CORROSION


coherent corrosion over several km: usually reported as one anomaly

per pipe joint (length = joint length, depth = peak depth)

Reporting of Detected Anomalies

0

2

4

6

8

10

0 20 40 60 80 100 120

Wall

Th

ickn

ess

Distance

uncorroded WT anomaly 1

feature box girth weld position

dep

th D

length L



coherent corrosion over several km, usually reported as one anomaly

per pipe joint (length = joint length, depth = peak depth)

peak depth & length: no meaningful description of complex anomalies

Reporting of Detected Anomalies

0

2

4

6

8

10

0 20 40 60 80 100 120

Wall

Th

ickn

ess

Distance

uncorroded WT anomaly 1 anomaly 2


dep

th D

length L



different codes/standards for calculation of safe operating pressure

Psafe of metal loss anomalies

list-based methods:

e.g. B31.G, DNV-RP-F101 single

input: maximum depth, total length

same Psafe for anomalies 1 & 2

data-based methods:

e.g. RSTRENG (Effective Area), DNV-RP-F101 complex

anomalies described by actual remaining wall thickness profile

(river-bottom profile, RBP)

well suited for assessing complex shaped anomalies

all conventional methods: impact of continuous metal loss ( many

bad joints) on system PoF not accounted for

Assessment of Detected Anomalies

0

2

4

6

8

10

0 20 40 60 80 100 120

Wall

Th

ickn

ess

Distance



dep

th D

length L

AGENDATopics


1. Introduction: Long Axial Corrosion

2. Impacts of Long Axial Corrosion on ILI and FFP

Inspection Technology

Cleaning

Data Processing

Reporting

Assessment

3. DNV Method: Assessment of Long Axial Corrosion Defects

Main Ideas

Application Examples

4. Summary & Conclusions

ASSESSMENT OF LONG AXIAL CORROSION


JIP (DNV, Statoil, DONG Energy) “Assessment of long axial

corrosion defects – Specification”

DNV Method: Overview

results will be incorporated in revised

DNV-RP-F101

NDT Global involved in testing &

reviewing of algorithms

DNV method gives guidance on

extraction of RBPs from UT ILI data

calculation of pipeline pressure capacity

determination of corrosion growth rates

extrapolation of pressure capacity







DNV-RP-F101










rugged corrosion anomalies and rough internal pipe surface

echo loss (missing data) and/or outliers in UT WT data

important: identification & replacement of erroneous WT values before

calculation of RBPs

use of stand-off (SO) data:

strong signal (1st echo)

usually no echo loss/outliers

WTSO = WT + SO

= distance sensor – outer pipe wall, ideally constant

WT missing or outlier WTSO outside tolerance band

WT replaced by RWTSO = WTSOmedian – SO

Filtering of WT Data & Extraction of RBPs

WTSO

SO

WT

SO

WT



Filtering of WT Data & Extraction of RBPs: Example

original WT

SO




original WT

processed WT

SO




river-bottom profile

processed WT







DNV-RP-F101





calculation of pipeline pressure

capacity





Requirements:

complex corrosion anomalies

assessment based on RBPs

standard methods:

Psafe (pipeline) = Psafe(worst joint)

however: minimum Psafe not sufficient to

describe condition of pipeline

example: Psafe histograms with same

minimum Psafe but different number of

“bad” joints

many bad joints (e.g. channeling)

“system effect” higher PoF

Calculation of Pipeline Pressure Capacity

0

10

20

30

40

50

60

70

80

60 70 80 90 100 110 120 130

Nu

mb

er

of

an

om

ali

es

Pressure capacity Psafe [bar]

0

10

20

30

40

50

60

70

80

60 70 80 90 100 110 120 130

Nu

mb

er

of

an

om

ali

es

Pressure capacity Psafe [bar]



Requirements:

assessment based on RBPs

account for potential increase in PoF

DNV Method:

basis: DNV-RP-F101 Complex Shaped Defects Method (Part A)

affected area divided into subsections

Psafe calculated for all subsections

Psafe(section i) PoF(section i) for considered assessment pressure

total PoF(pipeline) calculated from PoF of all sections i

PoF(pipeline) vs. max. allowable PoF (safety class)

Psafe(pipeline)




Example:

water injection pipeline affected by channeling corrosion

assessment based on 190 pipe joints with remaining WT < threshold

RBPs extracted according to DNV method

Psafe calculated for sections of 1.7m length (DNV-RP-F101 complex)

Psafe(pipeline) = 260 bar

Psafe(worst joint) = 268 bar

Psafe(pipeline) is 8 bar (3%)

below Psafe(worst joint)

system effect

more joints with low Psafe

higher system effect


0

20

40

60

80

100

120

140

270 280 290 300 310 320 330 340 350 360 370 380 390 400 410 420 430 440 450 460

Fre

qu

en

cy

Pressure capacity [bar]

Pdesign







DNV-RP-F101






determination of corrosion growth

rates




basis: results of consecutive UT ILIs

list-based CGA (change in peak depth):

not sufficient for long complex corrosion features

Level 4 of DNV Method: calculation of corrosion growth rates from

comparison of RBPs, i.e. data-based CGA

Corrosion Growth Analysis (CGA)

0

2

4

6

8

10

0 20 40 60 80 100 120

Wall

Th

ickn

ess

Distance



dep

th D

length L



Corrosion Growth Analysis: One Pipe Joint

13

14

15

16

17

18

19

0 2 4 6 8 10 12

Wal

l th

ickn

ess

[mm

]

Distance to USGW [m]

RBP(2014)




13

14

15

16

17

18

19

0 2 4 6 8 10 12

Wall

th

ickn

ess [

mm

]


RBP(2014)

CWT(2014)




13

14

15

16

17

18

19

0 2 4 6 8 10 12

Wall

th

ickn

ess [

mm

]


RBP(2014) RBP(2011)

CWT(2014) CWT(2011)




13

14

15

16

17

18

19

0 2 4 6 8 10 12

Wal

l thi

ckne

ss [

mm

]


RBP(2014) RBP(2011)

CWT(2014) CWT(2011)

0

0.1

0.2

0.3

0.4

0.5

0.6

0 2 4 6 8 10 12

Co

rro

sio

n g

row

th r

ate

[mm

/yea

r]


2011->2014

13

14

15

16

17

18

19

0 2 4 6 8 10 12

Wal

l thi

ckne

ss [

mm

]


RBP(2014) RBP(2011) RBP(2010)

CWT(2014) CWT(2011) CWT(2010)




0

0.1

0.2

0.3

0.4

0.5

0.6

0 2 4 6 8 10 12

Co

rro

sio

n g

row

th r

ate

[mm

/yea

r]


2010->2011

2011->2014



Corrosion Growth Analysis: Results for 190 Pipe Joints

0.0

0.1

0.2

0.3

0.4

0.5

0 1 2 3 4 5 6 7 8 9

Co

rro

sio

n g

row

th r

ate

[m

m/y

ea

r]

Distance [km]

average 95% quantile section joint avg moving avg.

50

100

150

200

250

300

350

400

450

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 1 2 3 4 5 6 7 8 9

Ps

afe

[b

ar]

Co

rro

sio

n g

row

th r

ate

[m

m/y

ea

r]

Distance [km]

growth rate (section) growth rate (joint avg.) Psafe



Extrapolation of Pressure Capacity: Psafe vs. Growth Rate

low Psafe + high growth rates!

50

100

150

200

250

300

350

400

450

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 1 2 3 4 5 6 7 8 9

Ps

afe

[b

ar]

Co

rro

sio

n g

row

th r

ate

[m

m/y

ea

r]

Distance [km]

growth rate (section) growth rate (joint avg.) Psafe



Extrapolation of Pressure Capacity: Results

150

170

190

210

230

250

270

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Pip

eli

ne p

ressu

re c

ap

acit

y [

bar]

Time after latest ILI [years]

joint avg.

0.22 mm/year

0.32 mm/year

MAOP

Psafe(pipeline) reaches MAOP

5.2 – 7.5 years after latest ILI

SUMMARY & CONCLUSIONS


long axial corrosion impacts on ILI & assessment

can be reliably detected & sized using UT ILI

feature list information not sufficient to characterize complex anomalies

data-based assessment methods (pressure & corrosion growth)

required

methodology specifically designed for assessment of long axial

corrosion was developed by DNV:

filtering of WT using SO, especially helpful in case of non-optimum

data quality

accounts for higher PoF resulting when many pipe spools are

affected by severe corrosion

NDT experience: DNV method proved good applicability

NDT Global GmbH & Co. KG

Friedrich-List-Str. 1

76297 Stutensee, Germany

www.ndt-global.com

THANK YOU!

Documents

INTERNAL AXIAL CORROSION IN OFFSHORE … · DNV-RP-F101 NDT Global involved in testing & reviewing of algorithms DNV method gives guidance on extraction of RBPs from UT ILI data