External corrosion Direct Assessment Seminar - NACE...

NACE ECDA

Seminar

External corrosion

Direct Assessment

Seminar

A Spectra Energy Company

Houston 2009

NACE ECDA

Seminar

ECDA „ Clean‟ Data

&

D.E. Success Rate

NACE • ECDA Seminar Houston 2009

Agenda

• Union Gas (A Spectra Energy company)

• ECDA Step Overview

• Indirect Inspection - „Clean‟ Data

• Direct Examination „ Success‟

• Questions?


Union Gas Ltd.

• Transmission, Distribution, and Storage

• Transmission integrity program per Canadian Regulations

• Utilizes ILI and ECDA

• ECDA

– Started in 2004

– To date 34 pipelines (or partial pipelines)

and 142 DE (111 excavations)


ECDA Steps Overview

• Pre-Assessment

• Indirect Inspection

• Direct Examination

• Post Assessment

Note:

– Excellence in Data

– Accountability Steps 1-4


Indirect Inspection – „Clean Data‟

• Influence testing

• CIPS / DCVG (ACVG)

• AC Attenuation

• Soil Resistivity

• AC Voltage


Indirect Inspection

Influence Testing

• Line needs to be „clean‟

• All influencing rectifiers are simultaneously

interrupted

• No dynamic stray currents (tellurics)


Checking that the Line is “Clean”

• Record a waveform during the OFF cycle and search for single-phase and three-phase rectifiers fingerprints.

• Install recorders for tellurics

• Check for obvious “false OFF” potentials

• Assess the magnitude of lateral gradient in Off cycle

• Complete telluric compensation as required


Waveform(As Captured by a Field Oscilloscope - OFF Cycle)


Frequency Spectrum(As Displayed by the Instrument)


Spectrum Analysis

DC Component – Matches survey value

60 Hz Component – Filtered by the survey equipment

1200

1620

270340

0

200

400

600

800

1000

1200

1400

1600

1800

DC 60 Hz 120 Hz 180 Hz

Frequency

Am

plit

ud

e (

mV

)


Spectrum Analysis

120 Hz Component – Fingerprint of a single-phase rectifier left ON or out of sync. With a 270 mV value, the line is not “clean”.

1200

1620

270340

0

200

400

600

800

1000

1200

1400

1600

1800

DC 60 Hz 120 Hz 180 Hz

Frequency

Am

plit

ud

e (

mV

)


Spectrum Analysis

180 Hz component - Fingerprint of a three-phase rectifier left

ON or out of sync and/or harmonics of 60 Hz. A 340mV

value versus 1620 mV 60 Hz is probably a harmonic.

1200

1620

270340

0

200

400

600

800

1000

1200

1400

1600

1800

DC 60 Hz 120 Hz 180 Hz

Frequency

Am

plit

ud

e (

mV

)


TelluricsCIPS Data. As Measured.

-2500

-2000

-1500

-1000

-500

0

2000 2050 2100 2150 2200 2250 2300 2350 2400 2450 2500

Chainage (m)

Pote

ntial (m

V)

ON Potential OFF Potential -1000 mV Criterion

To T

B6

To T

B a

t R

d. 2


TelluricsCIPS Data. Tellurically Compensated.-2500

-2000

-1500

-1000

-500

0

2000 2050 2100 2150 2200 2250 2300 2350 2400 2450 2500

Chainage (m)

Po

ten

tia

l (m

V)


To T

B6

To T

B a

t R

d. 2


Interrupter Failure (Telluric Record at Remote TP)

-2000

-1800

-1600

-1400

-1200

-1000

-800

-600

-400

-200

0

0.65625 0.66125 0.66625 0.67125 0.67625

Time (GMT)

Po

ten

tia

l (m

V)

OFF Potential ON Potential

Problems During Indirect Inspections


High Contact Resistance

( CIPS in Northern Ontario)-2500

-2000

-1500

-1000

-500

0

1740 1760 1780 1800 1820 1840 1860 1880 1900 1920

Chainage (m)

Po

ten

tia

l (m

V)


Severe CIPS Indication

Rock



When the contact resistance (Rc) is within the same range as

the internal resistance of the voltmeter (Rc), the measured

value would be only half of the real potential.

High Contact Resistance

V

c

meas

R

R

VV

1



The area was „surveyed‟ twice (once using a 1M spoiler) and

the “true potential” was calculated using simple math.

Double-reading Survey-2500

-2000

-1500

-1000

-500

0

1750 1770 1790 1810 1830 1850 1870 1890

Chainage (m)

Po

ten

tia

l (m

V)

True OFF Potential Measured OFF Potential -1000 mV Criterion

Real CIPS Indication



-1400

-1200

-1000

-800

-600

-400

-200

0

1000 1050 1100 1150 1200 1250 1300 1350 1400 1450 1500

Chainage (m)

Po

ten

tia

l (m

V)

-20

0

20

40

60

80

100

120

Gra

die

nt

(mV

)

ON Potential OFF Potential -1000 mV Criterion Lateral Gradient @ 3m

89.9

%IR

19.2

%IR

27.2

%IR

46.5

%IR

26.8

%IR 59.5

%iR

Low Shifts during DCVG Survey

(CIPS/DCVG in Northern Ontario)



To validate the calculated %IR, we measured both the

lateral gradient and the pipe-to-soil potential to

remote earth


– Direct Measurements

RE

REOL

V

GIR%



95.0%

63.0%

89.9%

59.5%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1101.6 1485.7Chainage (m)

%IR

Measured Calculated

The results show a very good match.


– Validation Results



Extended Coating Damage at Chainage 1101.6

m.


– DE Results (Photo)




– DE Results (Coating Inspection

Map)


FACTORY APPLIED

COAL TAR

Very Poor

Adhesion

12:00

1:00

2:00

3:00

4:00

5:00

6:00

7:00

8:00

9:00

10:00

11:00

1m

12:00

1:00

2:00

3:00

4:00

5:00

6:00

7:00

8:00

9:00

10:00

11:00

Ch. 1100.5m Ch. 1102.8m

FACTORY

APPLIED

COAL

TAR

N0m1.50.5

Disbonded Coating Unexcavated

LEGEND

Bare Pipe & Disbonbed Coating

BARE PIPE &

DISBONDED COATING

(SEE NOTE)

Note: Part of the disbonded coating came off during excavation. The entire coating was removed.

2m

Very

Poor

Adhesion


AC Attenuation. Rate of Loss.

Coating Quality Under New Asphalt

(No Permission to Drill Holes)

0

100

200

300

400

500

600

700

800

900

1000

5550 5600 5650 5700 5750 5800 5850

Chainage (m)

Sig

nal (m

A)

DCVG Surveyed Area Asphalted Parking Lot

Rate of Loss: 10.74 dB/km Rate of Loss: 8.57 dB/km



Indirect Inspection• Criteria for identification of indications

• Criteria for classification of indications

• Prioritization

• Select D.E. sites

Direct Examination

Flag:

– How well we do on DE?

– Need to predict what we expected to find!


DC Voltage

Gradient

Indication

Close Interval

Potential Survey

Indication

DC Interference (DCI)

SV MD MN NI

5 6 7 8

DCVG-SV

CIPS-SV 1 I I I I

CIPS-MD 2 I S S S

CIPS-MN 3 I S S S

DCVG-MD

CIPS-SV 4 I I I S

CIPS-MD 5 I S S S

CIPS-MN 6 I S M M

Prioritization Table Sample


Prioritization Table (Cont‟d)

DC Voltage

Gradient

Indication

Close Interval

Potential Survey

Indication

DC Interference (DCI)

SV MD MN NI

5 6 7 8

DCVG-BT

CIPS-SV 10 I S S S

CIPS-MD 11 I S M M

CIPS-MN 12 I S M N

DCVG-NI

CIPS-SV 13 I* N N N

CIPS-MD 14 I* N N N

CIPS-MN 15 I* N N N

* Consider excavating a short section of line under severe risk of

external corrosion, even if DCVG indications were not found.


Direct Examination Success

• Expectation of findings from the predictions

(for each DE)

• Actual findings from each DE excavation

• Compared the predictions to the actual

findings


Direct Examination - Prediction

Coating Condition and Metal Loss

(Only two areas to predict)

• Relatively simple, straight forward

statements in ECDA reports

• Variety of terms used in the reports to

describe the severity of each area on 122

„recommended‟ sites


Direct Examination - Findings


• Detailed findings documented by

measurements & photos for each area in the

reports

• Again a variety of descriptive terms used


Direct Examination - Comparison


• Categorized and scaled the descriptive

terms used from both coatings and metal

loss

• Done for both predictions and findings

• Made relative evaluations within and

between all categorizations


Small holidays / minor holidays

DE Descriptor Expectation FindingSuccess

Rate

DE#2. 8" Augusta Lateral

Ch. 4504.70 m- Minor holidays - Four very small holidays (jeep indications) (two pinholes, 0.5x0.1cm, 0.2cm diameter) 90

DE#2

Ch. 1009.40 m- Minor holidays

- Eight very small holidays (jeep indications) (two 0.3cm, 0.4cm, 0.8cm, 1cm

diameters; 0.4x0.2cm, 1.0x0.5cm, 1.3x0.5cm)

- Some of the jeep indications appeared fresh and may be the result of probing the line

during excavation 100

- Five of the jeep indications were on the longitudinal weld

DE#5

Ch. 3896.40 m- Small holidays

- One small holiday (5cm diameter) and nine very small holidays (jeep indications) (0.1

to 0.5cm diameter dents, 0.5x0.1cm scratch) 100

DE#4

Ch. 1454.90 m

(Validation with indication)

- Minor holidays- Five "minor" coating holidays (3cm, 4cm, and three 5cm diameters) in field applied

Denso tape, 20-30% damaged100

DE#1

Ch. 256.60 m- Minor holidays

- Eight very small holidays (jeep indications) covered by calcareous deposits (3cm,

6cm, 6cm, 10cm, 10cm, 15cm diameters; 10x3cm, 30x20cm)

- Extent of coating damage could not be measured due to adherent calcareous

coverage

100

- Spot of poor adhesion (1-2cm dia.) was found at jeep indication with largest deposit


Direct Examination - Comparison

For each Direct Examination

• Compared coating expectation to finding

• Compared metal loss expectation to finding

• „Scored‟ the comparison by %

• Averaged the two % comparison


Direct Examination - Results

Prediction vs. Finding

• 4 years (2004, 2005, 2006, 2007)

• 27 pipelines

• 122 DE (some validation)

• Approx 4 DE = n/a

• Overall success rate of 95%


Questions?

• Questions?

External corrosion Direct Assessment Seminar - NACE...

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