Final summary

- This final summary contains 19 conclusions which have been copied here for the record.

1. The Certifying Authority (Bureau Veritas) role in ICON was to ensure that the production of equipment performance data was done in a very rigorous manner thus giving high confidence in the use of results, which were certified together with the trial procedures.

2. Thirty two procedures were produced and tested for both manual (diver) techniques and CAT deployed techniques.

3. Most currently available techniques for crack detection and sizing have been compared across the same range of specimens.

4. CAT deployed techniques using precise tracking (single sensor) for tubulars (450mm max dia) and 'pick and place' (array) for plates have been assessed and been shown to be practicable for use offshore deployed from an ROV.

5. Capability and reliability comparisons have been made for several techniques (best and worst performance) showing the sensitivity to operator.

6. POD success data together with false call data has been produced giving some measure of reliability operating characteristic (ROC) of NDT systems.

7. New formats for POD data have been produced which are suited to fracture mechanics analysis.

These include plots against crack depth and also crack lengths defined using PD6493 criteria.

8. Data has been produced on the accuracy of crack sizing for surface breaking cracks.

9. For manual (diver) crack detection it has been possible to show that 7 systems are suitable for of tubulars. These are, in alphabetical order, ACFM, Cx EC, Lizard EC, MPI (Coil), MPI(Yoke), UCW. The ACFM array had successful laboratory trials but no results were obtained in sea trials due to accidental damage to the equipment.

10. For manual (diver) crack detection on tubulars, tee butts, metal difference, corroded tee butts and coated tubulars. ACFM, Cx EC and Lizard EC gave good crack detection performance. The systems also had a low false call rate although considerable variation in operators was observed.

11. For CAT deployment the number of cracks tested are fewer in number and hence statistical confidence is much lower than with the manual diver system results. However, ACFM, ACFM array and MPI (Single Leg) all detected over 80% of the cracks inspected with a very low false call ratio for the trials carried out.

12. Crack sizing was found to be accurate with ACPD (TSC) and also possible with ACPD (BG), ACFM and Lizard in descending order of accuracy. For ACPD (TSC) the overall accuracy of the mean prediction was within +10% with a standard deviation of about 1 mm (see Figure E4).

ROVPROBE equipment both recorded as filled all samples of 50% full or more.

14. Measurement of remaining ligament and wall thickness was found to be possible and accurate using both manual (diver) and ROV deployment.

15. Anode current measurement using GSCAN was found to be possible with errors limited to about 0.3 amps.

16. Visual inspection using the TV Trackmeter deployed from an ROV, was found to be quite practical for member sizing. Accuracy was found to be within about 2%.

17. Measurement of dents was found to be quite practical using photogrammetry. Using the Camel 70 sizing within about 10% was possible.

18. Detection of lack of root penetration and simulated erosion/corrosion in circumferentially welded tubulars was found to be quite practical with TOFD. 33 out of 35 lack of root penetration defects>1mm deep and 20mm long were detected (16 out of 16 >2mm deep), and 9 out of 9 root erosion defects >2mm deep and 30mm long were detected.

19. All the equipment details, procedure, and trials results have been assembled in three databases.

This software package allows the choice of the most suitable equipment on the basis of a chosen task.

coplanar surface flaws

a

₁

a

₂

2

c

1

2

c

2

c

2

s

criteria for

interaction for c₁ = c₂: s = 2 c₁

effective dimensions

after interaction a = a₂ 2 c = 2 c₁ + 2 c₂ + s

Figure E1 PD6493 coplanar surface flaws combination

ICON: various MPI trial results Lizard: EC tubulars FR (C) TSC: ACFM tubulars FR TSC: ACFM tubulars UK UCW: tubulars UK

Figure E2 ROC diagrams for various ICON trials⁴²

1. Comex Hocking performance trend for geometry (depth) (tubulars and T-butt)

Ref. 44 Fig. 2b

2. MPI yoke performance trend for dissimilar metals (depth)

(tubulars and metal difference butts) Ref. 44 Fig. 3b

3. ACFM performance trend for corrosion (depth)

(tubulars and corroded T-butts)

Ref. 44 Fig. 4b

4. Comparison of tank and sea results for MPI coils system (depth)

(tank tests and sea trials)

Ref. 44 Fig. 6b

5. Comparison of CAT and manual results for Comex EC on tubulars (depth) (tubulars and CAT) Ref. 44 Fig. 8b

Figure E3 ICON depth dependent POD results⁴⁴

a. ACPD results for three ‘regularly shaped’ defects ^12,40

b. BG and DNV ACPD crack sizing data⁴²

c. ACFM crack sizing data⁴²

Figure E4 Crack depth calibration^40,42

Table: ICON some results for FCR and POD

method total total detected FCR FCR POD

all >1mm >1mm all >1mm >1mm

1 OIS: MPI coils FR 52 42 42 17% 21% 100%

2 OSEL: MPI coils UK 84 66 65 47% 60% 98%

3 BG: yoke at sea 19 15 13 11% 14% 87%

4 OIS: coils at sea 19 15 15 58% 73% 100%

5 BG: yoke UK 37 26 26 32% 46% 100%

6 BG: coils UK 37 26 26 5% 7% 100%

7 BG: yoke corr.T (FR/UK) 66 28 20 1% 2% 71%

8 BG: yoke metal diff. UK 38 24 14 7% 11% 58%

9 BG: yoke 8560 T butt UK 36 26 24 13% 18% 92%

10 BG: yoke UW2 T butt UK 36 26 23 16% 22% 88%

11 Hocking: EC tubulars FR 46 39 35 23% 27% 90%

12 Hocking: EC tubulars UK 87 68 63 10% 13% 93%

13 Lizard: EC tubulars FR(C) 29 20 13 3% 4% 65%

14 Lizard: EC at sea 19 15 13 21% 27% 87%

15 TSC: ACFM tub. at sea 14 12 12 0% 0% 100%

16 TSC: ACFM epoxy coated 12 10 10 8% 10% 100%

17 TSC: ACFM tubulars FR 45 37 35 80% 97% 95%

18 TSC: ACFM tubulars UK 89 68 67 9% 12% 99%

19 TSC: ACFM array UK 9 8 6 0% 0% 75%

20 TSC: ACFM CAT FR 13 5 4 38% 99% 80%

21 TSC: ACFM corr.T (FR/UK) 52 23 22 13% 29% 96%

22 UCW: tubulars UK 75 55 48 29% 40% 87%

Table: UCL: some results for FCR and POD

22 MPI 88 73 71 53% 97%

22 EC AV100 92 75 69 8% 92%

22 EC EMD 88 71 54 10% 76%

22 EC Harwell 92 75 67 25% 89%

22 ACFM 92 75 72 15% 96%

22 UCW 72 55 50 45% 91%

Some points on ICON:

- Vast amount of information.

- Many variables both in equipment and in the types of test specimens.

- The ROC (reliability operating curve) in ICON is different from PISC:

- ICON takes all defects into account

- PISC takes only rejectable defects into account

In view of the (perceived) acceptance of 1mm deep defects the results for ROC are given using the number of defects > 1mm deep only.

- The three ROC diagrams contain some interesting observations:

- both for MPI and non-MPI methods the variation in FCR between two organisations (10-90%)

- the similarity in results for MPI and non-MPI methods - similar performance between sea trials and land trials

- only Lizard on land has an unacceptably low POD of 65% for 20 defects >1mm deep - The UCL findings have been indicated for comparison

- confirming the high FCR for MPI and UCW

- the below average performance of EC-EMD 9Which was not part of ICON) - Harwell (then) did much better than Lizard (now)

- From the table with some ROC data the following conclusions can be drawn:

- the table contains only 25% of the total number of records - low POD (POD = 80%) were observed for:

- whenever trials were done at different locations the results were similar - Variation in FCR

- large variations in FCRs were observed

- The main tables in the ICON database are for the POD versus defect length or depth.

- However, only when the dataset contains more than say 25 defects > 1mm deep can a POD curve be established.

- For the same reason the POD curves with confidence levels have been abolished, probably because not many of the results had enough datapoints

- On the other hand for many methods the POD for defects >1mm is close to 100% hence then no new information is obtained from a POD curve.

- The tables with length comparison were missing from my copy of the ICON database.

- Spurious results in the database could be either in number (according to the ROC tables) or in percentage (according to the ROC graphs. The latter is assumed for the figures in Note 007.

Executive summary

- Defects are based on the PD6493 method of combining adjacent cracks.

4.2.8 Performance trends

- This section comprises both an overview of the tests performed as well as some of the results.

However, results will be based on the ICON database itself.

- The two tables on the next page are worth recording: crack detection trials and crack sizing trials.

- The predictions for crack depth from 1-6mm using TSC ACPD on plates and from 6-25mm on tubulars is good. Additional information on this issue can be found in the UCL review report.

4.3 Intercalibration

- This section describes details of the various testsites of the full POD trials, POD as a function of method and crack length, ROC.

- On ROC (reliability operating characterisation): this is more involved than indicated on p.57.

** It is interesting to note that ICON concentrates on POD whereas PISC on probability of detection and correct rejection.

- p.61, in Fig. 12 and 13 information on crack depth sizing is given in the range 4-25mm showing a small negative bias.

- The predictions for crack depth from 1-6mm using TSC ACPD on plates and from 6-25mm on tubulars is good. Additional information on this issue can be found in the UCL review report.

** It is interesting to note that ICON concentrates on POD whereas PISC on probability of detection and correct rejection.

- p.61, in Fig. 12 and 13 information on crack depth sizing is given in the range 4-25mm showing a small negative bias.

uncoated tub.

tee butts metal diff. corroded T coated nodes sea trials

MPI coils C C C Table 11 Crack detection performance trend trials (p.46, title misleading: crack detection trials)

Nodes Plates Tee butts corroded T

Table 12 Crack sizing performance trend trials (p.47, title misleading: crack sizing trials)

C = completed - Other tests involve:

- measurements of dents - FMD

- measurements of sub-surface flaws using TOFD

- Crack detection through coating using ACFM and EC for coating thicknesses up to 2mm is also mentioned.

5. Project management

In document 2000/018 OFFSHORE TECHNOLOGY REPORT. POD/POS curves for non-destructive examination HSE (Page 98-105)