Magnetic Flux Leakage (MFL) Inspection Limitations

API 2009 Storage Tank Conference

Presentation

Aaron Lund

Regional Sales Manager of Gulf Coast

HMT Inc.

Don’t Discard the Technology and go backwards

MFL is the “Best”

method to

evaluate a

tank bottom

condition

quickly and

cost effectively

All Limitations

• Technology

• Human (Training and experience)

• Physical

Information on Technology Limitations

• A lot of information has been available and presented on in regards to technology limitations. However, the information is not common to all brands and types of scanners, so it is not without some controversy.

• API has been trying to quantify these technology limitations through a task group performing the re-write of non-mandatory Appendix G in API Standard 653 which call for operator qualification testing and certification. This effort is on-going but still has not happened thus far.

• This presentation will identify most of the physical limitations and offer some solutions to overcome those physical limitations

Let’s Talk about the Physical Limitations

• Tank Bottom inspection preparation

• Bottom Plate Lap Welds seams

• Bottom Plate Shapes and Sizes (sketch plates)

• Shell (corner weld) radius

• Patch Plates

• Tank Bottom Obstructions (columns / re-pads, internal piping, etc.)

• Edge Settlement

• Uneven Bottom Plates – peaks and valleys

• Thick Reinforced Coating

• Thick Annular Plates

• Magnet and Sensor location

Bottom Plate Lap Weld Seams

Typical Full Sized MFL Scanner

Overall scanner width = 14”

Bridge Width = 12”

Overall

Length = 36”

Front to base

sensor = 10”

Limitation Zone

Corner Weld – No Scan Zone

Sketch Plate Example

Typical Patch Plate

Typical Column with repad

Floating Roof Leg Striker Pad

Tank Bottom Obstructions

Solutions/Options

• Following an informed “risk assessment” on limitations– what are your best options:

– Do Nothing!!

– Extensive Visual Exam (should already be standard in any scope of work)

– Vacuum Box Testing (leak detection only)

– Helium Testing (leak detection only)

– Manual Ultrasonic Scrubs (corrosion locator)

– Hand/ Mini MFL Scanner (corrosion locator)

– ACFM Crack Detection / Magnet Particle Examination (surface breaking crack-like indications on welds only)

Patch Plate near lap seam – hole/extensive visual exam

Vacuum Box Testing

Helium Testing - Equipment

Helium Testing – Weld Seam Scanning

Manual/Mini Scanner Solution

Hand scanner width = 6”

Overall Scanner

length = 9 ½’

Scanner width = 6”

Front to back of

sensor bar = 6”

Manual/Mini Scanner for Near Corner Weld

ACFM Crack Detection Equipment

HISTORY

• This Technology was introduced in 1991.

• The method was initially developed for offshore structures

• Since then it has been applied to:

– Theme Park Rides

– Bridges

– Ships

– Petrochemical/Refinery Equipment

– Tanks

APPLICATIONS

• Weld inspection

• Detection of Crack-like indications

• Depth Sizing

• Monitoring Dimensional Propagation

SURFACE PREPARATION

• With the Magnetic Particle (MT) and Dye Penetrant Testing (PT) Methods, the quality of the surface preparation is critical to the ability of the method to detect discontinuities.

• This level of preparation is not required for electromagnetic techniques as the method of detection is not based on the migration of inspection media to the site of discontinuities.

SURFACE PREPARATION-Cont’d

• Reduced surface preparation does not imply no preparation

• The presence of ferromagnetic scale will impair the ability of the method to identify discontinuities

• However, the presence of surface rust will not significantly impair the sensitivity of the test

• Coatings-less than .200 does not need to be removed

ADVANTAGES

• No set up Calibration required

• Single direction deployment unlike MT

• Inspection time is reduced

• Data can be recorded for later comparison, review, or audit

CONCLUSION

ACFM has proven effective for:

• Coated Components

• Internal/External Shell-to-Bottom Welds

• Internal Lap Welds

• Sump Welds

• After tank bottom replacement

• When Stress Corrosion Cracking is suspected

This techniques provides consistent results - at a lower cost

In Summary

• Be aware of real world Limitations that exist everyday

• Make an informed risk assessment

• Revise or develop a work scope for your inspection vendor that addresses either:

– All tanks

or

– Specific to particular tanks based upon tank characteristics, risk analysis or tank condition

– Be informed of the technology/tools that can help

QUESTIONS?