Benefits and Challenges of Ultrasonic Guided Wave Inspection by Terry M. Webb, BP Refining NDE Specialist

Presenter

Terry M. Webb, Refining NDE Specialist BP Refining & Marketing

Over 25 years of experience in the field of Nondestructive Testing in oil refining, chemical plants, nuclear power plants, fossil fuel power plants, and synthetic fuels (coal liquefaction).

Current job position• Provide NDT support to five BP Refineries in the USA and six

overseas in the Netherlands, Germany, Spain and Australia.

• BA Degree from Marshall University in general studies with a major in Nondestructive Testing and minor in Engineering.

• Certified ASNT NDT Level III in Radiographic Testing, Ultrasonic Testing, Liquid Penetrant Testing, Magnetic Particle Testing, API-510, API-653 and AWS CWI.

Purpose of Presentation

Educate the inspector and engineer on the benefits

and challenges (pros and cons) of guided wave pipe

inspection.

Sources

TWI, “Long Range Ultrasonic Technologies Part of the

TWI’s Non-Destructive Testing Technology Group”

broacher downloaded from website, www.twi.co.uk

GUL website, www.guided-ultrasonics.com

PetroChem Inspection Services, Inc. 1475 East Sam

Houston Parkway South, Suite #100, Pasadena, Texas

Contents

Abstract – Introduction Sensitivity or Detectable Metal Loss General Restrictions Level of Inspection Difficulty GUL System – Challenges and Benefits Teletest System – Challenges and Benefits Conclusion

Abstract

Many inspectors and engineers do not realize there are three main commercial guided wave systems available globally and the differences in those systems This presentation will discuss two out of the three systems and provide information to help the inspector or engineer decided which guided wave system may be the best for a particular piping inspection situation. The physics or technical details will not be discussed

Guided Wave Introduction GUL system, Teletest system and MsS (magnetostriction)

systems can all be generally described as a ring of guided wave sensors used to generate guided waves in a pipe.

Guided waves are low frequency sound waves (in tens of kilo hertz sound waves as opposed to mega hertz in conventional ultrasonic testing) generated by transducers wrapped around the pipe circumference.

The MsS system (not discussed in details in this presentation) by Southwest Research is slightly more complicated.

Guided Wave Introduction

All three guided wave systems detect pipe wall thickness changes which generate reflective acoustic waves.

These sound waves sweep the entire thickness of the

pipe, the pipe acting as a wave guide - where the term guided waves originated.

Screen response signals are caused by reflections from

pipe features like butt welds, pipe tees, supports, clamps, etc.

Guided Wave Introduction

Guided wave system must be considered as a sorting or screening NDT tool instead of a flaw measurement tool.

Sorting or screening NDT tool will classify pipe in categories of wall loss levels.

Typically guided waves provide 100% initial pipe wall

screening coverage which should not imply 100% full reliable inspection coverage.

It is impossible to get response from small discontinuities 1% and less of pipe cross-section and longitudinal cracks 3% and less pipe cross-section.

Typical GUL Screen Response

Sensitivity or Detectable Metal Loss

Sensitivity or detectable metal wall loss for a cross-sectional area should conservatively be expected to be 5%, with perfect conditions down to 2%.

Sensitivity or Detectable Metal Loss

Guided waves do not measure wall thickness, just changes

At every change in pipe cross-section thickness a detectable screen indication is noted

Typical reflectors are pipe bends, circumferential welds, pipe tees, reducers, pipe supports, and of course corrosion

General Restrictions of Guided Wave Systems At each guided wave test, the acoustic

performance is situational. Restrictions include but not limited to:

- Temperature- Pipe contents will affect the acoustic waves- Surface condition of the pipe- Severe corrosion - Pipe coatings - Soil conditions - And many more parameters can affect the final results

General Restrictions of Guided Wave Systems

Basically if pipe butt welds can not be resolved on the screen presentation for a length of pipe, the exact inspection distance or how far the acoustic wave has travelled can not be determined.

Level of Difficulty Considering Test Conditions The following slides detail a guide for best,

intermediate and complicated conditions for Guided Wave inspection.

The guide takes consideration of many

factors for internal pipe product, external surface conditions, and pipe configuration

Note: Pipe flanges stop guided waves; pipe tees severely distort the acoustic sound; area immediately under transducer clamp and short distance on each side of test location not inspected

Level of Difficulty Considering Test Conditions

Best Conditions Internal pipe product

Gas; vapor

External pipe surface As new pipe surface, not coated/painted; well

bonded coating/paint; mineral wool insulation (only if dry, wet results in attenuation); good condition calcium silicate insulation; and above ground

Pipe configurationStraight runs of pipe; simple pipe supports (minimal

contact); loose bolted pipe supports; no elbows;

no smaller diameter pipe branches

Level of Difficulty Considering Test Conditions

Intermediate Conditions Internal pipe product

Low viscosity liquid (minimal acoustic absorbing); medium viscosity liquid (more acoustic absorbing)

External pipe surface

Slight corrosion pitting; thin plastic type coating; wet damaged insulation; underground sandy conditions (better); underground general soils (expect acoustic absorbing); soil-to-air interface

Pipe configurationMainly straight runs of pipeFew pipe elbows; reducers; tight encompassing or

clamped supports (tight bolted supports); smaller diameter pipe branches (large pipe and small diameter branches, for example 30” diameter pipe with 3/4” branch is not difficult to inspect)

Level of Difficulty Considering Test Conditions

Complicated Conditions Internal pipe product

High viscosity liquid (high acoustic absorbing); waxy, paraffin, thick sludge, bottoms type liquid (severe acoustic absorbing); brine product can result in salt out and sound attenuation

External pipe surface

Bitumen or thick plastic coating (high acoustic absorbing); moderate corrosion pitting; concrete casing tightly adhering to pipe; severe general corrosion pitting; underground compacted clay (most severe acoustic absorbing). Factory applied polyurethane coating very attenuating

Pipe configuration

Many elbows; many branches; pipe tees; welded pipe supports

Test Loop for Comparing GUL and Teletest

Add text

A permanent test loop was used to compare both GUL and Teletest systems

The same test clamp location was used for both systems and located about midway in the 6” test loop. Each system could easily display the pipe butt welds and the larger defects or machined anomalies placed into the 6” test pipe.

GUL System

The guided wave system is based on the piezoelectric array sensors developed by the Imperial College in the United Kingdom

GUL’s Wavemaker G3 Pipe Screening System uses low

frequency guided ultrasonic waves to inspected difficult pipe areas such as road crossings, while in service.

The G3 model has new advances to enhance focusing

capability with reportedly down to 1% sensitivity, GPS, and improved signal amplitude calibration. GUL tightly regulates its training scheme required for all users on GUL equipment

It has the capability of utilizing longitudinal, torsional, and flexural wave modes

GUL System

GUL System Inflatable Ring with Transducers on Pipe

GUL Challenges

Elbow - Sound loss or distortion Soil-to-air interface/Road Crossing: 3’ minimum and 8’

( optimum) of free pipe prior to the ground entrance Piping tees, flanges can not be inspected. Couplings, fittings, branches, and corrosion - acoustic

distortion Compacted clay deadens the acoustic sound beam. Maximum temperature generally 150°F Internal liquid or sludge material will dampen signal Longitudinal cracks in the pipe will not be detected,

unless they exceed 3% cross section using the torsional waves

GUL Challenges (continued)

Isolated small pin holes can be over looked Bitumen coating condition, if not brittle and disbanded,

limit test to 45’ or less Specialized Training required. Verification of Training and Qualification are not standard

but closely monitored by GUL Data Analysis is very operator dependent, software will

attempt to analyze but the operator must monitor and correct the software interpretations

Green line on the A-scan was the dead zone of the camp. Each side of the green line was grey line indicating the near field. Teletest did not show near field on their presentation

GUL Benefits

Rapid scanning of numerous locations in one shift Limited surface preparation. Painted surfaces good and

after local insulation removal (2’ to 3’) hand wire brush cleaning generally satisfactory. Coal tar wrap will require removal and wire brush

Avoidance of general pipe system insulation removal Long range capabilities (if conditions are right) 100% of the pipe wall inspected (screened). Internal and external pipe wall inspection Inspect insulated pipe Corrosion Under Insulation (CUI) survey with minimal

insulation removal Inspect inaccessible pipe areas

GUL Benefits (continued)

Inspect pipe clamps Inspect underground pipe Inspect underground pipe at road crossings Inspect river crossing pipelines Inspect pipe racks Inspect concrete encased pipe with restrictions Sensitive to 3% cross-section change but reliable at 5%.

If perfect Best Conditions, 1% sensitivity could be achieved

Set up time and results are faster compared to Teletest system

Typical Screen Response of GUL System Showing the Dead Zone and Near Field

Teletest System

The guided wave system is based on a piezoelectric array sensors clamped around the pipe developed by the Imperial College in the United Kingdom

The guided wave system is currently part of The Welding Institute (TWI) in the United Kingdom, Long Range Ultrasonic Technology (LRUT) group, and commercially available through Plant Integrity Ltd. (Pi)

The guided wave system is called the Teletest Focus.

The Teletest Focus can focus the ultrasound at points around the circumference of the pipe

It utilizes longitudinal, torsional, and flexural wave modes

Teletest System Inflatable Ring with Transducers

Teletest System with Transducers

Teletest Challenges

Same as GUL Challenges with following changes:

Many more wires to attach to the Teletest clamp than the GUL clamp

Takes a minimum of 15 minutes to download all test parameters from test location on pipe. This does not include evaluation and set up time at that same location

In an 8 hour shift, less test positions can be evaluated compared to the GUL system

Teletest Benefits

Same as GUL Benefits

Teletest Display of 6” Pipe at PetroChem Test Loop

Photo of Pitting on Pipe at 11:00 Position

GUL - Simulated Pitting located at 11:00 Position

Simulated pitting located @ 11:00 position.

Simulated pitting located @ 11:00 position.

Example showing both A-scan and C-scan display

C-Scan Display

Display showing both A- scan supplemented with C-scan presentation

C-scan display shows the amplitudes of the reflectors as a function of circumferential position

on the pipe and distance from the transducer ring

This helps in accurately locating the flaws and proper interpretation of the discontinuity

Conclusions

The purpose of this presentation was to provide the benefits and challenges in using ultrasonic guided waves for inspection of piping systems

Two of the major guided wave systems used through out the world was discussed to help the inspector or engineer decide which system may be the best for their particular piping situation

This presentation does not endorse any of the major commercial guided wave systems

Globally the guided wave manufacturers systems are in

almost continuous hardware upgrades and software improvements not only for piping but for other plant equipment such as storage tank floors and exchanger tubes

Questions?

Terry M. Webb

Refining NDE Specialist

BP Refining & Marketing