Surface & Weld Inspection

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Surface Sound
Surface Aircraft
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Time-of-flight Diffraction (ToFD)

Time-of-flight diffraction (ToFD) technique is an ultrasonic NDT technique, which relies on the diffraction of ultrasonic energies from 'corners' and 'ends' of internal structures (primarily defects) from the component being tested. ToFD being an advanced and automated weld examination technique, it assists in Fitness For Purpose (FFP) inspections as well. Using TOFD, the expert NDT team members at TCR perform amplitude-independent accurate flaw sizing on a wide coverage area. TCR Arabia has 4 crews duly qualified from Saudi Arabia ready to perform ToFD inspections in KSA.


ToFD is a fast and effective method of scanning a wide weld area in a very limited time period. While TOFD is a very powerful and efficient technique, it suffers from limited coverage resulting from two dead inspection zones:

  • The first dead zone: Near the surface, as a result of the lateral wave

  • The second dead zone: At the back-wall, resulting from the width of the back-wall reflection.


TCR Arabia’s NDT equipment allows inspections simultaneously combining TOFD with conventional pulse echo. Pulse echo complements TOFD and covers the dead zones.


TCR Arabia uses products from Olympus’s OmniScan technology which has capabilities to indicate to the operator the exact location of a flaw with respect to the weld centerline and bevel face.  An experienced analyst from TCR Arabia is able to characterize fusion flaws based on location and amplitude response. This technique has many advantages including: 

  • Wide coverage area using a pair of transducers

  • Accurate flaw sizing; amplitude-independent, Sizing technique using time-of-flight information

  • One-line volume inspection, provides highly efficient scanning

  • Setup is independent of weld configuration

  • Highly sensitive to all kinds of defects with no sensitivity to defect orientation

  • Amplitude-insensitive, acoustical coupling less critical 


ASME Boiler and Pressure Vessel Standard Section VIII Code Case 2235-9 states that is acceptable to use the TOFD for Ultrasonic examination in accordance with ASME Section V, Article 4. ASME Code Case 2235-9 mentions about replacing RT with UT and has resulted in incorporating TOFD into pressure vessel work for both detection and sizing of flaws. This now allows TOFD to be used on all Section VIII pressure vessels.TOFD is perfectly acceptable to use as per Code Case 181 and Code Case 179 of ASME B 31.3 for piping products.


API 579 in its current draft form states the Recommended Practice for Fitness-for-Service (The crack depth, length, angle and distance to other surface breaking or embedded cracks is typically determined using UT examination techniques, either TOFD or angle beam. Draft-API 580 states the Risk Based Inspection Recommended Practice (Base Resource Document recommends automated ultrasonic shear wave testing as a highly effective inspection technique for crack detection and sizing. The capability of the Automated UT technique/type is evaluated using the probability of detection (POD) curves from round-robins in the past where TOFD showed the best performance). British Standards Institute's welding standards policy committee has created the BS 7706 as a guide for the calibration and setting-up of the Ultrasonic Time of Flight Diffraction (TOFD) technique for defect detection, location, and sizing of flaws. Another well-documented guide is Pr EN 583-6.


Phased Array Ultrasonic Technology (PAUT)


TCR Arabia’s team of qualified technicians provide PAUT services (using a TCG or DAC) to industry leaders using state of the art equipment and probes manufactured by Olympus. Multiple crews are available to take up major projects. The technical team is trained by Eclipse Scientific of Canada.


Phased array ultrasonic systems utilize multi-element probes, which are individually executed under computer control. By exciting each element in a controlled manner, a focused beam of ultrasound can be generated. The software enables the beam to be steered. Two and three-dimensional views can be generated showing the sizes and locations of any flaws detected.

The team at TCR with its decades of experience have extensive clues to the characterization of various types of flaws using TOFD with the exception of a few instances where definitive conclusions are rare. In the case of Phased Array technology, an experienced analyst has a greater chance of determining flaw type based on the percentage of sound transmitted back to the probe.


The team has done a number of noteworthy ToFD projects: 


  • 100% weld inspection of Storage Tanks at Kuwait as per API 650 appendix U

  • Random inspection of pipelines in Rabigh, Saudi Arabia as per ASME Code Case 181

  • Pressure Vessel inspection in India as per ASME Code Case 2235-9 


In the Middle-East, TCR-Arabia has the most talented and experienced team to perform Automated Ultrasonic Testing on weld joints based on the Time of Flight Diffraction (TOFD) technique. Senior NDT testing team members from TCR-Arabia, TCR Kuwait and TCR Engineering Services, India visited Québec, Canada to undergo intensive hands-on training on practical usage of TOFD.


TCR-Arabia has also collaborated with a number of international partners including world-renowned NDT Level III experts in USA and Canada to supervise on the test procedure and scan plans. Omniscan MX for TOFD TCR-Arabia acquired the state-of-the-art OmniScan MX test unit with a number of probes of different angles, EPOCH LT Ultrasonic Flaw Detector and the TomoView software from Olympus NDT, Canada.

Corrosion Mapping

Corrosion mapping is an ultrasonic technique which maps and identifies variations in material thickness due to corrosion. Corrosion is the deterioration of metallic material by the chemical (or electrochemical) attack. This is normally caused by the environment (most often water), and sometimes by another material.

There are several types of corrosion:

  • Uniform corrosion that extends evenly across the surface

  • Pitting corrosion that is uneven and has smaller deep areas (pits)

  • Exfoliation corrosion that moves along layers of elongated grains

  • Inter-granular corrosion that grows along grain boundaries

To perform corrosion mapping an automatic or semi-automatic scanner is used to scan an inspection surface, using various ultrasonic techniques including pulse echo, eddy current and phased array. Corrosion mapping is widely used in the oil, gas and nuclear industries for the inspection of pipework, pressure vessels, storage tanks and reactors. In the Aerospace sector, corrosion mapping is often referred to as ‘C-Scan’ for the inspection of composite materials. Results for corrosion mapping provide a high degree of repeatability and the advantage of position and size data for every flaw which can be compared for repeat scans of the same area to track flaw growth or corrosion rates both generally and for individual pits.

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Electro-Magnetic Acoustic Transmission (EMAT)

Using the EMAT technique with panametric probes, TCR Arabia can measure the high-temperature (up to 325° C) surface thickness. Above this temperature, the thickness readings become unstable, unreliable and non-repeatable. 
The surface for thickness measurement needs to be fairly smooth, free from rust, scale or any other kind of deposits. To get a clean surface for thickness survey, a metallic file, wire brush, small chisel and emery paper can be used for cleaning. Hammering is strictly not advisable for removal of scale/deposits. In case the above method does not yield the desired cleaning, then mechanical cleaning by power brush should be used. Under exceptional circumstances, grinding is used as a method for cleaning, with prior permission from the inspection engineer.
Thickness can be measured on painted surfaces, provided the surface paint is visible without any blisters. For critical measurement where the corrosion rate calculations are important from the remaining life point of view, paint removal is done before doing thickness survey.



Thickness measurement across different mediums



For all on-site piping, corrosion loops are the basis for carrying out thickness survey whereas, for offsite and tank farm piping, special loops are made for thickness monitoring:

  • Each corrosion loop (for on-site piping) have a combined isometric where Thickness Management Locations (TML) are serially marked

  • If any base readings are taken before commissioning, it is done with random values measured on the components

  • Routine, on stream or shutdown thickness measurement at these locations, is done in the form of a scanning. The scanning format is in a grid of size 1.5” x 1.5”, with each component marked with chalk before thickness scanning

  • Out of all the locations, few TMLs are identified for regular scanning. The selected TMLs are identified by the inspection engineer, based on the probability of corrosion at these locations (as compared to other locations in the loop) and accessibility considerations.

  • Respective maintenance departments provide access to ladders, scaffolding or portable trolleys for thickness scanning. In case corrosion is observed in these TMLs, then other TMLs in the loop are included for thickness scanning


Hot Tap Locations

In case of thickness survey of equipment and piping for hot tap locations, following steps are undertaken:

  • The maintenance team marks the location of the new nozzle as per the exact type and dimensions of the component to be welded on the parent pipe

  • The Inspection engineer verifies the type of component to be welded viz. weldolet, pipe of pipe connection, a nozzle with reinforcement pad, split sleeve nozzle etc. The Inspection engineer marks the centerline of the proposed weld joint: A width of 1.5” to 2” shall be marked on either side of the proposed weld centerline. A close thickness survey is undertaken along the centerline and on either side and the minimum thickness measured is reported in the hot tap file.


If the thickness measurement is comparable to nominal or previously measured values (if available at the same locations or at different locations in the same pipe), then it could be assumed that there is no corrosion at the location.


If the thickness measurement indicates severe corrosion, and thickness measured is very close to the minimum allowable for hot tapping, then hot tapping should be avoided at the location, as it will be difficult to pick up a thickness point with minimum thickness through this procedure.


Minimum thickness required for hot tapping is 4.8mm. If the pipe is corroded and actual thickness is in the range of 6 – 8mm, then alternate methods should be used to check the pipe thickness and certify the same fit for the hot tap.


Thickness Locations In Tanks

  • In case of storage tanks, the thickness is measured from outside first, followed by shell course from the bottom

  • In all the other shell courses, the thickness is measured along the staircases. Few thickness points are taken near the weld and few at the center of the shell course plate

  • In case of roof plates, the thickness is measured on each plate, with two thickness points at the center of each plate and one thickness point at the corner of each plate

  • In case of bottom plates, thickness measurement is possible only during an internal inspection. Under this, the thickness is measured on each plate, with two thickness points at the center of each plate and one thickness point at the corner of each plate



It is also not unusual to record thickness values more than the previously measured readings at the same locations or in the same grid. This is considering the inherent limitations in the thickness measurement technique. Some of the factors that contribute to the increase in thickness could be:

  • Inability to put the probe exactly at the same location. If the probe is kept even a couple of millimeters away from the previous location there could be different and probably a higher reading.

  • Corroded surface profile on the inside surface of the component from where the sound waves are reflected back.

  • Surface preparation prior to the thickness survey

The inherent accuracy of the thickness meter itself is +/- 0.1mm. Hence a thickness value 0.2–0.3mm more than the previously measured value. is considered to be acceptable.


A measured thickness value more than the above-mentioned limits needs to be re-checked again especially in a grid scanning exercise. The following steps could be followed for verification of the readings. ➢ Check the calibration of the instrument using a step wedge and using a standard block of thickness close to the thickness range being measured.

  • Check the thickness measured with another meter and probe at the same location

  • Check surface preparation before taking readings Based on the repeat thickness survey report can be verified and corrected if required.


In case of piping where spot readings have been measured at Thickness Management Locations (TML), against each TML number, measured readings are filled in.

In the case of equipment, a development drawing of the equipment needs to be submitted showing an approximate location of thickness measurements. The thickness may be entered on the sketch itself. Alternately the TMLs can be marked on the sketch and the corresponding thickness values for each TML submitted separately.


In case of close scanning of a location in equipment or a pipe, the readings can be submitted as a grid. The grid will have the orientation (N/S/E/W) with possible reference from a nearby nozzle, weld etc. The grid identification at the site is required in order to check the thickness at the same location and compare the same for corrosion if any. The grid size shall be clearly mentioned in the sketch.


Measured thickness data shall be evaluated by the respective inspection engineer. Random thickness measurement shall be compared with the nominal thickness of the vessel and also with the previously measured thickness. In case the thickness values (min/max) compares well with the previously measured thickness or nominal thickness, the values measured shall be considered to be satisfactory.


In case of random thickness survey indicates a sharp difference from the previous readings (apparently indicating a corrosion rate of more than 0.5mm/year), then a detailed scan has to be done at that location (grid scanning). The inspection engineer will also find out whether such steep corrosion rates are possible by discussions with operations/CTS. This will help in identifying other corrosion prone areas in the equipment/piping. Based on the grid scanning results, if corrosion is confirmed then thickness measurement is repeated should be repeated after a short period (period to be decided based on the corrosion rate, remaining corrosion allowance and the ability to do repeated UT survey and the criticality.


During any scan, for each TML, the minimum thickness can be compared between successive thickness measurements surveys and corrosion rate can be calculated.

Internal Oxide Scale Boiler Measurement

The high-temperature operation of steam boilers (in excess of 10000F or 5000C) can cause the formation of a brittle iron oxide called magnetite on the inside surfaces of tubing. It reduces heat transfer and increases operating tube wall temperature. This shortens the creep life of the tube. If detected in time, it can help for de-scaling decisions to increase the life and efficiently. It is possible to judge the remaining life of the boiler tube by measuring internal oxide scale.

Alternating Current Field Measurement (ACFM)

TCR Arabia undertakes ACFM at offshore platforms and onshore installations in Saudi Arabia.

Alternating Current Field Measurement, also known as ACFM is a one-pass method to inspect welds and to locate and size surface breaking cracks. An electromagnetic field is induced into the surface being inspected. When the probe is passed over a surface breaking crack, the electromagnetic field is disturbed allowing detection of the anomaly. TCR Arabia measures this field using the proprietary software which allows crack depth and length measurements on a real-time basis. Probes of almost any configuration can be customized for nearly any application imaginable. 


Digital Crack detection method covers:


  • More Precise than Conventional methods 

  • High-Temperature Applications 

  • No Recoating required 

  • No Metal Contact required 

  • Sizes Cracks (Length & Depth) Applications 

  • Detects through Coatings, Paint & Scale 

TCR performs ACFM in association with its international partner. This technique replaces conventional dye penetrants, magnetic particle testing and ultrasonic testing for size defects.


Applications of ACFM includes: 

  • Structural Welds on Platforms 

  • Structural Welds on Drilling Rigs 

  • Cooling Tower Welds 

  • Compressor Fin Surfaces and Threads 

  • Drill Collar Threads 

  • Pipeline Girth Welds and Supports 

  • Pressure Vessel System Welds 


Robotic Inspection of

Coker Drums

TCR Arabia in partnership with CIA of Canada provides Robotic Inspection of Coke Drums using Laser Inspection Technique, Remote Visual Inspection and Robotic Crack Detection System.


TCR Arabia is proud to collaborate with CIAI, one of the world's premier coke drum inspection company. As a Full-Service Partner in Coke Drum Reliability, we are in a position to deliver additional value and benefit to its refinery clients. The dimensional data provided with comprehensive coke drum inspection service is used in a combined approach with other follow-up techniques to develop proactive strategies for improved vessel performance and life, including:

  • Engineering Analysis (Finite Element Modelling)

  • On-line Monitoring of Damage (Strain Gauge location)

  • Operational Control and Optimization

  • Pre Turnaround Vessel Assessment

  • Recommendations on Repair and Replacement

  • Balance of Life Modelling

  • Fitness for Service Assessments

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Laser Profile Inspection is a remotely deployed, laser-based, range-imaging inspection tool designed to profile the internal surface of the coke drum in order to locate and measure vessel distortions in a consistent and accurate manner.

Remote Visual Inspection utilizes a state of the art, high-resolution video camera with zoom capabilities to visually inspect 100% of the internal surface condition of the coke drum, including the dome, cone and nozzles.

Robotic Crack Detection System is a telescopically deployed robotic crawler equipped with an NDE sensor (ACFM) used to quickly and precisely confirm the presence of ID forming cracks by accurately sizing the length and depth of the indication.

Ultrasonic Examination for Welds in Ferritic Materials in Saudi Arabia

TCR Arabia conducts ultrasonic examination for welds in ferritic materials. The UT examination team adopts a well-defined procedure for detecting, locating and evaluating indications within weld metal and heat affected Zone and adjacent base material in Carbon steel and alloy steel welds by pulse-echo contact method. The UT examination crew members undertake testing of full penetration weld joints in wrought (Rolled, Drawn, forged, Extruded) or cast materials.

Codes and Standards

  • ASME Boiler and Pressure Vessel Code, Section V, Nondestructive Examination

  • ASNT Recommended Practice No. SNT-TC-1A, Personnel Qualification and Certification in Nondestructive Testing 

  • ANSI / ASNT CP 189, Standard for Qualification and Certification of Nondestructive Testing Personnel

  • ASME B 31.1 Pressure Piping

  • ASME B 31.3 - Chemical Plant and Petroleum Refinery Piping, latest edition.

  • ASME B & PV Code Section VIII Appendix 12, latest edition.

  • AWS D1.1 Structural Steel Welding Code


The metallic surface to be tested shall be free from all extraneous materials such as scale, grease, rust, dirt, etc. which may interfere with the testing. The base metal on each side of the weld shall be free of weld spatter, surface irregularities, or foreign matter that might interfere with the examination. As far as the weld metal is concerned, the surface under examination must be prepared as needed to permit examination.

The surface temperature must be monitored and must be such that it does not exceed the probes working temperature range.

Documentation And Reporting Of Test Results

  • Each inspection shall be reported together with the interpretation of flaws, defects, etc.

  • Test results shall record the presence, location, type and size where applicable of all relevant defect indications that do not comply with acceptance standard. Where remedial action and re-test is undertaken, this shall be recorded in the identification or test results

  • Standard terms and abbreviations shall be used. Where necessary sketches or drawings shall be used to clarify reports

  • All reports shall be handed over against signature to the Client representative at relevant stages

  • TCR Arabia's responsibility shall be limited to ensuring the integrity of the weld or part within the confines of the ultrasonic test requirements of the governing specification


By delivering a safe, accurate, and comprehensive inspection service with superior value and benefits, CIAI is widely recognized as the premier coke drum inspection company in the world.

Hydrogen Induced cracking - Stepwise crack inspection (HIC-SWC)

Hydrogen damage is a degradation mechanism active in the oil and gas industry. The hydrogen atom is the smallest of all atoms and hydrogen attack is similarly insidious and hidden from simple inspection techniques. Hydrogen damage takes place at two temperature regions, elevated temperatures and temperatures at ambient and slightly above. The following details non-destructive inspection techniques aimed at identifying, quantifying and tracking this form of damage. The operation consists of utilizing advanced ultrasonic techniques to detect Hydrogen Induced cracking- Stepwise crack inspection (HIC-SWC), metal loss and other laminar defects in the shell material of vessels. 

UT techniques include manual UT, TOFD, Phased Array Ultrasonic and High-resolution Automated Ultrasonic Testing. 
Hydrogen Induced cracking HIC: Planar cavity formed as a result of hydrogen charging. Individual cracks are generally quite small in area (length and/or breadth less than 25mm) and have no measurable through-thickness extent. HIC may be isolated (i.e. one by itself) or form clusters of cracks. Clustered HIC involves areas of individual HIC in close proximity to one another, both in terms of area and through-thickness extent, normally within 1 to 3mm. Note, although the cluster might show some through-thickness extent, the individual cracks in the cluster do not connect with each other.

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Stepwise crack inspection SWC: The CGI image of SWC is similar to that obtained for Clustered HIC (above), however, SWC also exhibits through-thickness cracking, resulting in the linking of individual HIC cracks on multiple planes. These features are normally detected by the use of high resolution automated UT, Time of Flight Diffraction (TOFD) and 45° shear wave ultrasonic. The extent of the through-thickness cracking is normally established by TOFD.