Boiler Inspection

TCR Engineering Services is a Bureau of Indian Standards and NABL accredited laboratory. TCR Engineering is among the few organizations in India that have been recognized by Central Boilers Board as a "well-known Material Testing Laboratory as per Indian Boiler Regulations Act of 1950.

Electro-Magnetic Acoustic Transmission (EMAT)

Using EMAT technique with panametric probes, TCR 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


Recording of Thickness Measured 

The thickness is measured and recorded by TCR in a standard format that includes the following details:

  • Plant

  • Tag Number of equipment/pipeline or appropriate description (in case tag number does not exist for the component/job)

  • Date of measurement

  • Sl. No Meter used for thickness measurement

  • Details of the meter used for thickness measurement like frequency etc.

  • Identification number of the standard block used for calibration of the meter before starting the job

  • Nominal thickness of the component being checked for thickness

  • Name of the technician measuring the thickness

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 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.

Thickness Values More Than Previous Readings

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 done considering the inherent limitations of 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. Even If the probe is kept only a couple of millimeters away from the previous location, there could be a 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 is +/- 0.1mm. Hence a thickness value that is 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. Based on the repeat thickness survey, the report can be verified and corrected if required. The following steps are undertaken for verification of the readings:

  1. Checking for instrument calibration using a step wedge and a standard block of thickness close to the thickness range being measured

  2. Checking of the thickness measured with another meter and probe at the same location

  3. Checking of the surface preparation before taking readings

Automated Reformer Tube Inspection System (ARTIS)

TCR has indigenously developed an automated robotic crawler to aid ultrasonic inspection of reformer tubes. It provides a tabular and interactive digital output. The 1st point on every tube is referred at the bottom of the tube, climbing up to 14 meters height and provides tube data at every 0.1-meter distance. The ARTiS can simultaneously collect tube data such as ultrasonic dB level of attenuation, the diameter of the tube and bowing angle at every location. An interactive, graphical user interface is part of the digital report along with a conventional hardcopy printed in a tabular format.
Few of the key advantages of using ARTiS:


  • The method follows a similar technique of manual ultrasound coupling making it an industry-wide proven technique of inspection

  • A macro-level view of the overall tube condition in the reformer is also reported, emphasizing troublesome areas/corner of the furnace if any

  • The outcome of inspection work becomes more systematic and traceable with point-wise reading on each tube for ultrasound attenuation and creep strain

  • It avoids the need for scaffolding, saves total tube inspection time and helps to achieve reduction in shutdown time of the plant

  • Automation deploys limited water source for coupling and nearly eliminates the need for overhead water drum arrangement, which overcomes additional issues related to drum filling, vacuum water clogging, etc.



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.