NIP SERIES PROBES

NIP - 2

ADVANTAGES  OF  STASUK  TESTING  NEAR

DRUM / TUBE-SHEET  INSPECTION  PROBE  SYSTEM

History  &  Nature  of  the  Problem 

Stasuk Testing has the privilege of being the first NDT Company to develop equipment and procedures, which can accurately measure the remaining tube wall thickness in the difficult swaged area of boiler generating bank tubes near the upper or lower drum where corrosion and/or erosion problems are increasingly commonplace.

      The problem was identified and documented by the Procter & Gamble Company in 1988. It was first discovered at one of their pulp mills after several tube failures resulted in the need to replace the entire Generating Bank during an unscheduled shutdown.  As a result of this finding, all their critical Recovery Boilers were inspected to determine if this problem existed elsewhere.  The best available testing technology at the time indicated that other Generating Bank tubes might also have the thinning to various degrees of severity.

     Ultrasonic thickness measurements of the tubes in this area are only possible from inside the Drum during shutdown periods.  However, the irregular tube inner surface caused during tube rolling/expanding operations interferes with conventional ultrasonic signals.  Subsequent inspections showed that the test data they were receiving from different sources and methods of inspection was inconsistent and therefore unreliable to be able to predict wear trends and tube wastage rates accurately.  Similar problems were also being reported across the United States and in Western Canada.

    Stasuk Testing & Inspection Ltd., a private Canadian company, independently developed a manually operated ultrasonic probe in 1983 to address the same problem for one of their Canadian boiler operator  clients.  This original probe was unique in design (using the immersion method) and overcame many of the difficulties of obtaining accurate, repeatable data. In 1989 we  developed a totally new and improved manually operated probe  and in 1991 a completely automated, computer controlled Ultrasonic Probe also giving consistent, repeatable tube thickness measurements was completed.

    A patent was applied for and granted for the manual version and the probe was successfully used in over 60 Recovery Boilers across the United States and Canada before it was replaced with our newer automated version.

    Our newer automated version has been even more successful by increasing the speed and accuracy of the inspection, typically lowering the cost of this type of inspection by up to 40%.  Our proprietary equipment and method has become the leading system of accurately assessing this problem of Boiler Generating Bank tube thinning at the Drum Level in North America.

 Previous Experience

     Some of the Boiler operations where we have carried out generating bank tube thickness surveys using this technology includes such companies as Procter & Gamble Cellulose (Weyerhaeuser Corp.), Georgia-Pacific Corp., Mead Paper, Container Corporation of America (Jefferson Smurfit Corp.), Stone Container Corp., Canadian Forest Products, Irving Pulp & Paper, Inland-Rome, Boise-Cascade Corp., Canadian Pacific Forest Products, Petro-Canada Refinery (Edmonton), Maritime Electric - PEI, CXY Chemicals as well as overseas corporations such as Australian Paper Manufacturers, Tasman Pulp & Paper Ltd. (NZ), Carter Holt Harvey (NZ), Sabah Forest Industries (Malaysia) and Smurfit Carton de Colombia.

     Statistics to‑date has shown that Generating Bank tube thinning at the Lower (Mud) Drum level exists to varying degrees in 75% of the Recovery Boilers that our company has inspected in the last 9 years. This includes both Babcock & Wilcox and Combustion Engineering (ABB) units.

     In addition to tube inspections at the Mud Drum level, we have also carried out several inspections of generating tubes at the Steam Drum level. We have found similar tube wastage near the steam drum in several cases, particularly in Power Boilers using oil, wood or plant waste for fuel.

     Mr. David Stasuk presented a paper on this subject at the TAPPI (The American Pulp and Paper Institute) conference in September 1990. Our company has also worked with PAPRICAN (Pulp and Paper Research Institute of Canada) on this matter and supplied them with statistical data on generating Bank tube thinning. The accompanying paper has some examples of graphs, which were part of a presentation at the TAPPI Conference, which show the relative number of thin tubes discovered during several boiler inspections we have carried out and some wear trends for some Recovery boilers.

     In early 1995, a crack detection unit was added to inspection system.  Since that we have use this crack detection capability in several boilers.  Attached is a paper presented by Mr. David Stasuk on crack detection at the near drum level in boilers.

    This system has also been used in inspecting near tube-sheet thinning in heat exchangers involving such material as nickel, stainless steel, titanium and carbon steel.

 Tube  Cleaning

     In many boilers that we inspect, there is excessive scale and dirt in the tubes, which can make it very difficult to inspect. In order to avoid inspection delays due to excessive scale on tube interior surfaces, we recommend that you have all tubes high pressure water-blasted (at least 10,000 psi) for the first 8-10" from inside the Drum. This is only necessary where there is evidence of scaling. At any rate, it is desirable for the interior of the tubes to be relatively free of scale and any other deposits for the first 8 inches or so.

 Equipment  and  Personnel

     Typically our equipment would be shipped ahead of time to a job site. The equipment typically comes in 6-7 cases, weighing 35 to 70 pounds each, and consists of lightweight mechanical and portable electronic equipment.

     Our personnel typically include an experienced, certified Professional Engineering or Technologist Supervisor and 2 to 4 ultrasonic Technicians (ASNT Level II), each with over 2500 hours experience inspecting boiler generating bank tubes at the drum level.  They would be equipped with our proprietary Automated Drum Probe, digital ultrasonic instrument, portable computers and assorted accessories.  Each technician/assistant crew averages approximately 250-400 tube scans per 12-hour shift  (thickness only; for thickness and crack number of tube read is halved), depending on how clean the interior of the tubes are from scale and pitting.  The system can also be operated by a single personnel, if time is not a constraint.  The equipment can be placed in the drum or outside as required.

    Our crews typically work 12-hour dayshifts (8am ‑ 8pm) and 12-hour nightshifts (8am ‑ 8pm), on a continuous, 24-hour basis, or we can schedule our time to suit your schedule.  We require 2 to 3 hours to set up the water supply system for the probe, run electrical power and lighting, place equipment in the drum etc., and calibrate the equipment.

    Prior to leaving the job site, we  provide the client with a summary report of the lowest thickness reading found for each tube inspected, color-coded according to the client’s specifications.  Upon return to our office we produce a final report complete with sample color B & C-Scan images of typical tubes showing any wastage, as well as graphs and charts showing averages, data distributions and wear trends, as applicable.

ADVANTAGES 

 (1)    Fully  programmable

    All linear in/out and rotational movements are controlled individually by stepper motors and can be changed at will to suit scanning requirements for higher or lower resolution and coverage.  Note that fixed scan "helix", "spiraling" or "corkscrew" style probes such as the "UBIS" cannot be re-programmed without major mechanical changes.

 (2)   High  resolution  scanning

     The resolution of an automated ultrasonic scan is determined by the number of readings taken per unit area.  Obviously the more readings taken, the better the "image" that can be produced and the better inspection achieved.  The Stasuk probe can be programmed to scan in increments as small as 0.007" in the axial direction and 1.8 degrees in the circumferential direction.  This results in the highest resolution available in the industry today.  Typically we run the system with a resolution of 4,000 readings per inch of tube, or 8-12,000 readings for a 2-3 inch scan.  This resolution is twice as high as our nearest competitor using the "corkscrew" style system.

 (3)   Full  coverage

     The Stasuk Probe system scans in a logical X-Y Cartesian co-ordinate system which enables the data to be plotted in several different views including 3-D images of the outer tube corrosion surfaces. This method is also the optimum for high resolution scanning of the first 0.100" at the tube/drum interface to detect very narrow corrosion bands. These corrosion bands are as little as 0.050" wide and have recently been suspect in tube failures due to circumferential cracking at both steam drum and mud drum interfaces. Helical or corkscrew type scanning probes do not allow parallel scanning at right angles to the tube axis which therefore minimizes the chance of detecting these corrosion grooves.

  (4)   Two  Operation  modes

The Stasuk Probe system can be operated in either of two modes for data collection and analysis:

Immediate Analysis or Data Collection only.  All data is saved in compressed mode on hard drives and floppy disks for review at any time.

 (i) Immediate Analysis

We collect data and analyze it right in the drum which yields immediate results. This involves moving a cursor on the computer screen (while the 3-D images are still on screen) to evaluate the individual readings to find the lowest valid thickness +/- 0.001".  The computer program does try to select the lowest reading automatically but sometimes factors such as scale, pits, etc. cause non-valid low data to appear which needs to be overridden in this manner.  The benefit for using the Immediate Analysis mode is that the actual minimum thickness for each tube is determined as the job proceeds, although it takes more time in the drum (approx. 30-60 seconds per tube).

 (ii) Data Collection Only

We collect data only and do the final analysis later in the hotel or back at the office.  This involves scanning each tube in the usual manner and estimating the lowest valid thickness from the screen without using the slower cursor routine.  This usually results in estimates with an accuracy of +/- 0.005".  This number is saved in a special "estimate" file which can be recalled at a later date to perform the detailed analysis for the final report. The benefit for using the Data Collection Only mode is that the actual scanning can be done faster, thereby reducing the time needed in the drum.  With current software, a 2 inch (20 spi - scan per inch) would take approximately 15 to 18 seconds.

  (5)     Detailed  Color-coded  Images  of  Wear  Areas  on  Tubes

    The Stasuk Probe software is the most advanced of all near drum systems to-date, giving instant color coded cross-sectional views (B-scans) through the lowest wear areas found, as well as high resolution contour mapped surface profiles (C-scan) of the entire tube area scanned, plus the ability to view each tube profile as individual "slices" from the first scan inside the tubesheet, to the extent of the scan coverage 2-3" up the tube, easily observing all 8-12,000 readings.  Our software is very useful in determining not only the remaining tube wall thickness, but also shows the shape and surface area of the corrosion which allows you to better evaluate the severity of the wastage area.

 (6)   Computer data file compatibility

   Stasuk Testing has collaborated with TCRI Systems of Charleston, S.C. to allow our data files to be made compatible with their extensive Recovery Boiler Technical Database software.

  (7)   Personnel Qualifications

   All Stasuk Testing technicians used in near drum inspections are certified to ASNT (SNT-TC-1A) Level 2  have had extensive experience in near drum           ultrasonic inspections. We continue to use the same  technicians whom we initially trained in 1989 when we patented the first successful manual Mud Drum            Probe.  Since then these same technicians have now acquired over 2,500 hours each in near drum ultrasonic inspections. No other company can match us for         highly trained, experienced personnel in this area.

 (8)   Predicting Remaining Life of Tubes

     The Stasuk Probe system accuracy and repeatability has been carefully evaluated by independent trials carried out on the Procter & Gamble/Tappi Mud Drum Simulator.  A rigorous test carried out in August 1992 yielded a perfect score.  Accuracy and repeatability are essential ingredients for reliable tube wear trend prediction.   A number of our customers have used our inspection data in their tube monitoring / replacement program at the near drum level.

The Stasuk Probe system's proven accuracy and repeatability, together with the best software in the industry will ensure that you will have confidence in the data analysis that you will receive.

 (9)   Use  of  dual  tube  images  for  analysis

     This system uses an ancillary software which enables the display of two tube images for comparison during analysis.  For instance, if a user wanted to compare the previous inspection data with the current tube data, he can use the software to aid in the analysis.  Please see example below.