Furnace and Heater Tube Inspections

by Ron Lucier, ASNT NDT Level III
One of the more challenging applications of infrared thermography is in the measurement of process heater and furnace tubes. In fact, we get dozens of inquiries each year from our clients on this very subject. Quantitative thermography is the practice of measuring temperatures accurately and with furnace tubes this requires experience and knowledge.  Success in this science is gained by being properly trained and certified as a Level I Furnace Inspection Thermographer. Certification training from the Infrared Training Center (http://www.infraredtraining.com) teaches you the techniques required for determining these values and will provide a complete understanding of temperature measurement and heat transfer.

Process Heaters
There are as many uses for process heaters as there are designs. The basic configuration consists of a shell (outer casing),   tubes (where the process fluid flows) and a heat source. These units are both thermodynamically and hydraulically complex.

The simple drawing illustrates convective gas flow, which is turbulent, and radiant heat from the flame, refractory and other tubes – all non-uniform and time varying. When you view tube from an access port typically you can only see a portion of the tube or the tube at an oblique angle. Sometimes tubes are in rows, difficult if not impossible to image.

Why are heater tubes of interest anyway?

Tubes in a fired heater

There are several reasons for inspecting tubes. Qualitatively scale buildup on the outside of the tube can be readily identified. Buildup on the inside of the tube (coking) is a bit more difficult but commonly performed. In both cases the scale or coke prevents the transfer of heat into the process fluid. In the case of scale buildup, the process fluid may not be sufficiently heated, affecting downstream processing. The case of coking on the inside of the tube is more serious. Since the coke has an increased resistance to heat transfer, the tube surface temperature increases. After all it is the flow of the process fluid that is keeping the tube “cool” in the first place. The external tube surface, unable to conduct its heat to the water, increases dramatically, causing a failure (opening) in the tube. Metallurgists use the measured temperature to calculate the life of the tube so accurate measurements are critical.

Sample Thermal Images

Tube with restricted flow

Coking on bottom of tube

Conclusion 
IR offers the operators of process heaters the ability to visualize the heat transfer and provide vital temperature data to help determine remaining tube life.  Certification training from the Infrared Training Center (http://www.infraredtraining.com) teaches you the techniques required to successfully implement this technology at your facility.

Thermography Certification Dates and Locations

• Training Dates and Locations in the US and Canada: http://www.infraredtraining.com/schedule
• Training Dates and Locations in Europe, Middle East and Africa: http://www.irtraining.eu

To learn more about these certification classes, as well as upcoming training dates and locations, please visit the Infrared Training Center online at http://www.infraredtraining.com

Blower Door Inspection for Air Infiltration in a Remodeled Cottage

By Tom Coffey, Infrared Training Center 

A small cottage (700 sq. ft) outside of Knoxville, TN was completely remodeled from January to March 2010. It was an existing cinder block structure with no insulation except ½ inch of airspace between the nailers and the block wall as well as the empty block core. The R value of existing building walls was approximately 2.97. After the remodel an R-value was calculated and determined to be 12.6

2 x 4 studs were used to build the interior walls the insulated with 4” of backed fiberglass bat insulation. Old windows were removed and new double pane sash type windows installed during the remodel.

The house was depressurized to approximately 50 Pascal and allowed to equalize for 30 minutes. A thermographic scan was performed after the equalization period. Infiltration was found around the sash windows where the top and bottom pieces join in the corners of the windows.

There was some expected infiltration around the front door which was missing a sweep on the bottom of the door. Also infiltration was found at the attic access.

All of these small problems are easily correctable and will be done as time permits.

The installation of the blower door took approximately 30-45 minutes. Reaching the right depressurization took another 30 minutes and the IR scan took another 45 minutes. For a house this size, allowing for the small footprint I did not do an air exchange calculation. The purpose of this exercise was to determine if the house remodel and adding insulation was sufficient to keep the house at a comfortable level during East Tennessee summers and winters. It was determined during the remodel process that R-13 insulation in the walls and R-19 insulation in the ceilings would be sufficient for the weather conditions in this area of the country.

Getting Started with R&D Thermography Online Course

Video tutorials on IR Camera Properties and getting started with ResearchIR. For any SC camera including A300, A320, SC645, SC6000, SC6700, and SC7000, SC8000 cameras.  There is NO CHARGE for this FREE  course.

Includes information on:

• Camera Technology
  • Cooled vs Uncooled Thermal Cameras: Field of View
  • The difference between cooled & uncooled thermal detectors?
  • Cooled vs Uncooled Thermal Cameras: Speed
  • Cooled vs Uncooled: Sensitivity
• FLIR ResearchIR Max
  • Connecting to the Camera
  • Image Enhancement
  • Image Subtraction
  • Recording Data
  • Triggering
  • Super Framing
  • Analysis Tools
  • Analysis Charts
  • Measurement Functions
  • Sharing Data
  • File Extraction Tool
• FLIR ResearchIR and MATLAB
• FLIR Thermal Face Detection and Tracking in Matlab
• Opening FLIR Movies with Matlab Software
• Connecting FLIR Systems GigE Cameras to MATLAB
• Applying MATLAB Filters in FLIR ResearchIR Max Software

   Course Registration and Information

IR finds Yellow Jackets Nest in House

by Sanin Mulic, Barber Foods

After attending my level one instruction during the week, and ITC wetting my appetite for thermal imaging, I returned home with my company's P-65 camera.  I decided to scan my own house to practice what I was taught all week.  All looked good until I went upstairs and noticed a bright spot on the inside wall.  I took several images of the spot and come Monday, I talked to two level 2 associates about what I had found.  There were several possibilities and I was told to take several more shots at different times to see if it moved or varied in temperature.   When we found it never moved I suggested that it might be insects (wasps, hornets, etc.) and talked with one of the other thermographers who would bring in a stethoscope to see if  I could hear them before opening up the wall.

   
Thermal image of the wasp nest (left).

I couldn’t wait, so that night armed with a drill, a can of flying insect killer, and the enthusiasm of a new thermographer,  I went up to the room; my pet cat, who loves to lay in the window there, had to investigate with me too.   I approximated where the hotspot was and drilled a 1/8 “ hole through the wall board. As I removed the drill bit, about 8 to 10 yellow jackets came charging through the hole and I started to spray the bug spray at the hole.  By this time, the yellow jackets were in an attack mode and I started to swing at them in defense.  Out of the corner of my eye I saw my cat speeding to the door with his tail bigger than I have ever seen it.  I finally killed the last one, sprayed about 1/3 of the can, and plugged the hole; but not before being stung twice.  I went outside and saw a swarm just outside the window. I drilled a second hole a few inches above it and knowing what was going to follow,  I had the spray ready to go as soon as the drill came out.  I sprayed about 1/3 of the can and then plugged the hole. I returned several hours later and the swarm was gone.  I climbed a ladder and found a small hole where they were coming and going.  I plugged that from the outside.  As I came back inside I saw my cat peaking from around the door as if to ask “Is it safe to come out now?”

After a few days I took another thermal image and there was no evidence of the yellow jackets remaining.  I submitted this investigation as my level one field report and it passed, but the memory of this initial experience will last a long time (the cat won’t forget it either!)

No wasps after removal.