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Inspect steam reformers and catalyst tubes with infrared thermography

02.01.2014  |  James, S.,  Thermal Diagnostics, San Fernando, Trinidad & Tobago

Keywords: [Infrared thermography] [steam reformer] [catalyst tube] [hydrogen] [furnace] [infrared pyrometer ]

Infrared thermography is a useful inspection tool to help locate problems in steam reformers while the units are online and fired. There are three main areas in a reformer that can be efficiently inspected with thermography. While there are common and codified inspection and diagnostic practices used in the industry today, some of these practices are unknowingly wrong and may have a large impact on the data collected over the years.

Before explaining how thermographers can inspect steam reformers, it is necessary to address what these units are, along with their main purpose in chemical and petrochemical plants. Steam reformer furnaces are used for hydrogen production. A hydrocarbon feedstock is mixed with steam and heated in the presence of a catalyst to produce crude hydrogen, which is then purified. The most common hydrocarbon feed is natural gas, but propane, butane or liquefied petroleum gas (LPG) are also used.

Steam reforming takes place in a steam reformer furnace. The furnace is usually a large refractory-lined box with gas burners, heating many catalyst-filled tubes that carry the feed (natural gas) and steam. Depending on the design, the reformer’s firebox or cell may contain only a single row of tubes (Figs. 1 and 2) or it may contain multiple rows (Figs. 3 and 4), making it more difficult to obtain accurate temperature data.

  Fig. 1.  A horseshoe-type
  design with one row of tubes
  per firebox/cell.

  Fig. 2.  Side view of a
  horseshoe design reformer.

  Fig. 3.  Single firebox-type
  design with multiple rows of
  tubes in one firebox/cell.

  Fig. 4.  Side view of single
  firebox/cell design reformer.

Refractory and insulation problems

The most obvious use of thermography on a steam reformer furnace is to consider refractory and insulation problems. Because of the high temperatures inside the reformer, the steel shell is lined internally with refractory material to prevent burn through, efficiency loss and structural failure.

When inspecting the refractory on a reformer, the key is to notice large differences in temperature. Many variations in temperature and thermal patterns will undoubtedly be found throughout various sections of the reformer, so knowing the construction, process flow, heat transfer principles and emissivity variables is very important in determining whether an indication is relevant or non-relevant.

Refractory furnaces are usually painted with a metallic silver paint (Fig. 5). Emissivity is an important issue when it comes to temperature accuracy. While many inexperienced thermographers and inspectors take emissivity for granted, temperature accuracy is an important aspect of reformer refractory inspection, as it assists design and plant engineers in troubleshooting safety and efficiency problems.

  Fig. 5.  Low-emissivity silver
  paint common on reformers.

The low emissivity of the paint not only poses a temperature measurement problem, but it also poses a relevant indication determination challenge. Surrounding a reformer is a melee of hot flanges, piping, and vessels that can easily be reflected off the surface of the paint, resulting in false indications. Plant inspectors using spot radiometers often misinterpret reflection problems as true indications. Also, changes in paint surface conditions due to scrapes, scuffs and charring can result in emissivity changes and can show a Δ T > 40°C, easily confusing an inexperienced thermographer and leading to data misinterpretation.

With reformers, the most common areas for refractory problems are at the peepholes (Fig. 6), burners, manways and penthouse roof flooring, although it is not uncommon to find problems in other areas.

  Fig. 6.  Thermal image of
  refractory failure located
  around a peephole.

Burner firing efficiency

Because the main driving force behind steam reforming is heat, a reformer has many burners (usually natural gas burners) that fire directly into the fire box. A reformer is usually fired from either the top or sides or sometimes both.

The way a burner fires is crucial to the reformer efficiency and to the service life of the refractory and catalyst tubes. Ideally, the flame will fire inside the box, but not impinge on the tubes.

When inspecting inside a reformer with thermography, a 3.9-micron filter is used to see through the gas flames. Although the flames will not be visible during the inspection, the flame’s thermal pattern from the surrounding tubes, walls and burner tiles can be observed.

Performing a thermographic survey of the burners and burner tiles can help determine whether the injectors used are functioning properly, if the burner is firing and if the burner tiles are overheating (Figs. 7 and 8). Proper burner firing is important to maximize the efficiency and service life of the reformer and reformer tubes.

  Fig. 7.  Thermal image
  showing flame impingement 
  on burner tiles due to
  improper or defective burner
  injector tips.

  Fig. 8.  Thermal image
  displaying replacement of a
  new design burner injector
  tip, solving the flame
  impingement problem of
  the burner tiles.

Reformer catalyst tubes

This part of the inspection is one of mystery, controversy and misconceptions. The main problem with inspecting reformer tubes is attempting to determine the tube surface’s actual temperature. It is common knowledge that the most effective way to use thermography to ascertain temperature accuracy is via means of reference. This usually means using a contact thermometer or a known emitter.

The problem with reformer tubes is that obtaining reference temperatures is easier said than done. Depending on how many tubes and rows there are in the reformer, obtaining reference temperatures to cover all tube areas is usually impractical. One controversial issue is how to take the best reference temperatures. Some argue that embedded thermocouples are best, while others vow that a gold-cup pyrometer is better for the job. Some folks even fabricate their own reference coupon from the same tube material.

It may be surprising to learn that although temperature accuracy is extremely important with reformer tubes—with the industry rule of thumb being that every 20°C rise above the maximum design temperature of a tube halves the tube life—temperature accuracy is not required to identify and diagnose most tube problems.

Single-point infrared pyrometers

Almost every petrochemical plant uses a portable, handheld spot infrared pyrometer to trend and monitor tube temperatures (Fig. 9). The main reason plant engineers and operators use these devices is because they are relatively inexpensive and easy to use. They are also very accurate and stable; they are almost never used properly by plant engineers and operators. Users have the notion that all they have to do is aim, pull the trigger and get a temperature. Many fail to understand that these instruments are infrared thermometers and are susceptible to the same errors as thermal imagers and other infrared thermometers.

 Fig. 9.  Single-point (spot)
  infrared pyrometer.

Spot-infrared pyrometers are very useful to plant personnel and do help tremendously in “trending” reformer tube temperatures. However, knowing the equipment limitations and basic infrared theory is extremely important and definitely required before anyone uses these devices to monitor reformer tube temperatures.

Application and equipment training programs specifically geared to the plant operator and engineer on the proper use of spot-infrared pyrometers are important (Fig. 10). From observing a wide array of training programs across a variety of companies, it has been determined that temperature consistency within 1°C to 6°C has been achieved from operator to operator, where previously it was an average of 20+°C (Fig. 11).

  Fig. 10.  Plant operators
  and inspectors approach
  a reformer for hands-on
  single-point infrared
  pyrometer training.

  Fig. 11.  Plant operators
  and inspectors applying
  the knowledge learned
  during training.

On some reformers, temperature accuracy cannot be achieved on certain tubes using spot-infrared pyrometers, mainly because of spot size limitations. That is why it is better to be consistent and precise rather than accurate when it comes to operators and plant inspectors trending reformer tube temperatures on a frequent basis. With a consistent and precise temperature trend, inspector error, calibration drifts and minute variations in tube temperatures can quickly be identified. If problems can be identified quickly, then corrective measures can be taken and there will be much less chance for an actual tube problem to go unnoticed.

Accuracy can come later on, during troubleshooting or diagnostics of problems found during routine trending and monitoring. This approach is usually recommended because achieving temperature accuracy for most reformer tubes can be an expensive and a time-consuming job. This makes it impractical and unfeasible for most routine tube monitoring programs by operators and plant inspectors.

Although spot-infrared pyrometers are invaluable and extremely cost-effective tools, they should be used regularly by plant personnel to grasp the temperature trends of their reformer tubes.Complete thermographic survey using a radiometric imager should always be performed. This is because an imager will be able to locate and diagnose tube problems, while a spot-infrared pyrometer cannot. The pyrometer can only give a temperature measurement at the point it is aimed. To locate and diagnose tube problems, a complete thermal pattern and profile of all relevant tubes should be viewed.

Thermographic imaging survey

With reformer tubes, operators are looking for overheating problems. Some common problems that can be found with thermography are:

  • Flame impingement (Figs. 12 and 13)
  • Gas flow restriction
  • Burner associated issues
  • External tube scaling
  • Catalyst problems
  • Afterburning (gas from burners or tube leaks).

  Fig. 12.  Side view of
  reformer tubes in a certain
  row showing normal
  thermal patterns.

  Fig. 13.  Same reformer
  as Fig. 12, but a different
  row showing flame
  impingement problems due
  to damaged burners.

Can thermography be used to locate reformer tube leaks? Finding such a leak is somewhat tricky, but not impossible. Although the leak may not be seen, there are some telltale signs to look for. These include: localized flame impingement, due to afterburning at a location where there is not supposed to be any; and localized cooling of the refractory wall or an adjacent tube, indicating that a surrounding tube is leaking (Figs. 14 and 15).

  Fig. 14.  Leaking tube
  detected by cool band on
  adjacent tube and localized 
  afterburning of hydrogen gas.

  Fig. 15.  The same leaking
  tube as Fig. 14, crimped
  while online. This stopped the
  afterburning and tube
  overheating with no downtime
  and no failures.

As mentioned earlier, there are various reformer designs. This means that there are also various tube configurations. A reformer can have vertical tubes or horizontal tubes. One such example is the convection section within a horseshoe designed reformer (Fig. 16).

  Fig. 16.  Horizontal convection
  section reformer tubes in a
  horseshoe design reformer.

Pigtail-reformer tubes can also be inspected. Pigtail tubes are the smaller tubes that are external to the furnace and connect the reformer tube to the supply and exit manifolds (Figs. 17–19).

  Fig. 17.  Location of multiple 
  reformer tube rows and
  pigtail tube sections within
  a single firebox reformer.

  Fig. 18.  An overheated
  pigtail tube section.

  Fig. 19.  Another overheated
  pigtail tube section.

A meaningful tube survey

Reformer tube inspection is sometimes said to be an art. There is so much that can happen inside a reformer and not all infrared equipment can effectively deliver useable data. To conduct a meaningful thermographic survey or even a spot-infrared pyrometer survey, know the equipment limitations. Limitations are what make reformer tube inspections difficult. Inspectors often run into problems because they do not identify these issues. The biggest limitations are:

  • Untrained and inexperienced inspectors
  • Equipment spot sizes
  • Equipment wavelengths
  • Equipment optics and imaging capabilities
  • Equipment overheating
  • Access
  • Viewing angles
  • Distances
  • Fields of view
  • Tube sizes
  • Tube orientations.

To achieve a meaningful reformer tube survey, first determine the survey’s desired result (Figs. 20 and 21). Then identify any limitations before and during the survey, and know how to correct or avoid them. Reformer tube inspections may seem difficult and require thermographers who can think and adapt to ever-changing conditions, but the information that is gathered during a proper infrared survey is worth every penny to the plant and every eye-stinging bead of sweat to the thermographer.

  Fig. 20.  Direct view of
  reformer tubes from
  peepholes give better
  temperature accuracy, but it
  is more difficult to diagnose
  problems due to limited field
  of view for a complete
  thermal profile.

  Fig. 21.  The same reformer
  tubes as Fig. 20, with a side
  view from parallel peepholes
  to give a complete thermal
  profile making it easier to
  diagnose problems.
  However, this decreases
  temperature accuracy due
  to viewing angle.

Proper inspection and training

Steam reformer furnaces are high priority pieces of equipment. A failure in any of the three areas discussed can result in a loss in efficiency or even a total unscheduled plant shutdown. Repairs can be very simple to very extensive, requiring days and sometimes weeks of downtime. Proper and regular thermographic inspection of a reformer’s three key areas is essential to the operation and life of the unit.

No matter what infrared equipment is used, proper training and experience are essential. Without proper training and guidance, too many important factors are frequently taken for granted or are unknown to the inspector. These unknowns may lead to premature failures or a loss in total confidence in the reliability and effectiveness of infrared technology. HP

The author
Sonny James is founder and owner of Thermal Diagnostics and the NDE Institute of Trinidad. Both are located in Trinidad and Tobago. He is an American Society for Nondestructive Testing (ASNT) nondestructive testing (NDT) Level III certificate holder in various NDT methods (including infrared) and is American Petroleum Institute (API) 510 certified. Further, he is accredited as an American Welding Society (AWS) certified welding inspector.

Mr. James has over 20 years of experience inspecting reformer and heater tubes and has established tube inspection and monitoring training programs for the petrochemical and chemical industry. He is routinely called upon by plants around the world to help troubleshoot reformer and heater tube problems and to come up with solutions for in-house temperature monitoring and accuracy programs. Mr. James is considered as one of the few specialists and experts in reformer and heater tube temperature diagnostics. 


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niall oconnell

There is a strong emphasis on proper training but little information on what that would be.

Ganesan Kumar

Very useful article. But, methods to avoid susceptible error with spot infrared pyrometers while measuring would be much more useful.

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