What went wrong with my furnace?
We should learn from our own mistakes and experiences, but it is wiser to keep track of and learn from all past mistakes and experiences, including those made by others.
We should learn from our own mistakes and experiences, but it is wiser to keep track of and learn from all past mistakes and experiences, including those made by others. This same philosophy is applicable, and rather useful, in the execution of engineering projects. One should always keep all feedback handy to accommodate all past experiences, decide preemptive actions, and eliminate cost and schedule impacts on similar projects.
In refinery and petrochemical projects involving the execution of fired heaters, reformers and cracking furnaces, listing and sharing feedback are of paramount importance, since the actual cost of each feedback/learning is sizeable (e.g., even minimal impact is magnified due to inherent high-temperature conditions and the involvement of explosive fluids). The best way to learn from this data is to assimilate these in a systematic manner and to establish improved systems/practices for future use.1,2
In the past, the gaps/issues that could slip through drawing preparation and review stages could only be detected during or after the construction stage of a project. Accordingly, the cost of rectification also used to be moderate-to-high in terms of cost, quality and schedule. More recently, however, with technological advances, an emphasis on 3D model reviews during the engineering stage has eliminated these issues from percolating to the construction/commissioning stage, minimizing their impact. The final check-listing of heater systems at the site—prior to mechanical completion—by heater and refractory specialists is crucial for recognizing and eliminating critical design and engineering implementation issues, as well. It is very likely that an experienced, updated and knowledgeable engineering consultant can save clients from such events by pointing them out prior to mechanical completion.
This article illustrates a few incidents regarding heaters, reformers, cracking furnaces and auxiliary equipment associated with the refining, petrochemical, fertilizer and steel industries for future reference and information.
Introduction to fired heater systems and their components
Furnace systems comprise several critical components, such as process coils, coil supporting systems (e.g., fixed supports, spring supports and counterweights), refractory, burners and the structural steel for holding it all in place. Further, an optimized system with a heat recovery arrangement contains auxiliary equipment, including induced draft/forced draft (ID/FD) fans, an air preheater, measuring instruments, expansion bellows, control and guillotine dampers, skin point thermocouples and flow meters.
Feedback on components is important, since they impact timely completion and/or safe and satisfactory performance of the system. Depending on the stage of execution, any frequent problems encountered must be addressed and analyzed for the appropriate approach.
The “angle of impact” concept
The simplest way to demonstrate the impact of any event for any engineering execution is to draw the angle of impact, with respect to the execution stage of identifying and correcting the incident. This will determine the magnitude of its impact in cost/time.
Although the angle of the impact is constant, the magnitude of impact (in terms of cost/time) can vary significantly. The severity of the impact (FIG. 1) depends on the stage at which it is noticed and corrected:
FIG. 1. The angle of impact concept.
- Early design stage—minimal impact
- Construction stage—significant impact
- Post-commissioning stage—possibly catastrophic impact.
The guiding curve may not be linear in actual cases.
Selection categories for incident reporting
Responses may be noticed during any stage of the project (e.g., conceptualization, layout, logic, design and engineering, construction or operation). Sometimes, a propagation of errors may percolate in many downstream stages of the project. Therefore, it can become difficult to isolate these errors for the purpose of reporting, along with their linking with any single stage.
There are many ways in which these experiences can be sorted out, grouped and/or reported for future reference and feedback. A few examples include:
- Stage of occurrence
- Heater system-specific component
- Magnitude of impact in terms of cost, time and/or quality.
From an owner’s point of view, the best categorization will be based on the magnitude of impact of cost/time/quality, since these are the major concerns for any owner. The magnitude of impact can be further classified as minimal, average or significant. Incidents of major concern include potential experiences having an average or a significant time, cost and/or quality impact on the project.
The normal cost of the heater system varies from $1 MM–$20 MM, depending on furnace duty and associated auxiliary equipment/arrangement. In addition, the normal execution time of heater system projects (i.e., availability of an engineered package to mechanical completion) is approximately 12 mos–24 mos, depending on the duty, size, burners, coil/casting MOC and proprietary supplies.
Any incident that has a minimum cost impact of 10%–20% or a time delay (above estimated agreed values) should fall under the “average impact” category. Impacts greater than 20% should be listed in the “significant impact” category.
Incidents in the ‘average impact’ category
Issues relating to heater steel structure, individual tube supports, individual coils or banjos, local refractory and isolated auxiliary equipment fall under the “average impact” category. Several examples include:
- A fire occurred in a storage area during the construction stage due to a short circuit inside the radiant cell. The fire was extinguished using water, which, in turn, damaged the ceramic-fiber lining (FIG. 2).
FIG. 2. The ceramic fiber lining was damaged by water used to extinguish a fire.
Event: A consultant inspected this damage during a site visit.
Rectification impact: Replacement of material and rework.
Cost: Lining material and repair work.
Time: Rework involved.
Quality: A minimum amount of lining was retained, with the unusable lining replaced.
Feedback: The use of water to extinguish the fire damaged water-sensitive ceramic-fiber refractory material. This incident should be made part of safety training modules for site engineers and workers.
- A reformer ID fan was installed on a concrete foundation (FIG. 3). Since proper access was unavailable between the fan casing and the foundation, the external insulation could not be properly installed in embedded areas of casing located between the foundation and the fan casing.
FIG. 3. View of the reformer ID fan.
Event: A consultant discovered this incorrect insulation installment while going through a site checklist and minimized its potential impact.
Rectification impact: External insulation was installed without removing the fan.
Possible cost: External insulation was provided in the embedded area, without removing and then reinstalling the fan in that area.
Time: Rework was not done.
Quality: The foundation may be exposed to higher-than-normal atmospheric temperature, and possible earlier-than-normal deterioration of foundation may occur because of scaling phenomenon.
Feedback: The correct insulation installation procedure was added to the site checklist, so that, in the future, this work will be properly completed prior the installation of fans on the foundation.
- In any asymmetric system or unconventional/unique designs, carefully monitored implementation should be mandatory. In this case, due to the asymmetric design, and despite specific caution in the general arrangement drawings for the heater, the ladder-type support cross bar (FIG. 4) was installed at the site in the delayed coking unit heaters at the first support location from the radiant outlet. An extra cross bar was generally used from available spares and installed, considering the complete system to be symmetrical during construction.
FIG. 4. View of the ladder-type support cross bar.
Event: A consultant pointed this out and minimized its impact.
Probable impact: Coil deformation and failure.
Possible cost: Coil material and replacement, and/or tube support material/replacement costs.
Time: Could result in shutdown and rework.
Quality: Coil deformation/support failure.
Feedback: Caution for this situation was added to the site checklist.
- Air-cooled structure columns: In certain heater configurations, it sometimes becomes inevitable that the heater support structure’s vertical column passes through the hot flue gas path. This column is required to be refractory lined to eliminate its exposure to the high-temperature flue gases. For this purpose, a box-type cover is provided around the structural column, and the enclosed passage must remain open to allow air-cooling of the steel structure. These openings are often closed by contractors based on their own understanding/interpretation, considering it as a source of water ingress.
Event: A consultant pointed this out during a site visit, minimizing its impact.
Probable impact: High temperature in an enclosed area can result in structural deformation under loading.
Cost: Rectification of the column and associated issues.
Time: Could result in shutdown and rework.
Quality: Structure deformation/lining failure.
Feedback: Caution for this situation was added to the heater section of the site’s checklist.
- A projected floor refractory dome-type detail was constructed by mistake at the bottom of the vertical tube onsite (FIG. 5).
FIG. 5. Dome-type detail constructed at the bottom of vertical tubes.
Event: A consultant warned the operator about the possible negative impact of this plan.
Probable impact: Obstruction in coil-free expansion, resulting in deformation.
Cost: Coil/spigot material and replacement and/or tube guide, support material replacement cost.
Time: Could have resulted in shutdown and rework.
Quality: Coil/support failure.
Feedback: Caution for this situation was added to the site’s checklist.
- The locking plate of the expansion bellows/spring hangers was left in the locked position after installation (FIG. 6).
FIG. 6. Locking plate of expansion bellows/spring hangers was left in the locked position after installation.
Event: A consultant pointed out the possible negative impact of this, thereby preventing it from occurring.
Probable impact: Deformation.
Cost: Possible deformation in the duct, refractory damage, leakage and/or support damage that could involve material and rework costs.
Time: Rework time.
Quality: Leakage, high temperature and/or deformation issues.
Feedback: Caution for this situation was added to the heater section of the site’s checklist.
- An access door was in an improper location, with respect to the foundation/platform location (FIG. 7).
FIG. 7. Improper location of an access door.
Event: A consultant pointed this out during a site visit, allowing for extending the platform to the access door.
Probable impact: Improper/unsafe access.
Cost: Additional platform structure/grating support or foundation extension.
Time: Rework.
Quality: Improper/unsafe access.
Feedback: Caution for this situation was added to the heater section of the site’s checklist.
- During revamp work, the tube support system counterweight rested on the manifold; it was left in position after completion and has remained inactive (FIG. 8).
FIG. 8. The tube support system counterweight rested on the manifold and was left in position after revamp work completion.
Event: A consultant discovered this situation during a site visit, preventing its possible impact.
Probable impact: Tube deformation and/or pin failure.
Cost: Coil/hair pin material and replacement and/or tube support material and replacement costs.
Time: Could have resulted in shutdown and rework.
Quality: Coil deformation and/or support failure.
Feedback: Caution for this situation was added to the heater section of the site’s checklist.
- Castable refractory and debris had fallen on top of cast/glass tube air preheaters during construction (FIG. 9).
FIG. 9. Debris that fell on top of cast/glass tube air preheaters.
Event: A consultant discovered this during a site visit, preventing its possible impact.
Probable impact: Fouling of tubes and corrosion due to water retention, increased pressure drops and improper heat transfer.
Cost: Minimal.
Time: Minimal.
Quality: Not significant if manually picked up or pneumatically removed by blowing. It should not be cleaned using water.
Feedback: Caution for this situation was added to the heater section of the site’s checklist.
- External insulation was applied on the heater casing area in a multi-cell furnace to facilitate the operator’s movements in an enclosed area. The casing temperatures had increased due to inside refractory damage.
Event: A consultant pointed out the possible negative impact of this application, preventing potential damage.
Probable impact: This external insulation application could cause further deformation and/or failure of the heater columns/casing/refractory and linked structure without any warning, since the wall casing was already covered from the outside and was not visible.
Cost: Column casing/structure/refractory material and rework.
Time: Major rework, if not noticed and corrected in time.
Quality: Possible deformation of the heater supporting columns and casing due to obstruction in natural air cooling from outside of the heater casing and structure, along with exposure to increased temperatures.
Feedback: Caution for this situation was added to the heater section of the site’s checklist.
- Proceeding with construction work without basic feasibility checks. In case of a revamp, the foundation for a proposed fan relocation was prepared without checking the condition of the existing fan, which could not be relocated due to corroded casing and supports during a shutdown.
Event: During a site visit, a consultant noticed that this had occurred.
Impact: Non-productive efforts.
Cost: Foundation material and laying costs, and space consumed without use.
Time: Time lost in non-productive work.
Quality: Loss of crucial ground space, which is always a costly commodity within any plant.
Feedback: Older reports regarding any revamp should be verified for on-date status and added to the site’s heater checklist for future revamp/modification jobs.
Incidents in the “significant impact” category
Issues related to the failure of several coils and tube supports, major refractory changes and required shutdowns prior to safe operation of the furnace are grouped within the “significant impact” category. Examples of these incidents include:
- Thermal expansion provision missing in refractory retainer plates (FIG. 10).
FIG. 10. View of the refractory retainer plates.
FIG. 10. View of the refractory retainer plates.
Event: After a forced shutdown, a contractor discovered this situation and its root cause.
Probable impact: The failure of arch channels/refractory, resulting in a forced shutdown.
Cost: Heater arch steel and refractory material and rework, as well as loss due to the shutdown.
Time: Complete rework and unplanned shutdown time.
Quality: Absence of thermal expansion provision in the refractory retainer plates.
Feedback: Awareness was increased toward engineering review observations, which should not be neglected due to demanding schedules.
- Not verifying the current status of structure deformation onsite prior to the implementation of old report recommendations.
Event: Occurred during the construction phase and discovered during a site visit.
Probable impact: The structural column had deformed further from the time when recommendations were made a few years prior. Implementing the project via older reports would have resulted in a skewed structure, since it had not accounted for further deformation in the structure column.
Cost: Recutting the heater column to eliminate the heater column deformation and achieve the desired verticality limit tolerances.
Time: Rework and realignment.
Quality: If not identified and corrected in time, this situation could have resulted in a misaligned heater column, which could deteriorate further over time during operation.
Feedback: Old reports regarding any revamp project should be verified prior to implementing a project. It should also be made part of the checklist for all revamp/modification jobs.
- Free thermal expansion provision for tube supports.
Event: Cracks occurred in the intermediate tube sheet (ITS), and these cracks were noticed during a shutdown (FIG. 11).
FIG. 11. These cracks in the ITS were observed during a shutdown.
Impact: Successive ITS failures and shutdowns for short-term rectifications.
Cost: Temporary additional support was required below the failed ITS, with a long-term solution of measuring and replacing the cracked tube sheet.
Time: Rework.
Quality: Absence of free thermal expansion gap provision at the end of the ITS.
Feedback: ITS expansion gap ends need to be checked prior to inserting coils during the convection module fabrication stage and should be done along with proper liquidation of past checklist points. Structural column tolerance limits and over-tolerance specified for ITS casting should also be considered for the ITS expansion gap. This expansion gap check becomes difficult to measure and to rectify after erection of the module/tube supports when the tubes are in place.
Takeaway
Sharing, listing and learning from similar incidents—such as the ones listed in this article—can prevent unwanted risks and losses during future executions. A forward-looking, progressive company, with a robust feedback recording system, can better ensure quality deliverables and services by timely eliminating the repetition of all past errors and by utilizing captured feedbacks through necessary pre-emptive actions. HP
REFERENCES
- Dutta, H., “Building blocks of process safety,” Hydrocarbon Processing, October 2018.
- Grisi-Frisbie, J., “Causes interact in industrial accidents and life,” Hydrocarbon Processing, February 2019.
The Authors
Patel, R. - Engineers India Ltd., New Delhi, India
R. Patel is the General Manager of the Fired Equipment Department for Engineers India Ltd. in New Delhi, India. He has 23 yr of experience in the design, execution and revamping of furnaces. Mr. Patel earned a degree in mechanical engineering from the Indian Institute of Technology–Roorkee, India.
Mahra, R. K. - Engineers India Ltd., New Delhi, India
R. K. Mahra is the Manager of the Fired Equipment Department for Engineers India Ltd. in New Delhi, India. He has 10 yr of experience in the design and execution of furnaces. He earned a degree in mechanical engineering from the National Institute of Technology–Bhopal, India.
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