Inspectioneering
Inspectioneering Journal

Heater Tube Inspection and Remaining Life Evaluation

An Interview with Rich Roberts, VP and General Manager, Quest Integrity Group

By Jeremiah Wooten at Inspectioneering, LLC.. This article appears in the May/June 2014 issue of Inspectioneering Journal

Understanding the uncertainties associated with heater tube remaining life analysis is critical to the quality and accuracy of your predictions.  Heaters are vital pieces of equipment in most plants.  A heater coil failure can result in the loss of life, millions of dollars in lost production, and equipment replacement costs.  Generally, inspection is performed to gather information used to reduce the uncertainties in the engineering analysis when assessing the current state of damage and remaining life of heaters, so that appropriate action can be taken well in advance of a tube failure.  Typical types of inspection include UT thickness readings, strapping (diameter measurements), field metallography and replication, etc.  Sometimes, heater tube inspection can be impeded by access limitations.  The following interview with Rich Roberts provides answers to some of the questions our readers have about small, specially designed pigs carrying NDE technologies that can inspect nearly every area of a tube from the coils interior surface.  We hope you find the interview valuable.  Please drop us an e-mail with any additional questions on this topic or any others related to asset integrity management.  We will do our best to get you the answers!

What are some relatively new NDE techniques (and how are they) helping to supply critical data and information necessary for engineering assessments of coils in fired heater?

RR: Inspection of serpentine coils in fired heaters has historically been a challenge for the owner/operator due to limited physical access, especially within the convection section.  Most conventional NDE approaches (i.e. manual ultrasonics) attempt to inspect from the coils exterior surface; however, access is typically limited to only the coils radiant section, leaving the convection portion of the coil uninspected.  More importantly, conventional NDE is time consuming and the inspection coverage typically only encompasses 2-3% of the coil’s surface.  Engineers attempting to carry out Fitness for Service (FFS) applying manually obtained inspection data results in a lot of guess work needed to fill in the information voids.  Use of ultrasonic based intelligent pigging technology has eliminated these challenges.  100% inspection coverage of both the Convection and Radiant sections now provide engineers with a much higher lever confidence in the FFS analysis, ultimately allowing plants to operate the heaters longer and often at higher throughput.

How many ultrasonic (UT) sensors are necessary on the Intelligent Pig to ensure adequate inspection coverage when inspecting coils in fired heaters?

RR: The diameter of the heater coil should ultimately dictate the number of ultrasonic (UT) sensors the intelligent pig should have designed into it.  For example, a 3-inch diameter heater coil should have a minimum of forty-eight (48) ultrasonic readings acquired around the coil circumference, while a 12-inch diameter should have one hundred sixty-eight (168) ultrasonic readings taken around the coil circumference.  Additionally, the intelligent pig should be acquiring a minimum of four (4) samples for every one inch (25mm) of axial length.

What is the maximum diameter of the ultrasonic (UT) sensor on the Intelligent Pig instrument to ensure both adequate inspection resolution and sensitivity?

RR: The physical dimension of damage mechanisms such as pitting, isolated corrosion and mechanical fretting can be small and in locations where it is impossible to access externally using manual NDE.  Intelligent pigs applied from the interior surface should have a maximum of ¼” diameter (or smaller) ultrasonic (UT) sensors in order to ensure adequate resolution and sensitivity to reliably detect these flaws.  Both of these key elements are compromised if the UT sensor is larger in diameter.

What better information/data do we need from advanced NDE to improve our engineering assessments of heater coils?

RR: It’s the critical, delicate balance of maintaining both accuracy and inspection coverage.  If one or both of these two critical elements is missing, the engineering assessment output is compromised.  Damage mechanisms in heater coils can often be localized to a specific region within a coil and the physical dimension of the flaws (i.e. pitting, fretting, etc.) can be very small.  Without 100% inspection coverage, a flaw can be missed resulting in premature failure of the coil.

What further improvements in NDE techniques are needed to provide more and better data for engineering assessments of heaters?

RR: Intelligent pigging technology designed specifically for the fired heater coil inspection application has rapidly advanced over the last few years and continues to do so.  Many specialized heaters in chemical and upstream industries contain coils which are 2” diameter.  Ultrasonic base intelligent pigging for these small diameter coils is currently in development and expected to be available in a matter of months.

What typical types of industrial heaters justify complex remaining life analyses and specialized inspection? And why?

RR: There are many different types of process heaters throughout refineries and chemical plants.  Their designs are specific to the process for which they are intended.  Many heaters operate at elevated temperatures and pressures, making the internal coils susceptible to both corrosion and creep strain. Ultrasonic based intelligent pigging is capable of detecting and quantifying damage caused by both.  Having the ability to import all inspection data captured by the intelligent pigging technology into one software platform and perform an engineering assessment is critical in understanding the coils’ degradation and remaining life.

Is engineering input provided in advance to give the direction needed to create the inspection strategy?

Prior to starting any inspection it’s critical for the plant operators who manage the fired heaters to share information relating to heater upsets or abnormal operating patterns (i.e. elevated temperatures, plant trips, etc.).  This ensures the data analyst and engineer who are working with the inspection data are paying particular focus to damage that may have been caused as a result of the asset’s operating history.  Additionally, it’s critical the service provider conducting the intelligent pigging inspection service has a strong engineering and heater background to ensure all elements are combined and leveraged to gain maximum output for the dollars spent.

What dictates the degree of accuracy needed for the inspection and results?

RR: As the old adage goes “garbage in, garbage out”.  If the accuracy of the inspection results is in question, so is the engineering assessment output.  Selecting an inspection method with a proven history of accurate and repeatable results is critical in ensuring reliable engineering recommendations.  Many clients today proactively conduct internal live performance evaluations of any vendor supplying intelligent pigging which I feel is essential in qualifying both the technology and vendor’s capabilities prior to arrival on site.

What dictates the amount of area to be inspected?

RR: Coils in fired heaters are constantly being exposed to harsh high temperature and corrosive environments on both the interior (process side) and exterior (environmental side) surfaces.  Damage mechanisms can vary broadly over the entire coil length and surfaces.  Without 100% inspection coverage it’s nearly impossible to ensure the owner/operator has good control on what damage is present and how long the heater can continue to be operated without the risk of failure.

What type of access is needed for the various types of heater tube inspection technologies?

RR: Standard heater coil designs typically are flanged at both ends, allowing mechanical cleaning of their interior surfaces.  Use of intelligent pigging to inspect this type of coil design is fairly straight forward, especially since the intelligent pig is sent through the coil directly after the mechanical decoking pigs.  More complex heaters that contain Common Headers used to be a challenge to both clean and inspect; however, with Header Deliver Systems (HDS) readily available on the market today, cleaning and inspection for these types of heater coils has also become routine.

How much time does it take to perform the inspections?

RR: The intelligent pigging instruments typically travel through the coil at 2 feet (0.6 meters) per second while providing 100% inspection coverage.  A typical coil length of 1,200 feet (366 meters) would require 10 minutes, running from one end to the other.

What are surface preparation requirements?

RR: The interior of heater coils are routinely cleaned (decoked) to ensure heat transfer efficiency.  This cleaning is also necessary prior to applying the intelligent pigging technology.  The intelligent pigging technology is also capable of confirming that all foreign materials (i.e. scale, coke, etc.) have been removed from the coil’s interior.

What is the total cost of engineering + NDE implementation?  What is it worth to the operator (i.e. versus a potential loss)?

RR: Cost is driven by many variables such as coil complexity, length, pipe diameter(s), etc.  An operator interested in obtaining a cost for the services should provide detailed coil drawings and complete a Pre-Job Questionnaire (PJQ) form, which will then allow a Technical Advisor to calculate a total fixed cost for both engineering and inspection.  Feedback from several clients indicates that the cost of applying intelligent pigging is a small fraction of cost compared with an unexpected heater shut down or a catastrophic failure in the worst case.

Because intelligent pigging technologies are complex instruments, what type of formal procedures and technical training does a company need to provide their field teams in order to ensure accurate test results within the inspection reports?

RR: Without question, intelligent pigs are advanced technologies which require specialized training in order to operate them during the data collection exercise.  Detailed formal procedures are a natural requirement of the NDE community; however, the importance of a well-documented process is essential when applying these complex instruments.  More importantly, the training of each data analyst is critical to ensure that they understand both how to process data and the unique characteristics associated with damage mechanisms commonly found in process heater coils.  We’ve concluded that there is a tight connection between the internal service companies NDT Level-III personnel and Fired Heater Reliability Engineers when preparing the training curriculum for all field personnel.  We also encourage clients to audit their vendors to ensure they have robust procedures, training and certification programs in place.

Where do you see the future of NDE & Engineering service companies who provide fired heater inspection and engineering services headed?

RR: I see a much tighter partnership between customers and NDE & Engineering service providers.  Building relationships with the heater’s owner/user elevates the service provider familiarity with the asset they are evaluating, ultimately providing an outcome customized to that particular unit.  The relationship ensures client access to historical inspection & engineering results the service provider commonly archives.


Comments and Discussion

Posted by Dharmesh Patel on July 8, 2014
Very good article. Some more information or... Log in or register to read the rest of this comment.

Posted by Rehan Jamil on November 19, 2016
Very good article.. Mr. Rich if pigging like... Log in or register to read the rest of this comment.

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