Criticality of Radiant Tube Support Systems
The number one leading cause of unplanned shutdowns or reduced throughput rates for a fired heater is the imminent or actual rupture of a coil tube.
Today’s heater operation is using newer technology burners with drastically different flame profiles to process the most economical shale crudes. Both factors are contributing to a sharp rise in the frequency and magnitude of coil movements (vertically and laterally) seen during operation, often compromising the existing tube support system.
When the tube support system is compromised, tubes inside the radiant section can 1) become overstressed from lack of sufficient support and 2) can slowly creep towards the burner flame resulting in higher tube metal temperature and reduced strength. Both factors jeopardising the life of the tube itself.
Failings of Traditional Radiant Tube Support Designs
Traditional radiant hook support designs are a cast alloy, incorporating a tee or wide flange cross section that bolts or is pinned to tabs directly to the interior of the heater enclosure at the existing structural column/ beam locations. On heaters where tube movement is a concern, the tube support system design will incorporate a tube “keeper” feature in the castings comprised of bump outs or extended hook tips. When the keeper design is removable, separate cast guide keeper bars are inserted in/ over the hook tip(s). All keeper designs intended to aid in the lateral restraint of the tube.
While traditional support and keeper systems have been in use since the 1950’s, they have several fundamental limitations:
- “At the tip” keeper designs are inherently ineffective, the minimal cross sectional size and proximity to the burner flame weakens the keeper, severely limiting the keeper’s ability to restrain the tube long term.
- Failure of one support will transfer the loading, cascading the failure to the adjacent supports, eventually leaving the entire tube length unsupported.
- Replacement is difficult (time consuming) with the coil in place, requiring all the work to be performed in between and around the coil tubes.
- When welding or grinding is required, the proximity of the tubes increases the likelihood of a welding arch strike or grinding wheel hit against the tubes, potentially impacting coil operational integrity and outage schedule.
- Damage to the wall insulation system occurs not only in the immediate area but beyond, requiring enough insulation removed to access and manipulate the cast support in between the tubes.
- The shape of the casting base makes it difficult to properly install the wall insulation around the cast supports encouraging long term heat damage of the heater casing/ structure.
BUSA’s Patented Radiant Coil Tube Support System
Unmatched Performance and Flexibility
Designed to address each of the limitations found with traditional tube support systems, BUSA’s tube support system consists of a cast alloy support hook and keeper that work collectively to provide unsurpassed support and restraint of each coil tube without damage to the tube itself. Round the clock access to the support and keeper is through tube support box enclosures installed adjacent to the existing heater columns.
Ease of Installation
BUSA’s tube support system is designed to allow for as much as 100% of the tube support installation to take place while the heater remains in service, even when implementing the support system on an existing heater for the first time. Key tasks of cutting of the existing casing/ insulation and installation of the support/ tube keeper is performed through each pill shaped opening within the tube support box – all from outside the heater enclosure. All or part of the replacement of the tube support system can be performed in advance of the scheduled outage, making time for other scopes to be performed and ensuring the heater remains off critical path for the outage. Existing supports can remain in position untouched, further reducing outage cost/ schedule impacts.
BUSA’s design captures a separate tube keeper that cradles the tube from behind and above. This design runs cooler during operation maintaining its strength and with a tip of approximately 2 inches in width, providing a distributed point of contact between the tube and support/ keeper. This is how greater restraint while keeping localized tube stresses to a minimum is achieved. For cases where significant coil tube bowing/ movement is experienced, custom support and keeper castings can be utilized – greater in length to allow for the restricted telescoping of the support and keeper (as one) with the tube, still functioning as a tube support and guide. The uniform profile of the casting’s base allows for optimal sealing between the castings and the wall insulation, providing cooler temperatures at the radiant wall where the coil load is carried.
The ingress of tramp air is minimized through removable, gasketed front panels on the face of each tube support box enclosure, each of which can be selectively removed during heater operation to inspect/ monitor the support castings and even immediately replace should there ever be a need.
BUSA is an API Member Company
To find out more – get in touch
Birwelco USA Inc.
20405 SH 249 Suite: 600, Houston, TX 77070 USA
Tel: (832) 916-4130
Safe operation of API 560 heaters is rooted in the maintaining of negative pressure (draft) internal to the heater. This draft works to draw in the correct amount of combustion air required to support the fluctuating combustion rates and corresponding production rates. While a heater’s draft capacity is set by the heater design, adjustment of that draft relies solely on performance of the heater dampers.
Birwelco USA Inc. (BUSA) is a leading supplier of specialized services and support for fired heaters and furnaces from design conception to turnkey implementation. Solutions include studies, on-line services, revamps and complete rebuilds, all with a focus on minimising downtime and maximising return on investment. Understanding the owner’s unique needs and delivering the turnkey solutions to meet those needs is at the core of every BUSA project.