Written by a Refinery Maintenance Engineer
Synopsis of technical content
Refineries have experienced many spring support failure/malfunctions in critical piping and valves. Improper spring supports can cause loss of positive containment (LOPC) piping failures, vessel damage, and serious safety events.
Generally, this is due to a lack of understanding of the severity and consequence of constant and variable spring support failures. Major failures have occurred due to a
- Lack of improper spring settings (COLD/HOT)
- Lack of proper environmental corrosion protections
- Lack of PM (preventive maintenance) and routine inspection schedules by qualified personnel to conduct a proper health assessment
To facilitate proper movement of the supports, springs should be designed with double corrosion protection with detailed PM & inspection schedules. To facilitate proper inspection by operations, they should be designed to provide a travel indicator that visually verifies movement towards COLD/HOT position as per load/spring datasheets. Sometimes, the movement can be counter intuitive with large piping systems. Time to time, sites should invite spring vendor to provide support, advice and training to the maintenance and operations teams. The vendors recommendations are key to understanding critical support functions, troubleshooting and ensuring reliability for plant operations. It is highly recommended to involve the spring vendor prior to every turnaround for joint inspection with Coker units so that any deficiencies can be properly addressed during the turnaround. Thermal cycling of the delayed Coker unit requires more dynamic spring support scenarios than any other unit in the refinery. Following any major turnaround, it is important to have a comprehensive inspection and verification plan for all types of supports, especially those who have been worked on during the shutdown.
Detailed technical content
Standard features of critical piping spring supports are position (cold/hot), travel scale, load adjuster, level rotation indicators, and locking (lock pin) or balancing devices. Pipework stress and load analysis is calculated based on deadweight, thermal and dynamic effects, system stress levels, and equipment loadings along with loads and movements acting at the support positions. Various codes and calculation methods should be considered, such as but not limited to ASME B31.1, B31.3, Finite element analysis (FEA) and relevant design codes. There are two major types of spring supports (Constants & Variable) used in Coker plants based on the nature of the process and piping/equipment. The piping around the coke drum is especially complicated and each licensors has different strategies to manage piping and the coke drums which utilizes additional types of struts and snubber supports due to the nature of drum piping, support and special spring support for BUD (Bottom Un-heading Device) to control BUD movement with Coke Drum.
Constant Spring Support (photo):
Variable Spring Support (photo):
Common Problem/Issues Observed in Refineries:
- Springs are put in service without unlocking
- Setting of COLD positions are not verified before plant start up
- No check point of HOT position is conducted to ensure spring load movement
- No periodic inspection and action conducted during plant operation
- Coating of spring coils are not aligned with Coker unit environment severity
- Simply hot dip galvanized, as per ASTM A123, is not enough to prevent coils corrosion & cracks due to regular steam around the supports
- No plastic or equivalent corrosion protection (double) to ensure zero environmental corrosion
- No mechanical box (open/close) by aluminum or equivalent metal sheet, installation to prevent coils from coke dust, steam, water and high temperature environments
Spring Coil Coating Process (photo):
- Springs are to be procured with double corrosion protection for long life of springs accessories
- Springs are to be unlocked and set in COLD position before unit startup
- Survey to be conducted to ensure all springs are in COLD position (departmentally or through spring vendors)
- Check travel indicator and ensure HOT position as per Spring datasheet (departmentally or through spring vendors)
- Localize fabrication box to prevent spring accessories environmental corrosions
- Include spring PM schedule in maintenance SAP system (turnaround to turnaround OR as per spring vendor manual)
- Industry best practice to inspect (health assessment) for spring support in every six months
- Operator training to ensure they can spot the signed of support malfunctions between formal inspections
- Detailed procedures for installation and setup of critical supports such as those related to the BUD, drum inlet/outlet piping.