Mitigating Safety Concerns of SRU Stack Using Advanced Analytical/Optical Technologies
Authors: Al Awadhi Ibrahim , Sharma Ashok , Subramaniam Krishnan 
Published: December 2021

Abstract

Objective/Scope (25-75 word)
In SRU, Tail gas exhaust stacks are provided with external cladding, preventing condensation beneath refractory surfaces. External cladding is made of individual Aluminium sheet panels, each 1.7mx1.5mx3mm thk, weighing 60Kg, attached by screws / rivets. Stack size is 6.5mdia × 90m height.
Due to high wind, panel sometimes detaches from stack, falling down from 90m height, posing serious HSE threat to plant personal safety. This paper details an analytical design approach, supported with high resolution, remote controlled drone inspection technic to resolve one such issue.

Methods, Procedures, Process (75-100 word)
Initially, detached and dropped screws were observed, due to wind loads & vibration, which lead to falling of a clad panel from 80m height, fortunately, when no personal was below.
Detailed finite element analysis of external cladding was performed, considering wind loads and thermal loads on panels with stack to panel joint configuration.
Periodic inspection of the joints is vital to confirm reliability of the joints, which is not possible during operation with conventional inspection methods in an SRU exhaust stack. Hence, a latest technology, high-resolution, optical camera assisted, drone, controlled & monitored by remote computers were employed to assess the panel integrity.

Results, Observations & Conclusions (100-200 words)

Analysis Results
Finite element analysis was performed for the stack cladding. As this analysis was non-conventional, there is no well-established industry acceptance criteria for the analysis results. Hence, an acceptance criteria was jointly developed with Contractor, which is fundamentally the minimum number of screws per panel, required to be intact, during the 2 year period, to confirm the panel integrity.

Distance Drone inspection
Manned inspection was not feasible in a running plant. Also, conventional aerial survey drones could not be engaged, as it was unsafe to fly the drone above live plant. Hence, an aerial drone with high-resolution optical camera, with overlapping method was employed. Advanced post processing software was used to analyse the images for best results.

Conclusion
To ensure clad panels integrity and 100% personal safety,
Based on Finite element analysis, the original screws have been replaced with rivets with the following acceptance criteria. The integrity of the cladding remains intact even if 20% of the screws / rivets are lost whether it is consecutive or random. Above 20% there may be impact and further investigation is advised.
Panels were monitored three times periodically in 2 year span to assess the fasteners intactness. The images from the optical camera, after software processing confirmed the fasteners integrity.

Novel/Additive Information (25-75 words)
100% Plant and personal safety is ADNOC's principal objective. Occasionally, achieving this target require unorthodox analysis and acceptance criteria development. Most of all, the conventional monitoring technics, due to their limitations, pushes us to explore alternate technologies.
The new high-resolution, optical camera assisted, drone technic can be engaged in a running plant and the images are processed using proprietary software to achieve best results of minute details.