OQ Refineries and Petrochemicals – Resolving the small bore connection failures in ethylene cracker plant

General description of role:

Sundaravel has been a Team lead in OQ Refinery and Petrochemicals, Oman managing Asset Integrity Engineers, Senior Inspector and Senior Engineers. OQ commissioned its first Ethylene Steam cracker project worth 3 Billion Dollars investment in the Sultanate of Oman. He is a Tier-3 Technical Authority in Inspection. He was entrusted with quality assurance through approval of materials, suppliers and fabrication shops proposed by Engineering, Procurement and Construction (EPC) contractors and monitor the quality both at shops as well as at site.  

  1. Summary of the project, product, framework

Operations reported failure of Small-Bore Connections (SBC) in Medium Pressure Steam service at 19 barg pressure. SBCs include PG connection, Vent and Low Point Drain (LPD) downstream of a Pressure Control Valve (PV-68A) in Ethylene Plant.

Inspection was notified to assess the condition and evaluate the options.

Sundaravel formed a task force after inspecting the site and found that the vibration is a potential cause of failures with more than 2 failures occurred since commissioning of the plant. Advised to check the design of the PV against the actual operating condition. Upon verification by Instrument team, Flow Induced Vibration (FIV) was identified as a root cause of the problem with design change request triggered.

  • Description of project or framework addressing the assessment criteria

Background: Oman commissioned its first Ethylene production plant with an investment value of assets worth close to 3 billion dollars in 2020. With over 300 pressure vessels, 6 heaters, 50 storage tanks and over 200 piping circuits, managing the assets with widest range of operating conditions starting from minus 103 Deg C to 1000 Deg.C is a challenge.

Plant was commissioned successfully and commenced operations in 2021. As per the Reliability principles, early failures of equipment and piping are imminent that follows the “Bathtub Curve”. This means that the rate of random failures will be high, will come down sharply and will flatten as the plant operations gets stabilized.

Ethylene Plant has wide range of steam service viz. Very High-Pressure steam, High Pressures Steam, Medium-Pressure Steam, Low Pressure steam. As a part of the process, Steam is also generated from the Heaters during the cracking process.

Just few months after commissioning, Operations reported failures of vent and PG connections in MP Dilution Steam system, which was repaired by the Engineering Procurement Construction (EPC) contractor during the warranty period. Cracks were observed on the gusset plates welded to the header as well. Again, the failure occurred within few months after the repair. Asset Integrity Team was informed of the repeat failure and tasked with thorough analysis of the piping circuit.


Asset Integrity team under the stewardship of Sundaravel, visited the site and found abnormal noise at the section of the piping that had repeated failures of vent and drain connections. After studying the Process and Instrumentation Diagram (P&ID), it narrowed down the cause to be likely from the Pressure Control Valve (PV). The control valves are designed for a specific pressure drop.

Upon scrutiny of the PV, it was found that the design pressure drop for that PV is around 0.35 barg. while the actual conditions were suspected to be deviated far from the design. When the PV is operated outside the design regime, it can lead to a “Flow Induced Vibration (FIV)”, which in turn could cause the failure of SBC’s due to high or low cycle fatigue, depending on the frequency and amplitude of the vibration.


Sundaravel advised to check the vibration of the piping at the vent and drain, which could not be done due to the temperature limitations of the vibration probe. I tried to identify the source and cause of vibration in the piping and connections. Possibility of accumulation of condensate (due to non-functioning of steam trap) in the upstream resulting the 2-phase flow vibration was checked and ruled out.

The bye-pass valve was opened and observed the that the intensity of the vibration got minimized. With that narrowed down the cause of vibration. It was mainly coming from High DP with high opening of the valve versus presence of condensate and advised to do the pressure survey of the system to map the pressure differentials across the system.

Upon completion of the pressure survey by Operations / Process Engineering, it was found that the pressure drop across the valve is more than 20 times that of the design basis. With the new parameters recorded in Operations case, the design verification of the control valve was performed by the Engineering team and reported that the existing control valve design is not suitable to handle the huge pressure drop and proposed a different design to minimise the impact of the vibration downstream.

Damage Mechanisms and Materials Design Envelope:

Flow Induced Vibration (FIV) has been a problem in the industry resulting in failure of SBCs’ catastrophically, which potentially lead to a safety incident when the process fluid steam comes out from the pipe scalding the people around.

Energy Institute’s Guidelines for the design, installation and management of small-bore tubing assemblies was referred to and identified the gaps in the existing loops. Reference was taken from similar industry issues and steered the team to carryout the SBC assessments in critical services.

Cost vs Risk vs Performance:

Having witnessed failures in a short period of time, Maintenance cost is about 2000 Dollars per event. However, the risk of unavailability of the unit due to breakage steam piping is approximately one million dollars per day. Apart from the economic impact, steam leak results in personal & process safety concerns (causing scalding). Environmental perspective, the noise pollution from the increased pressure drop is beyond the allowable limit of 85 dB, is quite high for free movement of Operational staff for their rounds. Noise from the control valve coupled with vibration cause the poor performance in the downstream process. To manage and improve the situation, an interim short-term solution was recommended by the team to crack open the by-pass valve to minimize the impact of vibration until the pressure control valve is fixed permanently. Identification of the source of the problem is a key for a safe, reliable plant operations.

  • Opinion as to specific contribution made by the nominated individual /team/ organization

Based on the study, it was found that dilution steam piping was subjected to Flow Induced Vibration (FIV) which was causing frequent failure of gusset plates and vent and drain connections. Mean Time Between Failures (MTBF) was as low as 4 to 5 months.

To improve the reliability of the piping system and avoid the potential process safety incidents due to leaking steam at 20 bar g Pressure, Sundaravel insisted that the engineering study shall be carried out to identify the root cause of vibration and resolve it holistically. He initiated the study of SBC connections applying the industry best practice as recommended by the Energy Institute.

He checked the design data sheet of the control valve and challenged Operations team for actual values and upset scenarios. He facilitated the informal Root Cause Analysis (RCA) with Engineering, Process and Operations team and got the buy-ins from Instrument Engineering. Constructive engagement of Engineering team resulted in identification of the root cause and got the solution to overcome the issue.

To resolve this issue, he coordinated well with the Predictive Maintenance Team, who advised on the vibration measurements and process Engineering in mapping the pressure survey across the circuit that gave the clear picture of the issue. By implementing the evolved engineering solution, the pressure control valve is being ordered with an engineering change that will eliminate the process safety hazard in the site, safeguarding the employees and workers at site.

  • General comments you may wish to add

Sundaravel’s persuasion with the stake holders in getting to the root cause saved the company from having frequent steam piping failures and improved the personal and process safety of the unit holistically, re-engineering the valve to meet the operational requirements.

Design error or operational errors may lead to a process safety incidents and timely intervention by Asset Management Professional could help to minimize the impact or consequences when done diligently. Improvement in Process safety measures pays off the company with reputation, and a good community with preferred workplace for employees. Small changes in design can have a big impact, if resolved timely.

I acknowledge the team members from Operations, Predictive Maintenance Engineer, Process Engineering Teams and special thanks to Instrumentation Engineer, who collaborated with EMERSON Engineering team in validation of control valve design, to highlight the limitations of the current design and proposed the engineering changes.

I am proud of my team members who gave their professional judgement in their areas of expertise, without which the Asset Integrity of the system could not be possible.

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