This is a case study explaining the failure of an inlet nozzle to a Main Cryogenic Heat Exchanger (MCHE) used in a LNG plant, causing the refrigeration compressors to be in shutdown for 6 weeks. This resulted in loss of LNG production. The failure analysis of the nozzle indicated the cause of failure was Mercury embrittlement that is made of Aluminum, which caused flange leakage. Main Cryogenic Heat Exchanger (MCHE) is made of aluminum and part of refrigeration process in a LNG plant MR (mixed refrigerant) loop. The Mercury embrittlement is a form of liquid metal embrittlement (LME) and a complex metal fracture mechanism that occurs without any warning indications. Mercury embrittlement, being a significant problem in LNG Plants using aluminum MCHE, have led to number of major plant incidents worldwide. Mercury is always present in natural gas feed stocks, sometimes in quantities sufficient to cause severe attack and failure of Aluminum heat exchanger. To avoid Mercury embrittlement failure in aluminum heat exchanger tight limits have been placed on allowable mercury levels in natural gas passing through Aluminum heat exchanger. The natural gas is pretreated with mercury removal units before entering the refrigeration units in a typical LNG plant. Root cause of this failure is identified as the failure of mercury removal units to remove the mercury efficiently. In this case study, Different type of mechanisms has been highlighted by which the mercury degrades the aluminum heat exchanger that includes LME, Amalgamation and Amalgam Corrosion. The importance of mercury removal units in LNG plants is emphasized. Different types of mercury removal technology are explored and discussed. This case study Introduce the newly developed high activity mercury removal absorbents that allows greater flexibility in the design of LNG plants. These absorbents allow for smaller beds, which coupled with new reactor designs improve savings in compression costs. It is now possible to locate the mercury removal units upstream of the main gas processing plant and thus avoid mercury emissions and contamination of any co-produced Natural Gas Liquids (NGL) in a LNG plant.

Why can even the most reliable turbomachinery get tripped up? In some cases, it's all about bad vibrations--literally. This paper explores the challenges one site had with repeated centrifugal compressor trips caused by high vibration over a period of 25 days. It outlines the troubleshooting attempts made to remedy this issue, it's root cause, and the resulting solution. This issue occurred at a site with a train configuration of gas turbine driven centrifugal compressors. After 48 hours of its first startup, the machine tripped due to high vibration at the compressor drive end. Initial attempts to fix the problem included checking the vibration probe gap voltage setting, as well as swapping vibrations probes. After these tasks were completed, the site again attempted to run the machine. 48 hours later, it tripped again. During this time, the vibration gradually increased, staying above the alarm of 50 microns and tripping at 70 microns. The trip setting was increased to 75 microns, but after restarting, the unit continued to trip due to high vibrations. All components were removed and thoroughly examined. Clearances were measured per the standard checklist. The condition of the couplings was found to be normal. The journal bearing pads had minor scratches. The thrust bearing pads were not affected by the failure. Alignment readings were found to be normal. However, residual unbalance was found on the rotor. This residual unbalance was found to be the root cause of the tripping issue. The journal bearing clearances were thus adjusted from 0.17 mm to 0.13 mm. It was also advised to perform high speed balancing checks in the manufacturer's facility. The lube oil inlet pressure was adjusted to meet the requirements for the new bearing clearance. Adjusting the bearing clearance, along with the adjustments in lube oil inlet pressure, resulted in improved vibration readings. This case study provides the detailed analysis of the root cause of the frequent trips as well as the process that was followed to fix the problem.

Case study – Dry Gas Seal Boosters’ Failure and Impact on Centrifugal Compressor Auxiliary System Seal gas boosters are used as part of dry gas seal's sealing system in centrifugal compressors. Centrifugal compressors are used to pressurize the process gas in oil and gas plants. It is considered as one of the most critical equipment in the plant and needs highly safe and reliable operation. Process gas leakage from the compressor are sealed by Dry Sas Seals (DGS). Inorder to have proper functionality of DGS positive clean gas supply is required which is provided by seal gas booster. This case study represents the repeated failure of seal gas boosters and potential impact of dry gas seal system DGS systems are specially designed to seal the process gas leakage in centrifugal compressor. The seal gas is extracted from the discharge of same compressor and supplied to DGS after filtration with necessary control (Pressure or flow) based on the requirement in the seal cavity. Ingression of foreign material into the running gap of the seals leads to degrade sealing performance and eventual failure of the seal. After sealing the process gas, a very small amount of the sealing gas passes through the primary seal faces which are connected to the flare. Providing the positive pressure and flow is most important to dry gas seals. Usually process gas is extracted from discharge and supplied as seal gas after filtration. But during start up and shutdown condition compressor positive pressure will not be available to dry gas seal. Absence of positive supply to dry gas seal gas contaminate the seals. To avoid this issue seal gas boosters are used so that boosters can provide positive supply during start-up, shutdown and even during slow run of compressors. Mainly seal gas boosters are divided into pneumatic or electromagnetic type. They are normally divided into two types such as magnetic transmission type which will be driven by electric motor. Other one will be pneumatic type which will be driven by mechanical transmission. Magnetic type / Electro magnetic type is used in case of sour gas service and pneumatic type is used in case of non-sour application. Booster is used to provide conditioned seal gas flow and not just to increase the pressure. In case of high pressure requirement external gas souce can be used. Site is configured with 44 motor driven centrifugal compressor trains. Most of seal gas boosters were tested in supplier facility before shipment. But consecutive failures such as high vibration, noise, low differential pressure and reverse flow were observed during the startup of the first 4 boosters. The boosters are motor driven having magnetic type piston to develop the required flow. Initial checks were performed as per the trouble shooting guide but the root cause could not be identified as the problems were different case by case. During the first unit commissioning, electric motor which drives the booster got overload trip. Entire loop was checked thoroughly and no abnormalities were found. Initially it was understood could be caused by some foreign particles between the pistion and cylinder. After disassembly, heavy scoring was found but no foreign particles were found. Rootcause analysis revealed that the wear was caused by excessive sliding force. The forces were caused by wrong size of bush. It was communicated to the supplier and replaced by new one which sorted out the issue. During second unit commissioning, seal gas booster was not developing the required pressure and flow so it was decided to perform the internal inspection on seal gas booster. After disassembly, the piston was found struck and not having free movement inside the cylinder. This was resulting in low differential pressure across the seal gas booster. It was also noticed with excessive wear was found on the magnetic piston. Sand particles were found on internal which suggested that the preservation procedures were not followed properly, as indicated in supplier manual. During third unit commissioning, similar low seal gas flow was noticed across the seal gas booster. After several hours of operation also the pressure did not get developed across the booster. Booster was developing negative pressure instead of positive pressure. Entire loop was checked and no blockages were found. Non-return valve located at the inlet of the compressor was removed out and function of the valve was completely struck and the valve in discharge was not working properly. They were repaired and during next re-start the unit was found working normal. During fourth unit commissioning, seal gas booster was not deliverying the required pressure and flow. All inlet and outlet lines were checked and no abnormalities found. Internal inspection on booster confirmed the wear between the piston and cylinder. It was caused by magnetic misalignment between the magnetic driver and cylinder. The components were replaced and repositioned as per manufacturer instruction and restarted. After the re-start unit was found working normal. All corrective actions were carried out on these units and preventive measures were taken to avoid similar problem in other boosters. All storage and preservation procedures were followed as per site quality check list. Site team also verified the downstream lines and seal gas filters to ensure the foreign materials or damaged component materials were not carried forward and affected the seal gas filter cartridge. This case study is providing the trouble shooting experience and useful information for all the gas compressors incorporated with dry gas system with seal gas booster in oil, gas and petrochemical industry to have more reliability.

Gas Turbine Generator (GTG) availability is one of the most critical requirements for any plant production in oil & gas industries. The subject case study provides the information and root cause analysis done on the number of trips happened on a dual fuel Gas Turbine due to high exhaust temperature spread while operating on liquid fuel, that affected plant power production requirements. An exhaust temperature spread refers to a high differential in temperature readings between the thermocouples placed radially around the exhaust of a gas turbine. Spread indicates the difference between maximum and minimum temperatures recorded by exhaust temperature thermocouples. If spread is allowed without correction, it will result in reduction of residual life of downstream components of the Gas Turbine. The worst exhaust temperature spreads occur when the hottest and coldest spot are nearer i.e. exhaust thermocouple readings are grouped very closely adjacent. Most exhaust temperature spreads are the result of combustion section problems that can lead to premature failure of turbine blade /bucket. Site is configured gas turbine running on dual fuel that is fuel gas and liquid fuel driving generator for power generation. During the commissioning and unit start-up the exhaust spread was normal on both fuel gas and liquid fuel. After running the unit for almost a year there was a trip event. Evaluation of the trip data indicated that the exhaust temperature spread is very high when the unit was running on Liquid fuel. It was agreed to start the unit again and perform the fuel transfer from gas fuel to liquid fuel at lower load of 5 MW, the unit tripped again when it was switched to liquid fuel due to same issue of high exhaust spread. Further checks were performed, and it was established that the high exhaust spread is due to hardware issue, related to the fuel nozzles and liquid fuel or purge air system check valves There are number of factors that caused the high spread exhaust issue, all of them are verified by engineering in details and recommendations are provided for the future operation of the machine without the subject issue of high exhaust spread. Most probable causes identified was the Clogging of Fuel Nozzles and issues with the Liquid Fuel check valves and Atomizing Air Purge System Check Valves. High exhaust temperature spread is one of the major concerns in liquid fired Gas Turbines leading to low reliability of Gas Turbine & more down time. In this case study some of the rare reasons for the high spread issues & troubleshooting are analyzed and presented in detail. The information contained in this case study is broadly applied in Oil and Gas plants where Gas Turbines are installed for power generation.

Turbo machineries are considered as one of the most critical equipment in oil, gas and petrochemical plants which needs highly safe and reliable operation. Generally, turbomachineries will be driven by Electric motor or steam turbine or gas turbine in process plant which depends upon the application. This case study represents an experience on complex turbo machinery driver misalignment which is electric motor. In this specific case, electric motor drives Gearbox and centrifugal compressor. Centrifugalcompressor is used for process gas pressurisation. This misalignment was observed between electric motor and gearbox. Electric motors are basically electrical machines which converts electric energy into mechanical energy. So, they are used as driver to drive gearboxes, compressors or pumps and other machines. These machineries have rotating parts at hot at high speed. While units are in new installation phase, machinery alignment shall be performed between the driver and driven machineries. Unlike other rotating machines, electric motors have high thrust clearance. During operation rotor will come to magnetic centre. Prior to the installation of coupling solo run will be performed on the motor to evaluate the performance of motor and to ensure the magnetic centre.