Cold Box Failure, A Rare and Troublesome Phenomenon
Saeed Moshayedi
Deputy Head Of Inspection Department at 6th Refinery of South Pars Gas Complex
Cold box is a complete package of brazed aluminum heat exchanger contained in carbon steel casing with structural support, insulation containment, and protection for the internal equipment. Insulation work of heat exchanger and piping assembly can be easily done by Perlite insulation and inside of cold box will be pressurized and purged by dry nitrogen gas
Cold Box is mainly used in Gas refineries and Air Separation units (ASUs) and usually classified as medium risks equipment and they don't have scheduled inspection plan as it's complicity, high cost and time especially because it needs Perlite to be removed for internal inspection.
However failure is an inseparable phenomenon in oil and gas industry in which no equipment is fully immune of and cold box is no exception to this rule! As you know cold box is made up of Al and the process gas has to be free of Mercury due to LME (Liquid Metal Embrittlement).
This is what happens when Aluminum meets Mercury, and for prevention of LME, Mercury Guard is usually placed before Cold box.
Cold Box cools down natural gas for fractionation of Methane from other composition and in gas sweetening units is placed after dehydration unit. In spite of the fact that no water expected after dehydration, sometimes adsorption beds lack their duty and water vapor carry-over to the cold box and perform ice pieces which block the streams. Here is where Methanol comes in handy and is injected to the system by a reciprocating pump. You can see the pressures of different streams in the table below.
Mechanical Fatigue was diagnosed by the RFCA team as a main damage mechanism of failure and high pressure of gas caused further erosion of Aluminum cap.
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As in a failure many parameters take a role and each plays it's own one, in this failure 3 parameters were determined as the most important reasons by the investigation team.
1- High rate of Methanol injection as adsorption beds could not remove enough water vapor from the stream.
2- Lack of Pulsation Damper in down-stream of the reciprocating pump, so high amount of vibration induced to the piping system.
3- Insufficient support in piping system of the failed injection point. Other injection points have different support system and the failed one as you see, has a free end!
We learn from the past and we share, maybe it helps others to prevent a future failure.
Head of process engineering at South Pars Gas Complex (SPGC)
2 年Mr. Moshayedi, thank you for wise analysis.
Quality Control Specialist en ACCIONA
2 年Thanks for sharing. Excellent post ??
Lead Asset Integrity and Reliability Consultant
2 年Mercury level control is key to predict amalgam.
Deputy Head Of Inspection Department at 6th Refinery of South Pars Gas Complex
2 年Great question, I am going to write another article about the inspection methods in which removing perlite is NOT needed. We could use some methods, Helium test, pressure leak test and acoustic test.
Corrosion & Integrity Manager l Petrochemicals l RBI l IOW l Data Driven Inspection l
2 年Good sharing, regarding LME mercury to cold box, what is the proper inspection method during Turn Around, and where the suspect location. It seems challenging because cold box has perlite insulation. so we need to remove all it before inspection as my experience. Anyone would like to share, I appreciate. Thanks