The Story of a Leaking Heat Exchanger

Stories of leaking heat exchangers arise in old plants like ghost stories in abandoned houses. But this story is worth telling because it happened in a new plant. This is a story of engineering behind the scenes.

In the beginning …

It was a fairly new gas plant. But, the Amine Plate Heat Exchanger started leaking, causing the plates to corrode. The plant was shutdown. The plates were cleaned. The gaskets were changed. The plant was started again. Within months the heat exchanger started to leak again. The tiresome and expensive process of shutting down, cleaning, changing was repeated. The plant was restarted once more, only to shut down once again. Each shutdown cost the operator millions of dollars. The operator contacted the vendor demanding a resolution to the issue caused by the malfunctioning heat exchanger. The vendor said that they were not at fault. That model of heat exchanger has been around for a while, used widely and no one else was facing a problem.

We got a call

The operators were wise. They took the sensible option of engaging independent third party engineers. As independent third party engineers, our focus was mostly on looking into the defects of the plate heat exchanger and to proceed to FEA if needed to simulate and prove those defects. Time was of the essence as we were engaged during the 4th shutdown. A quick solution was needed to stop the recurrence of leaking incidents and loss of revenue.

We went to have a look

• We visited the site to examine the heat exchanger and the condition of the plates and gaskets. We collected first-hand information and looked at the process of running the plant as a whole.
• We found that the Plate HX was dismantled, the plates were corroded and the gaskets were torn
• Installation MDR was showing that everything was in order
• The maintenance log was showing right torqueing of the heat exchanger bolt
• The exchanger plates were made from stainless steel and the gaskets were made of rubber as per the MDR
• No significant pressure or temperature spikes or excess flow condition was noted in the operation log
• We gathered, after interviewing operators, that the leaks start within a few days of startup and the quantity continues to increase as the days go by
• The gaskets were replaced to the specification of the OEM. A few plates were also changed to the OEM specification
• We walked the line armed with the piping layout in our hands and discovered that the first support of the pipes in front of the heat exchanger was restrained on all sides. This looked a little suspicious.

Our Reasoning 

We thought long and hard about what we found. We came to these conclusions:

• The heat exchanger selected and installed as per API 662 was fit for the purpose from the process point of view
• The materials used were certified as per EN10204
• The process data showed that there was no flow induced forces
• So, we thought, the problem must be with the piping. The pipe stress analysis as per ASME B31.3 for the piping configuration showed induced forces and moments on the heat exchanger nozzles. These loads were being transmitted in its entirety to the HX body, thereby distorting and compromising its integrity. The liquid was finding its capillary path through the gaskets, corroding the faces not designed for exposure. The liquid was eventually making its way out through the HX plates’ path.
• Restraining the pipes on the axial direction, was inducing loads beyond the allowable limits of HX nozzles
• Why was this? Well, the earlier stress analysis did not get the confirmation for the loads from the HX vendor

Our Solution

We provided the following solutions to ensure a fully functioning, hassle-free plant:

• Remove the guides on the pipe supports in the axial direction to the heat exchanger nozzle from all first supports in front of the HX
• Provide a Teflon pad under the pipe support fixed with a counter sunk screw to the base plate on the steel member
• Put a position mark for the pad to monitor the pipe movement. Keep regular vigil on the condition of the Teflon pad
• Modify a few support locations and type of supports at the heat exchanger and air cooler end to satisfy allowable nozzle requirements of the equipment as per API 662 standards

A Happy Ending

In short, the story had a happy ending. We helped reduce unplanned shutdown hours. The availability of the plant was increased due to our investigative and consultancy work. The owner was saved millions of dollars. We were happy to help.

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by Soumen Guha

Principal at Sustech Engineering Pty Ltd