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Re-commissioning a mothballed unit

Re-commissioning a mothballed unit

Re-commissioning a mothballed unit


I work at a processing plant and have been tasked to re-commission an inlet separator and its associated filters,strainer and condensate wash system that has been under N2 purge and out of service for 13 years.

I have never attempted such a daunting task and was wondering if the senior members can provide some much needed guidance

RE: Re-commissioning a mothballed unit

What kind of inspection can be done on the vessel? Are the internals accessible via a manway? Should you be doing any x-ray or other non-destructive tests?

You have to look at how the system has been isolated from the "in operation" process system and whether any flushing or cleaning of the system is needed.

Would the condensate washing system require flushing?

How will you put the system into service with the actual process fluids?

The above are only some of the questions you need to consider and are not really answers to your OP.

I would think you would want to approach this from the same standpoint as commissioning a new piece of equipment.

I don't know that this is something you can do completely by yourself without the assistance and input of the plant operations and maintenance personnel.

I have attached a typical commissioning spec downloaded from the internet

RE: Re-commissioning a mothballed unit

Confirm your your startup and operations requirements: (pressure, temperature, cleaniless, etc.) and then verify your "normal" startup procedure.

Confirm you "can do" that sequence.

Open and inspect the interior of ALL piping and equipment: Manually if possible, with see-snakes and TV video and pigs and inspection ports and handway ports.

Confirm that erosion and corrosion and failues are not present in the out-of-way places.

Confirm ALL valves and instrument (1) still exist, still can be controlled, and still physically oeprate.

Bring ALL instruments out of the unite units and thermowells and pits and "open and inspect" ALL instrument boxes and panels, and ALL instruments and controls are back in calibration. (You will need to walk down your P&ID's while doing this - because the "Oh Yeah! I forgot we put that one in backwards" factors have been been forgotten.

Confirm ALL controller programming and instrument control function actually still work: Assume a few are NOT Y2K compliant, a few will only run on DOS, a few are not Windows 95 compliant, a few are ONLY Windows 95 compliant and can't run under the new operating systems and graphics.

Have your startup team SEPARATELY run THEIR simulations and control and accident and shutdown and emergency routines on a simulator.

Have your electrical team walk down ALL boxes and cables - look for rats, mice, badgers, porcupines and anteaters, as well as elephants and kangaroo nests. Meggar test ALL motors and power cables and transformers.

From your P&ID, plan your startup flush and "wet-down" sequence so there are no leaks and surprises.

Confirm ALL rigging and cranes and elevators and manlifts are certified.

RE: Re-commissioning a mothballed unit

Thank you for the responses!


The spec you attached was very helpful.....below are some answers to some of your questions

the system has been isolated and is under constant N2 purge

both the condensate system and the inlet separator require flushing I would imagine?

I plan on doing NDT (ut,rt and hydro) and than introducing the process fluids by opening the blinds


your response was very thorough and well thought. I can see this is not your first rodeo !

Do you have any tips on how to inspect/test instrumentation that has been sitting around for just over a decade doing nothing? (I imagine I have to replace it all)

Would it make sense to service the control vavles in place or take them to a shop (max size and class is 6" class 600...most are smaller are rated lower)

What would you suggest in regards to welded/threaded valves that seem to be "stuck"

RE: Re-commissioning a mothballed unit

It will always be better to take the control valves to your facility's shop. The valve can be disassembled, inspected, repaired (if needed), and stroke tested. Such tasks are not normally done in the field. If you cannot do this on site, then you will need to find a valve repair facility and this will be very expensive (almost the cost of a new valve) unless you rigorously monitor the scope of work.

You need to take all your field instruments to your instrument shop and have them tested. You may want to replace them. You will need some time to order the replacements if your warehouse does not have equivalent replacements.

The welded valves should have removable "bonnets" to access the valve internals. The threaded valves should be easily removable.

If you have any pumps in the system, they should also be disassembled and inspected. Typically the bearings will be "flat" after sitting in one place for all these years.

Again, I would HIGHLY recommend soliciting the aid of your operations and maintenance personnel to complete this task.

I would also recommend preparing a written "put into operation" that can be reviewed and signed off by all relevant parties.

RE: Re-commissioning a mothballed unit

I would bring in the original equipment manufacturer to help with a pre-start up audit, integrity checks and replacement parts list from the audit/integrity checks. The OEM engineer can then:
- together with your maintenance team prepare a repair plan
- together with your operations team prepare a commissioning procedure including programming and calibration as may be required

Really, you don't want to fiddle with an equipment you are not too familiar with and you typically will want to get it right the first time for safety and production reasons

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