WhatÆs the difference between pre-commissioning and commissioning?

[sjohnr]

For starting up a process control system I am used to this routine:

1. Install the various subsystems.
2. Perform hook-up of the subsystems.
3. Post-installation testing of the subsystems: this is usually basic things like testing of connections for integrity and continuity, no functional testing.
4. Pre-commission the subsystem: functional checks, particularly against interfaces, but may also include leak and continuity tests.
5. Pre-commission the system: end to end functional check of the system, i.e. very few, if any, forced or simulated inputs.
6. Commission the system: this ends up being very little because all the work was done in pre-commissioning the system. Hence the question. What should be in pre-commissioning and what should be in commissioning? Is pre-commissioning at the subsystem level and commissioning at the system level? Our commissioning would normally also include displacing storage or transportation fluids from process and utility lines, replacing them with the working fluids, but most of this would be outside control system scope.
7. Startup of the process: operations take over here and follow their own procedures for opening valves and controlling the subsequent behavior of the process.

This routine is used for bringing on the control system for a reasonably complex process on a fairly large scale. The control system comprises everything from the HMI through to hydraulic actuating devices, remote PLC based I/O systems, pneumatic control of hydraulic and utility supply systems, interfaces to process shutdown systems.

The general definition seems to be that commissioning is the work required to bring a system to the point where it can be used. This may include leak tests, continuity tests and functional tests. Or should it be just functional tests as leak tests would have been done in pre-commissioning?

 

[jsummerfield]

This is an excellent topic subject to a wide response from many groups outside of the control system world. I wonder if any standards define these terms. I regard these as subjective terms unless the client has a definition in the contract - or contractor defined the terms in the bid. This is a not a big issue for a small project that requires two-months from construction completion to startup. The terminology is a bigger issue for a large project that may require over a year to test and commission.

Where does commissioning end and startup begin? Does commissioning include the first fills? For a gas-turbine compressor commissioning might include running the turbine with driven equipment uncoupled. Is the initial equipment startup with the compressor coupled and moving gas for surge testing part of commissioning or startup?

Let's hit the common items of easy agreement, expand the list to include a variety of activities and table which each regard as construction, hookup, pre-commissioning, commissioning, maintenance, preservation, startup, etc. We need to operate some utility systems to perform much of the completion work. Is there differentiation between the utility systems and process systems?

Construction should be complete for systems or subsystems before any testing begins. There should be commissioning procedures to define the various steps. Inspection Test Records should be recorded in a database to track the construction completion status.

If we commission an instrument system to soon there may be other activities that undo our work. Some examples include the reinstatement after flushing, chemical cleaning, helium leak detection, etc. If we break something that was commissioned and replace it, what is the status of the various QA test records?

Consider preparing a table with the activities, your definition among the completion or commissioning status then invite a vote.


John

 

[xnuke]

In my opinion, construction is about building the system, and pre-commisioning is all about hardware and construction checks (e.g., checking wiring continuity, filling piping and performing hydrostatic checks). Once you start checking the functional operation of any equipment, even subsystems, you're into commissioning. By the listing above, I would call steps 1 and 2 as construction, step 3 as pre-commissioning, and the remainder as commisioning.

xnuke

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[lcleveland]

to put it simply pre-commissioning is crossing the 't's and doting the 'i's.commissioning is when the rubber is put to the road.without putting the system through a total test you have not commissioned it.

 

[jsummerfield]

Just when does the rubber hit the road? This sounds like startup.

Site activities extend beyond instrumentation and control system checkout. Instrument types like to talk about loop checks and functional system testing. Other pre-commissioning activities may include some of the following:
Hydrostatic testing
Flushing
Chemical Cleaning
Helium leak detection
Starting utility equipment without process - air compressor, power-generator, water maker, ...
Starting process motors and turbines while uncoupled from the pumps and compressors
First fills

Introducing the process fluid.

John

 

[lcleveland]

the rubber hits the road when a commissioning agent,this should be someone out side of the installation team or the startup team, tests the equipment to determine if it will do what it was designed to do and if he design intent was meet by the installers .startup takes care of all of the pieces commissioning takes care of the whole . the trick is sometime when to dtermine what is a part and what is the whole . the whole of a system could be determined by inputs and outputs.if an input is connected to or can influence an output they should be commissioned together.this could be a train yard or a desk top pc.
test it, stress it , if you don't break it ,you've commissioned it.

 

[CMfgE1]

This is my experience as a control technician invovled in "new construction" ( I define new construction as a change in the process, invloving adding to or taking away from a process and/or a complete turnkey installation)

I have worked in the pharmaceutical industry and currently work in the beverage industry directly with the control of the manufacturing process.

What I have experienced is whats called an IQ/OQ. This is an Installation Qualification and a Operation Qualification check of the construction.

Installation Qualification-A set of parameters (usually defined by the company commisioning the work) is examined and checked to ensure that all equipment was installed or built to specs. This could be FDA standards, EPA, or specific codes that exist.
This is where process connections (i.e. welds and flanges, etc.) are checked as well as properly secured pipes ,tanks, and anything else mounted.

Operational Qualification-A set of parameters to ensure that the "control" portion of the installation is correct.
This includes programming of batch production all the way down to a manual mixing process. This is where electrical and instrumentation is checked.

Well thats the jist of it. Of course there are pages and pages of details that better define the guidelines.



Good Luck

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