Erection and Commissioning


Thread Starter

erection lead

i'm a mechanical engineer. i worked as erection supervisor in GE machines and also some other turbines. is erection interesting?? (talking about knowledge and making money) i'd like to change to commissioning, what should I learn? how should I prepare myself?
In general, people with mechanical backgrounds make better control engineers than people with strictly a controls background. And, I believe that a commissioning engineer needs to have both experience sets because they have to understand how plant equipments are supposed to work, how they are supposed to work together, and how to make the equipment work together in the plant they are installed in. And, many times it's <b>NOT</b> about making a software change to make it all happen correctly.

Sometimes it's necessary to re-configure the as-found installation, which can be very difficult to get done ("Nobody told us it couldn't be mounted upside down!" or "It doesn't look like it should be rotating in THAT direction!" along with a lot of whining and whinging and complaining.

One of the things I find most distressing about commissioning people (the ones without much experience or who never leave the control room) is that they usually don't understand very basic wiring of various control instruments and devices. For example, RTDs (Resistance Temperature Devices) can cause prolonged problems for people who will NOT go out to the device and verify the wiring has been installed properly. They are VERY simple devices, but some control systems require very specific connections. And some plant/equipment designers don't always provide the wiring one would think would be necessary, but do provide the capability to make things work properly with the wiring provided--if one would only take a few minutes to work out and understand.

Many commissioning people mistakenly believe that the as-received wiring drawings are 100% correct, and that's simply never true. I don't care how many "Approved for Construction" rubber stamps appear on the drawings; they're usually stamped by interns or draftspeople with little or no understanding of the circuits or details of the requirements of the circuits.

Understanding how 4-20 mA circuits work, and when a dropping resistor is required and what value of dropping resistor is required for the control system to properly scale feedback is also very important.

Understanding how thermocouple extension wire circuits work is also very critical in some cases. I've seen several Combined Cycle Power Plants nearly fail their performance test during commissioning just because two or three thermocouples were not terminated properly with the thermocouple extension wires. Once corrected, the plants passed performance test, sometimes with 1% or more margin, when they were failing by fractions of a percent just because thermocouples had not been properly terminated with thermocouple extension wires.

As a mechanically inclined person, you should be able to read and understand P&IDs--which in my opinion is one--if not the--most important abilities of a commissioning engineer. If one can't read or understand or be bothered to read or understand P&IDs, they are going to fail miserably. And, part of the need to read and understand P&IDs comes from the need to identify components (such as check-valves and control valves) which might be installed backwards because they were drawn backwards, or were installed backwards because someone looked at the drawing and thought it was shown backwards on the drawing and instead of asking someone they just made a command decisions to install it the way they think it should be installed--which can create a lot of problems during commissioning. (I'm speaking to some double block-and-bleed valve configurations which place the valves back-to-back and which just seems confuse the heck out of most pipefighters, ...,er, ...,uh,.. pipefitters.

So, as a commissioning engineer, one needs to be able to take a P&ID and walk down a system and verify that all devices are properly installed, and be able to recognize that sometimes they are installed per the drawing, but the drawing is wrong.

Then, the rest of it is becoming familiar with the control systems in use at the plant to be able to view processes and values to be able to determine if what is supposed to be happening is actually happening. But, the most important part of that skill is to know what is supposed to be happening when, and that unfortunately can't be learned from a book. Sometimes, though, the manuals provided by the Architect/Engineer of the plant have some very good information and they should ALWAYS be consulted along with the review of the P&IDs.

Lastly, if you plan to work on GE gas turbine equipment try to learn how to "read" signal names in the Speedtronic turbine control system. Properly written, they can be very descriptive--and also very important to understand and know when commissioning the systems. Specifically, discrete (contact) input signal names describe when the signal should be a logic "1", and it is NOT ENOUGH just to see a change of state when loop-checking discrete inputs (to any system). The signal must be a logic "1" when it's supposed to be a logic "1", and a logic "0" when it's not supposed to be a logic "1". A lot of "experienced" GE commissioning engineers don't get this concept and do a very poor job of loop-checking.

It's still important to other control systems that the indication from a discrete input be a logic "1" or logic "0" at specific times, but a lot of times it's not possible to discern from the signal name for that input when it should be a "1" or a "0"--and that can also cause a lot of problems during commissioning if the commissioning person doesn't sort that out before trying to start the plant.

So, you really have a lot of good skills--presuming you can read P&IDs and are not averse to reading them and being able to go out to the field and identify devices and instruments and see if they are properly installed, and if they are properly wired.

The rest comes from experience. You will learn something from every person you work with during commissioning--just never forget to take some time, either in the evening or in the morning, or after a particularly difficult job is over, to sit down and review how things could have gone better, what could have been done to make things go smoother. Sometimes, it's as simple as taking the time to read instruction manuals BEFORE working an an unfamiliar piece of equipment. Or, asking for information about a system or piece of equipment you're not familiar with BEFORE you are trying to make it work properly.

Review and preparation are two of the most important parts of any commissioning job. And by review, I also mean that period of post-job contemplation when one thinks back on the good and bad aspects of the job just completed, with an eye towards improving one's performance on the next job.

Best of luck!