Monitoring pipe expansions 2

[athomas236]

I am involved in a project comprising 3x350MWe coal fired plant and the client wants to be able to monitor the thermal expansions and movements of the boiler to steam turbine critical pipe work such as the main steam and hot reheat pipes. These pipes will operate at 540C.

Does anyone have any thoughts on how this can be done.

Regards,

athomas236

 

[C2it]

Depends how permanent you want, and whether you need remote or local monitoring. For local, some simple ruled marker might be ok. For remote ... sounds expensive, maybe adapt position monitoring equipment for a CNC machine ?

 

[MJCronin]

athomas,

Many, many years ago, I was involved in a program where the expected thermal expansion of various nuclear piping systems were compared against the calculated theoretical ( piping stress analysis) movements.

The program that was developed used LVDTs to measure thermal expansion movements and compared that movement against those of the analysis. A margin of + or - 20% was used on all measurements.

Some suggestions:

- Select monitoring points only on important piping systems where at least 1 inch of thermal movement is expected. Allow a generous margin in the measured values.

- Allow a couple of "shakedown" thermal cycles to occur before the final measurement. There can be influences, such as pipe support friction, that will change after a couple of heat-up cycles.

- Do not be afraid to revise the stress analysis to reflect reality with regard to actual spring hanger defections, pipe shoe friction actual operating temperature etc.

The field thermal expansion evaluation described above was required by the utility (USNRC) to enable a more secure feeling about the calculated stress analysis - it was a contract requirement.

Why are you performing your field evaluation on a fossil fired plant ?

Hope that this helps...

Regards

-MJC

 

[mizzoueng]

Well, I would first try to figure out why you need to do this?

I am assuming you are wanting to verify a stress analysis like Cronin said, also, you could use this to make sure you hangers are still operating like they should.

I would pick some critical points (high stress or high movement) in the system, then place guides around the pipe and place a flat steel plate extending from the side of the pipe. this flat plate will mate with another that will turn a dial or send an electronic signal through your DCS system. Think of a giant caliper but in all three axies.

You really don't want a guide persay, but just some structural support to hold the sensors that can handle the loads of the pipe moving.

To prevent undue stresses, you would want to make the maximum reading of the sensor to be about 30% greater than what the expected movement is now. This gives extra room for future expansion and it also allows your pipe to move in each direction without having a force acting on it from yuor sensor steel.

This is just an idea, I haven't actually done this, this would be my stab at figuring this out.

 

[athomas236]

Gentlemen,

Thank you for your advice.

It is the Owner's Engineer who wants to monitor pipe displacements to verify the stress analysis and confirm the satisfactory operation of the of the supports.

We as one of the largest UK power consultants have no experience of such monitoring, hence my question. As part of my investigations on this matter I have become aware that LVDTs have been used on fossil fired power plant in Korea and that TUV have used draw wire sensors on a nuclear plant. I am currently trying to find out more details of these applications but welcome any other comments.

athomas236

 

[athomas236]

MJCronin,

Are you able to provide any additional information on the nuclear test programme. I am most interested in how the 3D displacements were determined and how the locations for such monitoring were selected.

athomas236

 

[JohnBreen]

Hello,

It is common practice to install "tell-tale" trams at key locations on Power Piping high energy piping systems. You will note that we even refer to trams in B31.1, Appendix V, Recommended Practice for Operation, Maintenance and Modification of Power Piping Systems. Surveillance of pipe supports and hangers should be continuous and they should be examined by "walk-down" examination at least every 6 months. The positions of the trams should be recorded during each "walk-down" and if a great difference in the positions is noted from one examination to the next it should be brought to the attention of the plant management as it indicates something has changed. See B31.1, Appendix V, paragraph V - 6.0, Piping Position History.

We usually make our trams from 1/4 x 1/4 inch square section carbon steel rod stock and attach one to the piping (e.g., at a hanger clamp). We attach the opposing tram to a point on the structure that will not move much. The ends of these trams are each ground to a point and they are bent into position such that they are each (the pipe tram and the pipe tram) "point-to-point" with the systems shut down and at ambient temperature (take care to allow for the expected expansion so they move away from each other upon heat-up rather that colliding with each other). When the system is at operating temperature we measure the travel (north-south, east-west, and vertical) from the "cold" position and record that movement. That measured "gap" should not change much in a base load plant unless the pipe temperature changes so any change in the gaps indicates something that should be investigated. Similarly, if the two points do not "come together" as the system cools to ambient temperature, the cause should be investigated. Often, when the pipe movements as recorded at the trams are "surprising" it indicates anomalous behavior of one or more spring hangers (internal friction due to springs rubbing on internal parts, break-down of lubrication, broken spring coils, collecting debris in the internal parts, etc.). Anomalous movements can also point to unseen interferences between piping systems and this might indicate a broken rigid rod hanger due to a damaging dynamic event (water hammer, steam hammer, slug flow, etc.).

Installing and periodically observing tram movements can tell you a lot about the "health" of the various high energy piping systems and their supports.

Regards, John.

 

[Sid7]

Thank you very much John for the explicit explanation and a star too.

I would request you to share some diagram/photograph of such feature, as for me I havent seen anything like this before, rest leave my imagination on its own.
regards,

Siddharth
These are my personal views/opinions and not of my employer's.

 

[MJCronin]

athomas, John Breen,

I would like to add to my post above that the LVDT devices that were used for thermal expnsion monitoring were temporary devices. As I understand Mr. Breen, his devices are permanent.

The LVDTs were attached to structural steelwork and wired to a recording device. A square cube "target box" was fabricated from mild steel and welded to a pipe stub; the stub was welded to a bolted clamp. Only one direction of movement was measured per target, but measurement of two directions was possible on one box. LVDTs could measure movements to a tenth of an inch very easily.

The same setup was used to monitor piping transient movement events (pump/steam turbine startup)to satsify other plant testing requirements.

You must have a clear idea of your goals and then select piping monitoring events and equipment with care.

All of this info, recollections and methodology is 20+ years old....I do not know what the current crop of nuclear plants are doing for thier piping certification and testing. I would be very interesting for me to find that out......anyone ???

Regards

-MJC

 

[athomas236]

John Breen,

Thank you for response, it is much appreciated, especially as I didn't know that B31.1 included such recommendations.

Having read section V-6.0 Piping Postion History, it seems that the approach described allows the changes in the hot and cold displacements between inspections to be measured.

What I am not sure about is if this approach could identify problems with the locking of pipe supports, say, during the first start after erection. It also seems that if a problem does arise with pipe supports then this would not be identified until the next walk down/inspection which could be a period of 6 months.

With the increased use of advanced supercritical plant with steam temperatures of upto 600C, I just wander if the V-6.0 approach will be sufficient in the future.

As part of my investigations, I have read about some work in Germany that involves continuous monitoring of pipe displacements using draw wire sensors, which could, in principle at least, overcome the potential difficulties with the V-6.0 approach. It also appears that knowing the actual pipe displacements on a continuous basis might allow a more accurate assessment of the pipe life consumed.

Monitoring of life consumption seems to be a requirement in Germany.

Best regards,

athomas236

 

[athomas236]

MJC,

You may be interested in the following which I bought yesterday from the British Lending Library for £10 with delivery within 24 hours. (Sorry for the plug.)

"Reliable detection of pipe supplort malfunctions with the Displacement Monitoring System DIMOS" by Martin Winterstein and published in the proceedings of the 21st ESReDA Seminar, Erlangen, Germany, November 5-6, 2001.

It describes one system that uses draw wire to monitor pipe displacements on a nuclear power plant.

Regards,

athomas236

 

[athomas236]

Gentlemen,

You may be interrested in the following:

1. The TUV system that that is described in the paper in my previous post uses draw wire sensors and has been used to electronically store details of pipe displacements and temperatures which have then been used to periodically compare calculated and measured displacements as a function of temperature and detect malfunctions such as the fracture of spring supports, blocking of supports and changes in the frictional behaviour of pipe guides.

I have no evidence to indicate that the TUV system is commercially available but two German companies do commercially offer systems that appear to be similar to the TUV system. These companies are Technip-Coflexip who offer their MLM system and Steag Ketek IT who offer their SR1 system. There are two versions of the SR1 system, one for boiler headers and one for pipes.

2. The MLM system is installed at the Scholven, Schkopau, Schwarze Pumpe, Lippendorf and Niederaussem power plants in Germany and gives DCS displays that indicate actual and target pipe movements, the target values being determined from the pipe flexibility analysis. The operator is warned when the target movements are exceeded.

3. Use of systems such MLM and SR1 offers the possibility to use these systems to monitor pipe lifetimes based on actual measured data. RWE are developing such a system so they can extend the periods between internal inspections from the 3 years required in Germany to 5 years and eliminate the need for pressure tests which are currently required in Germany at 9 year intervals. This information is taken from a RWE presentation.

Regards,

athomas236