The 150 MW turbines

We got a two turbine units. Both of them are a subject of the overhaul project and both of them are the 150 MW turbine but this feature will change as one of the project aims is to increase the trubine efficiency. The IP steam path is about to replace and two stages at LP rotor as well.
Let me present a drawing of this turbine:

1. HP part
It is impulse part with 18 stages, one outer casing, two bearings. The bearing no.1 is a radial one and the bearing no. 2 is a combined one axial-radial.

2. IP part
This has 15 stages and similar to HP, one casing, two radial bearings (no. 3 and 4)




3. LP part


A double-flow rotor, the two radial bearings (no.5 and 6), the rigid couplings

4.The Generator left in power plant, so no activities on our workshop linked with this turboset part - at least I do not know what is work scope for gen. parts.

november's news

I got an info regards the turbine start up after the outage my company did.
It seems we did good job. There was no problems during start and trial period. The additional balancig activity is forseen as the dynamic state of whole machine can be improved. The overhaul agreement includes the vibration limits after assembly, so we are just now slightly above what was written down.

I am back

Short explanation why such long break.
The summer is the overhaul time, so each company in my sector is busy. I was tired after work and had no power to open my blog but I going to continue and this "diary" will be enriched with more posts.
During this weekend the start up of turbine, I described in my previous post, is planned. Coming back to office on Monday some details will be known. Certainly, I will touch this then.
In the mean time I has supervised the outage of ten rotors - 4 HP rotors, 3 IP rotors and 4 LP rotors but it is not the end as maybe fifth LP rotor will come. It is intersting story what we went trough with last two LP rotors but I will mention this later.
All rotors are the rotors of the 200 or 225 MW turbines. In fact it is the same desing but each turbine has been modernized up to certain level and that is why the turbine efficiency is different.
The first turbine is 200 MW. We got 3 rotors from this turbine for the overhaul process in the same time but very quick was obvious that the HP rotor is in worse technical condition than was foreseen. The first and secound stage were damaged. Blades and shrounds should be exchanged but no money was budgeted for such operation, so after meeting with customer it was decide to leave the rotor as it is and repair the spare one bought a several years before. Customer thoght that rotor HP no. 2 is in better technical condition. After NDT activity we did, it was clear that blades are ok but shrounds in 2 stages needed repleacement. The secound customer meeting took place to spread info and propose solution.
The power plant people agreed with us what to do and I prepared the technology charts accordingly.
The new shrounds were put on.
The IP rotor overhaul was enlarged in similar way like HP rotor case. Here the one shround was exchanged only.
It is easy to write that overhaul scope was increased but the the overhaul deadline was not changed at all. It means, we were forced to do more job in originally planned period of the time even when the scope was wider. Anyway we managed to do it. Honestly, the new repair circumstances affected the timing and we got one week more.

The secound turbine is the 225 MW turbine with different LP rotor. It is larger, heavier than previous one. It was modernized in 2001 by Westinghouse.
It made some troubles for us, as our sand blasting room is not big enough for such rotors. I found soultion. I had read about dry ice blasting. This technology seemed to be great in this particular case. It does require seperat place to clean dirt turbine part. I found 3 companies offering this technology. All of them saw our rotor and one of the did a little trial to see if it is possible to clean our "fan".
We saw results and took a challange. Dry ice blasting is very noisy and not as good as it looked like doing the trial.
Usually we need 2-3 days (with 1 shift daily) to clean the big rotor but now was necessary to devote 5 days with 2 shifts daily to get the LP rotor cleaned. Uff... dry ice blasting is not the best idea, is too slow.

to be continued ...

the rotors to be repaired

I had opportunity to supervise overhaul of a couple of rotors.

The first one and the most complicated is the the repair of the LP rotor of 100 MW turbine.
It is double flow rotor and have 10 discs mounted on it.

During the NDT technicians found the cracks in the corner of keyway at 6 discs.
Let me present the pictures taken before discs dissasembly.

"Naked" rotor shaft with no discs, the bigest ones are visible.

Next pictures present the dissasembled disc

These cracks are the beginning of possible disaster, that is why we and customer took decision to repare the discs.
We proposed the followin steps :

- dissasembly of all discs,

- NDT examination,

- machining the internal diameter of discs to remove the craced area,

- prepare the bushes,

- mount the bushes into discs with light interference,

- drill radial holes through the bush and disc and install pins with light interference.

The customer accepted our solution, so we started to collect the material and parallel prepared the discs.

I ordered the bushes at foundry and prepared the drawnigs how to machine the discs.

After 4 weeks we got row bushes then they were machined and put into discs.

The next step was to drill radial holes inside the discs. It seems to be qiute easy and in fact it is easy but we have too big angle head for our milling machine them we had a lot of problems to obtain what was designed. At bigest discs, which has the least hole I asked designer not to drill holes as deep as it was drawn.

In the same time the pins were prepared, then we put them into drilled holes. I wrote, the pins to be installed with light interference but to make the assembly quick we used nitrogen to cool them down.

This part was finalized but it is not the end. Now is final machinig. The discs are installed onto rotor with interferance ~ 0.60 mm, so the diameter is very important and tolerances are very tide.

The very last step of machining is keyway milling. We did it partialy inhouse, and using external subcontactors.

I put a couple of pictures taken at differt assembly steps

This is the end of machining and the assembly phase was started.

Below we have the hanging rotor shaft a few secounds before 1st disc assembly

It took several hours to heat up the disc and get enough internal diameter. The interference is 0.6 mm. To mount discs on the rotor we decided to heat them untill the clerance is 0.5 mm.
We needed almost one week to put 10 discs on the rotor but it was not the end as the steam gland bushes and finally couplings had to be assembled as well.
We managed to it and after run out measurement it turned out that some surfaces should be machined when done the very last step - low speed balancing.
I will write a few words about turbine start up but wait some time.

welding repair of the rotor

In my previous post I mentioned about the rotor welding repair. Let me add more info.
During the NDE it was found that it has crack placed next to journal under thrust collar. On the picture below (arrow) it is visible - thrust collar is diassembled.

Firstly, the rotor end was cut and shaft chamfered. The stub shaft was sent to us by our colleagues and welded by TIG to the main part of the rotor. The most important activity was carried out next - putting the material by SAW. It took several days and was splited into a few phases. After welding certain material thickness we machined it and did NDE to be sure if weld is free from any mistakes.
When welding was done I took over the responsibility. The two last steps remain. The rotor PWHT and machining.
To perform PWHT the rotor had to be positioned vertically. It is not usual to see rotor set in vertical position and to do it the special equipment was necessary - based on former solution I designed some devices.
The pictures below show the rotor uplift:

- rotor after rough machinig before PWHT

- the rotor uplift

The rotor is hanging and will be fixed for PWHT

The rotor PWHT is starting ...

Original rotor design was changed. Just now the thrust collar is an integral part of the rotor shaft when previously collar was a seperate part and mounted on the shaft with negative allowance.

The repair last step carried out in our workshop and supervised by me was the final machining. I got the drawing, but the technology chart prepared on my own. As usually not all info was put on the drawing but I manged to get the missing data and below we can see the rotor end after final machining:

Once machinig was finished the rotor was moved to the our subcontractor - for high speed balancing.

I know that the customer has more rotors (2 pcs.?) with similar crack and maybe the repair process will done again... who knows...

outage season

The Spring has come already and as usually this time during the year, a couple of new overhaul projects have been started. I have taken part in some of them:
- reapair and machining of the axial bearing,
- assembly and machining of the modernized steam glands (retractable seals),
- welding and machining of the rotor.

This last one is especially intersting as the rotor after welding has to be fixed in vertical position for PWHT. I think, such advanced rotor repair is uniqe and my company is the only one in this part of world, able to perform it ( Am I wrong? Please advice).
I wanted to post complete report, I did after small repair back prassure turbine - too much work just now but having more time I will do it.

small back preassure turbine repair

The next project, I was responsible for, is the small turbine overhaul.
It is 6 MW machine. The majority of such turbines were installed in Sugar factories.
The scope of works was not complicated:
1. Upper part of external casing.
- cleaning,
- hand processing of casing surface,
- NDT examnation,
- elimination of discoverd crakcs and welding repair if neccesary,
- corrosion protection.

2.The Steam glands.
- cleaning,
- NDT examionation,
- dimensional checking,
- corrosion protection.

3. The rotor.
- cleaning,
- NDT examination,
- geometry checking,

4.The Diaphragms
- cleaning,
- NDT examination,
- dimensional checking,
- corrosion protection.

5. The diaphragms carriers
- cleaning,
- NDT examination,
- dimensional checking

I am going to post the complete report I did after this overhaul.

generator's bearing machining.

The next task I supervised was the machining of the generator's bearing. My company is not specialized in generators repair but a review of the mechnical part of this machine very often is included in overhaul scope.
I am going to present only small element of whole turboset outage.
I do not remeber what was wrong exactly with generator's rotor but its journal was machined, and a diameter was decreased. It such case is a technical correct to decrease the bearing's clerances which is imposible without supply of the bearing with new, smaller internal diameter.
We used support of bearing suuplier described in my previous post but in this case they were responsible only for rough machining as we wanted to do rest of operations on our own.
Firstly, just after we received rough bearing my colleagues carried out the US NDT, to check if the "white metal" adheres good enough to bearing casing.
The next step was the hand processing of the bearing's surface. The lower and upper part have to fit to each other with special conditions - no clearance and the fitting trace has to be visible on ~ 80% of the surface. This demand can be obtain by grinding.
Than we put a metal plate between both parts of the bearing. I mentioned in my previous posts that internal shape of the bearing is lemon/ellipse shape, this is why the plate is needed. After bearing machining it will be removed and we will get, what we want to.
Next is the machining of the internal diameter, when done the surface metal plate are removed and again bearing is assembled on the lathe to machine oil seals and the external diameter.
Now, we can start the last part of the maching - the internal details for lube oil inlet and lift up oil. The major is done on lower part of the bearing.
The last activity was to clean holes for vibration and temperature sensors.
This bearing's ovehauls was done under the client preassure , so we worked during the weekend to send the part as quick as possible.
We managed to do it and a day after I had a phone call with our site supervisor to discuss some dimensions but a couple hours later he confirmed that turbine is closed and ready to be launched. I have not had any news related to this turbine, which means it is ok.
It was quite fast job under the preassure of time but we succed to do properly without mistakes

reaction turbine overhaul - part five

This part is the last one, dedicated to reaction turbine overhaul, I supervised. In last Friday I got info from our departament resposible for on site activity, that the trial run of this has been finished and no major defects were found.
Today, I would like to spend a couple of minutes, presenting bearings overhaul.
As it was not a point of outage scope and rotor's journals were not machined, the bearings could be used again.
In general, the most important features of the bearings are: geometry with right clearancess and the condition of the white metal. The clearancess depend on journals diameter. Sometimes, at small diameters, rotating machines can be operated with equal clearancess (bearing is a circle) but very often clearancess are not same on the sides and up, bottom. The bearing has lemon shape.
The another problem that can cause supply of new bearings is the lack of right adhesion between white metal and bearing casing. It is checked by US examination. Certain, % of surfaces can have a lack of adhesion.
In my case project managers wanted to have new, round bearings. NDT examination done on site showed the lack of adhesion and it was necessary to manufacture new bearings.
We used support of external supplier and it prepared bearings for us. However, I refused to accept first delivery, as geometry was out of tolerance. I required that the diameter is 0.00/+0.02 mm and the shape defect (cone) is not more than 0.02 mm - the bearings are very precision parts of the rotating machines and such requirements are nothing strange. Unfortunatelly, our supplier sent us bearings wrong machined and ... thought we did not discover it or whatever.
I asked our Quality Control to check dimensions against documentation I prepared prior the bearings were sent to supplier. It turned out that we have bigger diameter than can be and additionally they have ~ 0.20 mm of shape defect (cone) it is completly not acceptable and bearings were sent back to new white metal cast and machining.
The supplier did the mistake for the secound time, what is horibble but we were very sensitive and found it. The third time was the best. I think that after these mistakes we have right opinion.
What, I wrote above did not affect the overhaul deadline as the bearings were prepared parallel to other works. Anyway it can happen that new bearing delivery date is the critical one and "supplier's issue" can make us very nervous.

reaction turbine overhaul - part four

I am going to present what we did at outer upper part of the casing.

The first step like with the previous turbine parts was cleaning. The casing was moved to the special chamber and blasted using aluminium oxide. It is not the only one material we use. If customer have a special whishes we can use glass microballs, copper abrasive. These two are used very rearly as glass micrballs are not abrasive enough (it takes long time to get surface cleaned) and additionally round shape of the balls can make the surface too smooth, so the NDT - PT is unable to discover micorcracks and copper abrasive is too sharp and if used in wrong way can cause cavities on the surface, which especially at rotors are unwanted.

The next step is NDT examination. What we used the most at casings is MT examination but if necessary PT and UT can be applied as well.

During the overhaul I led, no big defects were found - the most important was discoverd inside the valve chamber at diffusers, see the picture below:

There are 5 diffuseurs and 3 of them were in conditon like photo shows. The customer gave us 2 diffuseurs (spare parts), they order third one to be manufactured by my company. Certainly, to install new diffusers is a must to remove the old ones, we did it but it is not complete scope of works prior to assembly the new diffuseurs. Firstly, is technical correct to machine the all cooperating surfaces inside the casing to get parallelism and perpendicularity. The diffuseurs are mounted with the negative allowance, in this case the diameter of diffusers should be 0.08 - 0.10 mm bigger than holes in casing, so after maching of the casing obtained hole geometry should not be bigger than customer's diffusers. Unfortunattely it was not the case. When we got right geometry of the seats, it turned out that provided diffusers are too small to install them and get right interference fit. We inform customer and got agreement to supply all new diffusers. Below we have the drawing of the new diffuser:

reaction turbine overhaul - part three

Just now I would like to put here description of rotor overhaul.

Usually, we start repair activity with cleaning. In this case was the same - the rotor has been blasted and moved to next known step like NDT examination is.

It depends on the ovehaul scope what kind of NDT examination should be carried out. The most frequent are: Visual Testing VT, Magnetic Particle Testing MT(UV - in Ultraviolet light), Ultrasonic Testing UT.

However it is possible to perform more sophisticated test, like: Phase Array - to check if the blade groove is free from cracks without blades disassembly , Borasonic Test - to check the rotor from the inside trough the central hole (for impulse rotors) if it is free from cracks, defects. Results of this test can be used to define the rotor life). One of the quite modern methods of rotor's testing, but not only dedicated to rotors is Metal Magnetic Memory Method.

In ovehaul, which I led, the VT, MT and UT were used. Certainly, I was not the person who did it, as I do not have right training and certificates to carry out such testing.

The VT gave us a lot of info what is the current state of the rotor - corrosion/erosion is the main problem, let's see a few pictures, startin with the general rotor's view:

erosion presence

Similar material condition we met on the carriers, that is why we recommended to exchange stationary blades and rotor's blades as well.
So, we left the rotor as it is and moved to the next ovehaul step - rotor's geometry measurement. To perform this step we needed a lathe. The rotor was installed on the machine and than we measure what is the run out. The measurement sheet is too big to put here but the biggets radial run out was 0.08 mm, it means still acceptable.
Next we started to remove the seal strips, as the old ones were damaged.
There are several areas of the seal strips on this rotor:
- front steam gland seal strips,
- balance piston seal strips,
- seal strips installed between the stages,
- internal steam gland between HP (high preassure) and IP (intermediate preassure),
- rear steam gland seal strips.

The seal strips have "l" shape and are fixed to the rotor with the wire, see the drawing below:
We can see only one seal strip before rotor's stage it was done in this way as we welded the shrounds with the tanon blade in the carriers. We wanted to avoid, the strip touches the welded place on the shround during turbine work. We could put two strips, machined them to have right diameter including proper radial clearance but in this case would be good to machine the welded shround, as well. It could create some machining problems, as shround was not welded on whole circumference. Finally it was faster to put only one strip without carrier machining. It was emergency repair ... .
It was the end of the manual job. The two last step in rotor overhaul were machining and low speed balancing.The machining was not so complicted. The rotor's journals, throust collar, oil guard surfaces were polish only. The longest part of the machining was the seal strips machining as there are a lot of strips and the machined diameters have to be quite accurate. I required +0/ -0.05 mm tolerance for seal strip diameters.
The last rotor overhaul step is the low speed balancing. We reduced the amount of weights from previous balancing and changes the angles a little bit.

The very last step before dispatch was to put corrosion protection on the rotor.

reaction turbine overhaul - part two

Let's start with the glands overhaul.
The overhaul scope was not so large.
- cleaning by blasting,
- NDT examination,
- dowel pins and screws exchange,
- seal strips exchange,
- machining,

This turbine includes 3 glands. Two of them as a external ones and one as an internal one beetwen HP and IP turbine's part.
After blasting our NDT inspectors found no important defects, means no removing and welding works before next steps.
Prior to new pins machining, the pinholes were reamed to get right geometry of the holes, than turner got diameters included proper clearance - I do not remember, but for sure not more than 0.10 mm.
To remove and put new seal strips was the most labour-consuming task. We used vertical lathe to remove old strips and correct the shape/geometry the grooves but anyway it required to be very carefull. Certainly, producing new gland, especially by CNC machines is easier and faster.
Very important thing is worth mentioning - gland setting on the lathe. This activity is one of the most important steps during any machining of used turbine parts. All of them, because of high tempeature, and steam preassure have some deformation even if they were round with accuracy of 0.01 mm as new ones.
Very often detail setting on lathe,boring machine or miller takes hours particullary if they are large but machining itself can last minutes - it is feature of turbine repair...

Hello,
I realize, that for somebody out of power industry service, can be hard to understand what I have here - technical details, I mean .
I am not going to explain just now all the issues but I will try to include some description or even publish posts clarifying more questions regarding structure of turbines

reaction turbine overhaul - part one

In my previous post I mentioned about reaction turbine overhaul projects I supervised in our workshop.
We repaired following parts of this turbine:
- rotor,
- upper outer casing,
- bearings,
- glands,
- internal casings (carriers - is it right technical word?) with stationary blades,

Like usually, the first step before any activity is to take a pictures of parts. It will be an evidence of parts conditions and ( in case when customer does not have documentation) helpfull in further overhaul steps.
The next move is cleaning/blasting and just now we eneter to this moment, which can affect the rest - NDT examination.
This step discovers the real condition of parts. All craks, defects will be found and decision what to do with them will be taken.
In overhaul, describing by me, we had a problem with one of internal casings (carrier).
We found that blade shrounds are not fixed to the blades.
Please see the photos of casing (carrier) no 1

It would be very dangerous to leave it as it is and against technical routines we follow.
Neither we nor customer did not expect such suprise so it was necessary to organize meeting and inform what we found and what are our proposals.
The best way to repair the shrounds would be to exchange the blades into the new ones and put new shrounds as well, but not in this case, as
1. customer was not prepared for such cost,
2. there is no time to carry out this - they need power and steam, so there is a must to fix the issue as fast as possible using enough appropriate technical solution to launch the machine and operate it for some time period.

After the meeting it was decided to applied our proposal - to weld the end of blade - tenon with the shround. This emergency repair will let customer to operate turbine till to next year when wider scope of overhaul has to be taken into consideration.
The repair idea given by my senior management was drew by me and below we have more detailed drawings.

We suspected what are the steels used to manufacture the blade and the shround - each OEM uses the same group of steel but to be sure in 100% the analysys was done. It was especially important for our welding engineers - to define and apply right welding technology. A few welding samples were made to precise post weld heat treatment as weld hardness after PWHT should be proper one. We managed to reach right parameters.

If major overhaul takes place, like we adviced, in 2010 I will have possibilty to check results of this emergency repair - it will be great issue.

Hello,
I have decided to launch my own blog. What for, you can ask... ok, a few words of explanation are needed.
I have taken part in huge amount of overhaul projects during my job and even before, when I was a student. Just now, trying to refresh my memory and found some details on the bottom of my brain, I am not able to catch sharp picture, only general points left.
All of these projects have been very intersting, ... maybe some not, but anyway I missed such activity and even I came back again to power industry, as a couple of years I spent exploring automotive area but now I know that is too boring for me - daily routines in production... the same ones ...., I preffer to get new problems each day and fix them, with support of others if I am short of knowledge or experience.
So, I've thought of blog as a place to share what I am doing, to present projects I take part of or these ones which are driven by me.
All questions, notices, opinions are welcome. I think, would be good to give you a little amount of my personal info:
man, husband ,father, living in Europe, mechnical engineer from education. The English language is not my mother tongue, therefore please take it into account, if you suffer from my English, let me know what is wrong and I will correct this.
I am going to present my 3 projects, which were supervised by me
The first one is about reaction turbine repair, the 2nd, the smallest so far - bearing overhaul, in fact only, maching part of this activity (details will follow) and the 3rd one - very short overhaul of main internal parts of impulse turbine from Sugar Factory. I have several pictures and drawings, I hope these will help to understand what I am going to show.