Please visit Boiler Tube Research (Riser) Part 2 for previous explanation.
Of the analysis result of a photograph micro structure and the violence in the area around the crack:
1. Micro structure on metal parent good to the pipe and plate is ferrite and pearlite. There is no significant differences between them .While on metal welding and haz there was no evidence that the phase martensite brittle.
2. Difficult determine whether cracks in the form of intergranular or transgranular.
3. The photos of SEM look happened propagation crack where at the end of around cracks were many micro crack indicated a dynamic burden to climbing cracks.
4. Of the analysis result of EDX did not find any elements that causes corrosion as the cause of propagation crack as ions cl and s. And from a crack that there were also not characterizing the existence of the involvement of the process of corrosion on crack.
5. From the results of the violence it is evident that weld metal having value violence highest and metal parent to the pipe having value at the lowest violence where propagation crack happened
Mechanical analysis and thermal is hypothesized that appeared after analyzing the results of a visual inspection and micrography a pipe 5 is that a crack that happened to the pipe 5 most likely caused by the cyclic loading good thermal mechanical and.
Cyclic a mechanical loading to the pipe 5 occurred because the pipe near the bottom of a boiler. As a result vibration to the pipe may be due to the process of combustion that goes. Cyclic loading in thermal occurred because the possibility of not inconsistency in combustion temperature inside of a boiler in various points.
Hopefully with a the force of gravity enables bottom ash tending to move down and hit a pipe 5 with the variations of temperature different .Lacing bottom ash this is happening in a recurrent manner to the pipe 5. The phenomenon of this is that likely produces vibratory to the pipe , and in end up creating voltage concentration .
In addition to the external factor , profile of weld which is found in pipe connections 5 and plate was likely produce the concentration of high voltage in the area were. For that , the simulation was done to prove whether there is the concentration of high voltage over a given area in weld connection.
Simulation for pipe 5 aims to prove that hypothesis that crack that occurs more is because of the concentration of voltage on weld regions. Voltage this appears a consequence of the burden of thermal (inside and outside of the pipe) and fluid pressure from in a pipe.
Geometry for modeling and types of materials used for the purpose of computer simulation are presented in table 4.4 and 4.5.
The results of a picture 4.20 simulation shows the contours of the distribution of stresses von mises produced .Of these pictures , it was that voltage von mises concentrated in the weld area.Can be seen that von mises voltage maximum occurs in weld connection profile .In the area by concentration of the high voltage this is , crack will begin to form and spread to the direction of voltage is smaller .The results of these simulations according to the location of that crack found in a pipe 5 ( see figure 4.21 )
Please visit Boiler Tube Research (Riser) Part 1 for previous explanation.
What conclusions can be drawn from the observation the macro economic indicators is:
1. There is a crack that toe a crack or fractured foot.
2.The cracks started of metal and pipe line between weld (HAZ).
3.Cracks toward the spread metal ( a ).
Cracks started on the legs with the high-voltage and cracking can also occur in metals in a microcomputer that prone to hydrogen (source: ASM handbook vol metals Vol-Six: welding, brazing and soldering). The cracks are one of the cold crack that originates from the surrounding surface of metal and climbing stem from a welding ( toe of the weld ) where of the high profile of the welds that produces a high voltage source: ( AWS - welding handbook inspection )
In previous paragraph of information and analysis of the geometry of the welds profile will be conducted besides do analysis of the metallurgy of propagation retaknya to see , as seen in images 4.7 to 4.19
Continue to Boiler Tuber Research (Riser) Part 3 Final.
Earthquake 8.9 Richter Scale (RS) and following with Tsunami at Japan east beach last month made Fukushima Nuclear Power Plant broke out.
Fukushima Nuclear Power Plant is first generation that use boiling water reactor(BWR) system which steam is created to rotating the turbine.
Although old but Fukushima Nuclear Power Plant has stage of modern safety based on resistance caused by earthquake ground motion. It can resist at earthquake until 9 RS.
The safety procedure of Nuclear Power Station that if earthquake happen, reactor core will stop. However with stop fission reaction, the element that process area is not directly cold. It needs additional procedure to make cooling the element with the pumping cold water to element by emergency diesel generator if supply electric power fails due to earthquake.
There are three emergency diesel generators to supply electric power. If all is fail, it has battery reserve that can supply electric power for 8 hours but still not enough to make cooling the element.
The temperature of process element still above 1000c even though emergency cooling already done. This condition makes reaction between zirconium and water that created hydrogen gas until pressure inside reactor chamber increase. This condition makes force to open the manifold and release to the atmosphere and also potential to create explosive due to hydrogen met to oxygen with high temperature. Before open the manifold, the wind direction should be under consideration.
However, Japan government already do early anticipate by evacuated 170.000 people who inside radius 20km.
Accident in Fukushima on categorizes the 4th level because the reactor element doesn’t melt. That was still lower accident level than in Three-mile Island US which the 5th level and Chernobyl Ukrania the 7th level.
Japan now is planning to evaporate or store underground tritium-laced water from the Fukushima nuclear plant instead of releasing into the ocean.
Japanese electric utility Tokyo Electric Power Co's (TEPCO) plans to release the tritium-laced water into the ocean have been opposed by local fishermen as they are concerned about the impact on their livelihood.
The water, which is used to keep the reactors cool to prevent further radioactive releases, is contaminated with radioactive material and has since been leaking and mixing with groundwater that is seeping through the facility.
However, there is no available technology to remove tritium, which is a relatively harmless radioactive isotope left behind in treated water.
TEPCO outside adviser Dale Klein was quoted by Reuters as saying that evaporation method was used after the Three Mile Island nuclear disaster in the US but the amounts were much smaller.
"They have huge volumes of water so they cannot evaporate it like they did at Three Mile Island," added Klein.
The Reuters quoted Fukushima nuclear plant chief decommissioning officer Naohiro Masuda as saying that he is not clear when a final decision about evaporation will be made.
TEPCO is being forced to build hundreds of tanks to store contaminated and treated water.
Last week, the plant's operator announced plans to reveal all data on radiation levels recorded at the site in response to criticism over its lack of transparency.
TEPCO had also announced that it will not be able to process the radioactive water stored at the Fukushima plant by March as promised earlier, due to technical problems.
This excellent Electro-Hydraulic Control (EHC) scheme picture below is made by my friend Fatchurrohman. I would like to explore this topic due to at least twice we got Unit trip caused from EHC.
EHC is as energy to generate and control Turbine Control valves, Turbine Stop valves, High pressure and Low Pressure by-pass valve.
That normal pressure is quiet high 110 Barg or 11 Mpa so when start the EHC system, by-pass valve should be open first.
This is the procedure to start the EHC system.
1. Check hydraulic oil tank level.
2. Check accumulator pressure.
3. Check hydraulic cooling system is available.
4. Check the flow path.
5. Open By-pass valve.
6. Start selected hydraulic pump.
7. Adjusting hydraulic pressure by throttling by-pass valve till desire pressure (110 Barg).
The procedure to automatic back pressure test by Pump stand-by cut in.
1. Close Signal low pressure transmitter from transmitter header line.
2. Open reduce pressure valve from Signal low pressure transmitter to tank.
3. Transmitter will get signal low pressure.
4. Stand-by pump will cut in for back up pressure.
5. Open reduce pressure valve from Signal low pressure transmitter to tank.
6. Close Signal low pressure transmitter from transmitter header line.
The Procedure to normal change over.
1. Check the hydraulic oil pressure (110Barg).
2. Check Stand-by hydraulic Pump flow path.
3. Start Stand-by hydraulic pump.
4. Check hydraulic oil pressure (>110Barg).
5. Stop the 1st hydraulic Pump.
6. Check the hydraulic oil pressure (110Barg).
A specimen is number five segments of the riser. This is part of the pipelines that is concerned with processes occurring at of steam drum. Where the drumming cycle of steam is water down through the pipes of steam drum down-comer header under the header into the bottom to distribute the water to the pipes under the header heating ( riser ) are arranged to form a boiler room gas. Despite the riser water is warming and hoisted himself back into the drums of steam.
The pipeline 5 can be seen from figure 4.1. The pipeline is fitted with the 5 horizontal position of pipe with a pipe and other related to the plate mounted by welding.
The report from the improvement of the leak of a pipe at furnace lower header unit 2 by PT. Resounding mighty technique in November 2013, that this pipe never been repaired in November 2013 and operating back on the same month. Crack that there is eliminated by the process of grinding and die penetration done to ensure there is no crack.
Crack that is covered with welded back with the process of GTAW 70S-6 use electrodes in accordance with specifications. Die penetration the last of the results confirmed that the results of welding was in good condition .But not much later found back the crack on the connection between liaison plate and pipe welder (no information about when this incident).
Those who received the condition can be seen from figure 4.2. Next is a visual inspection and it's like looking at a picture 4.3 to 4.4.
It's a visual inspection result of the conclusion can be drawn 5 as follows:
1.There was a crack in the pipe was such a plate.
2.To pass through a crack on the inside of the pipe.
Metallurgy analysis to know the exact cause of the occurrence of cracked, then done tests as follows:
Testing chemical composition and violent material pipe 5 and plate testing aims to prove that there is no mistake in choosing material of a pipe used.Based on information obtained specifications of material 5 pipe used this is SA210C. While to the specifications of plate unknown. The results of the testing of chemical composition and violence will be compared with ASTM A210 standard specification for seamless steel medium-carbon boiler and super-heater tubes.
A conclusion that can be drawn from the results of testing material pipe 5 and plate is:
1 Pipe 5 materials used in accordance with specifications that has been determined.
2 Material plate used is similar with material pipe.
Metallography analysis and violent weld connection of pipe 5 and plate to view with exactly where cracks happened, then done observation macro structure as i was in this picture 4.5 to 4.6.
Continue to Boiler Tube Research (Riser) Part 2.
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