Annealing furnace and research report and test of galvanized line burner nozzles
A) Description of the current situation and problems created in the annealing furnace:
There are 156 burners in this annealing furnace, of which there are 78 on one side and 78 on the other side. The burners are placed inside the radian tube and heat is generated. The temperature of the burners is not measurable, but the output temperature of the combustion gas is between up to degrees Celsius.
The gas pressure of the burner is between 14 and 18 bar.
Of course, the conditions are different for each burner in the annealing furnace, for example, the burners at the beginning of the furnace inlet produce more temperature and these burners start or stop automatically.
The working conditions of the burner should be such that co is around zero, o2 is about 2 to 4% and co2 is about 10%, so if the working conditions are strictly observed, the flame condition should not be severely oxidizing. Cooling of the system is done through the exhaust fan (exhaust suction). Torches do not have an intermediate state, either on or off. The main burners (external parts last between 2 and 4 years and then deform when worn, and this deformation is visible to the naked eye at the end of the burner, indicating that the flame is not concentrated.
Built-in burners last between 1 and 5 months, after which the nozzles are severely damaged, which occurs both from the side holes of the burner and from the section welded to the nozzle body. Which causes the flame to escape from different parts and destroys the radians of the expensive tubes of the furnace and may cause a great blow to the whole furnace. In addition, shutdown time and replacement repairs have caused significant damage to the production process. These nozzles are made in such a way that only the head of the nozzle is made and its body is prepared from the previously destroyed part (external part) and the made part is welded to the body. One of the problems of these nozzles is the welding of this part. .
The material of these radian tubes is Iconel 601 (D), which has had many defects so far, and these defects have been repaired only by welding and sleeve.
Due to the opening of the welding nozzles, the furnace has been damaged twice so far.
It is possible to check the burner heads in foreign parts, but in Iranian parts, due to premature destruction, it does not have this advantage. Foreign samples are checked once a week to measure flame deflection, which in the Iranian sample is done daily due to the high probability of failure.
Currently, more than 20 broken burners are working in the annealing furnace.
B) Research method to find out the reasons for the destruction of the annealing furnace:
1- Several photos were taken of the four states of the nozzles in the annealing furnace:
1-1 – Non-installed external nozzles (in stock)
1-2-2 Non-installed internal nozzles (in stock)
1-3- Exhaust nozzles in the workshop with details of how to destroy
1-4- Internal consumable nozzles (in the workshop with details of how to destroy
2- Refer to the district officials to ask about the environmental conditions (if possible, measure the temperature of the nozzles during operation with a radiation thermometer) and the reasons for the destruction and operating time of foreigners in comparison with the internal ones and the problems caused by the consumable nozzle at work. Rial comparisons).
3- Analysis of internal and external samples to ensure the similarity of the material of the two samples.
4- Metallography in all four cases of paragraph 1 to study the microstructure of internal and external samples before and after operation with each other.
5- Research to determine whether it is or is not.
6- After performing steps 3, 4 and 5, it is determined which materials can be a suitable alternative to the existing materials and which can be provided in the domestic industry, and the feasibility of installation (amount) is also checked.
7- According to all studies, a solution to increase the life of the nozzles will be provided.
C) Presenting the results of research and tests performed in the annealing furnace:
1- Photos External and internal nozzles worked before and after
As can be seen in the pictures, despite the shorter working time of the internal samples, their destruction was more extensive and they had more deformation and deformation than the external sample. Another difference seen in the damaged internal part is the holes near the welding site, which are most likely due to non-compliance with the welding instructions using the appropriate welding electrode.
2- Field research and inquiry of environmental conditions from district officials
Regarding the results of the question from the district officials, the necessary explanations are provided in paragraph a of the report.
3- Analysis of internal and external samples to ensure the similarity of the material of the two samples
PMI test was performed on both internal and external samples by the Spectrotest portable quantum device belonging to the company, the results of which are listed in the table below. The print of the quantum device is also reported in the appendix:
According to the analysis of the table above, the two samples are according to the table below.
The detailed analysis of the standard in the above grade in the following table is based on the German standard:
As can be seen, the material of the internal sample is different from the external sample. The exterior material is HK-40, which is roughly equivalent to 310S non-cast steel. Steel is a heat-resistant steel. The most important difference between HK-40 steel in terms of analysis and 310S steel is the difference in the percentage of carbon, which increases the percentage of carbon in this alloy increases the creep resistance compared to the non-cast grade 310S. CF-8 material is equivalent to cast steel, which has a lower heat resistance than 310S steel. Detailed chemical analysis of 310S and 304 grades for comparison is given in the following table based on the German standard:
The reason for the lack of heat resistance of CF-8 steel compared to HK-40 steel is the much lower amount of nickel in the composition of this steel than HK-40 steel.
Comparing the creep properties of 304 and 310S steels, according to Figure 1 on page 5 of Appendix 2, although at temperatures below 750, 304 steel shows better creep resistance than 310S steel, but at temperatures above 750, due to drop Excessive creep resistance is not applicable at all, but 310S steel retains its creep resistance at temperatures above 750, due to the higher percentage of nickel in the 310S analysis and the fully austenitic structure rich in nickel.
On the other hand, HK-40 material, which is the main material of foreign samples, has a much higher percentage of carbon (0.3-0.5 compared to 0.07>) compared to 310S steel, which will increase the creep resistance of this cast steel. In fact, carbon will play the role of a high-temperature stabilizer by creating chromium cables. The following rules can be summarized for the content of chromium, nickel and carbon in cast iron-nickel-chromium heat-resistant alloys (Appendix 3):
1- As the percentage of nickel increases, the ability of carbon to be absorbed by the alloy in carburizing environments decreases. 2 – With increasing the percentage of nickel, although the tensile strength at high temperatures decreases, but the resistance to thermal shocks and thermal fatigue increases.
3- As the percentage of chromium increases, the resistance to oxidation and corrosion in chemical environments decreases.
4- As the percentage of carbon increases, the tensile strength at high temperature increases.
4- Metallography in all four cases of paragraph 1 to study the microstructure of internal and external samples before and after operation with each other:
Internal and external samples were performed before and after metallographic operation. The microstructure was prepared and its analysis is presented below:
4-1 – External nozzle sample worked before
4-2- Sample internal nozzle worked before
4-3 – External nozzle sample after work
4-3 – Sample internal nozzle after work
D) Provide a solution:
First of all, what attracts attention is the huge difference that there is in the chemical analysis of two fabric parts and internal construction, so that two alloys can be considered as two different categories, in other words, the material of the fabric part (HK-40) is steel. High temperature resistant austenitic casting and internal workpiece (CF8) is made of ordinary austenitic steels. In the first case, due to the high Ni content (about 21%), the microstructure of the workpiece is completely austenitic and absorbs this problem with a very simple test. Or non-absorption of the magnet can be proved (it is completely non-magnet, which indicates that the structure is 100% austenitic, but in the latter case, due to the smaller amount (about 12%), the structure has about 25% delta ferrite, which makes the piece semi-magnet. Significant differences in the shape of the structure were also shown in Section C, which in fact all PMI tests and metallography and magnet testing confirm the same thing. Regarding the effect of nickel content on the resistance of the part at high temperature, as mentioned earlier, in fact, the main effect of adding nickel is the elimination of delta ferrite phases, which do not have good strength resistance at high temperatures and facilitate material creep. Increasing the percentage of nickel will increase the resistance to heat shock as well as thermal fatigue. Increasing the percentage of carbon in the analysis will also increase the yield strength of the part at high temperatures, so due to the low percentage of nickel and carbon in domestically made samples of CF-8, the probability of creep (Creep) is very high. .
Regarding the other two possibilities of degradation, namely Corrosion and Erosion, according to the statements of the site officials, who considered the percentage of gaseous elements as 10% Co2, 3% O2 and no Co, it can be concluded that Corrosion is expected in such a controlled flame. It does not exist, and the probability of an unusual erosion is still very low, according to officials who put the gas pressure at 16 millibars. Therefore, it can be concluded that Creep has been the main cause of destruction and it is necessary to replace the home-made material, which is CF-8, with the fabric material, which is HK-40.
Regarding the assembly of nozzle parts to the body of the burner, an important point that must be observed is to pay attention WPS is suitable for the type of material and the use of the correct electrode. As can be seen in Appendix 4, the electrode made of ER630, which is a hard stainless steel, is considered suitable for welding.
Notable point: Because casting of high-nickel heat-resistant alloy steels is done at high temperatures, alloying of this type of alloy is associated with evaporation and burning of some elements, and thus achieving an ideal composition requires the use of modern equipment and methods. And is valid. Here, Part Ritek Company announces its readiness to select suitable workshops for execution and supervision during construction, according to the sensitivities and considerations necessary for the production of the part, along with repeating all the tests of the manufactured products.
