Flue Expansion Joint Material 316, When Should I Choose It? Three steps to help you decide
Two days ago, I met a customer, and as soon as he came up, he asked me, "My flue expansion joint leaked after less than a year of use. Did you choose the right material?" I asked him about the working conditions, and he said that the flue gas temperature was more than 400 degrees, and there was condensed water after wet desulfurization. Tsk, it's an old problem-the material choice 304 can't withstand chloride ion pitting. Then replace it withFlue expansion joint material 316Okay, okay? Don't worry, let's take three steps, and you can make your own decision after reading it.
Step 1: Figure out the hard indicators of 316 material-what exactly can it carry?
To put it bluntly, 316 is an upgraded version of 304, and the key is to add about 2% more molybdenum (Mo). Don't underestimate this 2%. Molybdenum can make steel resistant to pitting and crevice corrosion in an environment containing chloride ions. In vernacular, if you have desulfurized wet flue gas in your flue, or you burn waste with high chlorine content, 316 happens to be the player who can "carry it".
-Chloride ion resistance concentrationGenerally, 304 starts pitting in a 100ppm chloride ion environment; 316 can carry around 1000ppm, which has doubled several times.
-Temperature resistance limitThe temperature of 316 in oxidizing atmosphere can reach about 800 DEG C for a long time (it is recommended that the actual flue operating condition be controlled below 650 DEG C), which is higher than 500-600 DEG C of 304.
-Resistance to stress corrosion: 316 Stress corrosion cracking risk is one grade lower than 304 in chloride and oxygen-containing environments.
But don't forget, it is not a panacea either-if the temperature exceeds 800℃ and the temperature continues to be high, the strength of 316 will decrease, and then you have to consider 321 or 254SMo.
Step 2: Compare your flue working conditions and look at these three points to know whether to change 316
Do you think those numbers above are too abstract? Then let's just take our seats. Take the parameters on your work order, and look at these three items:
- First: Is there chlorine, sulfur and fluorine in the flue gas?For example, the concentration of Cl⁻¹ in the net flue gas after waste incineration and desulfurization of coal-fired power plants can always be several hundred ppm. At this time, candidate 316 is just needed.
- Second: What is the flue temperature range?The temperature is between 400-650°C, and not continuously high temperature (such as intermittent operation), 316 holds completely. If it exceeds 650℃ and runs continuously, then you have to consider 321 (with titanium stabilization) or higher grade alloys.
- Third: Is there any wet smoke condensation?After wet desulfurization, the smoke temperature drops to about 50℃, and the acidic water vapor condenses into a strong acid liquid (pH 1-2), which may be perforated in one week at 304. 316 molybdenum can withstand this "pickling" environment.
As long as you hit two of the above three points, go decisivelyFlue expansion joint material 316。 Hit one? It is recommended that you check the historical maintenance records of this station. If 304 was leaked before it didn't take long, it would be recruited.
Step 3: What is the difference between 316 and 304, 321 and 254SMo?
Compared with 304, the price is almost 30%-50% more expensive; Compared with 321, high temperature resistance seems to be inferior to it; Compared with 254SMo, I am afraid that I will choose low. Let's go through it all at once:
- 304: Cheap, but molybdenum-free. Suitable for clean flue gas, temperature
- 316: King of value for money. Carry chlorine, acid resistance and moderate temperature resistance. It is used in 80% of industrial flue conditions.
- 321: Add titanium to stabilize, focusing on high temperature resistance (above 800℃ for a long time). But the corrosion resistance is not as good as 316, especially to chloride ions. Don't listen to the fool of selling materials saying that 321 is universal, it is two ways from 316.
- 254SMo: Super austenitic stainless steel, corrosion resistance hanging 316, but the price is 3-4 times more expensive. Unless strong acid, high chlorine and high temperature exist at the same time (such as the flue gas desulfurization inlet), using 254SMo is "killing chickens with a knife".
To put it bluntly, as long as you are not in that extreme condition,Flue expansion joint material 316It's the "just right" choice.
Step 4: Practical operation of model selection-directly apply this set of formulas in combination with our product library
Enough theory, how to land? We have a variety of expansion joints to choose from in our product library, such asCorrugated expansion joint for power station industry、Metal rectangular expansion joint、High temperature axial expansion joint。 Just follow this formula:
Formula: medium corrosivity + design temperature + pressure grade → material grade
For example, if the flue gas composition contains Cl⁻300ppm, the design temperature is 500℃, and the pressure is 0.1MPa, then the material is directly selected 316L (low carbon 316, which prevents welding sensitization). If the temperature is higher and the pressure is higher, it is necessary to check the "temperature-pressure curve" of the product data.
How exactly to operate?
1. Open our product library and find the type of expansion joint you want (such as "corrugated expansion joint for power station industry").
2. Look at the "Applicable Materials" column in the technical parameter table of the product. If it is marked with 316/316L, select it directly; If not, you can contact customer service.
3. Note that the material of the guide tube should also be upgraded-if the guide tube is still 304, the smoke will still rot once it rushes. It is recommended that the guide tube be made of the same material 316.
OurRound Flap Door (Double Seal)AndDesulfurization flue gas baffle doorThe matching expansion joint is made of 316 material. Because the chloride ion concentration in the desulfurization system is high, using 304 is to dig a hole for yourself.
Step 5: Don't Think It's Okay After You Install It-These 3 Maintenance Actions Can Save Big Money
Choosing the right material is only the first step, and installation and maintenance are the keys to saving money. I have seen too many cases: the materials were selected correctly, but the result was that they were scrapped in advance without post-maintenance. You will at least double your life by following these three points:
- Action 1: Inspect the bellows surface once a week.Take a flashlight to see if there are yellow-brown rust spots or pits. Once found, it means that pitting has begun, so quickly reapply acid-resistant anti-corrosion paint or replace the local part. Early detection, change a piece of corrugated plate; Late discovery, the whole expansion joint is scrapped.
- Action 2: The drain outlet should be unobstructed.Many flue expansion joints are designed with drain holes or traps at the bottom, but the site is often blocked. If there is condensed water accumulated at the bottom of the corrugated valley, chloride ions will concentrate and the rate of corrosion will double. It is much cheaper to manually clean the drain every time the machine is shut down than to replace it with a new part.
- Action 3: Check whether the tie rod nut is loose.The role of the expansion joint tie rod is to constrain the excessive displacement of the bellows, and if the nut is loose, the bellows is forced to bear additional stress, accelerating fatigue cracks. During inspection, tighten with a wrench, and the torque should be according to the instructions (generally 50-70N·m).
And guess what? Do these three actions well, oneFlue expansion joint material 316It is the norm for bellows to last 5-8 years. If it is not maintained, no matter how good the material is, it will be useless.
To put it bluntly, material selection is a technical job, but it is not so mysterious-grasp the three elements of working conditions, compare them with our product library, and add these five steps. Next time you encounter leakage and corrosion of the flue expansion joint, you can judge for yourself: whether you should change the 316 or the maintenance method.