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  • ichudov
    started a topic Welding, hydrotesting a compressor tank

    Welding, hydrotesting a compressor tank

    I purchased a compressor recently. It is a Speedaire, 80 gallon compressor with 7.5 HP motor and 80 gallon tank.

    Based upon first impressions, the motor and pump run fine. However, when bringing the tank up to pressure, I heard a hissing noise at about 140 PSI, and realized that there is a hairline crack in the tank, near a 2" long weld attaching the engine/pump mounting platform to the tank.

    The crack does NOT track the heat affected zone of the original weld, in fact it is perpendicular to it.

    \====
    \
    \

    Here the "=" signs denote the HAZ, and "\" signs denote the crack.

    In any case, when I saw this happen, I almost dirtied my pants and immediately relieved the compressor of pressure.

    I am not yet sure what was the cause of this crack in the first place. I will try to find what I can.

    My question, obviously, concerns my repair options. I do weld and have some experience with both TIG, as well as with 7018.

    But, I can hardly think of any welding where more is at stake than here, due to pressure. So, I see the following options:

    1) Take off motor and pump, cut holes in the tank and throw it away, look for another tank.

    2) Repair the tank by welding and hydrotest.

    Considering option 2, the first question concerns welding. How would you weld? How do you identify where the crack ends? Would you drill relief holes at ends of the crack?

    The second question is about hydrotesting. I was thinking about something simple, such as replace tha gauge with a 400 PSI gauge, close off all openings besides one, fill tank with water, connect to a hydraulic pump or grease gun, and bring pressure to 400 PSI (the tank supports 200 PSI) and look for leaks.

    This is very time consuming and I would like to know how likely would it be that I would make some very bad mistake.

  • Blondie_486
    replied
    Originally posted by aametalmaster View Post
    Yes i am there until April 1st when i "retire". 10 years here is enough...Bob
    Well let me wish you a happy retirement.

    I used to live in one of the trailer parks, I was able to see the refinery (while I was in Ohio that is). I had a trucking operation consisting of 7 trucks and used the trailer as a crash pad when I was in the area. I hauled a lot out of the Timken Gamby mill, mostly pierced tubing going back yonder where I had my real home on the side of Magazine Mtn. in Yell Co. Arkansas (before the clintons became famous). With the brutal winters we have here I sure do wish I was back there!!!

    Leave a comment:


  • enlpck
    replied
    Originally posted by engnerdan View Post
    Build a smoker or a grill, do not attempt to use it! I just scored a 30 gallon tank from work that started leaking, when we cut it open there was crud in the bottom almost 2 inches deep the entire length of the tank. It had been drained but the drain was off set from the middle and there was always water left in the tank.

    -Dan
    This is why the drain should be at the end of the tank, and the tank should be set with a slight pitch toward it.

    Leave a comment:


  • aametalmaster
    replied
    Originally posted by Blondie_486 View Post
    That's been my experience as well. I worked at an ASME shop operating under the U,R & S stamps. We always hydro tested at well above operating pressure.

    Bob,
    Do you work at the refinery off Raff Rd.?
    Yes i am there until April 1st when i "retire". 10 years here is enough...Bob

    Leave a comment:


  • engnerdan
    replied
    Build a smoker or a grill, do not attempt to use it! I just scored a 30 gallon tank from work that started leaking, when we cut it open there was crud in the bottom almost 2 inches deep the entire length of the tank. It had been drained but the drain was off set from the middle and there was always water left in the tank.

    -Dan

    Leave a comment:


  • enlpck
    replied
    Originally posted by davinci2010 View Post
    You are correct to have dirtied your shorts and ceased operation. The most dangerous thing in the world is people that base saftey on the fact that they have never seen something happen. I used to be an air compressor technician for a living. I don't have the pictures to show it but have seen the results of a ruptured tank; It was a mobile unit in the bed of a 3/4 ton truck. The failure destroyed the truck. just for details a gasoline powered compressor has a control called a pilot valve that unloads the pump and controls the engine idler. Pilot valves fail all of the time; That's why there is saftey relief valve on the tank to prevent an over pressure situation. The saftey valve had failed, and to save a couple of bucks the owner installed a pipe plug in it's place. The pilot valve failed soon after and the compressor ran until the tank ruptured. Had the owner not been 300 ft. away using a paint gun he would be STONE COLD DEAD!!! Compressor tanks are assembled using submerged arc process at the factory and hydrotested at 1.5 times max working psi. You cannot duplicate these conditions; Scrap that tank and buy an new one. Remember 175 lbs is pounds per square inch. Multiply 175 by the number of square inches in your tank. Whole new respect!
    Heres a couple pics: http://www.cdc.gov/niosh/face/stateface/ca/05ca010.html and http://www.railpictures.net/viewphoto.php?id=176187

    Leave a comment:


  • davinci2010
    replied
    Don't do it!

    You are correct to have dirtied your shorts and ceased operation. The most dangerous thing in the world is people that base saftey on the fact that they have never seen something happen. I used to be an air compressor technician for a living. I don't have the pictures to show it but have seen the results of a ruptured tank; It was a mobile unit in the bed of a 3/4 ton truck. The failure destroyed the truck. just for details a gasoline powered compressor has a control called a pilot valve that unloads the pump and controls the engine idler. Pilot valves fail all of the time; That's why there is saftey relief valve on the tank to prevent an over pressure situation. The saftey valve had failed, and to save a couple of bucks the owner installed a pipe plug in it's place. The pilot valve failed soon after and the compressor ran until the tank ruptured. Had the owner not been 300 ft. away using a paint gun he would be STONE COLD DEAD!!! Compressor tanks are assembled using submerged arc process at the factory and hydrotested at 1.5 times max working psi. You cannot duplicate these conditions; Scrap that tank and buy an new one. Remember 175 lbs is pounds per square inch. Multiply 175 by the number of square inches in your tank. Whole new respect!

    Leave a comment:


  • Blondie_486
    replied
    Originally posted by aametalmaster View Post
    Wouldn't the proper hydro be more than the pressure it would run at? I also work in a refinery and the hydro's are always more than the service the vessel would see on a normal operating run.
    That's been my experience as well. I worked at an ASME shop operating under the U,R & S stamps. We always hydro tested at well above operating pressure.

    Bob,
    Do you work at the refinery off Raff Rd.?

    Leave a comment:


  • nocheepgas
    replied
    Darwin Award Winner!

    Kind of off topic, but tanks and explosions made me think of an item in the news just the other day.
    This kid was stealing gasoline from his uncle's truck, it was early in the morning and dark. He wasn't sure how full his gas can was getting. Being the Darwin Award Nominee that he is, he thought it would be a good idea to see how full his can was by illuminating the gas can with his cigarette lighter. This resulted in burns over 75% of his body.

    Leave a comment:


  • nfinch86
    replied
    Joe ;
    How much pressure is going to be in your's ?
    I Don't think I would worry about it !

    ............. Norm

    Leave a comment:


  • Joe from N.Y.
    replied
    Man,
    This thread makes me rethink my homemade sandblaster made from an old semi-rusty propane tank.

    Leave a comment:


  • Bodybagger
    replied
    Iraqi welder

    This thread and all the talk about welding pressure vessels reminded me of the Iraqi welder...

    Originally posted by 11b View Post
    We took a pic of this guy on patrol. Sadly, you see it all the time. Yes that is a propane tank and yes he lived.
    Attached Files

    Leave a comment:


  • usmcruz
    replied
    Im my experience, linear cracks develop on old tanks, probably due to the expansion and contraction of the tank on a daily basis when in operation. Old tanks are out of the question, and I wouldnt even attempt it, but I would weld cracked new tanks all day long!

    Leave a comment:


  • jbspeed
    replied
    welding preasure tank

    depending on the age of the vessel..I have welded many "vibration" cracks in compressor tanks. Just clean the area...stop drill it and tig it. But, if the tank is an older tank, as has been brought out, there more than likely are other stress cracks that cannot be detected and in such case the tank should be replaced.

    Leave a comment:


  • jweller
    replied
    IMO, it sure would be great to have a 80gal tank to build a real nice BBQ smoker out of. You could have worse problems

    Leave a comment:

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