De- Slagging the Interior

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Ok, weird question that's been bugging me for a couple of days now. Let's say I have to stick weld something, like a pipe or square tubing. The way the weld is done, there's slag on the outside of the pipe that gets removed with the usual chipping hammer and wire brush. What happens to the slag on the inside, though? Especially if I've just sealed both ends?Currently working as a Paralegal, but still interested in hobby welding.Miller Bobcat 225ntOne- Character Fractions: ¼ ½ ¾ ⅛ ⅜ ⅝ ⅞
Reply:I’ve wondered about this myself for quite some time. I worked around pipe welders all my life, but never thought about how they clean out the pipes after making open root welds with 6010. Don’t pay any attention to meI’m just a hobbyist!CarlDynasty 300V350-Pro w/pulseSG Spool gun1937 IdealArc-300PowerArc 200ST3 SA-200sVantage 400
Reply:In the HVAC industry, the entire system is cleaned using chemicals. Upon initial filling a water meter is used to determine gallons in the system. Chemicals are added per specs to the amount of gallons in the system.The chemicals are added and circulated through the system by pumps. The pumps have strainers on them which is a accessory that has a perforated metal screen inside. At initial start up the strainers have a screen [ like a window screen ] that slides over the the metal perforated one. This is what catches most of the slag or whatever else is left in there or what might have gotten into the system . The strainer prevents damage to the pumps.After cleaning a inhibitor is added to the system and the start up screens removed.The strainer catches all kinds of goodies. I replaced some large 24'' ones that was using river water for cooling down the condensers on chillers instead of using a cooling tower. We pulled out dead stinky fish and other unmentionables. Was a fun day.
Reply:You don't clean the interior of the pipe. If it is a piping system for oil and gas industry the pressure that comes through will blow the little bit of slag left inside away. AND if you are putting the piping system you build into a well that produces sand.... the sand acts as an abrasive cleaning agent that will blow it all out. Trust me the little bit of slag inside the pipe wont hurt a thing when it runs down the line. it eventually gets blown into small enough particles that it will disintegrate in the refining process. If you are running a pipeline offshore like I have done. You weld the entire line. let it lay off in the water and make your tie-in to the gas lift line. The gas lift line goes into the tree. But before you make your tie-in into the tree you turn one block valve on that has the gas pressure behind it. Blow all the water, mud and slag out of the line. Make your underwater tie-in to the riser and presto bolt the riser to the tree. Many ways to skin a cat. But never worry about cleaning the interior of the pipe. Just like in my profile picture. One joint after another being welded and it is pulled off the lay barge into the water. One end has a cap with a pulling eye and a roll barrel system to keep the nose out of the water so no water gets in it. Once you've ran your line as far as you can to the tie-in point. you drop the pipe over into the water and move to the tree. Tie it into the tree. Return to the other end. Diver hooks the pipe up and you pull it out of the water. Chain it to the side of the lay barge. Operator turns the gas on to blow the water and mud and slag out. Then we tie into the pipeline heading to the pumping station. Simple. Food processing pipes, chemical plant piping, refinery piping will generally be using stainless, other alloys which involve TIG root and hot pass. So you will never have the question of do I need to clean the interior of the pipe.Its like the old says goes. God made dirt and dirt don't hurt... when you drop food on the floor lol. Blow it off and roll on.Last edited by AndrewDavenport89; 05-14-2015 at 08:48 AM.
Reply:Piping for Internal Combustion Engines Cooling system is chemically cleaned(flushed) with screens to stop the debris. Oil Lube lines are wire brushed and flushed prior to install on same Engine. Depending on the Commissioning Agent, they may also require a bore scope visual inspection.
Reply:Yea that's for critical components. And that will be different alloys like nickel or stainless. I think they are talking about regular ole stick welding.
Reply:Yeah, I was referring to regular stick welding, and non- pressured situations like a pipe fence or something constructed out of tube where you might not be able to remove the slag. Would it necessarily hurt anything to just leave it in there?Currently working as a Paralegal, but still interested in hobby welding.Miller Bobcat 225ntOne- Character Fractions: ¼ ½ ¾ ⅛ ⅜ ⅝ ⅞
Reply:Leave it in there buddy. It wont hurt a thing.
Reply:The key thing with any hollow structural sections is to seal them off at the ends.  The oxygen will be used up as the inside starts to rust then corrosion will stop.  What is left inside a structural pipe is ignored.
Reply:Originally Posted by teh603Yeah, I was referring to regular stick welding, and non- pressured situations like a pipe fence or something constructed out of tube where you might not be able to remove the slag. Would it necessarily hurt anything to just leave it in there?
Reply:We had to get a reamer to ream out the slag on a cargo bike we built otherwise we couldnt get the seat tube down into the frame.Beyond that, I dont think I would give de-slagging the interior of a pipe/tube a second thought.
Reply:Originally Posted by lotechmanThe key thing with any hollow structural sections is to seal them off at the ends.  The oxygen will be used up as the inside starts to rust then corrosion will stop.  What is left inside a structural pipe is ignored.
Reply:Rust is iron oxide caused by interaction of oxygen in the air with the steel. If the ends of the tube are sealed, eventually there's no more oxygen available to form iron oxide and the rusting stops, regardless of if the interior already has a rust coating or not.
Reply:Look. say your building handrails. Like i have done on countless occasions offshore and on land. We dont worry about the interior of the pipe. And we make many different angles for staircases and such. BUT to minimize the oxidation on the interior of the pipe we blow holes in horizontal handrails in the bottom side corners. This will prevent the sweating of the pipe by letting the water release. Pipe will sweat over time in humid areas. The sweat will be trapped inside the pipe if you do not blow "weep" holes. And on the bottom of the verticals. I would not think twice on this subject. Your all good. weld it up and roll on my friend.