Welding tanks and steam myth .

[Eagleview]

Before all the OH&S regulations and people were less aware , we used to do things differently . There was no safety plan , there was no testing of the air , and there were no steam generators . We were simply told to stick the steam cleaner nozzle into the tank and run it for half an hour and then do the weld . I was the workshop manager of a large truck smash repair facility , we had a petrol/gasoline tanker come in which needed a bracket welded back onto the tank . I rang the refinery and asked what the correct procedure was in regards to making the tank safe to weld . I was told to stick the steam cleaner into the tank and run it for an hour and then do the weld . I stood on top of the Aluminum tank beside the welder (person) as i would not ask anyone to do something i would not do myself . By the sounds of it , it was shear luck we are not in orbit now . Probably only because the weld was on the outside and only heat and not spark was generated on the inside . I think now , if he would have burned a hole in the tank skin it would have been a different story . (Hence what i meant about it being a myth).

 

[Wis Bang]

You were lucky.

I worked for one carrier that was started by two brothers after their discharge from the army in WWII. They were getting ready to repair a tank that has just hauled acetone. Cleaning was not an option so they were going to pass a blazing bundle of rags over the manhole to 'flash' off the product b/4 welding. The tank exploded blasting apart the little garage in their residential neighborhood. Both of them lived and I remember seeing the pepper-like bits of steel imbedded in his face...

It was June 6th and after surrviving 'D' day and that episode he would not leave his house, ever, on June 6th. He said he used up all the luck he had for that day...

 

[polo1665]

The steam is to heat up the vessel to evaporate combustibles and carry them out of the vessel. Then the vessel is purged with air, checked for combustibles, oxygen and whatever other toxins may have been in the vessel. After that it may be entered wearing the proper gear for further checking and perhaps the cleaning of any remaining substances that are in the vessel. At no time would anyone be allowed inside the vessel if an explosive atmosphere was present or materials that could make an atmosphere explosive be present.

At times nitrogen may be used to flood the vessels as some chemical byproducts in vessels will react with oxygen.

Many companies will have set standard procedures on how to do this on a general basis but for the actual situation each and every vessel must have it's own procedure.


Note: my experience only applies to a very limited range of hydrocarbon facilities operations and as my memory fails a little every year I'm almost to the beginning of the learning cycle.

This explanation does not follow what was stated in the findings in the link from the original post. The write up of the actions taken prior to the accident stated that "it was decided to inert the inside of the tank and adjoining ventilation lines using steam to deplete oxygen within the tank and minimize the risk of igniting the residual material". Later on in the recommendations section it points out that steam should not be used for the purpose of inerting the atmosphere of such a tank and the fact that the pressure had been turned down had most likely led to a pocket of combustible gas collecting. Nothing about "steam cleaning" the tank to remove combustible materials.
I only asked because I am unfamiliar with using steam in this application and some of the comments made here did not seem to follow the gist of the write up. Sorry to be a pain but this sort of practice interests me greatly. I feel very badly for the welder and his family. It was truly a tragedy that could and should have been averted.

Mark

 

[Egon]

This explanation does not follow what was stated in the findings in the link from the original post

Of course it doesn't. There was an accident due to improper procedures in the original was there not?

 

[Wis Bang]

Steam shouldn't have been used...They were preparing to modify dirty process equipment by welding outside & on top of the tank. Steam vaporised the hydrocarbon residual and it was venting from the top of the vessel [report says the steam was entering thru the bottom] and while the steam was originally full flow; the after report says it was closed down to a small flow.

The welder probably cut down the flow, as the steam would have been billowing out the vent making it impossible for him to work. It would clean the hydricarbons out of the metal and concentrate it in the vapor exiting the tank. The tank needed to be cleaned and purged before the welding began. Instead it was turned into a bomb.

A consultant would have recomended additional cleaning methods, perhaps an air dirven impingement spinner with a cleaning solution to scrub the resudual away and a few rinse cycles plus O2 and combustible gas detection monitoring equipment to make sure the atmosphere inside the tank was safe.

 

[Scooby074]

Reading this thread is why cutting open old barrels scares the bejesus out of me. A few years back a local guy had his garage go up because he got his torch too close to the gas tank.

Last time i welded something that had contained anything flamable was a old propane tank. Left it upside down outside for a day with the valve off, flushed it for a couple times over several days with hot soapy water, And I was still shaking when i struck the first arc

And, ive heard that people used to ( and probably still do) run exhaust into a gas tank to inert it before welding . No checks or anything. Darwin must be salivating at the thought.

 

[Eagleview]

Reading this thread is why cutting open old barrels scares the bejesus out of me. A few years back a local guy had his garage go up because he got his torch too close to the gas tank.

This was the main reason i posted the thread , Ive seen a few threads on TBN asking about how to weld old tanks , barrels , LPG cylinders etc . A lot of advice has been given on how to do it , including using a steam cleaner , exhaust gases etc . As the average backyarder has no high tech cleaning and testing gear , i think it should not be done at all . Kids have a difficult time getting over the loss of their dad and growing up without him .

 

[polo1665]

This was the main reason i posted the thread , Ive seen a few threads on TBN asking about how to weld old tanks , barrels , LPG cylinders etc . A lot of advice has been given on how to do it , including using a steam cleaner , exhaust gases etc . As the average backyarder has no high tech cleaning and testing gear , i think it should not be done at all . Kids have a difficult time getting over the loss of their dad and growing up without him .

This is what I was getting at. This welding outfit had supposedly been in business for 15 years and still managed to get someone blown to kingdom come. I have never heard of using steam to expel atmosphere from a tank or container. While I agree that the safest course of action would have been to fully clean the tank of any residual combustible material, I do have to comment that this welding job could've been completed safely had there been adequate training, equipment and supervision on the job sight. I find it hard to imagine that this outfit was able to carry on a business in this field for so many years without some prior failure. The actions leading to this accident boarder on criminal IMO. There are ways to do this job safely providing you have the proper training and equipment.
DO NOT WELD OR CUT TANKS OR BARRELS AT HOME. I've seen the results. It can turn out pretty ugly.

Mark

 

[Egon]

I have never heard of using steam to expel atmosphere from a tank or container.

Polo, expand your horizons.

Using steam to evacuate a tank is very common procedure for some industries. After vessel isolation it may be the first step of many in preparing a vessel for entry. And yes, it works very well too.

By the way, exhaust fumes are not an accepted way of creating an inert atmosphere in a vessel. In the right combination with air they are also explosive.

 

[polo1665]

Polo, expand your horizons.

Using steam to evacuate a tank is very common procedure for some industries. After vessel isolation it may be the first step of many in preparing a vessel for entry. And yes, it works very well too.

By the way, exhaust fumes are not an accepted way of creating an inert atmosphere in a vessel. In the right combination with air they are also explosive.

You're right Egon, I certainly realize that I will always have room to expand my horizons. I need to be careful however. I sometimes think that my small brain is sated, any new knowledge seems to push some past experience out and it is forgotten. This one seems worthwhile though. Hopefully nothing important will be lost this time.

I can imagine for some applications that a steam purge could be useful, not in this one however. The pressure would have had to remain high enough to constantly expel steam from any orifice in the tank, making it extremely difficult to weld. It seems to me that the practice of using steam in this particular application lead directly to the cause of the accident (I can't see to weld, so let me turn this pesky steam down a bit). Unfortunately hindsight is 20/20. This poor fellow can't be brought back, but we are fortunate to have learned something from this. Thanks for posting it Iron Horse.