Welding tanks and steam myth .

[Redneck in training]

The problem was not if the vessel contained combustible substance or if steam released them from the deposits. The problem was presence of oxygen inside. If the welder would use full flow of the steam it might not explode. Oxygen not the hydrocarbon is the most dangerous substance in refineries. They usually use nitrogen to purge the piping or vessels, and then test before anyone is allowed to work on them. As somebody already noted refineries or chemical plants have very good system of procedures for every part of their equipment and therefore have very few close calls or accidents.

 

[polo1665]

The problem was not if the vessel contained combustible substance or if steam released them from the deposits.

That was my original point. (although the presence of a combustible substance most certainly did/would play a large role in this/any explosion)

The problem was presence of oxygen inside. If the welder would use full flow of the steam it might not explode.

Agreed, as per previous post.

Oxygen not the hydrocarbon is the most dangerous substance in refineries.

Would have to say that the combination of the two is what makes the situation truly volatile.

They usually use nitrogen to purge the piping or vessels.

I am partial to Argon myself (that is what we use in our process)

 

[greenmule]

Now,if you was just welding on outside[stuff on inside was sealed up,tight,like a gas pipeline],there are procedures for doing that,[plus its just different,gas is moving through pipe] ,but welding on aluminum ain't a gas pipeline,burn a hole or get inside hot enough to exceed flash point[different stuff has different flash points],Plus the whole area around the welder would have to be safe as far as vapors,etc.

But steam cleaning doesn't make inside safe for a spark,kinda like filling a tank 1/2 full of water,don't seem to me like it would accomplish anything,like was said,its the oxygen,that makes the thing blow up.

You know that rule that says if anything can go wrong,it will? Well,there are just so many things in doing something like this,that can go wrong,that its kinda like launching the space shuttle.

 

[Wis Bang]

Nitrogen or Argon would work well. During my time managing tanker yankers, we did work for Liquid Carbonic transporting liquified O2, N2 and some argon. N2 was alot cheaper and easier to obtain. The trailers transporting O2 & N2 had 'road valves' that allowed some of the expanding gas that was boiling off the liquid load [friction from the slosh was enough to do this] to escape to the atmosphere. The Argon trailer did not have this feature; they didn't want to loose any. A couple cylinders of Nitrogen would have worked to save this guy.

This was a waste water treatment plant not an experienced process construction company. The report showed that their safety plan was under review and did not contain a 'Hot Work' section. It appears to me that the welder was not trained in the existing safety program and was not properly supervised by someone who was trained; if anyone other than the plan's author WAS trained.

The fact that they had a Confined Space Entry section to their plan indicates that they should have had O2/combustible gas detection equipment and, unless their plan was just printing on paper, should have know how to use that equipment to insure that the area was safe to weld.

Having worked at several carriers w/ their own internal tank transport cleaning facilities; I understand that steam is part of a cleaning process yet any cleaning process will not remove 100% of the potential contaminants from a tank.

We had to provide tank trailers that were 'Clean, Dry, and Odor Free' but the tanks were assigned to the shipments based on the prior contents. Loading a 'water white' product after an oil was a potential for contamination.

In one instance the QA lab reported that the material was three points off in color, something you could not see but they could find. We were transfering the third of three loads, in the same tank, from one company to another and they decided to take the shipment because the delayed parcel tanker was docking that evening and was carring three million galions so they felt that would be enough to dilute this load.

The mixture of the hydrocarbons and O2 in this vessel was allowed to be in the explosive range between the LEL & UEL. Thier intention to 'inert' the atmosphere with steam would have possibly worked given enough time to cook the hydrocarbons out of the steel surface and push it out of the tank enough to reduce the mixture below the lower flammable limit [LEL].

Based on the location [AK] and what was found during the investigation, I suspect that this place did not have enough resources on hand and enough training in place to recognize the hazzard coupled with a frontier 'quick and dirty' mentality.

I have taught 'first responders' for the NJ State Police as part of a group of industry people explaining what they needed to know when approaching a chemical tank transport in an accident situation. The states are getting up to speed as my students ranged from state troopers and firemen to municipal managers and municipal maintenance employees.

I also provided an old aluminum fuel tank [on a stand] to the County Fire School for the training of first responders how to apply patches & plugs to stop fuel leaks from MV accidents. That tank was throughly cleaned and tested before our welder made the 'stand'.

Unfortunately alot of industries are not monitored regarding their safety plan and the level of training they have provided until it is too late!

 

[Egon]

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

Please note:

STEAM IS THE FIRST STEP, NOT THE ONLY STEP in preparing a tank or vessel for HOT WORK.

Hydrocarbon containing vessels:

Many vessels have baffles, trays, dead spots and other locations where liquid hydrocarbons may gather and not drain. Steam is injected into the bottom of the vessel and release out the top usually Thur a standoff on a blanking plate. The duration of the steaming process is such that all hydrocarbons should be vaporized and carried out the top with the steam flow. Catch pans are place underneath selected openings at the bottom of the vessel to catch condensed liquids which are mostly comprised of water. The length of steaming depends on vessel size and complicity of trays and or baffles.

Step two: Air educators are placed on the top of the vessel to allow air to be drawn through the vessel. This should remove the last vestiges of hydrocarbon vapor and also fill the vessel with a non combustible atmosphere. This process continues till no combustible show up on monitors, the oxygen levels are acceptable and the vessel is cool enough to work on or in. Remember the steam did heat it up.

Next step: Hatches are opened and more air quality testing is done.

Next step: some lucky soul gets to done some protective gear and self contained breathing apparatus plus supplied outside air with lines and then gets to tour the vessel from top to bottom checking for atmosphere and combustibles and anything else that might be amiss. he also has communication systems set up which may involve radios or the old standby of tapping on the wall every 30 seconds.

Now that is one type of procedure that is quite common and has been used for years. These procedures are well thought out well in advance as peoples lives may be endangered if all is not done properly.

Speculators and the "I Thinks" find short shift on job sites that have these processes in progress. Knowledge and constructive for-site are well appreciated though!

Is there a light at the end of the vessel yet.

 

[polo1665]

Please note:

STEAM IS THE FIRST STEP, NOT THE ONLY STEP in preparing a tank or vessel for HOT WORK.

Hydrocarbon containing vessels:

Many vessels have baffles, trays, dead spots and other locations where liquid hydrocarbons may gather and not drain. Steam is injected into the bottom of the vessel and release out the top usually Thur a standoff on a blanking plate. The duration of the steaming process is such that all hydrocarbons should be vaporized and carried out the top with the steam flow. Catch pans are place underneath selected openings at the bottom of the vessel to catch condensed liquids which are mostly comprised of water. The length of steaming depends on vessel size and complicity of trays and or baffles.

Step two: Air educators are placed on the top of the vessel to allow air to be drawn through the vessel. This should remove the last vestiges of hydrocarbon vapor and also fill the vessel with a non combustible atmosphere. This process continues till no combustible show up on monitors, the oxygen levels are acceptable and the vessel is cool enough to work on or in. Remember the steam did heat it up.

Next step: Hatches are opened and more air quality testing is done.

Next step: some lucky soul gets to done some protective gear and self contained breathing apparatus plus supplied outside air with lines and then gets to tour the vessel from top to bottom checking for atmosphere and combustibles and anything else that might be amiss. he also has communication systems set up which may involve radios or the old standby of tapping on the wall every 30 seconds.

Now that is one type of procedure that is quite common and has been used for years. These procedures are well thought out well in advance as peoples lives may be endangered if all is not done properly.

Speculators and the "I Thinks" find short shift on job sites that have these processes in progress. Knowledge and constructive for-site are well appreciated though!

Is there a light at the end of the vessel yet.

Thanks for affirming my statement:

"I can imagine for some applications that a steam purge could be useful, not in this one however."

Understand that when I made this statement I applied it to the actions in this particular instance. I would never be so bold as to imagine that I could know all of the preparations and safety precautions that go into making any number of different types of containers ready for hot work. However I did bother to read about the one that was posted.
Please do not take every post as an affront, and feel the need to argue points. That is not what was intended.

The light at the end of my "vessel" is still along way off. I am still relatively young and admit I have much to learn. We do not have much in common, do we?

Mark

 

[Egon]

"I can imagine for some applications that a steam purge could be useful, not in this one however."

You mean the proper cleaning of the vessel in preparation and removing any source of combustibles would not have prevented an explosion???

In any Hot work situation not only must the actual work piece be made safe but also the surrounding site.

Now depending on the configuration of the piping being welded on there may have been other options but this would only be determined by seeing the actual situation and the piping schematics in question and that we can't do here.

 

[greenmule]

You guys keep going here,just starting to get interesting.

 

[California]

This brought back memories of an old timer who welded up the leaky seams in a motorcycle gas tank for me. When I went back to pick it up I asked how he had purged the tank. He told me he kept it 100% full of water so there was no space for an explosive atmosphere. I still think his torch could have boiled gas vapors out of the leaky seam and ignited them.

 

[polo1665]

You mean the proper cleaning of the vessel in preparation and removing any source of combustibles would not have prevented an explosion???

In any Hot work situation not only must the actual work piece be made safe but also the surrounding site.

O.K., now I am beginning to understand the disagreement.

First of all I mean exactly that the proper cleaning of the vessel and removal of combustibles would have prevented the explosion. My point is, that is not what they were using the steam for. In this application they were using the steam to force (purge) oxygen (atmosphere) from the tank to prevent an explosion. They had no intention of cleaning the tank. My point was that using steam for this practice is a bad idea, too hot and its volume changes too much with temperature fluctuations. It also would make the hot work the welder was doing nearly impossible. So to summarize my position:

1. Steam used to clean a tank prior to hot work - Yes (following specific guidelines that you posted earlier)

2. Steam used strictly to purge oxygen and combustibles temporarily while hot work is performed - Absolutely Not, this is not a safe practice.

I apologize if I came across as miffed earlier. I was frustrated at not being able to get through with my point.

greenmule will have to start his own, I'm settled down now.