Leak testing.
This is a good one. One of our field manager's on a large ducting project has presented me with a situation I haven't experienced yet (it follows).
Our job spec requires all full pen. welds be verified leak tight. The spec goes on to list PT, UT, RT and vacuum box testing as suitable means to verify leak tightness (MT not allowed). The client offered the following and has said they will approve it if we cover the necessary bases (which include: safety, thoroughness, spill prevention and a couple others). Leak testing may be accomplished using a "Diesel Leak Test".
Here is what they said: We have successfully implemented a "Diesel test" for the erection inspection for the Baghouse Which is reliable and efficient for the task at hand. We will consider this option should it be proposed as a substitute. The procedure is basically performed by spraying the fuel oil onto the surface in sufficient volume to fully coat it with out substantial run off. Let it soak for a prescribed time period of from one to two hours and inspect from the opposite side observing any "wetted" areas. Mark and repair areas of indications and retest.
Of course our field personnel want to save a little money by doing the least expensive testing that the client will accept. Has anyone done this or even heard of it? If so, what are your recommendations?
Truthfully, my main concern is appearing simple minded by writing this up they way it has been presented to me.
Thanks, Charles Hall
Leak tests in ducting, breeching, windboxes, baghouses and other equipment handling gases (air among them), are usually made (or at least, I've always seen them done like that) by the so called "soap test", i.e., putting a suitable air pressure into the inside of the equipment (the gas side), and applying soap and water by the outside. If foam occurs, then there's a leak there.
I've also heard, but never seen, about the "halogen test", in which a bomb containg chlorine in one section and ammonia in the other is exploded within the equipment under test. White fumes of ammonium chloride form inmediately and escape through the leaks, denoting their existance.
Frankly speaking, I doubt that this "diesel oil test" will work for small leaks (the so called "pinholes"), but if the clients wants it go ahead and do it. A word of caution: have a client representative observe the test and approve it in writing, to avoid any future claims.
Giovanni S. Crisi
Sao Paulo - Brazil
This Diesel Leak Test has been used very succfully in shipyards on tugboats & barges for many years. Diesel fuel will penetrate wherever there is any opening of any kind.
This method was originaly known as the "oil and whiting" method which used diesel fuel and talc to locate cracks in the railroad industry. They teach this in the class for PT. It was one of the first NDT methods and is still used today (obviously not as often as PT).
Our instructor demonstrated this method, and it does work for any discontinuity open to the surface.
I'm glad to hear that it has some heritige.
I do have one more question, what is a good duration to wait before conducting the "close visual examination"?
Thanks for your help.
Charles Hall
"It is depends on the sensitivity level of the diesel fuel" is what we would be expected reply in the classroom.
All the technical bull s*!t aside, I would wait at least about 10 minutes or so to allow for the fuel to migrate into any voids.
Diesel Fuel leak testing is very effective at locating leaks in ductwork etc. Be cautios of areas that are obscured by other members laying over them. I try to make sure the fuel is sprayed on the surface with the most obstructions. The areas can be flooded and allowed to soak.
The increase in speed over vacuum box leak testing is VERY significant.
Good day
G Austin
OK Gentlemen. I've taken your experience for granted and have changed my opinion on the Diesel Oil Test. In any case, CHall, have the client's inspector witness and approve the test.
Giovanni
However,
Due to many variations in configuration, there are situations where the volume of fuel may not be sufficient to travel the distance needed to bleed out. An example would be a 20' seam in a piece of 1/4" plate. Double welded, one side has a pinhole through to the root (The weld is not cjp), the other side has a hole in it on the other end of the plate.
With a vacuum box leak test, this would show up immediately. With diesel it would not, it could take a varying amount of time.
So there are some shortcomings to diesel fuel leak testing. But I think the advantages outweigh the disadvantages since I am pretty sure the mechanical joints in most ductwork would not pass diesel fuel or vacuum box leat testing.
Good day
G Austin
One thing that I haven't seen mentioned in the previous replies is the safety factor. Lets see if I've got the math right... Fuel+confined space=potential explosive atmosphere. I don't think it's ever a good idea to create that situation...especially where personnel may be required to enter the space. If a leak is found how will you repair it? How will you remove the fuel vapors? Do you have the means to ensure a non-explosive atmosphere in the duct? Personally, I'd stick with the soap & water test.
The ductwork I have done this on is not a confined space. It is new. However the same procedure has been performed using water washable penetrant and viewed under a blacklight.
See the picture on this page.
http://www.weldinginspectionsvcs.com/WorkPictures.htm
Could you imagine building a vacuum box to fit around an expansion joint!
I would NOT suggest diesel fuel in ductwork that has been in service.
G Austin
Gerald,
I think I see what Dave is supposing, If you found a leak with the Dfuel test, how would you go about repairing it(in a confined space)?
Due to the fuel vapors that are present, I would not recommend striking an arc or grinding the weld until the area is made safe from the vapors.
Good question Dave! I think this method maybe used where fumes are not likely to gather.(lots of ventlation)
John Wright
I think the original intent of this post was wether or not it was (is) a valid test. Advantages/limitations of any test method can get quite lengthy.
We could mention everything dangerous about other test methods, but we would be overlooking the original question. I would expect a confined space permit would be required regardless of the test if performed (in a confined space...)
Good point DGXL,
I did get off the subject a bit, of the original post.
Yes, I think Dfuel is a valid test. Please excuse me, my mind wanders from time to time. Somedays it's hard to tell where it will end up.
John Wright
I have been monitoring this post with interest, because I have never actually heard of this test method before. My first reaction when it was raised, was that it would be dangerous, but after some thought I changed my mind.
Of the typical solvents used, diesel is probably the least volatile. Spilled diesel will lie around for ages before it evaporates. Often, when using DPI, solvents such as acetone is used for cleaning. This is MUCH more dangerous. I have personally seen an explosion occurring where static discharge ignited inside a confined space where DPI was being carried out, using acetone for cleaning. Luckily the inspector involved merely had his face burned lightly, but it could have been much worse! (He looked rather strange without any facial hair!)
Regards
Niekie Jooste
This test method has been commonly used for years because of it’s sensitivity as a “supplemental test” to check the inside corner joint (floor-1st shell course [tub ring]) on new, API 650 & 620 field erected storage tanks.
Once the inside fillet weld has been completed, oil (diesel fuel) is sprayed on the outside surface of the joint prior to the application of the outside fillet weld. When I say “sprayed” I’m talking in terms of a fine mist that just wets the surface. About as much as if you used a spray can of paint to just cover. If there’s a “through weld discontinuity” in the inside fillet weld, you’ll see a wet spot pretty darn quick at it’s location on the fillet weld face and a noticeable wet spot on the floor. After the test, forced air is generally used to blow out any remaining oil from the joint prior to welding. This comment and observation my cause heartburn for some but I’ve never observed any negative effects caused to the vessel or the subsequent welding of the joint if the little bit of oil that’s used is just allowed to burn out ahead of the arc. So for those that do frown on welding a minimally, oil contaminated joint, I’ve used water-soluble dye penetrant as an oil substitute with the same results.
From my experience, it works very well indeed as a supplemental check!
Seldom:
What you just described is known as a "Leak Through Test" and is a variation of PT/LT. Good reply.
The reason Diesel fuel was used was due to it's viscocity,when spraying it onto the surface the viscous liquid will migrate into the cavity due to capilary action.Like other individuals have mentioned, diesel fuel is viscous and like any other fuels has a flash point that can cause combustion when exposed to a source of ignition,and therefore may ignite.Remember the fire triangle(Oxygen,Source of ignition,combustible).
I strongly recommend using organic oils such as canola oil (viscous,and highly unlikely to cause any safety hazards).
regards
joe valdez
The Leak Testing Procedure we submitted was approved by our client. All the info it contained was gotten from here. I appreciate all the help.
For what it's worth, the client did require a 2 hour dwell time prior to inspection. They also wanted some wording included to cover the possibility that the test was "acceptable", but a leak was discovered afterward. Standard "you are responsible for making repairs as needed type of comment..."
Once again, thanks.
Charles
I appreciate the guys that come back and report how their situations turn out! Informative for the rest of us.
John Wright
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