First of all, i just began my carrier as a welding engineer,and generally it is my first job. the project i am involved at the moment is the construction of 3 tanks 23m width and 13m height, the shell and bottom plates are pre-assembled, my question is about the ndts required!..i have gone through api 650 and the only that i see is xrays in butt-welds between the annular-ring plates and also xrays between the shell and bottom plates. Is there any PWHT required or DYE PENETRANT testing and where can i find specs about it??

You won't be able to RT the shell to bottom plate T-joint. Also, unless you are doing a full pen weld there, there is no point to UT it.  However, if you do have a full pen weld there and you want to do a volumetric examination then use a UT exam.   Normally, you would only MT it, even with full pen welding, assuming it is carbon steel, for surface examination.  I would also specify a vacuum box test of the floor joints and the corner joint in addition to the final hydrostatic leak test.

There are PWHT requirements in the standard.  If you are using an electronic version of the standard, do a search using a key word "heat treatment" and you'll find it all.  Also read section 5.7.4

Read the entire Section 7 and section 8 and it will answer all your questions regarding NDE requirements.  If you are junior engineer and just starting, you should read the entire standard from cover to end.

Dye Penetrant would be a little overkill and isn't required for floor seams. Yes, you can do it to feal warm and fuzzy, but you're talking about a new tank. No product has been introduced to it yet.

LFET is also a good technique to use, but not in this situation. Like i said, it's a brand new tank and it's not required. There are no damage mechanisms yet that would call for LFET.

For the shell to bottom weld, refer to API-650, section 7.2.4.1. 99% of the time i've used option "d". You simply take a light diesel in a bug sprayer, walk around the outside of the tank, spray the diesel on that corner weld, and let it sit for 4 hours. After 4 hours, go inside the tank with a flashlight and look at the corner weld for diesel. If you've got a leak, it WILL come though.

Mag particle (option "a") requires electricity. With mag particle, you'll have to test the inside and the outside. Could take 4 hours or longer and possibly shut down other projects going on inside the tank.

Dye Penetrant (options "b & c") are also good options. Spray the penetrant on the inside or outside of the tank. Let it sit for 1 hour. Then go to the opposite side and spray the developer. The dye will show up almost immediatly, especially if using red dye and a white developer. Problem with this is the fumes. Usually, i would do the dye on the inside of the tank and the developer on the outside. The developer has a stronger paint smell that can be overwhelming if sprayed inside the tank. Then, the problem is that you have a HIGHLY flammable dye inside the tank. If there's welding or cutting going on in that area, they will have to shut down.

Vacuum test (option "e") is always a great test. The only downfall to using it in this situation is the availability of fingind a right angle vacuum box. Also, for a new tank it's normally not a problem, but if you have ANY crown or edge settlement, you're not going to be able to perform this examination.

In my opinion, option "d" is usually the more logical option to use. It requires no extension cords, no aerosols, no special equipment. All you need for that size tank is about a gallon or two of diesel and a flashlight. It will not affect any of the other projects going on inside the tank.

Most manufacturers will do their own vacuum testing, however many times it is requested by the Owner/User to have a competent inspector witness the procedure. Since it is technically a "Visual Inspection", there are no special certifications required by the inspector, aside from being qualified by their inspection company.

The actual vacuum box, itself, has no SPECIFIC construction details. As long as it's within the range of section 8.6, it will suffice. There are vacuum boxes that are constructed of cast iron. They're very heavy duty and have the gauges built into the cast; however, they're not always the best application. The viewing glass is raised approximately 4" above the weld and hinders the viewing ability of the welds you're testing. There's no flexability in the cast iron vacuum boxes. When you have thicker floor plates with lap-welded seams, the tester will have a lot of trouble trying to get a seal. Butt-welds you're ok. Not to mention, they are very overpriced.

My suggestion would be to make one in-house. Make one out of 1" thk. foam padding for the gasket. Use a solid sheet of padding and cut out the center of it to 6" x 30". Glue that foam padding (seal) to a 6" x 30", 1/8" or 1/4" thk. lexan or plexiglass. I recommend lexan as it is MUCH more durable and flexible. I also prefer the 1/8" thickness for the same reasons. Now you've got the viewing parts of a vacuum box. Unlike the cast-iron box, the viewing capability of this design is unmatched. With this design, you will be right on top of the welds as you are testing them. Now you need to get creative with the vacuum parts. Basically, you can drill a hole off to one side of the lexan. Attach a 1" threaded pipe coupler to the lexan over the hole. Make sure to use RTV or some type of sealer on the coupler. Now you can attach a 1" threaded pipe, with teflon, to the coupler. Make the pipe approximately 3ft tall so that you can perform this test standing up. You're going to want to do the same thing on the opposite end of the lexan so that there are two pipes standing up. One end is NOT going to have a hole drilled through the lexan though. Use "T" fittings to make it easier to hold. The other end of the 1" threaded pipe on the drilled side will be attached to your venturi valve. from there, figure out how you want to attach the venturi valve to your air hoses. One last touch.... Now you just need to thread your vacuum gauge into the lexan. you can use the same design that was used already with couplers. That's it. Now you have a vacuum box with two legs up in the air that's very flexible and durable. The best part about it.... it's within the requirements of API-650.

Tracer Gas Testing
--------------------------------------------
Personally, i dont recommend this test because of the amount of false indications, however, if you were to perform the test, here's some guidance.

Tracer gas testing is easy, but not 100% due to settlement issues that create pockets underneath the tank. The best application for gas testing, in my opinion, is a tank that has leak detection. Most of the time Helium is used. You'll want to mix that helium with CO2 to help move that helium around more. The helium detectors, which can be rented, are VERY sensitive and will pick up the helium even with a CO2 mixture. use a regulator to monitor the flow. That regulator should allow both the helium and CO2 to enter and leave one outlet line to go to the tank or separator tank if you use more than one hose.

Depending on the size of the tank, you can drill a hole in the center of the tank and tap a valved connection for the outlet hose to connect to. Open up the valves(Reducing Valves), let it run. If you have leak detection, you can test those locations with the helium detector. When all leak detection ports show helium, you're spread out. If you dont have leak detection, that's where this inspection becomes a guessing game. You can drill multiple holes around the perimeter of the tank floor. Tap those holes for a threaded plug. Test the holes for helium. When you get helium, plug it up. when all the holes have helium, you're good. The problem with this is that you now have multiple 6" patches to install over the holes when complete.

What i should have mentioned in the first place is that if you have SOLID leak detection, you can inject the mixture into one or more of the detection ports. Then you can test the remaining ports for coverage and go from there.

Once you've got full coverage of Helium, go inside the tank with the helium detector. Test all the weld seams. Test under all support columns.

MORE NEWS