API 650 Tank NDTS 4

[MazaTEK]

Hello All!

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??

Thank u in advance!

 

[vesselguy]

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.

 

[Bonswa]

Like vesselguy said, you wont be able to RT that T-joint, however you still have to RT the bottom of that vertical joint as close to the T-joint as possible.

As far as testing the T-joint itself, you can simply do a diesel test and visually inspect it for leaks.

Definately vacuum test those floor seams.

 

[ak1965]

You should DP test on weld seams (all). No harm in that and no standard is required to refer for this simple test.

Selective RT should be done...If many defects observed, increase the scope of RT.

Vacuum test is normally used to detect leaks in the bottom plate, however, You can possibly use LFET (Low Frequency Electromagnetic Testing)to inspect bottom plates. Testex is a US based NDT company involved in such services.

Details of LFET can be found out on TESTEX website...the link is

http://www.testex-ndt.com/

 

[IFRs]

API 650 11th edition section 7.3 and all of chapter 8 lists all NDE required. Appendix T is a good summary also.

 

[Bonswa]

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 immediately, 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.

 

[HightyHo]

First.....contact an NDT Inspection company.....you will need them for your x-rays anyhow. They can help guide you through all the testing needs. You will need certified examiners to conduct the tests required to be an "API 650" storage tank. The fabricator can help you with this and many times they have qualified inspectors on staff.

Second, I agree totally with Bonswa...here are a few other things to think about....

Welder qualification!! How many welders do you have on the Job will affect the amount and type of testing required also.

PWHT....Contact a Storage Tank Engineer....One who is knowledgeable and experienced in the engineering disciplines associated with evaluating mechanical and material characteristics that affect the integrity and reliability of the storage tank.....something to seriously think about depending on the climate you live in.....Your tank sounds like the typical million gallon storage tank made out of A36. See Section 2 in API 650 on this subject....


Shell to bottom weld:
Diesel test!!! Best way to go...I do not agree with the 1 hour time frame though...API states at a minimum test time of 4 hours!!....easiest way to do the test is spray on last thing at the end of the day and come back the next morning with flash light....I have found to many times as an API inspector that small leaks take more time!! Remember this test HAS to be done after the FIRST weld pass!! I recommend MT testing after final weld pass is complete this will help ensure no cracking is present in the critical zone!!! This is all weather permitting though!

Vacuum Box testing is required for final weld pass on the floor joints...pay particular attention to any arc strikes out in the base metal also...I have found many times leaks in these spots.

LFET (Low Frequency Electromagnetic Testing) is a great test on tanks that have been inservice as Bonswa stated above....you are looking for wall loss after the unit has been in service. Reference API 653 for this section of inspection and testing requirements.

Dye Penetrant testing....I do not recommend that you test each and every weld!! It is not recommended and is a painful process...but it will give you an even more warm and fuzzy feeling in the end!!

 

[LOUDOG]

Who is ordering this tank? Most likely they have specifications with regards to API 650 decisions. Most of these decisions are clint driven. Full pen floor welds, inspections, and testing are all things that are usually client decisions on most jobs that I work on.

 

[Bonswa]

LOUDOG made a good point there...

MazaTEK, are you contracted for this job, or do you work for the owner/user?

Reason I ask is because of LOUDOG's question. Most of your larger companies will have "their version" of the API & ASME codes, or they will have their own procedures. Usually, they are more stringent than the actual codes if not the same. If you are contracted for this job, you should find out if the owner/user has a specific procedure or if they want you to perform the inspections strictly according to API-650.

Example:
API-653 allows tombstone patches to be weled to the floor of a tank in the critical zone. However, the customer may not allow it. The customer may require that a full insert plate is installed. Their procedures may specify that no patch or weld overlay repairs are to be made in the critical zone of a tank. If a repair is required, a full insert plate is to be installed. <--- That's almost a direct quote from one of my client's procedures.

On the other hand, your smaller companies will most likely NOT have any additional procedures. Most of your small companies and tank terminals will allow you to decide what inspection techniques and procedures are used as long as they are acceptable to API-650.

 

[MazaTEK]

Well im not contracting for thid job but we re working for the owner.And u are right they do not require anything more than API. with your guiding and API infos i have decided to do diesel oil test to the bottom-shell welds, and vacuum box test on the bottom weld, then i have to stress relief the clean out door(flush type connection) and then RT it according to (5.7.8.11), U should konw tha the first 10m(6 courses) of the shell are prefabricated as a roll from another company so we have to assemply only the last 3m(2 courses in pieces) any comments on these RT'S ??.

And i think im done

THANK U

 

[Bonswa]

No comments other than following the same guidelines (5.7.8.11) for the RT's of the new shell courses. You'll be fine with the direction you're taking.

 

[sicktick]

I am interested in the vacuum box test of the floor joints procedure and equipment referenced in API 650 8.6. Where do you find details on the construction of the equipment? Where do you purchase one? How much do they cost? Can you rent them? Where do you find procedure training? Are there a contractors that do this testing only as a service? None are advertising the Thomas Register..... or maybe I am searching incorrectly. I guess that most field fabricators do this testing themselves. Right?

Then, how does the tracer gas testing work? Do you inject the gas under the tank floor and sniff inside the tank? How would you assure that the bottom of the tank is fully in contact with the tracer gas?

 

[Bonswa]

Where are you located? There are a few inspection companies in my area that perform this test.

Vacuum Box Testing
-----------------------------------------
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, 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.

 

[BUTCHCWIQAM]

sicktick look in these places

http://www.krautkramer.com.au/Silverwing/vacbox_brochure_lo.pdf

and

http://www.ndtint.com/vacuum.htm

http://www.tspndt.com/index.cfm?fuseaction=prod.product&ProductID=30

and this is for grins and giggles

http://www.k2technde.com/downloads/LeakTestAK.pdf

 

[Bonswa]

The vacuum box shown on page 10 in the very last link is the homemade design that I described. Note that they, too, use lexan instead of plexiglass. only difference between that last link and what i described is that we don't have bears in my area.

Although the box in the 1st link is all fancy pancy and high tech, I would stay away from it. Those are great pictures by the way. They show the differences I was talking about. You can see how the viewing area differs between the two. The fancy box has a viewing area that is raised up about 4" above the area of interest. The viewing area of the homemade box is about 1" above the area of interest. You have PREMIUM visibility with that design. the fancy box is also too sturdy. It will not be able to flex and seal like the homemade box will.

Also, with those pictures of the right-angled vacuum box, you can see how that would not be a good design if there is ANY crown to the tank in the critical zone. That is the exact reason that i push the diesel test of corner welds over vacuum testing.

 

[alidadkhan]

Dear Sir,
I am Making a reactungalar tank accordingly API 650 It's hights 12 feet and Lenght 38 feet. I will come to know taht how much percentage of radiography required this tank

 

[LOUDOG]

API 650 doesn't cover the design of rectangular tanks. For rectangular tanks I use good engineering practises to come up with tank wall thickness and stiffeners, then use API 650 weld procedures and inspection.

It depends on the joint efficiency used. You can find that answer in Section 8 of API 650.

12' high x 38' long... If that is for fluid storage I hope that you have it adequately stiffened.