Tank Inspection- Dents and Gouges 1

[cwigg66]

I am scheduled to do a tank inspection at an asphalt plant in Florida. The tanks are vertical single wall ASTs (20,000 gallons). The pictures I have been sent of the tanks show that the tanks appear to have been dropped on the ground and dragged and hit with a loader and various other abuses. The tnaks are currently in service containing diesel fuel. I plan to use an ultrasonic thickness gauge on the exterior of the tank shell and roof, taking measurements at regular intervals and also in badly corroded areas. My questions are:
1) What is the best and most correct / safe way of removing rust and paint to take measurements on the damaged areas?
2) Will it even be possible to get measurements on rusty dents and gouges?
3) Is it appropriate to utilize a man-lift that close to small diameter (10-12') tanks? Do I need fall protection?
4) Am I approaching this the corretc way?

The testing is being undertaken to satsfy SPCC and corporate audit requirements. The tanks are in contianment and under a pole-barn type steel roof structure. Any recommendations or experiences from you all would be greatly appreciated. Thanks everyone,

Chris
Mechanical Engineer
Fuel Farm Deisgner
API 653 Inspector

 

[JStephen]

One thing I'd check out first is if they were built to any particular code in the first place- API-650, UL, or what? My thinking is, if they never met a standard in the first place, there's not a lot of point in trying to keep them in line with the standards.

Secondly, doesn't API-653 have requirements on dings and dents in tanks? If the existing tanks don't meet those requirements, is it necessary to check every other aspect of them?

 

[TankDude]

I would recommend trying a wire brush first to see how effective that is at removing the rust. You could use a grinder with a wire brush attachment as well. I would not recommend grinding the area in this condition.
Depending upon what type of u.t. instrument you are using you should be able to get a reliable reading if you are successful at removing the scale. Otherwise I wouldn't trust the reading.
I don't know why you couldn't use a man-lift on this tank. I'm not aware of an diameter restrictions but that doesn't mean they aren't out there. I've just never come across them in my experience.
I would say that trying to obtain u.t. readings is a good approach. You could also try to get a measurement of the depth and overall area of the indentations. One thing to look for are sharp creases in the material. This could often be considered justification for repair.
It would be a good idea to learn what code the tank was designed/built to, however using API 653 for an inspection guideline would be, in my opinion, a good approach if you can't locate in information.

 

[JoeTank]

Chris,
As you are an API-653 Inspector, I know you took the certifcation exam. And, I am pretty sure you probably had to answer a question or two about the qualifications of an NDE Examiner on the exam. At first glance it looks as though you might be thinking of doing the UT work yourself. API-653 requires that such work be performed by an Examiner that has the proper credentials. You are asking such fundamental questions that I suspect you are just learning the basics of UT. Having an API-653 certification and a D-meter does not qualify you to do UT. I recommend that you seek the services of a properly qualified UT tech. He could show you first hand how to get the job done per the requirements of the Standard.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[cwigg66]

I need a little clarification. Where in the API-653 body of knowledge does it discuss the ispection requirements of tanks that have NOT been moved, altered, or repaired? The only UT testing information in the API 653 data that I can find refers to UT inpsections in place of radiography for newly constructed or reconstructed tanks. The tanks I will be inspecting are being inspected to determine corrossion rates and remaining lifetime, as this is a requirement of the federal SPCC regulations. I gues you would call this a maintenance inspection. I just want to be sure I am giving my client the best informatiojn possible. the tanks are in service, full of diesle fuel, have recently been recoated externally, and are tought o access due to nearby process equipment. Cheking the tank bottoms will be impossible, as will some areas on certain shell courses. I have experience using ultrasonic equipment to test thicknesses on horizontal tanks wehere all sides are accessible. This is a different animal. I appreciate all your help. I hope this does not come off wrong, but I passed the API 653 test and really feel that I still lack alot of knowledge that is necessary in dealing with large tanks, especially those that are moved alot, old and damaged, insulated, etc. Any helpful advice you more experienced folks have is always appreciated. Thanks

Chris

 

[cwigg66]

Here's a follow up point. I recently had an opportunity to review a tank inspection report compiled by a very reputable tank inspection company in Oklahoma. The report is a joke. While testing 50 year old tanks (vertical single wall), these guys only took about 6 thickness measurements per tank, did not address the bottoms at all apart from saying the foundations were concrete and okay, and really seemed to omit alot of important details such as leaking valves, non-compliant vents, non-existent fire valves, etc. The report format is top notch, but it seems like they spent about 30 minutes per tank and on a 50 year old tank, I would certainly wanna check the bottom and include that info in my report. Any thoughts? Anyone have a GOOD standard for a NDT report, checklists, etc. regarding maintenance inspections?

Along the same lines, what are my responsibilities when doing an inspectiojn on tanks that have recently been moved but in one piece. The tanks are small enough to be turned on their sides and trailered to a new site. No welding was done on the tanks, but they were blasted and coated. Help please!

Chris

 

[JStephen]

One issue is that API-653 is set up for certain conditions, and when your conditions are substantially different, it be my difficult to properly apply the standard.

For testing thickness of shell, see 4.3. Note that it never says how the thickness is determined in that section, just assumes that it is. Appendix G provides "guidance" for qualifications for bottom plate examiners.

Steve's comment about the NDE examiner was something that I was not aware of. I don't normally do this kind of inspection, but have see the ultrasonic thickness testers at seminars, and had the impression they were pretty simple to use- not something that required any kind of qualification. I find this poorly addressed in API-653 itself. However, I did find some additional information online, and evidently, it is intended that the person using these thickness testers be qualified to do so.

Section 6 includes requirements for inspections, and App. C includes some checklists.

I don't know about the specifics of the inspection report you mention, have some general comments. An API-653 inspection is concerned primarily with the tank itself, not with the installation as a whole. Leaking valves, inoperable valves, missing valves, etc., are piping issues, not tank issues. A non-compliant vent may be a legal issue for the owner, but is not necessarily a tank issue. There are all kinds of requirements for tank installations that COULD be checked, but are not included in API-653.

 

[cwigg66]

Great info JStephen... thanks. Got a link to the site you found the UT cert. requirements? I am interested in who the certifying agency is and what industries recognize the certification. I can't seem to find much on it online.

Like you, I was also under the impression that equipment such as the Panametrics 36DL+ were designed to be used by any field inspector, hence A-scan display and temp. compensation functions. I have personally used this unit and it worked great. You do have to know how the unit works but that is more of a familiarity issue. Anyone that can read and knows the principles of UT should be able to successfully operate this device without training. The display shows you when the reading is "clean" or when you have a couplant issue or some kind of weird echo.

I really would like to hear more about the certification requirements. Thanks again for all the information. You guys are great!

Chris

 

[TankDude]

I would concur with Mr. Braune that the better inspection companies require that their inspectors become certified on all NDE equipment, UT included. There are so many hours of supervised experience followed by an exam I think. This is all part of the NDE Level I-III training. Admittedly, using a UT indicator isn't rocket science. I have used them without having the proper certification. I think it's just the best way for companies to ensure quality within their own inspection group(s) and also give their clients that warm and fuzzy feeling.
On the other items, API 653 provides guidance (often vague) for inspection requirements for tanks that have been in both continuous service and are being brought back into service. If this is a routine maintenance inspection being done while the tank is in-service then you should be able to follow the guidelines and checklist provided. The title of the standard for repair and alteration is meant to simply provide guidance and recommended practices for those situations covered. I feel that it's a good baseline for tank inspection/maint/repair and that it does at times give good details of practice but often it is intentionally quite vague. Good luck to you.

 

[JStephen]

This is the document that I ran across:

http://api-ep.api.org/filelibrary/QUTB-API-UT-30.pdf

There are some notes in red that seem to indicate this is a work-in-progress and not a finished document, and I didn't research it enough to find the full story.

 

[JoeTank]

Chris,
You mentioned that the report you looked at was "a joke". Before you begin to think poorly of ther firm that did the report, note that API-653 requires the tank owner to specify the extent of NDE to be performed. The owner is responsible for NDE scope related issues. There is no such thing as an "API-653 tank inspection". It's whatever scope is assigned to the inspection team. Also, there may be several inspection grooups involved on one tank. There are Internal as well as External inspections too. That may explain why no internal bottom info was provided in the report you cited. Maybe it was external only. Hope this helps.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[JoeTank]

Chris,
A few other thoughts... The lack of reference to venting, valves, etc may be due to fact that often an inspection report is just the inspect data. API-653 requires that the tank be "evaluated" by personnel experienced in tank design. That person is the "storage tank engineer" referenced elsewhere in the Standard. Few API-653 Inspectors are also storage tank engineers, so that often explains the lack of completeness for many reports. The evaluation of the tank covers all of the other issues such a wind, seismic, piping loads, venting, fire protection, etc.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[JoeTank]

Chris,
Several here have commented about the vagueness of API-653 in regards to inspection scope. There's nothing vague about the fact that API-653 places the determination about the extent of NDE on the owner. Unfortunately, some owners do not step up to that requirement and do what is expected of them. Far too often owners ask for an inspection "in conformance to API-653." At that point most inspection firms will offer their own view of what an inspection should be. The result is somewhat predictable. Inspection firms with lots of NDE equipment (MFL units, UT crawlers, etc) offer inspection services using lots of equipment. Firms with very little equipment tend toward the visual inspections with some UT measurements. If the decision is made on only inspection costs the results are predictable.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[cwigg66]

Steve:

You bring me back to my original point. I am trying to conduct the most complete inspection I can and give my customer the most for his money. For most of our clients, they don't even know they have to inspect their tanks at all until a regulator or myself tells them so and point them towards the proper regulations. That being the case, they rely solely on myself to give them guidance and get them into compliance. You answered my question in saying that "most inspection firms will offer their own view of what an inspection should be." As with all my work, I will do my very best to keep customers compliant and more importantly, safe, while using their resources wisely and remaining ethical. It's all I can do. As always, all of your help is appreciated. These forums are a real asset to any engineer / designer. Thanks again

Chris