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Technical Discussions
Michael Canny
NDT Inspector
Rochester Gas & Electric Corporation, USA, Joined May 2000, 1

Michael Canny

NDT Inspector
Rochester Gas & Electric Corporation,
USA,
Joined May 2000
1
09:27 Jul-14-2000
Petroleum Storage Tank - Rivet Inspection

Hello, We are the process of inspection two 1920 vintage riveted storage tanks.
Can anyone out there provide me guidelines or practices on inspecting these rivets?
Some of the rivets are conical heads (bottom half of shell) others are flat-head (top half) on these tanks.
Thanks!


    
 
 Reply 
 
Sam Crotchmallnick
Sam Crotchmallnick
09:47 Jul-14-2000
Re: Petroleum Storage Tank - Rivet Inspection
: Hello, We are the process of inspection two 1920 vintage riveted storage tanks.
: Can anyone out there provide me guidelines or practices on inspecting these rivets?
: Some of the rivets are conical heads (bottom half of shell) others are flat-head (top half) on these tanks.
: Thanks!

DUH! Waht color are they? What size are they? Any round heads there? What do you want? Can they be removed?




    
 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1260

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1260
02:24 Jul-14-2000
Re: Petroleum Storage Tank - Rivet Inspection
Michael:
I have worked on riveted boilers for old traction engines (1900-1920) to our local Canadian provincial guidelines.
There are 2 main things that might occur; the riviets may shear or the plates they are holding together may develop cracks (usually radial from the holes).
Although some people have developed conical adapted delaylines for placement over the conical rivet heads, when modelled these are shown to be of little value.
Simply grinding a flat spot large enough to put a probe on (a small probe about 6mm diameter) will allow you to get an echo off the opposite rivet head.
All you can do is try to assess if there is a crack of any significant size. This would have the arrival time shorter that the distance to the opposite rivet head of a good rivet.

Some people have used UT to look for radial cracking in the outer plate by using a UT scan around the rivet. I preferred to use fluorescent MPI (aerosol spray fluorescent particles and an AC yoke).
Either way you are usually limited to investigating the condition of the outer or exposed shell. If you have access from both sides you could do the same test both inside and outside the tanks.
Depending on the joint configuration you may have 2 or 4 layers of plate in a riveted joint. Multiple layer testing by conventional NDT is not feasible (radiography can rarely be rationalised).

ASME had requirements for "Boilers or Parts Thereof Constructed by Using Riveted Construction" in Section 1 of the 1971 edition of ASME Code. (I do not have a copy so i cannot provide details).

Hope this is a bit more informative than DUH!

Ed

: Hello, We are the process of inspection two 1920 vintage riveted storage tanks.
: Can anyone out there provide me guidelines or practices on inspecting these rivets?
: Some of the rivets are conical heads (bottom half of shell) others are flat-head (top half) on these tanks.
: Thanks!




    
 
 Reply 
 
John O'Brien
Consultant, -
Chevron ETC , USA, Joined Jan 2000, 278

John O'Brien

Consultant, -
Chevron ETC ,
USA,
Joined Jan 2000
278
00:46 Jul-15-2000
Re: Petroleum Storage Tank - Rivet Inspection
Since the tanks are so old unless there is a specific reason for concern about the rivets leave well alone. Its not common to inspect individual rivets in tanks unless a problem has been determined. The rivets are constantly subjected to leak testing while the tank is in service so this would indicate a problem.

Other than this simply conduct an assessment of the tank shell as per Paragraph 2.3.4 of API 653. This provides what many would see as conservative Joint Efficiencies for assessing the shell condition of riveted tanks. This should be sufficient unless you have concerns about an additional loading factor such as wind, seismic, operations over 200 F, piping loads, settlement etc.

Corrosion thinning in the areas of the rivets is probably your biggest concern but if you do the assessment you may well find the tanks were over designed in the first place.



    
 
 Reply 
 
Meirion James
Meirion James
03:58 Sep-04-2000
Re: Petroleum Storage Tank - Rivet Inspection
: Hello, We are the process of inspection two 1920 vintage riveted storage tanks.
: Can anyone out there provide me guidelines or practices on inspecting these rivets?
: Some of the rivets are conical heads (bottom half of shell) others are flat-head (top half) on these tanks.
: Thanks!

We regularly inspect riveted tanks of this vintage and apart from occaisonal corrosion to the rivet heads (we sometimes use a simple cut-out profile gauge) there are rarely many problems encountered. Obvious leaking is picked up visually and can be dealt with accordingly.
I concur with the comments of John O,Brien

Meirion James


    
 
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