where expertise comes together - since 1996 -

The Largest Open Access Portal of Nondestructive Testing (NDT)

Conference Proceedings, Articles, News, Exhibition, Forum, Network and more

where expertise comes together
- since 1996 -

NDTSS - Non Destructive Testing Society of Singapore
Visit us at SINCE 2019
579 views
Technical Discussions
bill king
bill king
07:52 Jan-15-2006
Gas cylinder UT inspection

I wanted to find out about non relevent indications on the bottom of gas cylinders. I was talking with an Eng. who was having problems with a DOT inspection his company's been doing using UT instead of hydro. At the bottom og the cylinder were the transition is sometimes they get nonrelevent indications which cause excesive regection rates on some expensive cylinders. At that transition though there is some potential for some corossion. Is it possible to tell the difference using an A scan between the two. Thanks.


 
 Reply 
 
Richard Paciej
Richard Paciej
07:49 Mar-11-2006
Re: Gas cylinder UT inspection
The part of the cylinder that you are referring to is the SBT region or sidewall to base transition. It is a high stress area. If a crack forms here, it could grow and cause a cylinder to fail. Cylinders manufactured along time ago have a shaper transition region and this gives rise to higher stresses. Newly manufactured cylinders also have this region but the transition is much smoother. This is the area where the wall thickness of the cylinder increases as it approaches the base of the cylinder.

The DOT requires the reference standard or the reference cylinder to have a reference notch for the SBT. Typically, the size of the notch is 10% of Tmin or 10% of the minimum wall requirements of the cylinder. The Tmin of cylinders range from 0.1 to over 0.250 inches and it depends on its diameter and service pressure. So the reference notch would range from 0.01 to 0.025 inches deep and is typically one inch long.

Corrosion in the SBT region is a potential problem. If it is purely wall thinning(and does not reach below the Tmin) and does not have any cracks, it should be okay. However, cracks can develop from corrosion pits.
Line corrosion crack develop at or near the SBT where water or other corrosive liquid and gas meet. In the SBT region, it would be difficult to distingush between just corrosion and corrosion with a crack(s). Also, since it is near the bottom of the cylinder, it is difficult to approach the defect from both sides using typical ultrasonic equipment used to test cylinders. You would have to do it using a hand held unit. This would be a secondary inspection and is not permitted by the DOT(yet).

Of course, if you can state that you only can either get cracks or general corrosion in this region, you could use an A-scan to distingush the two. An A-scan for a crack would give a response similar to the reference notch and most likely be sharp. Corrosion would give an A-scan that is more broad. However, there is always a chance that the two defects are there mixed together.

CGA has a standard that describes ultrasonic testing of cylinders. If you an not a CGA member, you will need to purchase it. The title of the standard is

C-20 Methods for Ultrasonic Examination of Metallic, DOT and TC 3-Series Gas Cylinders and Tubes.


I hope that this helps.

----------- Start Original Message -----------
: I wanted to find out about non relevent indications on the bottom of gas cylinders. I was talking with an Eng. who was having problems with a DOT inspection his company's been doing using UT instead of hydro. At the bottom og the cylinder were the transition is sometimes they get nonrelevent indications which cause excesive regection rates on some expensive cylinders. At that transition though there is some potential for some corossion. Is it possible to tell the difference using an A scan between the two. Thanks.
------------ End Original Message ------------




 
 Reply 
 

Product Spotlight

NDT Master Lecturer

In the program both university professors and practitioners will give lectures, which guarantees the
...
oretical depth and practical inside. Academic Director: Prof. Dr. Christian Boller
The following lecturers are not complete: Prof. Tadeusz Stepinski, Prof. Wieslaw Staszewski, Prof. Frank Walther, Prof. Giovanni Bruno, Prof. Gerd Dobmann, Prof. Philippe Guy
>

Research and Application Development For NDT

Acuren’s Research and Application Development specializes in the development of advanced ultraso
...
nic inspection techniques and systems for challenging inspection applications, with an emphasis on practical solutions which are field deployable. Services include manual and automated ultrasonic inspection system development, inspection technique optimization using laboratory scale studies and ultrasonic modeling (CIVA, BeamTool), preparing technical justification for technique evaluation and qualification (Probability of Detection and sizing accuracy studies), inspection/calibration/analysis procedure preparation to support field deployment of custom techniques, and development of custom imaging algorithms to support challenging inspection applications.
>

Eddy Current inspection : RotoETscan Rotating Head

The rotating head RotoETscan detects the presence of longitudinal surface or sub surface defects a
...
t high speed. The rotating head is often installed directly on the production line. It is generally dedicated to the control of long products such as tubes, bars and wires, made of ferrous or non-ferrous material. It can also be used for inspection of small parts (billets).
>

Robotic laser shearography enables 100% inspection of complex, flight-critical composite structures

An article in “Composites World Magazine” showcases Non Destructive Testing of aero-structures
...
with Laser Shearography. Over the years Dantec Dynamics has supplied many solutions for the aerospace industry. Referring to specific customer projects several of these cases are examined to outline the advantages of using Laser Shearography for automated defect detection.
>

Share...
We use technical and analytics cookies to ensure that we will give you the best experience of our website - More Info
Accept
top
this is debug window