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 -

Controle Mesure Systemes
Contrôle Mesure Systèmes (CMS) is a leader in Non Destructive Testing (NDT) with a complete range of products for eddy current and ultrasonic i ...
613 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

Sci Aps Z-Series Portable Handheld Analysers

The world’s only handheld analyzer that measures carbon content in stainless (yes even L-grades),s
...
teels, and cast irons. Also accepted for low Si analysis for sulfidic corrosion analysis, and is widely used in the power industry for Cr analysis, for flow accelerated corrosion applications.
>

ISAFE3 Intrinsically Safe Sensor System

ISAFE3 intrinsically safe sensor system of Vallen Systeme is especially targeted at the petrochemica
...
l - as well as oil and gas transportation industry. The sensor system is designed for permanent monitoring or periodic inspection tasks. Sensors are available for different AE-frequency ranges optimized for corrosion and fatigue crack detection and other applications. The ISAFE 3 sensor system consists of an AE-sensor (model ISAS3) certified according to ATEX/IEC for installation in zone 0, gas group IIC, IP68, 20 to +60 °C, and a signal isolator (model SISO3) certified for installation in zone 2. An ISAS3 sensor can be mounted in atmosphere or submerged, e.g. in water or crude oil. It is supported by mounting tools for temporary (magnets) or permanent (welded) installation. ISAFE3 supports automatic sensor coupling test and can be used with any AE signal processor supporting 28V supply at 90 mA peak, e.g. Vallen Systeme ASIP-2/A.
>

Ultrasonic Probe Recharacterization Service

NDT Systems offers a comprehensive Aftercare and Recharacterization Service for all our ultrasonic
...
probes. The Recharacterization Service is fully compliant with International ASTM E1065 Standard Guide (and other applicable standards) and offers complete documentation, traceable to the ASTM E1065 Standard. For more details or to schedule Recharacterization Services contact ndtsales@ndtsystems.com
>

TraiNDE UT

TraiNDE UT is a virtual tool associated with a signal database which simulates real inspection con
...
ditions for numerous applications (Type A/V1 block, DAC block, welds and plates).
>

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