Iqi.docx

IQI (Penetrameter) Selection in Industrial Radiography Testing 8:19 AM

IMAGE OF ASTM IQI How to select the penetrameter (IQI) for radiography? Or How to ensure that proper sensitivity is there on the radiography film? IQI or Penetrameter is used to ensure that the minimum required sensitivity is there on the radiography film. What is sensitivity? Sensitivity of a radiography film is the minimum size of discontinuity that can be detected in that radiography film. How we will ensure that the required sensitivity is there on the radiography film? This is done by using IQI or Penetrameter Most of the codes and specification asks for a minimum sensitivity of 2%. In the below example you will understand what is mean by 2% sensitivity. Example - 1: You have to radiograph a plate to plate welded joint of 8mm thickness. The specification asks for 2% sensitivity. Now 2% of 8mm=0.16mm. So in the radiography film a discontinuity of size from 0.16mm should be visible. In other words, at least the discontinuity starting from the size of 0.16mm should be visible. In other words the minimum size of the discontinuity that should be visible in the radiography film is of 0.16mm. Now how will you measure that the radiography film is having minimum 2% sensitivity. We have to use the 'instrument' called IQI or Penetrameter. IQI is a set of standard wires having standard diameter.(Hole type IQI is also used. In that case it will be standard thickness plates with standard diameter holes). The IQI is placed on a radiography film while doing the radiography. The image will be caught in the film. If the wire having 0.16mm diameter is visible in the radiography film, then we can say that the film is having a sensitivity of this 2%. The IQI that is commonly used is of ASTM and DIN standards. We will discuss about how the IQI is selected based on ASTM standard. Below table (Table 233 T-233.2 in ASME BPVC Sec V) is the set of ASTM wire type IQI with its wire diameters.

Now to our above example, select the set of IQI to be used. How this is done? What

is

the

minimum

size

It

of

wire

to

be

shown

in

our

is

Select

the

radiography

film

in

our

example?

of

set

of

wire

0.16mm.

having

0.16mm

dia

wire.

It is in 'set A' in the above table and the wire is having a identity number of 4. So use this set at the time of taking radiography and if that wire is visible (3 wires minimum will be visible that is wire of thickness 0.16mm, 0.2mm and 0.25mm will be visible) in the film, then that radiography film is said to be of having 2% sensitivity. Example

2:

Radiography

to

Now

the

be

done

on

a

2%

plate of

with

thickness

32

of

32mm

that

with

is

a

minimum

32

sensitivity

x

of

2%.

2/100=0.64mm

Select the set having a wire of 0.64mm thickness from the table given above. It is set B and wire identity number is 10. If in the radiography film of the above 32mm thickness plate, the wire with identity number 10 is visible, we can say that the radiography film is having

2%

sensitivity.

Now do the reverse process to find out what is the sensitivity of a radiography film. We have taken the radiography of a 60mm thickness plate and in the radiography film used set C and the wire with identity number up to 12 is visible (5 wires will be visible in this radiography film). What is the sensitivity? Find

the

diameter

From

of

the

the

wire

table,

having

identity

it

number

is

1.02mm.

Sensitivity Diameter

12.

= of

the

smallest

IQI

wire

visible

x

100

/

Thickness

of

the

plate

radiographed.

So

in

the

above

case,

Sensitivity

=

1.02

X

100

/

60

So the sensitivity is higher than that is required and the radiography film is acceptable from sensitivity

=

1.7%

point of

view.

The 2% sensitivity is an old method or we can say that a thumb rule for calculating sensitivity. ASME BPVC Section 5 specifies the wire identity number that shall be minimum visible while taking radiography of material with minimum thickness range as in the below table.

Please note an interesting fact in this. Up to and including 6.4 mm thickness the IQI identity number that shall be visible is 5 for source side and 4 for

film

side.

The other important point to note in the IQI selection is that the IQI shall be made up of the same material as that of the material to be radiographed

or

the

IQI

shall

be

of

a

radiographically

In general, in most cases, film side radiography is done due to practicality in doing the settings for radiography.

similar

material.