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- since 1996 -
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Technical Discussions
Tuan Bui
Engineering,
Vietnam, Joined Apr 2016, 8

Tuan Bui

Engineering,
Vietnam,
Joined Apr 2016
8
18:38 May-14-2016
MT pie gauge indicator

Dear experts,

When we check the adequancy of magnetic field by using the pie gauge indicator, is it necessarily compulsory that we must set up the pie gauge right on the weld joint of inspected specimen? If yes, please show me where the standard code is used, as also help me make clear the meaning of that setting up.
Many thanks all.

 
 Reply 
 
Christian Duenas
NDT Inspector,
Corporación POK, Mexico, Joined May 2016, 5

Christian Duenas

NDT Inspector,
Corporación POK,
Mexico,
Joined May 2016
5
15:00 May-17-2016
Re: MT pie gauge indicator
In Reply to Tuan Bui at 18:38 May-14-2016 (Opening).

Dear Tuan

when you have doubt or when you want to comprobe the method gage its works for check if you have a magnetic field when you use the method MT and you can check it out on ASTM E709 20.8.2

Regards!

 
 Reply 
 
N B Rengaraju
NDT Inspector, NDT Level-III/Radiation Safety Officer(RSO)
Marine and Heavy Engineering Company, MALAYSIA., India, Joined Sep 2014, 106

N B Rengaraju

NDT Inspector, NDT Level-III/Radiation Safety Officer(RSO)
Marine and Heavy Engineering Company, MALAYSIA.,
India,
Joined Sep 2014
106
04:44 May-18-2016
Re: MT pie gauge indicator
In Reply to Tuan Bui at 18:38 May-14-2016 (Opening).

Dear Tuan Bui,

Magnetic Field adequacy in terms of field direction and to an extent, field strength are both verified by using pie gauge indicator.

Three factors, among other factors, that influence this verification are:
1. material to be inspected,
2. the leg span that is going to be used for inspection and
3. thickness of material.

Weld and Parent material are not the same, although they compatible with each other.
Also, weld has a reinforcement which shall cause thickness to be more than parent metal.
The leg span used for verification in other area than weld may not be adaptable while inspecting weld.

Because of these above reasons, for inspection of weld, its better to check the adequacy by setting up pie-gauge on the weld joint.

 
 Reply 
 
Lawrence Goldberg
NDT Inspector, NDT Inspector
USA, Joined May 2013, 13

Lawrence Goldberg

NDT Inspector, NDT Inspector
USA,
Joined May 2013
13
19:35 May-18-2016
Re: MT pie gauge indicator
In Reply to N B Rengaraju at 04:44 May-18-2016 .

The MT pie gage imprper in ASTM E-709 as it states the copper side should be up. API RP 2X states the copper side should be down. I will start with magnetization using an AC electromagnet, a HWDC electromagnet and a DC electromagnet, as well permanent magnets

Empirically if the copper side up; using the 4 methods above will not produce an indication when the particles are removed. If you use the copper side down only the AC yoke will produce an indication when the particles are removed.

There is a misconception that the copper side up simulated a subsurface indication and that DC electromagnets would produce the best indications. Even when the copper side is used up; an AC electromagnet produces the better indication without particle removal.

 
 Reply 
 
Dent
Consultant, NDE Manager NDELevel III/3
NDT Consultant, Canada, Joined Nov 1998, 250

Dent

Consultant, NDE Manager NDELevel III/3
NDT Consultant,
Canada,
Joined Nov 1998
250
19:31 May-19-2016
Re: MT pie gauge indicator
In Reply to Lawrence Goldberg at 19:35 May-18-2016 .

Just to clarify a point, the pie gauge is not suitable to be used to check the adequacy of magnetic fields using the yoke technique. ASME Section V does not allow it for this function. ASTM E709 par 14.3.2 only mentions 2 ways to verify the field adequacy of yokes. The pie gauge is NOT one of them. ASTM E709 par 20.8.5.1 indicates they are used primarily for training purposes.

Put your yoke on a piece of wood and use the pie gauge. You will get an adequate field indicated. We all know that is not possible on wood.

1
 
 Reply 
 
Lawrence Goldberg
NDT Inspector, NDT Inspector
USA, Joined May 2013, 13

Lawrence Goldberg

NDT Inspector, NDT Inspector
USA,
Joined May 2013
13
19:32 May-30-2016
Re: MT pie gauge indicator
In Reply to Dent at 19:31 May-19-2016 .

ASTM E-709 Under 14.3.2 states that lift strength for AC is 10 lb and for DC or permanent magnets. This implies that a DC yoke and permanent magnet are virtually the same. Nowhere is there guidance on HW lift strength. Under 20.8.5.1 it mentions that magnetic field indicator should be primarily for training. If the magnetic field indicator (pie gauge) is used primarily training with the pie gauge copper side up, it will provide training that is erroneous. My original post was about the use of the pie gauge copper side up usage.

While ASTM E-709 has a caveat of using permanent magnets; The same should apply to DC yokes.

Under 6.3 , Figure one shows the yoke being used improperly; it should be C-shaped.

The following was lifted out ASME Sec V

(a) Pie-Shaped Magnetic Particle Field Indicator. The indicator, shown in Fig. T-764.2(a), shall be positioned on the surface to be examined, such that the copper-plated side is away from the inspected surface. A suitable field strength is indicated when a clearly defined line (or lines) of magnetic particles form(s) across the copper face of the indicator when the magnetic particles are applied simultaneously with the magnetizing force. When a clearly defined line of particles is not formed, the magnetizing technique shall be changed as needed. Pie-type indicators are best used with dry particle procedures.

API RP 2X allows for only copper side down pie gauges as part for checking the adequacy of checking particle removable force. API RP 2X can be stated as follows:

An AC articulating electromagnet shall capable of lifting a ten pound weight;and having 20 Oe at the inspection site. The inspection area shall have a white contrast paint with 200 foot candles. Either visible dry or wet particles shall be used. A single leg yoke shall have 20 Oe at the area under test.

2X is used for weld inspection either as a topside or in-service inspection practice. 2X has two choices; wet or dry visible particles. ASTM has tens of choices for weld inspection.

The 5th edition will have guidance for performing PDI's,


 
 Reply 
 
lawrence goldberg
lawrence goldberg
22:51 Dec-14-2017
Re: MT pie gauge indicator
In Reply to Tuan Bui at 18:38 May-14-2016 (Opening).

Hi Tuan The pie gauge is a means to determine the field strength albeit it is not quantified. If you have the opportunity to have a Gauss meter to plot out the field for a given yoke set up, there is some transference.

You will note in API RP 2X that the Gaussian field shall be 20 Oe. It also has the pie gauge copper side down.

 
 Reply 
 

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