V-path vs Skip distance?

Date 02-09-2010 19:50

Here are the definitions per NDT-ed.org :

Skip Distance - In angle beam tests of plate or pipe, the distance from the sound entry point to the first reflection point on the same surface. See V-path.

V-Path - In angle beam tests of plate or cylindrical sections, the path of the ultrasonic beam in the test object from point of entry on the front surface to the back surface and reflecting to the front surface again. See also skip distance.

They have different equations. V-path of 1 inch is 2T/Cos = 5.84
SP of 1 inch is 2TxTan = 5.49

What is the difference?

By jwright650 (*****)

Date 02-09-2010 19:59

Skip distance is across the surface.....measured from the BIP(beam index point) across the surface to where the sound comes back to that surface.(shorter distance)

V-Path is the actual sound path(two legs) from the BIP to where it returns back to that surface(longer distance to travel)

By supermoto (***)

Date 02-09-2010 21:02

I was always taught what we call the surface distance is what your calling the skip distance. Surface distance formula is SINxSP.

By eekpod

Date 02-10-2010 01:25

so the v-path is longer because its the actual "length" of the sound path, vs the skip distance would be shorter becasue it's a straight horizontal length measured arcoss the plate.
Or to say it another way the v-path is longer becasue its not a straight line- it takes the down and then up length/ distance into account during the calculation, where as skip distance is again just a striaght line measurement.
Skip distance is the distance needed in the base material to allow the entire weld to be scanned/ inspected, vs v-path helps you determine where an actual disconuity would/may be located.
Right?
it's been awhile, actually 15 yrs to be exact.

By supermoto (***)

Date 02-10-2010 01:49

Sort of. All I know is that I have an Olympus cheater card that has mat. velocity and equations. The v-path and skip distance have different equations. I thought that they were the same by definition but apparently have different equations.

If anyone uses these equations please inform me of the differene and maybe an example.

By jwright650 (*****)

Date 02-10-2010 13:03

[quote]"If anyone uses these equations"[/quote]Krautkramer has those laminated charts too.

If anyone does any angle beam inspection at all, they will use these formulas over and over every time they inspect. You need these equations, unless you depend on the machine to do all of the calculating for you(which is kinda dangerous). Basically it is nothing more than a little trig that you apply to any triangle.

To make sure that you cover at least the three legs during angle beam inspection; use these 2 formulas to figure how far back from the welded joint that you need to cover enough of the material with your scanning pattern.

Hope this makes sense....

By dlmann

Date 02-10-2010 11:40

have an visual for you if I can remember how to attach it here, might help

Attachment: Picture1.jpg (26k)

By eekpod

Date 02-10-2010 11:43

perfect, thats what I was trying to describe, nice job, thanks

By jwright650 (*****)

Date 02-10-2010 12:09

A Picture is worth a thousand words...Thanks Donnie.

By supermoto (***)

Date 02-10-2010 12:35

I guess I had a brain fart or something, thanks.