By CWI555
Date 10-25-2008 19:25
Edited 10-25-2008 19:31
Theoretical throat is the designated weld size per drawings. the .707 comes from a right triangle on a standard fillet weld. For the standard fillet you'll have a 90 degree perpendicular member/face. for skewed T by definition you do not have that. .707 is short for .7071 which is the sin of 45 degrees.
Draw out a lines for an equal leg fillet weld and you will find that the angle created in the cross section is 45 degrees. If you had a 1" equal leg fillet, the face to root would be .7071 " at the center of the face.
you do not have that in a skewed T therefore the sin of 45 (.7071) does not apply.
For instance:
45 sin = .7071
45 cos = .7071
45 tan = 1
as compared to say a 50
50 sin = .766
50 cos = .643
50 tan = 1.19
What do you think that is going to do to your measurements. .7071 is derived for calcing out your throat when you have a concave fillet weld as the size is the largest right iscolese triangle that will fit when you measure the throat.
a)A right triangle has one 90° internal angle (a right angle). The side opposite to the right angle is the hypotenuse; it is the longest side in the right triangle. The other two sides are the legs or catheti (singular: cathetus) of the triangle.
b)An oblique triangle has no internal angle equal to 90°.
c)An obtuse triangle is an oblique triangle with one internal angle larger than 90° (an obtuse angle).
d)An acute triangle is an oblique triangle with internal angles all smaller than 90° (three acute angles). An equilateral triangle is an acute triangle, but not all acute triangles are equilateral triangles.
That is where the obtuse and acute terminology comes from.
You can break out the right forumulas and calculate by hand, but this is why I advised using the slide rule calculator. For the inspector, he or she should be working to a set of drawings, those drawings should give the required weld size, be it acute or obtuse in this case, and that value is what you plug in for Te.