Non Destructive Testing - Taylor 1200E Operating Manual

WELD TESTING

2. NON DESTRUCTIVE TESTING.

Generally the most practical way of testing threaded stud welds, without destroying the
stud, is with the use of proof tests. A torque wrench is particularly useful for this purpose.
Below and overleaf are some tables which you may find useful. However, it must be noted
that :
•
Formulas & data shown are intended for guidance only.
•
In applications where control of preload is important, the torque - tension
relationship should be determined experimentally on the actual parts involved
including any lubricants.
•
The coefficient of friction (k) varies with material, surface finish and lubricity of
threads and bearing areas of fastened parts.
•
For standard steel screws it is 0.19 to 0.25 and 0.13 to 0.17 for plated screws. Anti-
seize materials and lubricants can lower k to 0.05. For some stainless steel threads
and parts not coated or lubricated k may be as high as 0.33
•
All the figures are approximate and do not form part of any specification.
•
Designers and specifiers must satisfy themselves that the studs and materials chosen
are suitable for their particular application.
All torque figures are calculated by the formula :
Where : T = Torque (Nm)
D = Effective Stud Diameter (m)
k = Coefficient of Friction (0.2 used for calculations)
Material properties:
Mild Steel (4.8)
Stainless Steel (1.4301)
Note: safe loads are 80% of the yield
A broader explanation of these methods may be found in standard BS EN ISO 14555:2014, Section
11 (Examination and Testing).
T = kDP
(N/mm²) (N/mm²)
UTS
420
540
19
(N/mm²)
Yield Safe
340 272
350 280
V-21A