TPT January 2010

127 / 132

J anuary 2010 125 ›
Article
This procedure has certainly been successful in the past while the
specification for line pipe, as per API 5L did not restrict the upper
limits for yield and tensile values of the finished API product.
Now that the American Petroleum Institute (API) has written into
the specification of 5L-Line Pipe for two product specification levels
(PSLs), PSL-1 and PSL-2 the pipe manufacturers cannot exceed
the upper limit for yield and tensile values of the finished product for
the PSL-2 product.
So, is now the time for line pipe manufacturers to develop
data, by certain testing procedures, to establish the amount of
physical properties change of the incoming material during their
manufacturing processes?
If these opening statements have sparked an interest to examine
the amount of physical properties change the Bauschinger effect
has on welded steel tube and pipe the following extensive testing
procedures are listed as one way to arrive at the answer to the
question, “does the Bauschinger effect change the total physical
strength of the tube/pipe produced” in my plant?
Testing procedures
The testing protocol listed here was designed and used for
continuous roll forming, ERW welded type manufactured product.
A similar testing programme was performed on U-ing and O-ing
formed, submerged arc welded product. An expanding operation is
used on this product to greatly reduce the stresses induced during
forming and welding. The testing procedures as listed herein are of
little value on the finished product of this type.
The author is not aware of a published article dealing with the
Bauschinger effect on helical formed-spiral welded pipe.
Obtain four (4) standard tensile test specimen rings from finished
pipe, all from the same heat and if possible from the same coil.
Also obtain two (2) tensile test specimens from the flat skelp,
approximately 15 to 20 feet from either end of the coil and near the
centre of the width of the coil.
Of the flat specimens one is to be taken from the transverse
direction of the hot mill rolling direction and market 1T, and the other
flat specimen is to be taken parallel to the hot mill rolling direction
and mark it 2L. Mark each of the four (4) pipe ring specimens 3A,
4B, 5C and 6D.
Open three (3) of the pipe ring specimens, marked 3A, 4B and 5C,
by cutting through the welded area. The area to be tested will be
opposite the welded area. Pipe ring specimen marked 6D will be
tested in a ring expansion testing device as per ASTM A370, A2.3.
This test will determine yield strength only of the finished product.
The yield strength results from this test will be greater than the yield
strength results from testing specimen 5C.
All remaining specimen to be machined, 1T, 2L, 3A, 4B, 5C will be
machined as per ASTMA370 for standard tensile testing specimens.
See Figure 5.
After specimen marked 3A has been machined as per above
machine off 50% of the pipe inside surface in the testing area only,
as per Figure 3, to preserve the neutral axis area represented by
the OD surface.
For specimen marked 4B machine off 50% of the pipe outside
surface in the testing area only, as per Figure 4 to preserve the
neutral axis area represented by the ID surface.
After machining the two reduced thickness specimens and along
with the three (3) full thickness specimens, 1T, 2L and 5C, perform
a standard tensile test as per ASTM A370, recording the ultimate
Test specimen marked A, as illustrated herein requires additional machining.
This additional machining will remove 50% of the ID surface of the pipe body
thus retaining 50% of the OD fibres of the pipe body for physical testing
Test specimen marked B, as illustrated herein requires additional machining.
This additional machining will remove 50% of the OD surface of the pipe body
thus retaining 50% of the ID fibres of the pipe body for physical testing
 Figure 3
 Figure 4
ID surface
removed in
test area only
OD surface
removed in
test area only
 Figure 2 : A visual illustration of the forces on the internal fibres of flat steel skelp
and the location of the neutral axis when flat skelp is formed into round pipe
Neutral axis
ID fibres in
compression
ID fibres in
compression
OD fibres in
tension
OD fibres in
tension