TPT January 2010

A rticle

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

ID surface removed in test area only

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

 Figure 3

OD surface removed in test area only

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 4

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

 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

OD fibres in

tension

ID fibres in compression

ID fibres in compression

OD fibres in

tension

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J anuary 2010

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