49 CFR 195 "Pipelines Facilities for Transportation of Hazardous Liquids or Carbon Dioxide" states that "Butt welding type fittings must meet the bursting strength requirements of ASME B16.9". Further down, 49 CFR 195 allows changes in pipe direction by bending pipe. ASME B31.4 "Pipeline Transportation systems for Liquid Hydrocarbons and Other Liquids" also has similar language. ASME B16.9 applies to "Factory Made Wrought Buttwelding Fittings" and states that fabricators of wrought fittings can the specified burst testing method to qualify the fitting design. If, during the construction of a buried steel fuel pipeline, a 90° change in direction is required, and the Contractor has a fabricator make a 90°bend by bending pipe, does this bursting test requirement still apply? The pipe being used to fabricate the bend is thicker than the straight pipe being used; after bending, the wall thickness of the bend will exceed that of the adjacent pipe; and calculations per ASME B31.3 show that the wall thickness of the bend is abotu 4 times that required.
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ASME B16.9 Burst Pressure Testing of Bends 2
- Thread starter ChrisFK
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ChrisFK,
The fittings and bends should have equal or better strength compared to the pipe, in most piping systems. Bending always has some wall thinning associated with the forming, so fabrication starts with thicker wall material. Stress intensification factors applied to bends and fittings will result in thicker wall requirements compared to the straight pipe. Bend radius affects the stress intensification factor - a 1D radius has higher SIF than a 5D bend. If the real estate is avaiable for a 10D radius bend, then the pipe wall thinning might be small enough to use the same thickness as the straight pipe
The fittings and bends should have equal or better strength compared to the pipe, in most piping systems. Bending always has some wall thinning associated with the forming, so fabrication starts with thicker wall material. Stress intensification factors applied to bends and fittings will result in thicker wall requirements compared to the straight pipe. Bend radius affects the stress intensification factor - a 1D radius has higher SIF than a 5D bend. If the real estate is avaiable for a 10D radius bend, then the pipe wall thinning might be small enough to use the same thickness as the straight pipe
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It is a concern of the safety and quality (reliability) of the home made fittings.
Typically, the manifacturer has to follow the procedure to fabricate the pipe bends and perform the test. So, it could make sure the quality of the bends is the same.
You may have responsibility as a facilioty owner to make sure it meet the requirements not only the wall thickness but the shape, smoot surface, testing, etc. Also, you want to consider what if it bursted during service, how much damage it will cause?
The bottom line is that it is an engineering decision and you don't want to cause any problem later on just because of it.
Typically, the manifacturer has to follow the procedure to fabricate the pipe bends and perform the test. So, it could make sure the quality of the bends is the same.
You may have responsibility as a facilioty owner to make sure it meet the requirements not only the wall thickness but the shape, smoot surface, testing, etc. Also, you want to consider what if it bursted during service, how much damage it will cause?
The bottom line is that it is an engineering decision and you don't want to cause any problem later on just because of it.
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