PRCI Report 150

L51473e

Battelle Memorial Institute

Need: Severe problems with wrinkling when making field bends in ERW pipe coated with a fusion-bonded thin-film coating have been reported by several PRCI member companies in recent years. When these problems were encountered, wrinkling was controlled by careful alignment of the bending equipment, by procuring another lot of pipe for bending, or by increasing the bend radius. The occurrence of wrinkling results in considerable inconvenience, such as increased cost and construction delays, particularly when it cannot be controlled solely by realignment of the bending equipment.

Results: An investigation was conducted to determine the factors responsible for the development of wrinkles at low bend angles during the field bending of certain lots of line pipe. The investigation included both a survey of users to obtain information on field bending problems and laboratory studies at Battelle designed to identify factors responsible for wrinkling at low bend angles.

Benefit: It was found that wrinkling has been observed in a wide range of pipe sizes and grades. In all cases in which wrinkling has been observed at low bend angles during field bending, it occurred in pipe that had been coated with a fusion-bonded thin-film coating. However, not all fusion bonded thin-film-coated pipe has exhibited bending problems. The thermal treatments used to apply fusion-bonded coatings to line pipe can result in a change in the yield behavior of the pipe; that is, discontinuous yielding may be enhanced as a consequence of strain aging. Local-buckling theory suggests that the occurrence of discontinuous yielding should increase the likelihood of wrinkling during field bending. This factor is believed responsible for the greater susceptibility to wrinkling of pipe coated using a fusion-bonded thin-film coating, compared with uncoated pipe from the same lot of pipe.

Product Details

Published:

02/21/1985

Number of Pages:

32

File Size:

1 file , 820 KB