PRCI

Recent Results

Evaluation of the Need for Loading Specifications for Highway Transport of Line Pipe

The ability to accurately predict static load stresses at the bearing strips on line pipe in transportation has been relied on through the application of the American Petroleum Institute (API) Recommended Practice (RP) 5L1 for rail and API RP 5LW for water borne transport.  No practical application to predict the static load stresses on line pipe being transported by truck on highways has been developed because it was believed the highway transport distances were not sufficient to represent potential for a significant amount of pipe damage.

Occasionally, existing pipelines constructed at a time prior to the observance of the recommended loading practice still experience failures at defects that originated as shipping damage and subsequently enlarged in service. The National Transportation Safety Board (NTSB) Findings and Recommendations following their investigation of a liquid pipeline accident in 2002 included conducting a review of the API RP 5L1 and API RP 5LW for calculating the static load stresses at the bearing or separator strips for pipeline and revise the recommended practices based on that review.  The NTSB also recommended that loading specifications applicable to the highway transport of line pipe be developed. The objectives of this study were to establish whether a loading specification for highway transport of line pipe is actually necessary, and if so, to develop appropriate recommendations.

Key Results

This project determined that a recommended practice should be developed for line pipe loading on trucks for transport because the potential for
fatigue-related damage is present due to:

  • The dynamic stresses from vibrations during truck transport are approximately 2 times greater than those during rail transport.
  • A significant amount of line pipe is transported by trucks for distances up to 400 miles.
  • The peak stress estimated using the equation in API 5L1 should be multiplied by a factor somewhere between 2.25 and 2.5.

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