Specifications and Principle Characteristics of Continuously Milled Coiled Tubing for Pipelines
Authors: Stanley Roderic K. , Martin John R. , Van Arnam W.D. 
Published: October 2008

Industry acceptance of the cost advantage of using continuously milled carbon steel coiled tubing for pipeline applications has lead to a new proposed API line pipe specification; API 5LCP-Specification for Coiled Line Pipe. Grade ranges span material in the yield strength range from 52 kpsi to 80 kpsi, for a diameter range of 0.50" to 6.625". The cost benefit to the end user requires an understanding of the product's unique weldability, and reeling characteristics. This paper describes these welding characteristics and processes used to join coiled pipelines made of the HSLA material grades commonly found in coiled tubing. Unlike straight line pipe, coiled line pipe is designed to be spooled on to reels as it is manufactured for subsequent transport to the installation site. At the installation site, the pipe is then unspooled as it is installed. The effect of this reeling on the tubing's properties is detailed.

Introduction

Industry acceptance of carbon-steel coiled Line Pipe (CLP) is evidenced by the field installation of in excess of 1.8 million feet. Coiled line pipe is pipeline grade electrically welded pipe, manufactured by continuously milling tubing and reeling onto a spool for transport to the job location. CLP allows installation without having to make field welds every 40 to 120 feet. This allows installation where time constraints exist, permitting access to environmentally sensitive areas, and an overall cost saving on installed line cost. The American Petroleum Institute has recognized the value of CLP by developing a new proposed specification, API 5LCP, for the product. This paper outlines the specifications for CLP, and presents results of recent testing.

American Petroleum Institute Specification for Coiled Line Pipe

Following established convention for line pipe, CLP was manufactured in the early 1990s to requirements that were similar to those of the API for Line Pipe, but using hydrostatic test pressures that had been developed for coiled steel tubing. In order to establish CLP as a product approved by a national organization, the API Resource Group for Coiled Tubing (RGCT) began in 1996 the conversion of API 5L (41st Ed.)1 text to a new document that would specify manufacturing and testing procedures for CLP. Acceptable procedures unique to CLP were to be documented and included; these included skelp-end welding, weld and pipe NDE procedures, some testing frequencies that are different from those in API 5L, higher hydrostatic test pressures (up to 15,000 psi) for longer times (minimum 15 min. at test pressure), the replacement of full length visual inspection of the pipe in favour of full body eddy current inspection, drying and protection of the ID by backfilling with an inert gas, and stringent requirements for the contents of a mandatory test certificate (Table 1). API style and text from 5L have been accepted wherever possible. Attempts have been made to limit API CLP D/t ratios to less than 23, although this does not always occur.

The new Specification does not cover tube-to-tube welding that is performed outside the manufacturer's plant.