about rks
Work at the American Petroleum Institute.

Several years ago, while working for a manufacturer of coiled tubing, we collaborated in the writing of an American Petroleum Institute Recommended Practice for Coiled Tubing. This was published as API RP 5C7 (Recommended Practice for Coiled Tubing Operations on oil and Gas Wells). The first edition of this document appeared in 1996, and was re-approved in 2002. The document covers manufacture, testing an inspection of grades CT55, CT70, CT80 and CT90, and contains the theoretical collapse value. A section on fatigue and corrosion mechanisms is followed by details of coiled tubing injectors, and finally good operational procedures.

It was thought that coiled tubing could be used as long lengths of flowline, so we approached the API to produce a manufacturing specification for coiled line pipe. This was done by taking the test from the 41st edition of API Spec 5L (Specification for Line Pipe), and adding the welding and inspection of the skelp-end welds. Since CLP is manufactured from flat strip using the electric weld process, only that method is included.

The result was a document that covered CLP (API Specification 5LCP, 1999) in the size range from 0.500-in. to 6.625-in diameter, and grades X52C, X56C, X60C, X65C, X70C, and X80C. These grades parallel those in the 41st Ed of 5L, and allow the original coiled tubing grades to be classed as coiled line pipe. Thus purchasers of small-diameter line pipe can now buy lengths of many thousands of feet, rolled on a drum, and avoid many field welds.

The second edition is now ready for publication in early 2007.

Current work involves the following:

  1. Production of an API Specification for Coiled Tubing. This will parallel the coiled line pipe document 5LCP, and expand the manufacturing, testing and inspection section from 5C7.
  2. Production of a Recommended Practice for the Care, Maintenance and Inspection of Coiled tubulars. Since coiled tubing accumulates both low cycle fatigue, and surface imperfections during its use, a document that covers assessment of the degradation of the tubing in field use was thought to be very necessary. Field inspections are currently performed, especially on strings used in critical areas, such as regions with high levels of H2S, and offshore.

The API documents RP 5C7 and Spec 5LCP are available from the API. Follow the link to API in this website.

Coiled Tubing Inspection

At International Oilfield Services, we have performed inspection of coiled tubing, both new and used, for several years, and have almost reached 100 strings inspected. In the past year, we gave inspected strings at both coiled tubing mills that have gone on to perform in critical wells offshore Gulf of Mexico, and in the Hibernia field off Newfoundland. We even inspected two strings that were destined to be used on a platform in the GoM, but were submerged by hurricane Katrina, and suffered some corrosion from salt water.

Coiled Tubing Inspection Seminar

Along with the Intervention and Coiled Tubing Association (Icota) and a major oil company, we hosted a seminar of coiled tubing inspection in the Woodlands, TX in April 2006. Discs of the papers presented at this seminar are available from us.


We have recently given presentations on coiled tubing inspection to Society of Petroleum Engineers Roundtables in Aberdeen Scotland (Nov 2005, Nov 2006), and Galveston, Texas (Nov 2006). Copies of the presentations are available from us.

A seminar on Magnetic Flux Leakage Inspection was given in Houston, TX, for the American Society for Nondestructive Testing. The ppt presentation is available for the asking.

The Robot

At itRobotics, we have designed and built a robot that will travel up the bore of tubing, and perform inspections of the bulk of the tubing wall for changes in wall thickness and ovality, that are caused by the use of the tubing. The robot is totally untethered. A field trial was conducted in Norway.

It is anticipated that the robot will find use in installed tubing, such as in chemical plants, refineries, paper mills, desalination plants, and of course, small diameter pipelines.

NDE Information Consultants

last updated November 23, 2006