Pipeline liner material wears well in tests of field specimens.(polyamide-11 (PA-11))

Tests on two field-aged specimens of polyamide-11 (PA-11) pipeline liners in carbon steel crude oil and gas production pipelines indicate the material protects against internal corrosion when chemical inhibition programs, conventional liner materials, or specialty corrosion-resistant alloys are either infeasible or uneconomical. [1]

Two field-aged specimens were supplied for this analysis by oil field operators. The liners appeared in excellent condition, with residual mechanical properties close to those of the virgin liner.

In each case, the liner was operating without failure, the operating conditions were reasonably well documented, and unexposed reference samples of the recovered liner were available for comparison.

The tests measured polymer molecular weight, residual mechanical properties, and extractable fraction analysis. As the specimens did not age to failure, it is impossible at this time accurately to predict how long the liners will last, although there have been attempts at lifetime prediction. [2-4]

PA-11 has been used as a corrosion-resistant fluid barrier in flexible pipe for more than 25 years and, more recently, in rigid steel and composite pipes [4-8] Polyamides are generally stable materials that have found wide commercial application.

The chemistry and oil industry-related properties of PA-11 have been discussed elsewhere. [9] Based on the ability to withstand more severe operating temperature, pressure, and produced-fluid composition, operators may select PA-11 as the liner material over the more conventional high density polyethylene (HDPE).

PA-11 combines high dimensional stability, low gas-permeation rates, and high tensile strength that makes it suitable for installation as a liner in rigid steel pipes that transport crude oil, gas, and produced water.

It has been installed around the world by all the major liner-installation methods, and liners are commercially available from a variety of vendors. More than 10 km of PA-11 liner in various diameters have been operating in corrosive service pipelines in North America and Europe.

Specimens; test results

In November 1995, the first PA-11 liner was installed in a rigid steel production pipeline in western Alberta. [6 12] It was installed by a roller diameter-reduction method. [10] The 4-in. pipeline transported sour gas, gas condensate, and water at about 65[degrees] C. and 600 psi.

The pipeline was buried in relatively dry earth so that a nearly isothermal condition existed through the thickness of the polymer liner. Table 1 gives the details of the produced fluid.

The water pH was in the range of 5 to 5.5 in the flow stream. Several HDPE liners had previously been used in this pipeline; the longest service life observed before failure was about 18 months.

At the time of the PA-11 liner installation, a lined spool piece was inserted at the wellhead end of the pipeline with the intent of replacing the spool piece during a scheduled shutdown later to assess the condition of the liner.

This would prevent the premature replacement of the liner in this sour gas line and provide a reference piece to verify the performance expectations held at the time of installation.

The pipeline was shut down for 212 days in various durations from November 1995 to May 1998 due to problems unrelated to the pipeline. During these times, the temperature dropped to the ambient ground temperature, which varied depending on the time of year.

The annulus vents for the first case liner were checked periodically. The annulus …