EXTERNAL CORROSION DIRECT ASSESSMENT (ECDA)

Background:

External corrosion direct assessment (ECDA) is a structured process that is intended to improve safety by assessing and reducing the impact of external corrosion on pipeline integrity.

Purpose & Scope:

ECDA can be used to enhance the assessment of external corrosion by identifying and addressing corrosion activity, ECDA seeks to proactively prevent external corrosion defects from growing to a size that is large enough to impact structural integrity.

Method:

ECDA is a continuous improvement process. Through successive ECDA applications, a pipeline operator can identify and address where corrosion activity has occurred, is occurring, or may occur. Results from ECDA are used to prioritize future actions.

Procedure:

ECDA requires the integration of data from multiple field and pipe examinations, physical examinations and operating history.

1. Pre-Assessment: Collects historic and current data to determine if ECDA is feasible, defines ECDA regions, and selects indirect inspection tools.
2. Indirect Examinations: Conducts aboveground inspection(s) to identify and define coating faults, anomalies, and corrosion activity.
3. Direct Examinations: Evaluates indirect inspection data to select sites then conducts excavations for pipe examinations.
4. Post Assessment: Analyzes data collected from the previous three steps to assess the effectiveness of the ECDA process and determine re-assessment intervals. ECDA provides a proactive advantage over alternative integrity assessment methodologies, such pressure testing and in-line inspection, by identifying areas where defects could become an integrity concern in the future. Based on the preliminary data analysis, using a minimum of two aboveground techniques in comparison to ILI metal loss defect data, the indirect exams showed that a direct correlation to metal loss exists for the majority of the defects. However, additional direct examinations must be completed in order to have complete closure on the validation process.

INTERNAL CORROSION DIRECT ASSESSMENT (ICDA)

Background:

Internal corrosion has occurred on pipelines carrying gas specified to be dry. A simple method termed internal corrosion direct assessment (ICDA) has been developed to assess the corrosion impact of short-term upsets on pipeline integrity. The method is expected to enhance pipeline integrity, reliability, and public safety.

Purpose & Scope:

ICDA can be used to enhance the assessment of internal corrosion in gas transmission pipelines and help ensure pipeline integrity. The method is applicable for gas transmission lines that normally carry dry gas but may suffer from short term upsets of wet gas or liquid water (or other electrolyte).

Method:

The basis behind ICDA is that detailed examination of locations along a pipeline where an electrolyte such as water would first accumulate provides information about the remaining length of pipe. Simply stated, If corrosion exists, it will include location(s) of first liquid water accumulation. Results of multiphase flow modeling are used to predict the critical angle of inclination that would hold-up water. A simple spreadsheet was developed where the critical angle is calculated given pipe diameter, gas velocity, pressure, and temperature.

Procedure:

1. Calculate critical angle
2. Find upstream pipe inclinations, which exceed the critical angle
3. Inspect the upstream location for internal corrosion Negative result - Downstream corrosion unlikely
4. Consider features that might trap water (e.g., Drips, valves, etc.)

To date no extensive field work has been completed for the validation of this process, however, anecdotal information shows great promise. Several operators will be submitting data within the next 2 years to assist in the statistical analysis of this project. This information will then be used to determine if internal corrosion is likely or unlikely to exist in a chosen length of pipe. NACE will be rewriting a new internal corrosion recommended practice to replace RP0175. This new document will house the ICDA procedure developed for PRCI.  

PAGE 1 2 3 4 5 next