STRESS CORROSION CRACKING DIRECT ASSESSMENT (SCCDA)

Background:

SCC is one form of environmentally assisted cracking (EAC). EAC is a generic term that describes all types of cracking in materials where the environment and stress act together to reduce the strength or load-carrying capacity of the material. Other forms of EAC include hydrogen embitterment, sulfide stress cracking, and corrosion fatigue. EAC is an ongoing integrity concern for many industries including oil and gas, nuclear power, and chemical process.

Purpose & Scope:

SCCDA is a process of improving pipeline safety by identifying susceptible sites along the pipeline. This method is similar to ECDA that seeks to proactively prevent SCC defects from growing to a size that is large enough to impact structural integrity.

Method:

SCCDA is a continuous improvement process. Through successive SCCDA applications, a pipeline operator can identify and address where SCC activity has occurred, is occurring, or may occur.

Procedure:

Like ECDA, SCCDA 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 above ground inspection to identify and define coating faults, anomalies, and SCC activity.
3. Direct Examinations: Evaluates indirect inspection data to select sites for excavations and pipe examinations.
4. Post Assessment: Analyzes data collected from previous steps to assess the effectiveness of the SCCDA process and determine re-assessment intervals.

NACE expects to add SCCDA as separate clause additions in the first revision of TG041 expected to be balloted before 2004.

SUMMARY OF THE FOUR-STEP PROCESS

Direct Assessment (ECDA, ICDA, & SCCDA) provides a proactive advantage over alternative integrity assessment methodologies such pressure testing and in-line inspection by locating areas where defects could form in the future.

Extensive fieldwork has been completed by operators but not for the validation process. Statistical analysis of this project will need to be completed. This information will then be used to determine if SCC is likely or unlikely to exist in a chosen length of pipe.

The initial validity effort included the development of the NACE TG041 standard. The difficulties of trying to simultaneously write the NACE standard "rules" and to "do the verification" while "developing the rules" has been a learning experience. Data consistency was found to be extremely important, as the historical records and bell hole findings on corrosion wall loss needed to be correlated. Remember that above ground inspections measure the performance of the cathodic protection system only and can never measure wall loss. Wall loss is a correlation, and data consistency is extremely critical.

• The major conclusions for the ECDA program are:
• ECDA can find external corrosion integrity problems (anecdotal for mechanical damage)
• Two techniques are better than one,
• TG041 is required for consistency in collecting data and completing all four steps in the ECDA process
• NACE TG041 will improve the reporting consistency when prescreening inspections and interpretation that result from the chosen techniques; inadvertently some service providers prescreening and didn't report isolated indications therefore additional data sets will be required in this year's R&D

ECDA PROGRESS TO DATE

The NACE TG041 ECDA Standard was drafted, extensively reviewed, and presented and reballoted at the April meeting in Denver. Much of the effort in 1Q02 was focused on a consensus completion of the TG041 document. AGA, INGAA, GTI/PRCI, and the New York Gas Group are coordinating the individual R&D efforts to ensure they are complementary.

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