November 2009 Vol. 236 No. 11
Features
Mears Hosts Workshop On ECDA For Cased Pipelines
With the federal Department of Transportation Pipeline and Hazardous Materials Safety Administration (PHMSA) in the process of developing guidelines to further clarify baseline and integrity assessment requirements for cased pipe (per 49 CFR 192 Subpart O code of federal regulations), Mears invited a group of customers to its state-of-the-art test-and-research facility for a hands-on workshop of External Corrosion Direct Assessment (ECDA) applications of cased pipes.
Fifty-six integrity representatives from pipeline and gas utility companies across North America attended the day-long event at Mears headquarters in Rosebush, MI. Speakers included Max Kieba, Central Engineer, Office of Pipeline Safety, who gave directions to attendees on the upcoming PHMSA cased-pipe guidelines. Demonstrations included field indirect and direct inspections of coated and uncoated cased pipe, and a demonstration of wax filling a casing by Royston.
When cased crossings are located in a High Consequence Area (HCA), they fall under the integrity management (IM) requirements and must be in compliance with prescribed milestones. With best estimates, there are thousands of cased crossings nationwide and hundreds, if not thousands, located in HCAs that will be subject to these requirements.
Currently inline inspection (ILI), pressure testing and Direct Assessment (DA) provide the only assessment options for the pipeline industry. But in some cases, obstructions in the pipeline, the expense of pressure testing and the revenue loss from downtime eliminate ILI and hydrotesting as options. This has necessitated the development of DA methods using ECDA to assess cased pipe.
PHMSA, the pipeline industry and Standards Developing Organizations (SDO) are collaborating to provide additional guidance for assessing cased crossings. PHMSA assembled a core team of participants (CASQAT) to develop guidelines and expectations when operators assess cased pipelines using the ECDA process. PHMSA assembled a select group of representatives from NAPSR, PHMSA, AGA, INGAA, NACE and two representatives from contract vendors.
The guidelines will address acceptable protocols and practices when using ECDA to assess cased pipelines. More specifically, how is the baseline assessment to be conducted? What are the requirements for using ECDA? What is a continual process of evaluation and assessment to maintain pipeline integrity? What are the required intervals?
Other issues PHMSA will address are conditions to justify that the threat of external corrosion has been mitigated sufficiently as to not require full re-assessment and determine how to address casings filled prior to the IM rule.
ECDA employs engineering processes to proactively assess locations for the likelihood of corrosion, and to focus remediation where the corrosion exists. Pre-assessment requires the operator to organize the testing, analysis and remediation methods used by categorizing cased crossings into like-similar regions.
The Mears workshop addressed prompters for external corrosion of cased pipelines, including metallic contact, electrolytic contact and atmospheric corrosion. Attendees were given live demonstrations on various testing methods on both coated and uncoated casings including:
- PCM current attenuation across casing, which measures the magnetic field caused by AC current flow. This method can be limited by overhead AC power lines, parallel structures and points of inflection.
- PCM with A-Frame which measures voltage gradient and its direction. This is one of the most reliable indicators of electrolytic contacts. Its limitations are position-sensitive relative to the end of the casing and possible masking by coating flaws on the outside of the pipe.
- P/S and C/S On Potentials where current is applied and potentials are measured to a common reference electrode.
- P/S and & C/S Shift which is a good indicator of metallic shorts.
- Internal Resistance where current is applied between pipe and casing and uses Ohm’s law to calculate resistance, which can possibly locate contact.
All these tools are complementary and look for the same potential corrosive conditions in different manners. All have strengths and limitations depending on conditions.
The 2.75-acre Mears test facility can simulate all types of corrosion conditions from coating holidays to electrolytic contact. Testing results and results reported by customers in the field have allowed Mears to compile a large data base on the effectiveness of all ECDA methods.
The research facility also offers hands-on training for pipe excavation, pipe-coating removal, surface preparation, coating application, evaluating casing isolation, DA indirect inspection surveys and pipe-direct examinations. It allows the detection of coating flaws with DA survey techniques and/or available equipment. The impact of different coatings and cathodic protection configuration can be analyzed with the detection capabilities of the equipment. Real-world surfaces such as soil, gravel, asphalt and concrete are installed to demonstrate their impact on survey techniques.
Wax Filling
Using a clear casing pipe, a demonstration on the wax-filling process was conducted by Royston (Chase Corporation). Some considerations before doing a wax filling are:
- Repeat indirect inspections;
- Excavate both ends and remove a portion of the casing to examine the ends of the cased pipe;
- Clear all electrolyte with high-volume flushing;
- Clear metallic shorted conditions;
- Repeat indirect inspections;
- Use the guided wave test as part of PHMSA 18-point process;
- Vent the low side at the 6 o’clock position and the high side at the 12 o’clock position;
- Install good quality end seals;
- Backfill and compact;
- Blow air from high to low side;
- Air test up to 5 psi;
- Calculate fill volume (actual fill cannot vary from this by more than 15% or you must explain why);
- Fill casing low side to high side; and
- Repeat indirect inspections.
Testing and field results by Mears have validated the applicability of ECDA to cased pipelines. Indirect tests find metallic and electrolytic conditions. Process elements and guided wave assess for atmospheric corrosion. The process improves safety by identifying when potentially corrosive situations exist, mitigating those conditions, allowing examination of the pipeline and eliminating the EC threat with wax filling.
Baltimore Gas & Electric Program
BG&E has over 650,000 customers and a large part of its system is in high consequence areas, including 70 casings. They started a casing pilot program in 2007 in which they tested five casings with the guided-wave method and later removed to qualify the results. They wanted to prove out new ECDA-casing test procedures as well as gather statistical and economic data on GWUT and casing removal. BG&E also wanted to assess the economic impact and overall direction in remediating casings.
Results showed that the cost to remove casings was high; there is no proven method for removing casings and coordination of guided wave was difficult due to multiple holes remaining open. The guided wave results were confirmed after the casings were removed. During 2008-09, BG&E did nine casing removals, 17 ECDA digs and nine guided-wave tests followed with a wax filling of the casing.
FOR MORE INFORMATION:
PHMSA: http://primis.phmsa.dot.gov/gasimp/casedcrossing.htm
Mears Group: www.mears.net
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