Aboveground Survey Techniques for the Evaluation of Underground Pipeline Coating Condition
|Publication Date:||21 March 2009|
Aboveground Survey Techniques
This standard presents acknowledged procedures for the application of aboveground techniques to evaluate the coating condition of underground metallic pipelines.
This standard does not designate practices for specific situations; the complexity of some underground pipeline and environmental conditions preclude standardizing the application of some of the coating evaluation techniques. Deviation from this standard may be warranted in specific situations, provided those responsible can demonstrate that the objectives expressed in this standard have been achieved.
This standard does not include procedures for close-interval pipe-to-soil potential surveys (CIS). CIS procedures are covered in NACE SP0207.3
Alternating current (AC) attenuation surveys are used to provide an assessment of the overall quality of the pipe coating section by section; however, this technique is not typically effective in identifying individual holidays.
Direct current (DC) and AC-voltage gradient surveys are used to evaluate in detail the coating condition on buried pipelines and identify and classify coating holidays.
The Pearson survey, named after J.M. Pearson (the individual who developed the technique), is used to locate coating holidays.
The pipeline operator must determine which survey techniques are suitable for providing required coating condition assessment information for each pipeline or pipeline section.
None of the aboveground coating evaluation techniques included in this standard are capable of detecting pipeline steel that is electrically shielded from the bulk electrolyte by disbonded coatings with no electrically continuous path to the electrolyte.
The indirect inspection tools covered in this standard are less sensitive when pipe burials exceed normal depth ranges. Field conditions and terrain may affect depth and detection sensitivity.
The following information should be gathered and analyzed to establish applicability of the aboveground coating condition survey techniques for any given pipeline or pipeline section. The items in the list are not intended to address all possible variables that may affect applicability of a technique to a specific pipe section:
Pipeline diameter and pipe-wall thickness, fluid transmitted, temperature, direction of flow, and operating pressure;
Pipeline coating type, age, and whether pipeline/sections are under concrete;
Route maps and cathodic protection records, when available;
Whether or not in-line inspection (ILI) correlation point locations are used together with global positioning system (GPS) information to compare known aboveground and underground survey data;
Pipeline depth-of-cover and soil type;
Whether or not the pipeline section is under frozen ground;
Right-of-way (ROW) condition, including ground cover above the pipeline such as pavement, concrete, wetlands, bodies of water, and rocky terrain;
Location, separation distance, and electrical isolation condition of metallic structures adjacent to the pipeline;
Location, separation distance, and electrical isolation condition of underground parallel pipelines in the pipeline ROW;
Location and electrical isolation condition of casings;
Location, type, and status of CP systems influencing the pipeline section;
Location of foreign CP systems influencing the pipeline section;
Location and status of CP test points;
Location and status of electrical isolation from aboveground features, such as valves and piping in compressor or pump stations, and electrical grounding;
Location of overhead high-voltage AC transmission lines parallel to or crossing the pipeline ROW;
Location of buried power cables parallel to or crossing the pipeline ROW; and
Location and influence, if known, of DC traction systems, industrial facilities utilizing DC induction or welding equipment, or overhead DC power lines parallel to or crossing the pipeline ROW.
The provisions of this standard should be applied under the direction of competent persons who, by reason of knowledge of the physical sciences and the principles of engineering and mathematics acquired by education and related practical experience, are qualified to engage in the practice of corrosion control on buried or submerged metallic piping systems. Such persons may be registered professional engineers or persons recognized by NACE as corrosion specialists, CP specialists, corrosion or CP technologists, or the equivalent if their professional activities include suitable experience in the application of the aboveground coating evaluation techniques included in this standard.
Persons performing aboveground surveys included in this standard for the evaluation of underground pipeline coatings (who, for the purpose of this standard, are called surveyors) must be qualified to understand and follow the applicable procedures contained in this standard or work under the direct supervision of a person who is qualified. Such persons may be recognized by NACE as CP testers, corrosion or CP technicians, technologists, specialists, or the equivalent if their professional activities include suitable experience in performing aboveground surveys for the evaluation of underground pipeline coatings included in this standard.
Appropriate safety and regulatory precautions, including the following, shall be observed when electrical measurements are made:
Only qualified persons shall install, adjust, repair, remove, or test impressed-current CP equipment;
Only qualified persons shall install, adjust, repair, remove, or test the equipment detailed in this standard;
Appropriate personal protection equipment (PPE) shall be used where applicable;
Properly insulated test lead clips and terminals should be used to avoid contact with unanticipated high voltage. Insulated test lead clips and terminals must be rated for the highest anticipated voltage that is to be encountered during the survey. Test clips should be attached one at a time using a single hand technique for each connection;
Caution should be used when long test leads are extended near overhead high-voltage power lines that can induce hazardous voltages onto the test leads. Users should refer to NACE SP01774 for additional information;
Caution should be used when tests are conducted at electrical isolation devices. Appropriate voltage detection instruments or voltmeters with insulated test leads should be used to determine whether hazardous voltages exist before proceeding with further tests;
Testing should be avoided when adverse weather conditions are present, such as thunderstorms. Remote lightning strikes can create hazardous voltage surges that travel along the pipe under test; and
Caution should be used when work is performed near streets, roads and other locations subject to vehicular and pedestrian traffic. Appropriate measures such as barricades, high visibility clothing, flagging, and traffic control devices should be used when conditions warrant or as required by safety and regulatory agencies responsible for governing traffic control.
Project-specific safety considerations should include, but are not limited to, the following factors:
Wildlife indigenous to the area, to include identification, avoidance procedures, and emergency procedures;
Hazardous plants, insects, or reptiles indigenous to the area, including identification, avoidance, and emergency procedures;
Hunting/trapping seasons, including limited visibility areas and the use of high-visibility clothing;
Considerations for surveys over bodies of water and the use of specialized equipment;
Environmental extremes, including heat and cold;
Communications with survey crews and emergency personnel; and
Appropriate company safety procedures, electrical codes, and applicable safety regulations.
Survey equipment shall be calibrated according to manufacturer's recommendations and procedures.