NACE - SP0110
Wet Gas Internal Corrosion Direct Assessment Methodology for Pipelines
|Publication Date:||22 October 2010|
This standard covers the NACE internal corrosion direct assessment (ICDA) process for wet natural gas pipeline systems (i.e., WG-ICDA). It is intended to serve as a guide for applying the WG-ICDA process to onshore and offshore natural gas pipeline systems that:
(a) contain wet gas (gas-liquid ratio [GLR] > 5,000);
(b) are not covered by dry gas internal corrosion direct assessment (DG-ICDA); and
(c) meet the feasibility requirements described in Paragraph 3.3 of this standard.
The two primary purposes of the WG-ICDA methodology are (1) to enhance the assessment of internal corrosion in natural gas pipelines, and (2) to improve pipeline integrity.
The WG-ICDA methodology assesses where along a pipeline segment the internal corrosion severity is potentially highest. The methodology includes existing methods of detailed examination available to a pipeline operator to determine occurrence, as well as the extent and severity, of internal corrosion.
WG-ICDA also uses flow modeling results (e.g., dew point, flow velocities, liquid holdup, and flow patterns) and provides a framework to use those models.
WG-ICDA was developed for onshore and offshore natural gas pipelines that have produced or condensed water as a normal impurity. WG-ICDA is applicable to wet gas gathering and gas producing pipelines.3,4 The basis of WG-ICDA is for wet gas pipelines and consists of a detailed examination of selected assessment sites with the highest expected corrosion severity where there may be a reduction of the pipe wall thickness to an extent that would pose a threat to the pipeline if mitigation or other measures are not taken before the next assessment. This allows inferences to be made about the remainder of the pipeline segment.
One benefit of the WG-ICDA approach is that, for gas pipelines, an assessment can be performed on a pipeline segment for which alternative methods (e.g., ILI, hydrostatic testing) may be impractical.
WG-ICDA has limitations, and not all pipelines can be successfully assessed with WG-ICDA. These limitations are identified in the preassessment step.
Drips, compressing stations, vessels, and other equipment unrelated to pipelines are not included in this standard.
The provisions of this standard shall be applied by or 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 or related practical experience,
are qualified to engage in the practice of corrosion control and
risk assessment for pipeline systems. Such persons may be(1)
registered professional engineers, (2) recognized as corrosion
specialists by organizations such as NACE International, or (3)
professionals (i.e., engineers or technologists) with professional
experience, including detection/mitigation
For accurate and correct application of this standard, the standard shall be used in its entirety. Using or referring to only specific paragraphs or sections may lead to misinterpretation or misapplication.
In the process of applying WG-ICDA, other pipeline integrity threats such as external corrosion, mechanical damage, and stress corrosion cracking (SCC) may also be detected. When such threats are detected, additional detailed examination or inspections must be performed to ensure that pipeline integrity is not compromised, regardless of mechanism.
This standard does not address specific remedial actions to be taken when corrosion is found. However, guidance is provided in ASME(1) B31.85 and other relevant, jurisdictionally applicable documents. The pipeline operator should use appropriate methods to address threats other than internal corrosion, such as those described in ASME B31.8, ASME B31.8S,6 API(2) 1160,7 API 579,8 CSA(3) Z662,9 BS(4) 7910,10 ASME B31G,11 RSTRENG,12 NACE standards, international standards, and other documents.
(1) ASME International (ASME), Three Park Ave., New York, NY, 10016-5990.
(2) American Petroleum Institute (API), 1220 L St. NW, Washington, DC 2000-4070.
(3) CSA International (CSA), 178 Rexdale Blvd., Toronto, Ontario M9W 1R3, Canada.
(4) British Standard (BS), BSI Group (BSI), 389 Chiswick High Road, London W4 4AL, U.K.