External Corrosion Direct Assessment Research Articles

Challenges in the application of DCVG‐survey to predict coating defect size on pipelines

Corrosion is often the cause of pipeline failure potentially resulting in disasters causing damage and fatalities. To maintain the integrity of non‐piggable lines, NACE's external corrosion direct assessment (ECDA) methodology is commonly applied to assess external corrosion that can occur at coating defects on underground pipelines. Work presented here is from a validation exercise carried out on the results of ECDA assessment using subsequent excavation data. The ECDA was carried out over 300 km of crude oil pipelines with excavation carried out at 200 locations. This paper models the relationships between pipeline coating defect area (area with coating breakdown), corrosion depth, direct current–voltage gradient (DCVG) measurements (in terms of %IR values) and factors capturing diverse environmental conditions through novel application of regression models. This paper sheds light on the challenges in drawing conclusions in the assessment of corrosion from DCVG inspection data and other types of data that form key inputs to ECDA. We expect that the analyses shown here using innovative regression models will support more reliable predictions of external corrosion in pipelines.

외면부식직접평가 장비 개발 및 실증 시험에 관한 연구

매설된 강관의 피복이 손상되는 경우에는 부식이 발생할 수 있고, 부식으로 인한 핀홀이 발생하여 가스누출사고가 발생할 수도 있다. 미국과 영국 등 국외에서는 이를 방지하기 위하여 DCVG 또는 ACVG 등을 이용하여 매설된 배관의 피복손상을 탐측하고 이상부위에 대하여 직접 굴착을 통해 배관외면부식여부 등을 확인하고 필요시에는 보수를 하고 있다. 이를 외면부식 직접평가법(ECDA)이라 하며, NACE 기준 등에서 ECDA에 대한 기준을 규정하고 있다. 국내의 경우에는 2014년 중압배관의 정밀안전진단 제도를 도입하면서 KGS 코드에 외면 부식직접평가에 대한 내용을 포함하여 규정하고 있다. 본 연구에서는 매설배관의 외면부식을 탐측할 수 있는 장비를 개발하고, 개발된 장비의 실증시험을 위한 배관시험장을 구축하였다. 또한, 개발된 장비의 성능을 입증하기 위하여 배관 시험장에서 현장 실증시험을 실시하였다. 현장 실증 시험은 개발된 장비와 국내에 도입되어 사용중인 국외 장비와의 피복결함 탐측 성능 비교시험으로 실시하였다. 개발한 장비를 이용하여 매설배관 탐측 시험을 실시한 결과, 개발한 장비는 미국이나 영국에서 개발되어 국내에 보급되어 사용중인 장비에 비해 훨씬 사용이 편리하고 성능이 우수함을 확인할 수 있었다. When the coatings of buried steel pipelines are damaged, corrosion could be occurred on the surface of the damaged areas. Moreover the pinhole occurred by corrosion of pipelines may cause accidents due to gas leakage. To prevent these accidents, foreign countries including UK and USA have carried out coating defect detection on the buried gas pipelines by using a DCVG or a ACVG and have conducted direct assessment of pipelines through digging the ground, and if necessary, have repaired the pipelines. That is called ECDA i.e External Corrosion Direct Assessment which is regulated by NACE standards(SP 0502) and etc. In Korea, the ECDA provisions were included in KGS FS551 in 2014 when the regulations of Safety Validation in Detail for the medium-pressure piping were introduced. We have developed the equipment which can be used to detect external corrosion of the buried gas pipelines. We have also constructed pipeline test bed for empirical test of the developed equipment. In addition, we have carried out the verification experiments of the developed equipment on the test bed to demonstrate the performance of the equipment. The experiments were conducted by comparison tests of the developed equipment and other equipments which have been introduced and used in Korea. As the result, we have found the developed equipment is easier to use and has far superior performance compared to other equipment being used in Korea.

외면부식 직접평가법 개발 및 국내 도입 연구

Abstract - To minimize the risk of corrosion on buried pipeline and to maximize the efficiency of cathodic protection, various indirect inspection techniques have been used for decades. In the United States, 49 CFR has regulated the external corrosion direct assessment for buried pipelines. In Korea, there is no provision for external corrosion direct assessment but there is only, according to the KGS Code, provision that if the survey of the defects of buried pipeline and the leakage test for the pipe were conducted, it is deemed to leakage inspection. We, therefore, have suggested external corrosion direct assessment method appropriate to domestic status through the survey of the regulations and standards of UK and the USA and the investigation of domestic situation on coating damage detection method. The proposed external corrosion direct evaluation method was used as the basis when introducing the precision safety diagnosis regulation for the medium-pressure pipe in Korea.Key words : external corrosion direct assessment, buried gas pipelines, coating defects

New Technique for Studying Soil-Corrosion of Underground Pipeline

Pipeline integrity management programs address a wide range of threats to safe operations. Among these threats, external corrosion has been among the most dominant failure mechanism experienced by buried steel pipelines. External corrosion can be detected through a variety of assessment methods, including inline inspection (ILI) and External Corrosion Direct Assessment (ECDA). In the absence of data from inspection, the corrosion rate can be estimated based on the use of buried corrosion coupons, corrosion probes and corrosion rate modelling using data derived from soil analysis. The objective of the study was to design a methodology of the external growth modelling of corrosion on buried gas pipelines under various exposures to soil conditions. The technique can be used to generate field data so as to model empirically the corrosion dynamic in soil or for verification of corrosion data from laboratory testing. The potential model based on the proposed technique is highly potential to predict the likelihood of corrosion growth rate experienced by buried lines exposed to corrosive environment. Hence, can greatly assist operator to secure the integrity of their pipelines until the structure reaches its designed lifetime.