# Inspection of Coated Hydrogen Transportation Pipelines
###### Abstract  
The growing need for hydrogen indicates that there is likely to be a demand for transporting hydrogen. Hydrogen pipelines are an economical option, but the issue of hydrogen damage to pipeline steels needs to be studied and investigated. So far, limited research has been dedicated to determining how the choice of inspection method for pipeline integrity management changes depending on the presence of a coating. Thus, this review aims to evaluate the effectiveness of inspection methods specifically for detecting the defects formed uniquely in coated hydrogen pipelines. The discussion will begin with a background of hydrogen pipelines and the common defects seen in these pipelines. This will also include topics such as blended hydrogen-natural gas pipelines. After which, the focus will shift to pipeline integrity management methods and the effectiveness of current inspection methods in the context of standards such as ASME B31.12 and BS 7910. The discussion will conclude with a summary of newly available inspection methods and future research directions.  
hydrogen; hydrogen pipelines; inspection; NDT; NDE; pipeline transport +
Footnote †: journal: Medical Imaging  
1
Footnote 1: [[https://www.mdpi](https://www.mdpi)]([https://www.mdpi](https://www.mdpi)).  
consideration given that it costs 10 to 15% of the cost of a new hydrogen line to re-purpose a natural gas pipeline to a hydrogen line [5].  
While considering hydrogen transportation, it also becomes important to account for the deterioration of the pipeline. This tends to be seen in the form of Hydrogen Induced Cracking (HIC), Sulphide Stress Corrosion Cracking (SSCC) and Stress-oriented HIC (SOHIC) [8]. These forms of failure occur when atomic hydrogen finds its way into the interstitial spaces of the pipeline material and the Hydrogen Embrittlement (HE) that precedes such failures can be modelled either by the Hydrogen-Affected Localised Plasticity (HALP) model or the Hydrogen Enhanced Localised Plasticity (HELP) model [8].  
To mitigate against damage resulting from hydrogen degradation, there are a number of available strategies, one of which is coating the exterior and the interior of pipelines [8]. The strategy/strategies are deployed based on the extent of degradation and/or the risk level [8]. This, ostensibly, necessitates reliable methods to monitor the extent of damage during the service of the pipeline.  
Additionally, the fact remains that the failure of hydrogen pipelines has catastrophic consequences [9]. Ensuring the integrity of pipelines then becomes important, and non-destructive testing methods such as Magnetic Flux Linkage (MFL), Ultrasonic Testing (UT) and Eddy Current Testing (ET) offer an increasingly accurate method of detecting defects in pipelines, the majority of which are made from carbon steel, low alloy steel and, stainless steel [10; 11].  
So far, there has been very little research dedicated towards determining how the presence of coatings in hydrogen pipelines might affect the choice of inspection method for the purpose of pipeline integrity management. Therefore, this review aims to evaluate the effectiveness of inspection methods specifically for detecting the defects uniquely formed in coated hydrogen pipelines.  
The review begins with a background of hydrogen pipelines and the defects usually seen in such pipelines. This section will also explore related topics such as the suitability of various pipeline materials and the issue of blended hydrogen-natural gas pipelines. The following section details the steps of pipeline integrity management and the methods currently being employed for this, including inspection of pipelines. The next section evaluates the effectiveness of current inspection methods, alongside standards such as ASME B31.12 and BS 7910 and finally the last section details new inspection methods and future research directions.