51313-02534-Risk Ranking NDT Priorities & Damage Mitigation of TIP Unit Piping in High Temp. Hydrogen Service

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Product Number: 51313-02534-SG

ISBN: 02534 2013 CP

Author: Marco De Marco

Publication Date: 2013

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This work is inspired by a series of failures occurred in Total Isomerization Plants (TIP) in different Italian Refineries on piping systems made of carbon steel attributed to High Temperature Hydrogen Attack/Hydrogen Stress Cracking; in every cases the failure occurred in correspondence with not PWHT welded joints and on components operating below the carbon steel Nelson Curve of API 941.
Hence the need to develop a technical approach aimed to define NDT priorities types and extension for reliable detection and monitoring of damage.
Such a novel approach was developed by the definition of a risk level achieved by overlapping the classical API 941 Nelson curves approach for carbon steel with the Pv parametric approach reported in API 581 and first proposed by JPVRC. By the application of the above mentioned approach it is possible to establish a risk ranking for the different piping systems of TIP Unit potentially exposed to Hydrogen damage. Based on this ranking NDT priority&extension can be defined.

The presented approach has been applied in a specific TIP Unit; NDT prescribed have actually detected the presence of damage of hydrogen on different CS pipe component in in correspondence with not PWHT welded joints.
To better clarify the damage mechanism to verify the NDT reliability and to validate applied the approach presented a laboratory failure analysis on a specific damaged welded joint was carried out.
Finally some mitigation actions are proposed to lower the Hydrogen Damage probability of component in high temperature and H2 service in TIP Units together with the opportunity to update the API 941 Carbon Steel Nelson Curve especially for welded components without PWHT.