Impact of time of exposure on HIC testing of very high strength steel in low H2S environments

J. Kittel (1) , François Grosjean (1) , C. Forot (1) , N. Desamais (2) , Carol Taravel-Condat (2) , C. Duret-Thual (3) , P. Fourny (3)

1 IFPEN - IFP Energies nouvelles
2 TechnipFMC
3 Institut de la Corrosion

The methodology for testing hydrogen induced cracking (HIC) resistance of carbon steel in mild sour service is discussed. When H 2 S content is low, the use of steel grades with intermediate HIC resistance often presents many advantages, such as higher mechanical properties and economical benefits. As a counterpart, fit-for-purpose testing procedures are required in order to assess the HIC performance at the intended service conditions. With regards low H 2 S environments, time of exposure is recognised as the critical testing parameter. The environment encountered in the annular space of flexible pipelines is very often mildly severe. Due to the high confinement, pH level is higher than in bulk conditions with the same gas composition but a larger V/S ratio between the volume of electrolyte and the exposed steel surface. H 2 S content in the annulus is also less than in the fluid transported in the bore of the pipeline, due to permeation through inner thermoplastic sheaths and consumption. Qualification tests of very high strength steel wires are therefore usually conducted with one month exposure at the predicted pH and P H2S in the annulus, while standard testing procedures referenced in ISO 15156 specify 96 h immersion but a higher H 2 S level. In the present study, different grades of high strength steel wires were tested in environments containing as low as 100 ppmv H 2 S, with exposure times varying from 96 hours and up to 1 year. For the steels grades that have been studied, it is confirmed that the actual qualification procedure consisting in 1 month exposure is appropriate to detect HIC susceptibility. 1 Introduction Development of deep and ultra-deep water fields often requires the use of high strength and very high strength steel wires (UTS≥1000MPa) in flexible pipes in order to sustain mechanical loads [1, 2]. On the other hand, these fields are most of the time considered as containing H 2 S at design stage due to the possible souring of the reservoir. Hopefully, in flexible pipe, steel wires are not in direct contact with the conveyed fluid. They are located in the annular space (see Figure 1) which is a specific medium for corrosion, less severe than the bore. These high strength steel wires need to be qualified with regards to H 2 S (Sulfide Stress Cracking and Hydrogen Induced Cracking) [2]. Nevertheless, testing procedures referenced in ISO15156 are not appropriate for these high strength wires that have a low H 2 S resistance. Therefore for SSC and HIC qualification, environment closer than the one encountered in flexible pipe annulus are tested:

Domaines: Matériaux

J. Kittel, François Grosjean, C. Forot, N. Desamais, Carol Taravel-Condat, et al.. Impact of time of exposure on HIC testing of very high strength steel in low H2S environments. Eurocorr 2013, Sep 2013, Estoril, Portugal. ⟨hal-02475439⟩