Session: MF-02-05 Materials for Hydrogen Service (Joint with CS-02 and HT-07) - Specimen Size and Rate Effects

Paper Number: 105227

105227 - Challenges in Kih Testing Using Wol Samples for Pipeline Applications 

Natural Gas transportation systems have relied on carbon or low alloy steel line pipes for almost 100 years. The gas transportation through pipelines has proven to be very efficient in terms of costs and safety. Additionally, hydrogen has been identified as a valid energy carrier and storage gas and is becoming more and more important within the energy transition. Similar to NG, also for H2, the transportation through pipeline for medium-long distances is the most viable solution for an appropriate cost -efficiency balance.

When in contact with steel, hydrogen can have detrimental effect on the mechanical performance and this effect needs to be taken into account for the proper design of line pipes for H2 transportation systems. Option B of ASME Code B31.12 requires the evaluation of the threshold stress intensity factor KIH as specified in article KD-1040 of ASME BPVC Sec VIII Div 3. That, finally, remits to ASTM E1681 for the fracture toughness evaluation.

ASTM E1681 presents the possibility of testing in the aggressive environment (H2 in this case) under constant loading or under constant displacement conditions. Given the comparative simplicity of testing self-loaded specimens in constant displacement, this type of test has become a “standard” for the industry. However, filling the different validity checks required by the testing standard presents several challenges that seems to be very difficult to solve.

One of this is the level of Crack Mouth Opening Displacement (CMOD) necessary to reach the required stress intensity factor for material evaluation. If the specimen is not large enough, a large CMOD can cause the loss of linear elastic response of the load-displacement curve. Therefore, the equation to determine KI provided by the standard could not be longer valid. These and other reasons make the testing of Wedge Opened Loaded (WOL) specimens for fracture toughness evaluation of gas transportation pipes questionable.

The present paper explores the limits in terms of dimensional requirements and stress intensity factor solutions using finite element simulations and experimental validation. The numerical analyses comprises WOL specimens considering a range of crack length to specimen width ratios and different mechanical properties. The simulations provide CMOD-Load and CMOD-applied K curves that are compared against the linear elastic fracture mechanics equations and against some experimental measurements. Additionally, WOL tests in an X65 seamless pipe under 400 bar of pure hydrogen are presented and critically discussed.

Presenting Author: Sebastian Cravero Tenaris

Presenting Author Biography: Ph.D. in Naval and Oceanic Engineering at the University of Sao Paulo – Brazil.

Current position: Principal Researcher at the Materials Department of Tenaris R&D center in Argentina.

Twenty years of professional activity in the following fields: Fatigue and fracture mechanics evaluation of materials and structures, failure analysis, structural integrity assessment in aggressive environments, solid mechanics among others.

Several published papers in referred journals and conferences.

Authors:

Sebastian Cravero Tenaris
Mihaela E. Cristea Tenaris
Marije L. Deul TNO
Carey L. Walters TNO
Martín E. Valdez Tenaris
Philippe Darcis Tenaris