Flexible pipes have been widely used in offshore applications for transportation of oil and gas. These structures are constructed with various layers of steel wires for structural reinforcement and several polymers layers to contain the internal bore fluid and protect the metallic components from the seawater. The carcass main function is to prevent collapse. Once the carcass can be exposed to external pressure on the inner liner and the inner liner itself is not capable of carrying any particular external pressure and will therefore collapse if it is not supported on the inside. Thus the carcass is installed to provide the inner liner with this support. Another way the inner liner is subject to external pressure is if the outer sheath is damage and sea water enters the annulus. If the pipe is unpressurised the inner liner is subject to an external pressure equal to the water pressure e.g. on pre-salt field condition in Brazil this can mean 300bars at 3000m. The carcass is made of stainless steel or duplex steel; the material is selected in order to achieve the corrosion resistance according to the pipe fluid. Since fluid is allowed to leak through the carcass it is only subject to external compressive forces. Thus to test these components at field conditions it is necessary to consider the fluid composition pH pressure and the resistance to compressive tensions at that specific environment. Once at most of pre-salt fields in Brazil the conditions are sour or can eventually became sour due to H2S presence Sulfide Stress Cracking (SSC) may occur. Therefore Petrobras is changing their internal standard to flexible pipes (Petrobras standard NI-2409) and including the SSC tests on carcass. On this context the NACE Standard TM 0177 method C: C-RING test rises as a good alternative to evaluate these components. However the method as it is described on standard cannot be straight used to the carcass geometry. To load this kind of sample according to the procedure described on standard NACE 0177 would introduce oblique tensions as it was observed by our finite elements simulation. On samples that do not fit the proportion between diameter/thickness and width/ thickness described on NACE 0177 or present a non-conventional geometry the deflection equations presented on that standard should not be used. Thus our method to load non-conventional C-ring type samples can be resumed as:
1. To find tensions main directions by 3D modeling and finite elements simulation 
2. To monitor tensions  by strain gages: rosette
3. To develop a software for data acquisition and compilation
We are going to present and compare the applied load and the corrosion results from carcass samples loaded according to the current NACE TM 0177 procedure and according to our method. From the preliminary results obtained on C-ring test carried on  flexible pipes carcass samples according to the method described herein it was possible to reach reproducible and reliable results to non-conventional samples such as flexible lines used on oil & gas fields. Therefore it can be applied to qualify materials reproducing field conditions or the conditions specified on current standards.

References

1-NACE Standard TM 0177-2005: Laboratory Testing of Metals for Resistance to Sulfide Stress Cracking and Stress Corrosion Cracking in H2S Environments

2-Banke L Flexible Pipe End Fitting - PhD Thesis – Department of Naval and Offshore Engineering Technical University of Denmark January 2000.
3-API SPECIFICATION 17J / ISO 13628- Specification for Unbonded Flexible Pipe Third Edition 2008.
4-Petrobras Standard NI 2409 – Flexible pipe 2003.