OCAS proposes a method for early detection of weldability issues based on metallurgical investigation of the pipe material behaviour, simulations and stress corrosion cracking tests. Thus avoiding problems during the welding procedure qualification.
Material delivery generally requires quite some lead time, whereas offshore project requirements and deadlines are tight and often need short reaction times. So, it is tempting to order the offshore pipe material before the welding qualification contract has been awarded and the welding procedure has been defined. However, this can lead to bad surprises and delays once the welding procedure qualification is started. To avoid “surprises” during WPQ, a methodology has been proposed to screen the material. A testing program was defined and started to investigate the phase transformation of three materials in welding conditions, select conditions representative of girth welds and perform welding simulations plus SSCC tests. OCAS found that the results from the defined methodology reproduce the industrial experience. The outcome demonstrates that it is possible to detect issues with weldability early in a project (before the welding contract is awarded) by using a physical welding simulation tool. Potential issues were lateron confirmed in SSCC tests.
Related literature
The scientific paper “Pipe material weldability for sour service conditions”, was presented by Ph. Thibaux during the ISOPE 2016, the 26th conference of the International Society of Offshore and Polar Engineers, Rhodes, Greece, Jun 26 -> Jul 1 2016,. This work was done by OCAS in close collaboration with DEV/TEC/PLR Total France.
Abstract
Pipes are long lead items with respect to procurement on pipeline projects. They are manufactured in the early phases of an offshore project execution at a time where the welding contractor may not be selected yet. If problems are observed with the weldability of the delivered material, the planning of the project can become difficult. In the present research, a method for early detection of weldability issues is proposed, based on a metallurgical investigation of the behavior of the material during welding, simulation of the welding process for the most critical zones and finally stress corrosion cracking tests. Three materials were investigated, one of them having exhibited difficulties during welding. The same problems could be reproduced with the proposed method. They are linked to the chemical composition of the material, where a delay of the austenite/ferrite phase transformation is related to an increase of the process window where harder components are formed. Hardness above 250HV was observed in the critical process window.
“The physical welding simulation tool brings our customers a strong asset to detect potential weldability issues in an early stage.”
