API SC6 Casting Research Project Report on Initial Assessment of the Suitability of Castings in API 6A PSL3 Service 6 Feb 2013 SC 6 Meeting

Project Scope The objective is to propose revisions to API Spec 6A PSL requirements such that the integrity of cast equipment is equal to or similar to that of forged equipment. Propose revisions to Annex A, reflecting the changes in PSL requirements. 6 Feb 2013 SC 6 Meeting

Possible Departures from Work Proposal Current Spec 6A PSL requirements for castings are acceptable, so additional phases are not needed. Insufficient evidence exists to justify a change in requirements. A significant change to design criteria is needed or technology needed that is not readily available or used in industry. 6 Feb 2013 SC 6 Meeting

Outline of Work Phase 1 Research the requirements and the restrictions, if any, of castings used in applications similar to the oil and gas industry. Investigate best practices and current foundry industry technology. 6 Feb 2013 SC 6 Meeting

Casting vs. Forging Castings are isotropic. Mechanical properties are the same in all directions. Forgings are anisotropic. Mechanical properties are higher in the longitudinal direction, lower in the transverse direction . 6 Feb 2013 SC 6 Meeting

Casting vs. Forging Casting Forging Castings are best suited to complex shapes, custom or tailored chemistries and to applications that are subject to multi-axial stresses. Forgings are better suited to applications in which the principal applied stresses are the same as the direction of mechanical working. 6 Feb 2013 SC 6 Meeting

Casting vs. Forging Both are vulnerable to particular types of defects. Surface Discontinuities Sand Inclusions Porosity Hot Tears Shrinkage Inclusions Bursts Poor Grain Structure Laps (Folds) Seams Cold Shuts Cracks, Tears Inclusions 6 Feb 2013 SC 6 Meeting

Review of Available Data Foundry Technology 6 Feb 2013 SC 6 Meeting

Foundry Technology Graphitized alumina bottom pour nozzle to produce better casting surface quality. Ceramic foam filters to entrap and remove micro and macro inclusions Double ladle technique on large castings CAE systems that allow direct transfer of part drawing to casting drawing. Simulation software for thermal flow analysis. 6 Feb 2013 SC 6 Meeting

Foundry Technology 3D modeling for fluid velocity, pressure and fill time for the design of riser and gating system. Multi-dimensional transfer-function method for the analysis of computed Tomography (CT) data in assessing the quality of castings. Predicting the mechanical and fatigue behavior of cast steel utilizing measured porosity distribution in test specimens that is transferred to an elasto-plastic finite-element stress analysis model. 6 Feb 2013 SC 6 Meeting

Foundry Technology The use of improved foundry technology results in a much better casting, but would be difficult to make a requirement in a specification. Footer Text 12/8/2018

Review of Available Data Casting/Forging Research Data 6 Feb 2013 SC 6 Meeting

Notable Industry Data The superior weldability of steel castings was demonstrated in research performed by the University of Tennessee. Every cast grade was superior to its wrought "equivalent.“ The needle-like inclusions in wrought steels appear to be more likely sites for crack initiation than the round inclusions in casting steels. In terms of temperature, corrosion resistance and wear resistance, "equivalent" castings and forgings generally perform equally well 6 Feb 2013 SC 6 Meeting

Notable Industry Data Both the pitting and intergranular corrosion resistance of cast duplex stainless steel are equal to or better than their wrought counterparts. Charpy impact test results show that duplex stainless steel castings can have equivalent toughness to their wrought counterparts in the temperature range of –80°C to +20°C. 6 Feb 2013 SC 6 Meeting

A review of the available literature reveals that both castings and forgings are capable of meeting API 6A PSL 3 service requirements. Technical data was not found that supports limiting the service conditions of PSL-3 castings. Summary 6 Feb 2013 SC 6 Meeting

Consideration Consider including, as a normative reference in API Spec 6A, API Specification 20A, Carbon Steel, Alloy Steel, Stainless Steel, and Nickel Base Alloy Castings for Use in the Petroleum Natural Gas Industry Defines requirements for casting levels, CSL-1 – CSL-4 Requires qualification of a casting class and rules for production based on qualification. Structured similar to Spec 6A; a higher CSL has an increased level of technical, quality and qualification requirements. The highest specification level, CSL-4 does not permit weld repair. 6 Feb 2013 SC 6 Meeting

Documents Used in this Review Paper presented at 10th Heavy Structures Biennial Symposium 10/27/2004 “A Comparison of Steel Castings vs. Forgings for Large Structural Components” Steel Founders’ Society of America “Castings or Forgings? A Realistic Evaluation” Valve Magazine “Castings” Fall 2008 Issue 6 Feb 2013 SC 6 Meeting

References College of Engineering, University of Illinois “Review of the Mechanical Properties of Cast Steels with Emphasis on Fatigue Behavior and the Influence of Micro-Discontinuities” M. R. Mitchell University of Toledo “Fatigue Performance Evaluation of Forged Versus Competing Processes: A Comparative Study” Fitness for Adverse Environments pp. 325-31, “Optimization of the Weldability and Serviceability of 1 1/4Cr-1/2Mo for Petrochemical Applications 6 Feb 2013 SC 6 Meeting

References Proceedings of the International Congress on Advances in Welding Science & Technology for Construction Energy & Transportation Systems (AWST 2011), October 2011 “A Study of the Relationship Between Microstructure and Hardness/Toughness of Welded 2.25 Cr-1 Mo Steel 6 Feb 2013 SC 6 Meeting