Plasma arc cutting of steel plates can offer substantial advantages in terms of speed and economy when compared with oxy-fuel cutting. However, existing standards do not contain sufficient guidance for engineers, fabricators, and inspectors on plasma arc cutting or on the need for edge treatment. Therefore, there is a reluctance to use plasma arc cutting during fabrication of steel bridges.
Some of the concerns regarding the use of plasma arc cutting techniques and procedures are: (1) the effects of process variables such as speed, current and voltage, gases, pre- and postheat, and water quenching; (2) the effects of material variables such as steel grade and surface condition; (3) the characteristics of the free edge including hardness, toughness, fatigue resistance, edge profile, and paint adhesion; (4) the characteristics of edges affected by welding including porosity, and heat-affected zone (HAZ) and fusion boundary properties; and (5) the need for or extent of edge treatment.
Research is needed to assess the characteristics and performance of plasma arc cut edges and to develop specifications and guidelines that will eliminate barriers to the use of this process in steel bridge fabrication. The objective of this research is to develop a user's guide and recommendation specifications for plasma arc cutting of bridge steels. Recommendations shall be based on test results of representative grades of AASHTO M270 (ASTM A709) steels in the thickness range of 3/8" to 3/4". The user's guide and recommended specifications shall address the performance of both free edges and edges affected by welding.
The research will include at least the following tasks: (1) Review relevant current domestic and foreign practice, performance data, and research findings. This information shall be assembled from both technical literature and unpublished experiences of engineers, fabricators, and bridge owners, as well as plasma arc and flame cutting equipment manufacturers and suppliers. (2) Evaluate and summarize the information generated in Task 1 in order to determine current practice and the state of knowledge. Identify all conditions and parameters that may affect the performance of free edges and edges affected by welding. Identify and rank those areas where research is required to assess existing plasma arc cutting procedures and develop rational specifications. (3) Propose preliminary test procedures and criteria for evaluating the acceptability of plasma arc cut edges. Develop a detailed test plan based specifically on the available funding for this project. (4) From the Task 2 findings, develop a draft guide for designers, fabricators, and inspectors providing specific recommendations for the use of plasma arc cutting. The guide should provide appropriate precautions and limitations and also address repair of defects. (5) Prepare and submit an interim report summarizing the findings from Tasks 1 through 4. The interim report shall be submitted not later than 6 months after the start of the project. NCHRP approval of the interim report and the detailed test plan is required before commencing with Task 6. (6) Conduct laboratory tests` in accordance with the approved test plan from Task 5. (7) Analyze the results of the tests performed in Task 6 and summarize the findings. On the basis of these findings, develop recommended specifications and commentary for plasma arc cutting in a format suitable for adoption by AASHTO and AWS. Revise the draft user's guide to reflect the test findings. (8) Prepare and submit a final report documenting all research findings and provide recommendations for further research.
Status: The research has been completed. The report has been published as NCHRP Report 384, "Plasma Arc Cutting of Bridge Steels." the appendices are available at
https://onlinepubs.trb.org/onlinepubs/nchrp/docs/NCHRP10-40_NR384_AppxB-G.pdf
