Background: Piping is an important part in nuclear power plants.Purpose: In order to make piping meet the specification requirements

it is necessary to analyze and evaluate piping stress.Methods: This paper deals with the stress analysis and evaluation of the class 1 and class 2 piping of improved second-generation nuclear power plants

and discusses the calculation methods of piping stress due to various loads.Also

the effects of changing the RCC-M code edition on the calculation of piping stress are summarized.Results: Taking the LingAo Nuclear Power Plant Phase II engineering safety injection system as an example

the piping stress analysis and evaluation are performed

and the results meet the RCC-M code requirements.Besides

the interface parameters including the support loads

nozzle loads

displacements of the piping and so on are obtained.Conclusions: This paper will provide technical support for stress analysis and evaluation of improved second-generation nuclear power plant piping systems.