The remote field eddy current (RFEC) technique is widely applied for nondestructive testing of metallic pipes, but it always requires shutting down equipment to place the probe inside the pipe. In order to meet the demands of inservice inspection for pressure piping whose elbow regions are prone to corrosion, a novel RFEC probe placed outside the elbow is designed in this paper. Firstly, the probe structure and the pattern of its exciting field are simulated and designed by using finite element software. Then, the simulation model of RFEC testing for elbow defect detection is established, and the quantitative relationship of the inner diameter (ID) and outer diameter (OD) defect depth to the signal characteristics is analyzed. Finally, a test platform is set up and the detecting prefabricated defect experiments are conducted. The results show that: i) the probe signal phase decreases almost linearly with the increase of ID or OD defect depth, which can be used to quantify defect depth; ii) the phase of ID defect signal decreases more rapidly, and therefore, the defect depth can be quantified in the presence of only one type (ID or OD) defect by using the phase feature, but cannot be quantified when both two types of defect exist simultaneously.