Is there any standard (ISO or ASTM) that can be reference for a polypropylene spiral flow test?
Yes, there is a standard for this within ASTM D-4101. If you are looking to publish the results, then this can be very helpful. Unfortunately, the conditions, flow rates, and pressures used may not directly replicate your processing conditions. In practice, most of the companies I have dealt with create their own procedure based on the conditions of their process.
For example, if they are looking to compare the viscosity of two grades of material. they might replicate the melt temperatures and flow rates of the actual product, and measure the difference in pressure at transfer to represent viscosity.
Another company I have worked with uses many older, pressure-controlled, molding machines. This company uses a constant pressure with position transfer. The change in injection time and flow distance provides excellent information for comparing one material grade to another.
Basically, I recommend you review the standard procedures for the spiral flow test, but adjust the test parameters to meet the specific needs of your production facility. The key factor is to perform a test which provides information which helps the production department.