Evaluation of Technologies for Inspection of Riser Splash Zone
Authors: Pezzi Mario , Santos Rafael Wagner Florencio 
Published: June 2014

Corrosion at splash zones of risers and spool pieces of subsea pipelines, can be severe reading corrosion rates up to 1mm/year, due to the lack of effectiveness of cathodic protection and coating damages caused either by disbondment or object impact. So, it's highly recommended that this zone have a specific inspection plan combined with a special inspection program for preventing the occurrence of failure, as well as following up the evolution of any failure mechanism which eventually might be present. Traditionally inspection techniques applied at splash zone are: general visual inspection and local thickness measurement. However these techniques are not practical as they require marine growth and even coating removal.

After an event caused by corrosion at splash zone, a literature review was carried out to produce the state of the art of non intrusive technological solutions for inspecting the corroded areas of splash zones of risers and spools.

This paper describes the results of laboratory tests carried out with some of the identified technologies on full scale riser samples. Test results indicate that technologies such as guided waves and Saturated Low Frequency Eddy Current (SLOFEC can be complementary alternatives to the splash zone traditional inspection techniques, although the coating type and wall thickness have significant influence on these technologies' sensitivity and probability of detection. These technologies have the capability of inspecting/monitoring large areas of splash zones of risers and spools without marine growth and coating removal. This is an advantage when compared to the traditional inspection techniques.

1. INTRODUCTION

Statistical data collected in the last 30 years indicate corrosion as the main failure cause in risers [1]. At splash zone on risers and spool pieces, where cathodic protection is not effective, the higher probability of coating damage due to object impact or coating disbondment turns this zone highly susceptible to corrosion [1,2]. Studies published by U.S. Department of the Interior, Minerals Management Service (MMS) indicate that 92% of corrosion failures occurred in risers in the Gulf of México was caused by external corrosion [1].

In 2000, Chevron communicated a high pressure riser failure in one of their platforms in West Coast of Africa due to severe corrosion at splash zone caused by coating damage. Further studies on all 1027 production risers in that region revealed serious problems in the Integrity Management Program of risers practiced at that time [2].

At Petrobras, a working group was established after events that led to repair/replacement of spools pieces damaged by corrosion at splash zone. This group aimed at searching risers and spools pieces inspection techniques available in the industry, which would be adequate for application in the field. It was identified some technologies, that should be technically evaluated finding their limitations and actual capabilities for further application at Petrobras.

This paper describes the laboratory tests results obtained by applying some of these identified technologies on full scale pipe samples.