This paper promotes a proprietary approach meant to increase the operation lifetime of the J55 tubing.
The project driver was the premature and repeated failures of the J55 tubing, under different environments and various operating conditions. Detailed failure analyses have been carried out revealing the following damage mechanisms: wear, corrosion or both, assisted at times by erosion.
The tubing failures, macro and micro investigated in the laboratory, together with the material tests, revealed that the technological and mechanical properties of steels are directly correlated to their microstructure. After studying several variations of steel microstructure, in relation with the features of the damaged tubing, the root cause of the failures was established and a corrective measure was taken, respectively the type of steel was modified from low carbon steel to medium carbon steel. The newly designed carbon steel was assessed as able to result in tubing failure rate decreasing.
The laboratory research findings were validated by field trials where, by using the J55 tubing manufactured according to the new steel design (chemical composition and heat treatment), the lifetime improved significantly.
The average Mean Time Between Failures (MTBF) corresponding to the field trials has increased by a factor of 4.5 for the most aggressive conditions. There are tubing strings still operating after 969 days.
