Spray forming of wear and corrosion resistant bimetallic pipes : from the alloy design to the semi- industrial process
Abstract
The oil exploitation and production at the pre-salt fields in a safety and efficient
way depends on the development of materials that withstand the severe work
conditions found in these fields. For instance, pipes, such as drilling risers and
casings, are often subjected to severe wear and corrosion conditions. This thesis
is dedicated to evaluate the technical feasibility to produce wear and corrosion
resistant bimetallic pipes by spray forming. The processing-microstructure-properties relationship of the spray-formed boron-modified supermartensitic
stainless steel (SMSS) grades was comprehensively studied. Deposits of SMSS
with boron contents ranging from 0.3 %wt. to 1.0 %wt. were processed by spray
forming. The spray-formed boron-modified SMSS deposits had the wear
resistance evaluated through different wear tests and their corrosion resistances
by means of electrochemical techniques. It was demonstrated that the wear
resistance of the spray-formed boron-modified SMSS is determined by the presence of the eutectic network of M 2B-type borides resulted from the spray
forming process. On the other hand, the corrosion resistance of the spray-formed
boron-modified SMSS is controlled by the chemical composition of the martensitic matrix. Furthermore, spray-formed bimetallic pipes composed of
boron-modified SMSS and conventional SMSS were produced in the unique
semi-industrial scale spray-forming plant of the Foundation Institute of Materials
Science (IWT-University of Bremen, Germany). The relationship between the
process parameters and the metallurgical quality of the pipes was addressed. It
was shown that the key to produce a spray-formed bimetallic pipe with good
metallurgical quality is adjusting the process parameters in such a way that the
deposition zone’s temperature is kept within the alloy’s solidification temperature
range during the whole deposition process. Moreover, solidification and grain size
evolution models in spray forming were proposed. Finally, the mechanical
properties of one of the spray-formed bimetallic pipes in the as-spray formed
condition and after heat treatments were evaluated.