This paper presents the results of corrosion and mechanical testing ofwelded high-nickel, corrosion-resistant-alloy (CRA) lined pipes manufacturedusing various lining processes. The corrosion pipes manufactured using variouslining processes. The corrosion resistance of CRA-lined pipes for use as aflowline material in sour service was evaluated. The effects of themanufacturing process, CRA lining material, and welding on the corrosionprocess, CRA lining material, and welding on the corrosion performance ofCRA-lined pipes also were determined. performance of CRA-lined pipes also weredetermined. Introduction
Many recently discovered and developed oil and gas fields are deep and sour.In these severe sour environments, the use of steel pipes with inhibition isineffective or infeasible in combating pipes with inhibition is ineffective orinfeasible in combating corrosion and cracking. Therefore, CRA's have been usedmore frequently. The high initial cost of nickel-based CRA materials oftenmakes it difficult to provide the economic justification for use of solid-CRApipes. Therefore, several manufacturers are producing a steel pipe with only aCRA lining as a cost-effective producing a steel pipe with only a CRA lining asa cost-effective alternative to solid pipes. The double-wall, bimetallicCRA-lined pipe has an inner layer made of a very resistant CRA and an outerlayer made of low-cost steel. Some CRA-lined pipes have metallurgical bondingbetween the lining. and the steel, while some have only a mechanical bondbetween the CRA layer and the steel layer. The metallurgically bonded pipes(called clad pipes) usually are manufactured by such processes as coextrusion,hot-rolled bonding, explosive bonding, processes as coextrusion, hot-rolledbonding, explosive bonding, or centrifugal casting. The mechanically bondedpipes are manufactured by thermohydraulic gripping of CRA and steel pipes. Themanufacturing processes of CRA-lined pipes differ from solid-CRA pipeprocesses. Flowlines transport production fluids from the wellhead to treatingand processing facilities. They typically are constructed by girth welding pipesegments end-to-end. In sour fields, the fluids transported through flowlinesmay contain highly corrosive gases, like H2S and CO2, and highly corrosivebrines. The objective of this study was to evaluate the corrosion resistanceand suitability of CRA-lined pipe for use as a flowline in sour service. Theprimary questions included (1) whether CRA-lined pipe performs in sour serviceas well as solid-CRA pipe, (2) whether a performs in sour service as well assolid-CRA pipe, (2) whether a difference in performance exists betweenmanufacturing processes, (3) whether the CRA lining materials performdifferently from each other, and (4) whether a weldment performs in sourservice as well as the parent pipe. Three UNS N06625-lined and three UNSN08825-lined Grade X60/X65 pipes were tested in this study. These pipes weremanufactured by coextrusion of the CRA and steel pipe, coextrusion of CRApowder metallurgy cladding and steel pipe substrate, and thermohydraulicgripping of the CRA and steel pipe. Table 1 summarizes the manufacturingprocedure for each of the pipes investigated. A solid pipe of UNS N06985 alsowas included in the test program so that the corrosion performance of CRA-linedand solid-CRA pipe could be compared. Table 2 lists the standard chemicalcompositions of UNS N06625, UNS N08825, and UNS N06985.
Standard tensile, Charpy impact, shear-strength, flattening, andhardness/microhardness tests were performed to characterize the pipes. Becausemany tests were needed to evaluate the mechanical pipes. Because many testswere needed to evaluate the mechanical and corrosion performance of the pipes,the quantity of some welded samples acquired for this study was not sufficientfor all tests. Priority was given to making specimens for corrosion testing.Priority was given to making specimens for corrosion testing. Also, because themechanically bonded pipes lacked metallurgical bonding between the lining andthe steel, shear strength could not be measured. Therefore, not all tests wereconducted for each pipe. Table 3 summarizes the mechanical properties of thetested pipe samples.
Tensile Strength. Yield and tensile strengths of the steel layer weremeasured after cladding removal. The strengths of the liners also were measuredafter machining away the steel outer shell. Strengths were measured for bothparent and welded pipes. The yield strength measured from the CRA liners wasused to determine the deflections needed to stress the bent beams to 90% yieldfor stress-corrosion-cracking (SCC) testing.
Notch Toughness. Charpy V-notch impact toughness of parent pipe and weldmentwas measured. The Charpy impact toughness reported in Table 3 is the average ofthree 10 x 10-mm Charpy impact specimens tested at - 20 degrees F. The Charpyimpact specimens were extracted from the steel layer and oriented in thelongitudinal direction. The Charpy V notches were placed in three differentlocations: the center of the weld, the heat-affected zone, and the basemetal.
Bond Shear Strength. The shear strength of the metallurgical bond betweenCRA and steel was evaluated in accordance with the shear test of ASTM Std.A-265. This test was performed only at the parent pipe cladding. parent pipecladding. Flattening Test. This test was used to evaluate bond ductility inaccordance with ASTM Std. A-530.
Hardness/Microhardness. Rockwell hardness [using B scale up to 100 RockwellB Hardness (HRB) and C scale from 20 Rockwell C Hardness (HRC)] and Vickersmicrohardness (HVN) were measured in the CRA liners in both the parent pipe andthe weldment.