TENSILE STRENGTH OF A GIRTH WELD WITH A LOW-STRENGTH AWSR45 BUTTERING LAYER

摘要

A four-metal connection, in which a carbon steel pipe is welded to duplex stainless steel pipe, is analyzed. The four metals are shown in Table 1. A106B and 2205 Duplex are the two different pipe materials, 2209 is the weld filler material, and AWSR45 is the buttering layer that is used to control the cracking susceptibility of the welded girth joint. (Butter and buttering refer to the welding of a layer of low strength material, AWSR45 in this case, and are commonly used terms within the welding community). Due to the lower strength of the AWSR45 material, the question arises whether this joint performance would affect pressure containment capacity and meet the B31.3 code (and API 1104) tensile strength requirements. Nonlinear FEA was used to determine the girth weld joint pressure containment capacity and evaluate tensile strength requirements. This study found that: 1) The butter layer has no effect on burst capacity for typical weld dimensions. 2) The acceptable butter layer may approach approximately 70% of the wall thickness for approximated real material properties. However, a full pipe cross-section test will be required to show that the weld joint has the necessary strength. 3) If this is impractical, a lower butter limit of 25% of wall thickness would be necessary for the API-1104 recommended 1-inch wide tensile specimen to show that the weld joint has the necessary strength assuming approximated real material properties. 4) Strains exceeding 50% in the soft AWRS45 layer are possible in the root, face or side bend test. This may cause tearing making the code requirements difficult to meet. 5) The AWRS45 material must exhibit a smooth continuously increasing hardening behavior. If the soft AWRS45 layer exhibits lueder-band type tensile instabilities, the recommendations in this study may need to be revisited. In this study analyses is limited to the single-slope bevel and the double-slope bevel geometries recommended in [2] (See Figure 1). Any significant deviation from the specific materials and geometry may justify follow-up FEA analyses efforts prior to weld qualification. In particular, it may be possible to increase the allowable butter length for different weld geometries (e.g. J-bevel) than the two explored in this study. Also, for the full cross-section tensile case, additional 3-dimensional analyses may be needed to ensure that all possible modes of strain localization (e.g. non-axisymmetric deformation modes) have been addressed.