Early Engagement of ECA in Offshore Deepwater Pipeline Design

Welding acceptance criteria derived through ECA is typically performed after the detailed design. The design loads, together with pipeline and girth weld material testing data, are inputs to ECA and used to evaluate the pipeline girth weld integrity for determining the criticality of potential weld flaws. With ever increasing challenging environment (deepwater, HP/HT, aggressive fluid composition etc) in the oil and gas field, the fatigue damage and fracture failure may become a serious concern, consequently limiting the productivity of the pipeline fabrication. It is therefore essential to integrate ECA into the design loop to remove the uncertainty and risk to achieve a practically workable fabrication solution. In this paper, a strategy to integrate early ECA into pipeline detailed design phase is presented. A case study in a deepwater subsea channel crossing demonstrates that an early ECA engagement effectively mitigates the significant fatigue and fracture risk and obtains workable welding acceptance criteria for fabrication.

Weld Hydrogen Cracking Susceptibility

Weld hydrogen cracking has been recognized as an issue of concern and a wide range of hardenability criteria and single pass weld testing techniques have been developed to demonstrate material weldability, however, hydrogen cracks continue to be identified in welds. The potential for hydrogen cracking is related to the presence of hydrogen, the local tensile strain state and the susceptibility of the material microstructure. The weldment slow bend test and hydrogen effusion and cracking model has been used in Pipeline Research Council International (PRCI) research reported in this paper to support the development of an understanding of the interaction of these factors in promoting hydrogen cracking. The slow bend testing procedure is described with examples of the effects of increasing hydrogen and/or strain conditions are used to illustrate hydrogen cracking susceptibility. The slow bend testing procedure was applied to a range of steel weld metals to develop an understanding of the factors which make one more or less susceptible to hydrogen cracking. Combining the results of slow bend testing, the susceptibility of deposited shielded metal arc weld material to hydrogen cracking is defined using a hydrogen susceptibility curve that establishes the critical strain to form a crack as a function of hydrogen concentration. Cracking susceptibility is described through the definition of material ductility and embrittlement indices, which are derived from the hydrogen susceptibility curves. Cracking susceptibility is then correlated with mechanical, chemical and microstructure properties of the deposited welds. This model to predict weld metal hydrogen cracking susceptibility was developed to support electrode selection and welding procedure development to preclude hydrogen cracking. The results in this paper can be used to reduce the risk of hydrogen cracking and support the development of industry guidance.

LAJU PENDINGINAN PENGELASAN BAJA CARBON SEDANG PADA TEMPERATUR LINGKUNGAN BERBEDA

The quality of welding results is influenced by the shape of the microstructure of the welding material especially in the HAZ region. The shape of the welding microstructure is largely determined by the cooling rate of the weld material. The cooling rate of the weld is greatly influenced by the heat input from the arc and the ambient temperature. This study aimed to determine the effect of different environmental temperatures on the cooling rate of welding results. Welding of GMAW fillets on medium carbon steel plates S50C, with variations in welding currents 90 A, 100A and 110A and carried out at variations in environmental temperature of 15oC, 10oC and 5oC. Temperature data on the middle, welding part is taken with a digital thermometer to compare the effect of each variable. The test results show that the greater the welding current, the slower the cooling rate. Similarly, an increase in ambient temperature causes a decrease in the weld metal's cooling rate.

TDFAD Analysis of Creep Crack Initiation in 0.5CMV/2.25CrMoV Steel Weldments

The time dependent failure assessment diagram (TDFAD) is a convenient methodology to simultaneously assess whether a component is likely to fail by brittle, ductile or creep fracture, plastic collapse or creep rupture. In this work, creep toughness data, Kmatc, have been derived from experimental creep crack growth (CCG) tests on compact tension fracture mechanics specimens made of a weldment consisting of 0.5CMV parent material, 2.25CrMo, where the starter crack was located in the heat affected zone (HAZ). Time dependent failure assessment diagrams (TDFADs) are then constructed for each material condition and creep crack initiation (CCI) time predictions were obtained for the CCG tests performed on the weldment samples using both a TDFAD based on either parent and weld material data. The TDFAD based on the weld data provided the most conservative prediction of CCI times thus is recommended for use for weldment samples.

Trial Study of the Master Curve Fracture Toughness Evaluation by Mini-C(T) Specimens for Low Upper Shelf Weld Metal Linde-80

The Master Curve (MC) method can be used to directly determine fracture toughness of ferritic reactor pressure vessel (RPV) materials. CRIEPI has been working on the development of a testing technique to apply very small C(T) (called Mini-C(T)) specimens for the MC method. The appropriateness of using Mini-C(T) specimens for several materials including un-irradiated plate, forging, weld metal and irradiated plate has been demonstrated. Through a series of investigations, it was determined that more invalid data, due to ductile crack growth (DCG), can occur when using small size specimens. Linde-80 weld metal, used in the fabrication of some RPVs, is known as low upper shelf material, which tends to exhibit more DCG than high upper shelf materials. In the present study, two sets of 15 Mini-C(T) specimens were machined and pre-cracked from irradiated Linde-80 weld metal. Each set of specimens were provided to two different laboratories (A and B). The laboratories separately conducted the MC tests. DCG occurred even in the lower test temperature condition. About half of specimens for lab A showed excessive DCG and were subjected to the censoring. Some of specimens were rejected since the test temperature is outside of the specified range (T-To < −50°C). As a result, lab A could not obtain valid To with 15 specimens. Lab B also experienced DCG, however were able to obtain a sufficient number of valid KJc data points to determine a valid To. The obtained ToQ (lab A) and To (lab B) are sufficiently close to each other and suggests that Mini-C(T) can be used even for the low upper shelf material if the number of available specimens are sufficiently large. The combined dataset from labs A and B estimated To = 31.5°C, which is in the scatter band of To obtained by pre-cracked Chapry (PCCv), 0.5TC(T) or 1TC(T) specimens in a past Heavy-Section Steel Irradiation (HSSI) project. The overall result suggests that To can be estimated using Mini-C(T) specimens for the lower upper shelf weld material, but 15 is a marginal number of specimens for a valid estimation.

Experimental and numerical analysis of deformation patterns in notched heterogeneous welds

Standardized weld flaw assessment techniques assume the weld region to be homogeneous which is a strong idealisation of reality. Characterising the effects of heterogeneous properties of welds through the analysis of deformation patterns and slip lines is the major concern of this research. It is the goal to investigate which effects these variations in properties within the weld material have on the propagation of cracks within the weld material. Performed experiments are SENT tests on strongly heterogeneous welded connections. The same material is also simulated with a weld heterogenisation model in ABAQUS®. Results from both experiments and simulations are discussed and compared. It is shown that slip lines tend to avoid zones of high hardness in a way that a path of least resistance is found. Related to this, it is seen that the slip line angles deviate from the theoretical 45° for homogeneous material. Obtained results validate the numerical model used.