Circumferential Welds Research Articles

Effect of welding residual stress on plastic buckling of axially compressed cylindrical shells with patterned welds

An experimental–numerical investigation of the effect of welding residual stress on plastic buckling of axially compressed cylindrical shells with patterned welds is carried out. Two cylindrical shell specimens with different pattern of welds are made according to manufacturing process used in engineering. Their initial geometric imperfections, axial and circumferential strain, buckling load, etc., are experimentally obtained. Inherent strain method used for simulating welding residual stress field is presented. Two different numerical modeling methods for the purpose of evaluating the effect of welding residual stress on plastic buckling are illustrated and the validity is verified by experiment. It is found that, load–displacement curve before buckling is altered, plastic buckling critical load is decreased to some extent, and the buckling deformation such as the number and the uniformity of waveforms of circumferential welds are changed when welding residual stress exists. For the above phenomena, the reason why welding residual stress has an influence on plastic buckling is also quantitatively analyzed from the point of stress variation.

GAS Pipeline Leakage in Urban Subsurface Soil

Studies carried out for a natural gas distribution company are presented, in which the causes that led to a leakage in a 4“elbow are determined. The damage was detected in a tract under a highway; a major erosive process by solid particles from the outside was found during excavation. This erosive process, however, was not the cause of the failure, but a consequence of a gas leak from a through crack in the circumferential weld. The crack at the root toe of the weld propagated through the heat affected zone (HAZ) of the elbow. It was found that the chemical composition of the elbow did not match specification, high carbon equivalent contributed to brittleness in the HAZ. The failure is attributed to bending loads due to ground settlements and traffic of heavy vehicles on top of the right of way, during highway construction and repair.

Ultrasonic Phased Array for the Circumferential Welds Safety Inspection of Urea Reactor

Abstract Due to the multi-layer thick wall structure and coarse grain materials of inside liner, the circumferential welds safety inspection of urea reactor is usually not easy. The paper analyzes the problems and difficulties of NDT techniques used for circumferential welds of urea reactor and overviews the theory and advanced point of UPA technology. Then two related test blocks (RB-2/20 and Austenitic stainless steel butt joint test block) with artificial defects are selected to simulate the outer and inner layer. Experiments by UPA are carried out on the test blocks and results are analyzed. It is proved that UPA is effective and efficient in solving the circumferential welds safety inspection.

1307 アルミニウムパイプの全周突き合せ溶接における溶け込み監視システム(OS18-2 金属材料の生産加工II,OS18 金属材料の生産加工)

1307 アルミニウムパイプの全周突き合せ溶接における溶け込み監視システム(OS18-2 金属材料の生産加工II,OS18 金属材料の生産加工)

Stress and Strain Evolution Rule Research on Aerospace Aluminum Alloy Cylinder Structure Welding

The stress and strain in Aluminum cylinder longitudinal and circumferential weld seam are simulated by finite element analysis tools-ANSYS.Tube structure in aerospace is welded by the variable polarity plasma arc welding process.According to the characteristics of variable polarity plasma arc weld,surface heat source and cylindrical heat source are used to simulate variable polarity plasma arc weld.The program which is used to achieve loading and moving variable polarity plasma arc(VPPA) welding heat is wrote by using the ANSYS parametric design language(APDL) in ANSYS software.The same structure in different type of weld is presented by the different ways of loading heat source.The use of sweep meshing method to build complex cylinder structure analysis model is proposed.Through the simulation results,the complex cylinder welding deformation evolution process is explained.It is found that longitudinal seam ends have obvious stress-strain release in the process,and cross section deformation directly influenced the size precision of whole structure.

Study on Safety Assessment Methods of the Penstock of the High Head Hydropower Station Using the China Standard GB/T 19624-2004

Based on the finite element analysis, the general mechanical property tests and the CTOD (crack tip opening displacement) test of the penstock in the third deviated hole, the GB/T19624-2004, that is the criterion of safety assessment for in-service pressure vessels containing defects suggested by China, is applied to assess the five weld defects in the penstock, which experienced the failure of the pressure test. The assessment results indicate that 1# defect and 5# defect could be accepted, while the other defects should be repaired. According to the assessment results, the defects over criterion in the penstock must be repaired. After the penstock was repaired, it was checked by the ultrasonic flaw detection again. And the results indicate that all weld joints including circumferential and longitudinal weld joints in the penstock around the pipe close in the third deviated hole are acceptable, what provides a scientific basis for the second pressure test and the safe operation of the High head hydropower station.

Metal degradation of the methanator vessel

AbstractThe methanator vessel of a MW Kellogg designed ammonia plant developed severe material imperfections by hydrogen‐induced damage. This was most likely due to the doubtful acceptability of C–0.5Mo for hydrogen service, it is more than 30 years service life and some above‐design temperature excursions. Ultrasonic inspection during the 2001 turnaround revealed several discontinuities within 1 ft (30 cm) above the bottom circumferential weld seam. In following years these imperfections further deteriorated to form large sized voids within the shell material. Repair of the affected area was evaluated to be not feasible. Consequently, the vessel was replaced in the 2004 turnaround with a 1.25Cr–0.5Mo vessel. After replacement, the metallographic examination of the samples from affected portions of the old vessel confirmed the findings of the ultrasonic flaw detection and disclosed the presence of mainly transgranular and a few intergranular cracks and signs of overheating at some locations. The details of the ultrasonic inspection and micrographs have also been presented. Although the ultrasonic inspection was quite delayed, it prevented a catastrophic incident. © 2011 American Institute of Chemical Engineers Process Saf Prog, 2012

Methodology for non‐destructive assessment of integrity of steam generator shell welds

PurposeDevelopment of non‐destructive methodology for detection of arc strike, spatter and fusion type of welding defects which may form on steam generator (SG) tubes that are in close proximity to the circumferential shell welds. Such defects, especially fusion‐type defects, are detrimental to the structural integrity of the SG. This paper aims to focus on this problem.Design/methodology/approachThis paper presents a new methodology for non‐destructive detection of arc strike, spatter and fusion type of welding defects. This methodology uses remote field eddy current (RFEC) ultrasonic non‐destructive techniques and K‐means clustering.FindingsDistinctly different RFEC signals have been observed for the three types of defects and this information has been effectively utilized for automated identification of weld fusion which produces two back‐wall echoes in ultrasonic A‐scan signals. The methodology can readily distinguish fusion‐type defect from arc strike and spatter type of defects.Originality/valueThe methodology is unique as there is no standard guideline for non‐destructive evaluation of peripheral tubes after shell welding to detect arc strike, spatter and fusion type of welding defects.

Laser welding of vesicovaginal fistula—outcome analysis and long-term outcome: single-centre experience

The aim of this study is to evaluate the efficacy and safety of laser welding of vesicovaginal fistula (VVF) at our centre. Between January 1, 2001 and January 3, 2010, eight patients underwent laser welding of vesicovaginal fistula. The mean age was 44 years (35-55). The VVF were primary (failing to heal following conservative management) in five and secondary (recurring following primary repair) in three cases. The mean fistula size was 3 mm (range, 2-4). Neodymium yttrium aluminium garnet (YAG) laser was used for the initial case, and in the remaining seven cases, holmium YAG laser was used for circumferential welding of the fistula. Following the procedure, a catheter was kept for 3 weeks. The mean hospitalisation period was 1 day. The mean follow-up is 47 months (2-110). Seven patients were dry after catheter removal. In one patient, procedure was abandoned due to bleeding. Laser welding of VVF is a simple, safe and efficacious procedure in a select group of patients.

Numerical Investigation on the Behavior of Circumferentially Butt-Welded Steel Circular Hollow Section Flexural Members

This paper presents a finite element (FE) analysis to quantify the effects of weld-induced residual stresses on the flexural behavior of circumferentially butt-welded steel circular hollow section (CHS) members. FE modeling of the weld-induced residual stresses is first described. Nonlinear FE analysis in which the behavior of the CHS members subjected to bending is explored incorporating the residual stresses is discussed next. Two FE CHS tube models with different failure modes are developed in order to clarify the effects that the residual stresses have on the flexural behavior. Simulated results show that welding residual stresses can have significant effects on the initial stiffness and the ultimate strength of the CHS flexural members depending on the loading position; hence, they should be taken into account in assessing the behavior of steel CHS members with circumferential weld under bending.

The Features of the Integrated Multilayer-Wrapped High Pressure Vessel and its Fabrication Quality being Inspected by Hydrostatic Test

The integrated multilayer-wrapped high pressure vessel is a special kind of multilayered pressure vessel whose circumferential weld seams are able to be in an offset pattern. The fabrication quality is assured by controlling the gaps of the layers. The tightness of the wrapped layers can be inspected by the hydrostatic test. The stress at the outer shell of a DN1400 urea synthetic reaction tower of the integrated multilayer-wrapped has been measured at the time of the hydrostatic test. The results show that the longitudinal stress is identical to that of the theoretical value, and the ratio of the measured circumferential stress to the theoretical calculated one of the corresponding solid shell vessel is more than 0.5 when the hydrostatic test pressure reaches the design pressure. The averaged ratio of the measured circumferential stress to the theoretical calculated one is 0.61 of the two measured sections at the hydrostatic test pressure of 20 MPa. The conclusions are: (1) the fabrication quality of the integrated multilayer-wrapped high pressure vessel are able to be assured, and (2) the tightness of the wrapped layers can be inspected by measuring the circumferential stress at outer shell, and compared to that of the theoretical value of the corresponding solid shell vessel, and (3) it is realizable that the circumferential stress at outer shell of the multilayer-wrapped vessel being not less than 50% of that of the theoretical calculated one of the corresponding solid shell vessel at the design pressure.

Buckling Strength of Tapered Cylindrical Shells under Partial Axial Compression: Effect of Circumferential Weld-Induced Imperfections

Buckling is often the main design consideration for thin cylindrical shells. For most load cases, the stability behavior of the shell is acutely sensitive to circumferential weld-induced imperfections, and the corresponding residual stresses are some beneficial to buckling strength of the shell generally. However, these conclusions are all based on the cylinders with constant wall thickness, and the studies about the effect of residual stresses on buckling strength of tapered cylindrical shells under partial axial compression are few. This paper applies trapezoidal strain field approach to simulate circumferential weld-induced imperfections on tapered cylindrical shellls, and studies the stability behavior of the cylinders with single circumferential weld and multiple circumferential welds under partial axial compression respectively. By comparing the results derived from the models with/without circumferential welds and corresponding residual stresses, the effects of weld depressions and residual stresses on tapered cylindrical shells under partial axial compression are obtained.

Analysis of residual stress in stainless steel pipe weld subject to mechanical axial tension loading

This paper presents the characteristics of welding residual stresses in circumferentially butt-welded stainless steel pipe by utilizing three-dimensional (3-D) uncoupled thermo-mechanical finite element (FE) analysis method. Moreover, stress variations in welded joints of the pipe under superimposed mechanical axial tension loading are further investigated employing the welding residual stresses and plastic strains obtained from the thermo-mechanical FE analysis as an initial condition. Results show that spatial variations of the welding residual stresses are present along the circumference and a rapid change of the residual stresses exists at the welding start/stop position, hence 3-D FE analysis is essential to accurately simulate circumferential welding of a pipe component. When mechanical axial tension loading is applied to the circumferentially butt-welded stainless steel pipe, bending moment is generated at the welded joints caused by the circumferential shrinkage of the weld region during welding; thus affecting the axial and hoop stress evolutions in the course of the superimposed mechanical loading.

Effect of Weld on Axial Buckling of Cylindrical Shells

Large oil storage tank (oil tank for short) shells are vulnerable to buckling damage when suffering the seismic loads. Numerical simulation analysis was taken to estimate the effects of the weld form, number and their location to axial buckling stress of cylindrical shells, considering not only the characteristic of welding processes, but also the effects probably caused by magnitude of residual stress and deformation on elephant foot buckling to oil tanks. It is revealed that the existence of circumferential welds had obvious negative effect on axial buckling critical stress compared with the structure without welds, while the effects of weld number and location were not as much; longitudinal welds had no visible effect on axial buckling critical stress; controlling the residual stress and deformation range caused by circumferential welds should be the key point during the tanks welding process.

Recommended Design Fatigue Factors for Reassessment of Piles Subjected to Dynamic Actions From Driving

Calculated probabilities of fatigue failure depend on the analysis procedure used for design. Calculated probabilities of a fatigue failure also depend on long term stress ranges due to loading and uncertainties associated with this. In order to ensure the consistent safety level for assessment of fatigue failure, the design fatigue factors (DFFs) to be used for fatigue design should be dependent on the analysis procedure and premises used. In the present paper, an assessment of appropriate DFFs for piles subjected to dynamic actions from pile driving has been performed by probabilistic analysis based on: uncertainty with respect to dynamic cyclic stress during pile driving, and fatigue capacity of circumferential welds in piles. Accumulated probabilities of fatigue failures in pile butt welds are presented. An assessment of uncertainties involved in calculation of stress ranges during pile driving has been performed. It is shown that the uncertainty in loading when driving records are known is lower than that estimated on the basis of soil data. Thus, in order to obtain consistent safety levels, different DFFs should be used when calculated stress ranges are derived based on soil data only, as compared with the actual stress ranges and number of blows determined from driving records. The results from probabilistic analyses together with recommended design fatigue factors are presented in this paper.

Estimating main steam piping circumferential weldment creep life consumption

A high energy piping (HEP) program is important for the safety of plant personnel and reliability of the piping systems. These piping systems have been designed considering allowable stresses with some safety margin at 100,000 hours. Unfortunately, many of the main steam (MS) piping systems evaluated by the author have operated beyond 350,000 hours, for which the ASME B31.1 safety margin may no longer exist. Since creep and fatigue is a typical failure mechanism, the probability of HEP failures increases with unit age.The MS piping system is one of the most critical HEP systems. Weldment failures are typically due to a combination of high temperature creep and fatigue. The circumferential weld stresses for MS piping systems operating in the creep regime should include a weldment performance factor that is both multiaxial and time dependent. Application of the actual field stresses, considering malfunctioning supports, to weldment life consumption has resulted in more accurate weldment creep – fatigue rankings and remaining life estimates. This paper demonstrates that the evaluation of actual piping stresses and variations in the actual pipe wall thickness can have a significant effect on the estimates of remaining lives of the girth weldments.

Failure analysis of a stainless steel hydrotreating reactor

This paper presents an analysis of a failed AISI 316L austenitic stainless steel (SS) hydrotreating reactor that produces flavors and fragrances. Pitting and cracking were observed mainly in the vicinity of the circumferential and longitudinal shell welds on the internal surface of the reactor by dye penetrant testing (DPT). Ultrasonic evaluation revealed the cracks were within near-surface area, therefore remedial grinding was performed to remove them. In situ metallographic investigation revealed that the cracks were predominantly transgranular and multi-branching. Thickness gauge, hydraulic pressure testing, and acoustic emission validated the reusability of the repaired vessel. Analysis of the catalysts showed the source of chloride. SCC (stress corrosion cracking) susceptibility testing of the identical material proved its liability to chloride SCC in the environment of the suspect catalysts. Studies revealed that the failure was caused by chloride SCC. Recommendations are made to prevent the recurrence of the similar failure.

Effect of welding procedure on the properties of microalloyed steel-welded joints for metal piping

The objective of this work was, in the first step, to compare the mechanical properties and microstructure of the corrosion-resistant steel hydrogen-induced cracking, alloyed with Nb–Ti–Cu–Ni, to those of a normal steel NOR, microalloyed with Nb–V–Ti, characterized through chemical analysis, hardness measurements, metallographic studies and tensile and Charpy-V properties. The preheating temperature was established using Tekken tests at different temperatures, according to the JIS Z 3158 standard. Circumferential welds were carried out on piping manufactured from both steels, designing procedures for the use of coated electrodes on the one hand (shielded metal arc welding, with electrodes from various suppliers) for all passes, and for a first pass using automatic welding with low-CO2 solid wire on the other (gas–metal arc welding) and the rest with self-shielding tubular wire (flux-cored arc welding, self-shielding). The welds were classified in accordance with the API Code 1104. The results of the metallographic analysis and the mechanical traction, hardness and impact tests of the welded joints revealed the influence of the welding consumables and of the base metal on the properties of the joints. Differences were observed between the properties of the joints welded with consumables of equal specification and different suppliers. From the different combinations tested, optimum values for the welding of these steels were defined.

Stochastic Fatigue Assessment for Berthing Monopiles in Inland Waterways

As an unsupported structure, a berthing monopile is often expected to work under harsh conditions. Approaching vessels may introduce considerable berthing energy, resulting in substantial tensile stress on the pile. This vessel impact occurs frequently as a primary load over the service life of the berthing monopile. In this situation, the fatigue safety of circumferential butt welds on piles becomes a crucial aspect in monopile design. This paper evaluates linear elastic fracture mechanics (LEFM)-based fatigue reliability for circumferential splice welds on steel monopiles. Studied monopiles are those installed in inland waterways, for which the predominant fatigue loading is vessel berthing. Important factors involved in the fatigue reliability assessment are addressed. A geometry function for determining the range of stress intensity factor is identified, an approximate stress concentration factor for piles under bending moment is mathematically formulated, and the beta distribution is applied to characterize the doubly bound hot-spot stress range caused by operational water-level constraints. A detailed case study is presented for illustrative purposes. This paper provides a practical approach to assessing LEFM-based fatigue reliability for steel berthing monopiles. DOI: 10.1061/(ASCE)WW.1943-5460.0000063. © 2011 American Society of Civil Engineers. CE Database subject headings: Piles; Marine terminals; Welds; Cracking; Fatigue life; Joints; Reliability; Waterways. Author keywords: Steel piles; Marine terminals; Welds; Cracking; Fatigue life; Tube joints; Reliability; Inland waterways.

Assessment of weld reduction factors through experimental reference curves

The 2¼Cr1Mo (P22) is present in most of structural high-temperature applications, as results from a review on materials employed for the construction of both power and chemical plants. So, it fits well for an experimental activity in the laboratory as reference material. ISPESL, the Italian Certification Agency, carried out a low-budget program of creep and low-cycle fatigue (LCF) tests at 550 °C; the specimens (twelve plus two spare) of as-fabricated material came from a thick-wall pipe with a certified circumferential weld. They were base metal and cross-weld fusion-line centered ones. Comparison of the resistance curves obtained from LCF tests with those from codes (ASME and ISPESL) showed for the base metal good correspondence; therefore, showed the reliability of the test proceeding. For the weld it showed instead conservatism reduction at high-strain levels for the ASME design curve; moreover, it revealed an insufficient conservatism of the reduction factor proposed, which is 1/2, for the lower bound ISPESL curve. Comparison of the resistance curves obtained from creep tests with those from codes showed this: for both the base metal and weld there are a good correspondence and acceptable (low) conservatism of the strength reduction factor (SRF) proposed; for the load and temperature levels considered in the tests, it equals one. Still, the creep tests duration was within thirty hundred hours each; therefore the levels of the applied load (150.2–100 MPa) were not as low as those in typical operation conditions. For these cases, the code (ASME) proposes a lower-than-unity SRF: thus, longer tests (lower levels of the applied load) would be useful, also extending the activity to other materials.