KIMUA and Mondragon Goi Eskola Politeknikoa (MGEP) have presented together the results obtained from a study on fatigue life prediction in welded joints, focused on searching alternatives for optimizing engineering designs that allow a reduction of associated manufacturing costs of producing transport frames destined to be used in heavy cargo sea shipping.
The study started with the analysis of different types of mechanic-welded frames designed and manufactured by KIMUA, for sea transport of heavy cargo. From these case studies, we conducted a deeper analysis of the fatigue life in welded joints, considering the Residual Stresses (RS). The results of this study were presented in the 34th Encounter of the Spanish Fracture Group (GEF), which has been celebrated recently in Santander, Spain.
The main objective of the work presented in Santander was to compare the fatigue life prediction in High Cycle Fatigue (HCF) regime in three different cases. Applying the DNV GL IV-7-2 standard, which does not take into account the RS; considering yield stress as RS value, and determining the RS value by a numerical model developed by the Structural Mechanics and Design team of MGEP. This model has been experimentally validated and presented in previous works.
Due to the difficulty in the theoretical or experimental determination of the RS, they are usually not considered in the fatigue life prediction. This results in oversized designs, with the corresponding increase in material, time and transport costs.
Moreover, the difference in life prediction can be observed in a recent work (Figure 1), where we published the comparison of the fatigue curves for welded joints given by several standards with experimental results.
Figure 1. Comparison of fatigue life prediction by several standards and experimental points. Published in A. Lopez, et al., Comparación de diferentes métodos de predicción de vida a fatiga de un componente soldado a tope y su validación experimental, GEF31, El Escorial, 2014.
In the work developed, first, we determined the RS pattern in function of the plate thickness. For the analysed case, the RS value is around the 87% of the yield strength of the material. Subsequently, we estimated the fatigue life by the three proposed methods.
The results obtained show the tight restrictions imposed by the standards because of not considering the effect of the RS, in HCF regime (figure 2). In fact, according to the DNV GL IV-7-2 standard, the endurance limit of these joints is 25 MPa; while considering the RS the endurance limit increases to 77 MPa for the yield strength approach and to 93 MPa for the RS prediction model. In addition, it was observed that for plates with thickness less than 50 mm, the yield strength approach can be considered valid. For those thicknesses, the real RS value is close to the yield strength, so the work needed to carry out the numerical prediction can be avoided.
Figure 2. Comparison of fatigue life prediction obtained in this study.
The use of these methods for fatigue life prediction considering RS could lead to a reduction in the quantity of material needed in the welded joints, an important factor in the case of big mechanic-welded structures as the ones developed in KIMUA. Thus, KIMUA and the Structural Mechanics and Design team of MGEP will continue working together in order to generate new technical knowledge, with the aim of developing more efficient processes that enable a reduction of costs of material, manufacturing process and transport, for the benefit of our clients.
- M. Larrañaga, J.A. Esnaola, I. Llavori, U. Etxebarria, I. Oreja, I. Alzate, L. Martin, Predicción de vida a fatiga de una estructura mecanosoldada para sector off-shore teniendo en cuenta las tensiones residuales, 34º Encuentro del Grupo Español de Fractura (GEF34), Santander, Marzo 2017.
- Lopez-Jauregi, J.A. Esnaola, I. Ulacia , I. Urrutibeaskoa , A. Madariaga, Fatigue analysis of multipass welded joints considering residual stresses, Int. J. of Fat., Vol. 79, pp. 75-85, 2015.
- J. A. Esnaola, I. Ulacia, D. Ugarte, A. Lopez-Jauregi, I. Torca, J. Larrañaga, Analysis of the fatigue performance of thick T-joint samples considering residual stresses, ASME IMECE, Phoenix (USA), 2016.
Offshore Wind Energy 2017 will take place next June, from the 6th to the 8th in "ExCel London"; it is the world’s Wind Offshore largest conference and exhibition taking place this year.
KIMUA didn’t want to miss this great chance to exhibit in one of the main halls of the exhibition and there we’ll be, in stand N-F50.
We’d like to meet you there, hear from your needs and talk about successful projects, upcoming developments and cooperation opportunities.
We look forward to seeing you there; we'd be pleased to say hello and talk about future projects.
The exhibition will take place from September the 27th to the 30th in Hamburg Messe und Congress and KIMUA will be there waiting for you in Hall 2 - Stand 316, within the Basque Country’s Pavilion.
This event is the world’s largest Wind Energy Exhibition, it is a unique occasion for meeting not only offshore and onshore key leading companies within the Wind Industry, but also all sectors related across the supply chain.
KIMUA didn’t want to miss this great chance to meet you, hear from your Company’s needs and talk about successful stories on tools used for Heavy Lift, Transport and O&M in different projects.
Feel free to contact with us for setting an appointment or simply show up in our booth. We look forward to seeing you there!
Lucas Mejía, Sales Manager
Luis Martín, Project Manager
KIMUA Group has recently finished the process of engineering & manufacturing a certified offshore frame prototype that will transport the ADWEN’s 8 MW tower sections in an upright position on a vessel.
KIMUA Group’s team of engineers powered this project since its early stages and drove it through the process until achieving the Product Certification from DNV-GL, the scope of the certificate covers the main stages of the project: engineering & manufacturing.
In order to provide a complete set of services for its Client, a Fit Test was performed at KIMUA Group’s facilities prior to delivery; additionally, a Tutorial Video was supplied to ADWEN; in this sense, the video included not only detailed instructions for handling the frame, but also the safety protocols to follow when maneuvering the tool.
Los bastidores fueron producidos en las instalaciones de KIMUA Group en mayo pasado, y están siendo utilizados actualmente para el transporte marítimo de secciones de torre de ADWEN en posición horizontal.
En este proyecto, todo el proceso productivo, desde la selección de proveedores al acopio de materiales, estuvo supervisado por inspectores de DNV-GL. Por lo cual los bastidores no sólo cumplieron con las exigencias de manufactura del cliente en lo relativo a útiles Offshore, sino también a los requerimientos de DNV-GL.
Asimismo, entre las principales exigencias tanto del cliente, ADWEN, como de la entidad certificadora, DNV-GL, se encontraban buenas prácticas que KIMUA Group tenía ya desarrolladas e implantadas, tales como la adecuada selección de proveedores, un estricto control de materias primas, y un eficiente sistema de trazabilidad; todo ello, sumado a las cualificaciones y certificaciones tanto de soldadores como de los procedimientos de soldadura.