Purpose This clause specifies requirements for the detailed fatigue assessment of welded and unwelded components and zones of pressure vessels that are subjected to repeated fluctuations of mechanical and thermal loads. NOTE 1 In fatigue@ welds and welded material behave differently from plain parent (unwelded) material. Therefore@ the assessment procedures for welded and parent materials are different. NOTE 2 The fatigue assessment of welded components and regions is based on fatigue design curves (SN curves) obtained from welded specimens tested under load control@ except for applied strains exceeding yield (low cycle fatigue)@ where test data are obtained under strain control. NOTE 3 The fatigue assessment of unwelded components and regions and bolts is based on SN curves obtained from plain materials under strain-controlled test data. The requirements in this clause are only applicable to steels specified in EN 13445-2. This clause assumes that the vessel has been designed in accordance with all other requirements of this standard. These requirements can also be applied to steel castings@ but in case of welding or weld repairs on steel castings@ the requirements for welded regions shall apply. This clause includes the effect on fatigue of weld toe improvement where this is carried out. NOTE In the case of fillet and partial penetration welds@ where failure can occur from the weld root@ improvement of the weld toe cannot be relied upon to give an increase in fatigue strength of the joint. Plain material can contain flush ground weld repairs@ which may reduce in the fatigue life of the material. Hence@ only material which is certain to be free from welding shall be assessed as unwelded. These requirements are not applicable to testing group 4 pressure vessels. For welded joints in testing group 3 pressure vessels@ see the special provisions in 18.10.2.1. This fatigue assessment method is not intended for design involving elastic follow-up (definition below and see reference [1] in Annex N). The fatigue assessment shall be made at all locations where there is risk of fatigue crack initiation. Fatigue assessment shall be made at points of highest stress and stress concentration and at locations subject to high numbers of stress cycles. Fatigue assessment using this clause may be performed using either a given history of operating loads or specified design loads. Recommended methods are given in Annex NB. In this clause the equivalent stress range is used for fatigue assessment of all welded and unwelded regions. The determination of cycles and equivalent stress range is given in Annex NB. EN 13445-3:2014/prA20:2019 (E) 7 NOTE The maximum principal stress range is no longer used for fatigue design in this Clause. This clause applies primarily for components operating below the creep temperature range. It may@ however@ also be applied for components operating in the creep temperature range provided sufficient allowance is made for the effects of creep and high temperatures.
EN 13445-3:2014/PRA20:2019 history
2021EN 13445-3:2021 Unfired pressure vessels - Part 3: Design