RESEARCH PAPER
Fatigue strength improvement of steel structures by high-frequency mechanical impact:propod procedures and quality assurance guidelines
Gary Marquis &Zuheir Barsoum
Received:18March 2013/Accepted:29May 2013/Published online:16June 2013#International Institute of Welding 2013
Abstract High-frequency mechanical impact (HFMI)has emerged as a reliable,effective,and ur-friendly method for post-weld fatigue strength improvement technique for welded structures.During the past decade,46documents on HFMI technology for fatigue improvements have been prented within Commission XIII of the International Institute of Welding (IIW).This paper prents an overview of the lessons learned concerning appropriate HFMI procedures and quality assurance measures.Due to differences in HFMI tools and the wide variety of potential applications,certain details of proper treatment procedures and quantitative quality control measures are prented generally.Specific details should be documented in an HFMI procedure specification for each structure being treated.It is hoped that this guideline will provide a stimulus to rearchers working in the field to test and constructi
vely criticize the proposals made with the goal of developing inter-national guidelines relevant to a variety of HFMI technologies and applicable to many industrial ctors.A companion docu-ment prents a fatigue design proposal for HFMI treatment of welded steel structures.The proposal is considered to apply to steel structures of plate thickness of 5to 50mm and for yield strengths ranging from 235to 960MPa.Stress asssment may be bad on nominal stress,structural hot spot stress,or effec-tive notch stress.
Keywords High-frequency mechanical impact (HFMI).Weld toe improvement .Fatigue improvement .Quality control
1Introduction
In 2007,Commission XIII:Fatigue of Welded Components and Structures approved the best practice recommendations concerning post-weld treatment methods for steel and alu-minum structures [1].This recommendation covers four commonly applied post-weld treatment methods:burr grind-ing,tungsten inert gas (TIG)remelting (i.e.,TIG dressing),hammer peening,and needle peening.Burr grinding and TIG remelting are generally classified as geometry improvement techniques for which the primary aim is to eliminate weld toe flaws and to reduce local stress concentration by achieving a
smooth transition between the plate and the weld face.Ham-mer peening and needle peening are classified as residual stress modification techniques which eliminate the high ten-sile residual stress in the weld toe region and induce com-pressive residual stress at the weld toe.The methods also result in a reduced stress concentration at the weld toe.The guidelines also give practical information on how to imple-ment the four improvement technologies,namely good work practices,training,safety,and quality assurance.
The improvement techniques described in the recommen-dations are intended to be ud both for increasing the fatigue strength of new structures and for the repair or upgrade of existing structures.It has consistently been emphasized that,especially with respect to new structures,weld improvement techniques should never be implemented to compensate for poor design or bad fabrication practices.Instead,improvement measures should be implemented as a means of providing additional strength after other measures have been taken.
Doc.IIW-2395,recommended for publication by Commission XIII “Fatigue of Welded Components and Structures.”G.Marquis (*)
Department of Applied Mechanics,Aalto University,Espoo,Finland龙行虎步
e-mail:gary.marquis@aalto.fi
G.Marquis :Z.Barsoum
Division of Lightweight Structures,KTH-Royal Institute of Technology,Stockholm,Sweden
Weld World (2014)58:19–28DOI 10.1007/s40194-013-0077-8
Simultaneous with the development of the 2007recom-mendations,an increasing number of prentations within Commission XIII focud on high-frequency mechanical impact (HFMI)as a means of improving the fatigue strength of welded structures.From 2002to 2012,46IIW Commis-sion XIII documents reporting HFMI technology or experi-mental studies involving HFMI-bad fatigue strength im-provement were prented.HFMI has emerged as a reliable,effective,and ur-friendly method for post-weld fatigue strength improvement technique for welded structures.
This paper reprents an attempt to summarize and synthe-size the knowledge gained both within the IIWand prented in the open international literature concerning quality assurance of HFMI-treated welds.It covers procedure-related and quality assurance-related items such as relevant equipment,proper application procedures,material requirements,safety,training requirements for operators and inspectors,quality control
measures,and documentation.All HFMI devices have unique features,and the type of structure being treated (and especially the material grade and welding procedures)will greatly influ-ence the optimal treatment procedures.For this reason,the current document is intended to provide only general guidance especially with respect to operator training,procedures,and inspection.Specific operator training is provided by the tool manufacturers.Specific treatment procedures and requirements can normally be developed in cooperation with the HFMI device manufacturer.It is not the intention of this paper to compare HFMI tools or their efficiency.The goal is only to give an overview of topics which must be considered when preparing an HFMI procedure specification.
A companion document [2]prents a fatigue design pro-posal for HFMI treatment of welded steel structures.The design proposal is considered to apply to steel structures of plate thickness between 5and 50mm and for yield strengths ranging from 235to 960MPa.Stress asssment may be bad on nominal stress,structural hot spot stress,or effective notch stress using stress analysis procedures as defined by the IIW Commission XIII.The design proposal includes a pro-posal for the effect of material strength and a proposal for high R ratio and variable amplitude loading.Several topics for future study with respect to HFMI are given.
2High-frequency mechanical impact 2.1Background
The innovation of improving the fatigue strength of welded structures by locally modifying the residual stress state using
as-welded
after HFMI
HFMI
AW Fig.1Typical weld toe profile in the as-welded condition and follow-ing HFMI treatment [13,14]
Photo courtesy of Applied Ultrasonics.
Photo courtesy of Integrity Testing Laboratory (ITL) and Structural Integrity Technologies Inc. (SINTEC)
一月有什么节日Photo courtesy of Pfeifer Seil-und
Hebetechnik GmbH
Photo courtesy of PITEC GmbH
b
c d
Fig.2Examples of HFMI devices available worldwide.a ultrasonic impact treatment,b ultrasonic peening,c high-frequency impact treatment,and d pneumatic impact treatment (PIT)
ultrasonic technology is attributed to scientists and engineers working in the former Soviet Union [3,4].In the past decade,there has been a steady increa in the number of HFMI peening equipment manufacturers and rvice providers.In 2010,Commission XIII of the IIW introduced the term HFMI a
s a generic term to describe veral related technologies.Alternate power sources are employed,for example,ultrasonic piezoelectric elements,ultrasonic magnetostrictive elements,
or compresd air.In all cas,however,the working principal is identical:cylindrical indenters are accelerated against a component or structure with high frequency (>90Hz).The impacted material is highly plastically deformed causing changes in the material microstructure and the local geometry as well as the residual stress state in the region of impact.Various names have been ud in literature to describe the devices:ultrasonic impact treatment [5],ultrasonic peening
Photo courtesy of Integrity Testing Laboratory (ITL) and Structural Integrity Technologies Inc. (SINTEC)
a b
Fig.3a Examples of indenter sizes and configurations and b a double radius indenter developed by the Northern Scientific and Technical Company,Russia for Esonix UIT [18]
weld metal
HAZ
weld metal
ba metal
defect
ba metal
defect
开方表defect
shiny defect-free HFMI groove
a
b
c
Fig.4a Potential introduction of a crack-like defect due to HFMI treatment of a weld with a steep angl
e or with too large of an indenter and b resulting grooves for a properly treated weld toe (left )and an
improperly treated one (right );c micrographs of the induced crack-like defects due to
improper HFMI treatment [18]
[6],ultrasonic peening treatment[7][8],high-frequency impact treatment[9],pneumatic impact treatment[10],and ultrasonic needle peening[11,12].Figure1shows typical weld profiles in the as-welded condition and following HFMI treatment.In comparison to hammer peening,the operation is considered to be more ur-friendly and the spacing between alternate impacts on the work piece is very small resulting in a finer surface finish.
2.2Equipment
陈胜墓As previously mentioned,numerous new HFMI devices have been developed during the past10years,and the number continues to increa.Figure2shows some of the HFMI devices that are in u worldwide.A recent round robin exerci[15]and literature survey[16,17]have iden-tified veral HFMI tools which,when properly ud,pro-vide the degree of improvement noted in the propod fa-tigue design guideline for HFMI-treated welded joints[2]. Similar devices can be assigne
d to this group if they have the same operating principal and are objectively tested and are shown to have the same reliable and beneficial effect on the fatigue strength of welds as in the propod guideline.
Ultrasonic devices consist of a power unit and tool.The normally require compresd air or circulating water to con-trol the temperature of the tool.Other devices known to the authors are pneumatic.The indenters are high-strength steel cylinders,and manufacturers have customized the effective-ness of their own tools by using indenters with different diameters,tip geometries,or multiple indenter configura-tions.Indenters are consumable items which from time to time require replacement or refurbishment.Figure3shows veral examples of indenter sizes and configurations which are available.3Procedures
财务出纳员岗位职责
3.1Operator training
When delivering new equipment,tool manufacturers normal-ly provide1–2days of operator training.As new applications ari,tool manufactures can provide specialized training or customized procedure specifications.In some cas,HFMI treatment of structures with curvilinear weld ,weld toes in truss fabricated from circular hollow ctions,has proven to be very demandi
ng and will require more experti than for treating long straight welds or short weld corners.
Becau HFMI is normally specified as a fatigue strength improvement technology for new structures or during repair and retrofitting operations,it is always esntial to consult fatigue experts to ensure that all critical regions in a structure are identified and properly treated.Most fatigue-loaded struc-tures will normally have only a limited number of locations that are critical from a fatigue point of view.Proper identifica-tion of the regions is also important to avoid extra costs and treatment of regions which are not fatigue critical.Additional-ly,the possibility of a failure starting at some other location must always be considered.For instance,if the failure origin is merely shifted from the weld toe to the root,there may be no significant improvement in fatigue life.Some additional小杂粮
Table1Sample treatment procedure parameters for two HFMI tools
Parameter HFMI tool
香格里拉好玩吗
High-frequency Impact treatment(HiFIT)[21]Ultrasonic Impact Treatment(UIT)[22,23]
Power source Pneumatic Ultrasonic magnetostrictive
Number of indenters11–4
Angle of the axis of the indenters with respect to the plate surface,ϕ(e Fig.5)60°to80°30°to60°[22]
40°to80°[23]
Angle of the axis of the indenters
with respect to the direction of
travel,ψ(e Fig.5)
70°to90°90°(all pins should contact the weld toe)
Working speed3to5mm/s5to10mm/s[22]
5to25mm/s[23]
Other The lf-weight of the tool is sufficient[22,23]
Minimum of5pass[23]
travel speed
Fig.5Orientation of the HFMI tool with respect to the weld being
treated
comments on this topic may be found in the companion fatigue design proposal for HFMI-treated welded joints [2].In the ca of multipass welds,it is also needed to treat also the interpass weld toes [19].3.2Weld preparation
The weld cap and adjacent parent material shall be fully de-slagged and wire-brushed or ground to remove all traces of oxide,scale,spatter,and other foreign material.HFMI treat-ment of a convex weld profile or of a weld with a large weld angle can cau the plastically deformed metal to fold over the original weld toe and leave a crack-like lap feature that rembles a cold lap.The weld bead profile should meet the acceptance limits for the weld profile quality level B in ISO 5817[20].This requirement does not imply that the weld must fulfill all quality level B criteria in ISO 5817.However,weld profile-related quality criteria in ISO 5817need to be evaluated.The include undercuts (imperfection 1.7),ex-cessive overfill (imperfection 1.19),excessive concavity (imperfection 1.10)and overlaps (imperfection 1.13).If the weld profile does not comply with the acceptance limits,light grinding before treatment may be desired.It should be noted,however,that HF
MI treatment is most effective when the weld toe region itlf is treated.Thus,grinding operations which make it difficult for the HFMI operator to distinguish the exact location of the weld toe should be avoided.De-cisions on the need for weld grinding and the proper grinding procedure should be agreed on with an experienced HFMI operator.
The need for a proper weld profile before HFMI is illus-trated in Fig.4a which illustrates the formation of a crack-like defect due to improper contact between the indenter and the
weld toe.Surface inspection of such a defect reveals a dark crack-like line in the middle of the otherwi smooth and shiny HFMI groove as en in Fig.4b .Figure 4c shows ction micrographs of the defects.The resulting fatigue performance of a welded joint with such defects may actually be less than that of the original as-welded joint.The same type of flaw has been obrved in welds with adequate profiles but with improper indenter lection or too vere ,too many pass over the same region.For specific applica-tions,it may be needed to consult with the HFMI tool manu-facturer in order to lect the proper treatment procedures and optimal indenter configuration to avoid crack-like defects.3.3Safety aspects
Noi and vibration from HFMI is significantly less than for more traditional peening equipment.HFMI
treatment can be a noisy operation,and it is esntial that the operator and others working in the vicinity should u ear protection.Normal protective clothing for working in a fabrication shop is ade-quate but it should include approved eye protection.Vibration from HFMI equipment is usually low enough so that contin-uous operation is permitted without restriction during a nor-mal 8-h work shift.If the vibration of the specific HFMI tool has not been determined,it may be needed to limit the amount of time per day for performing HFMI treatment.Equipment-specific safety issues are provided by the tool manufacturers.3.4Weld toe treatment
Specific weld toe treatment procedures will vary greatly from application to application and depending on the tool being ud.Thus,only general topics can be covered.Table 1
weld metal
黑链代码ba metal
Fig.6The HFMI groove in a shows a thin crack-like defect which reduces or eliminates the effectiveness of the HFMI treatment [21].b shows a defect-free groove but with an individual indenter strike still visible,indicating the need for additional pass [27
]
Fig.7a Proper profile of an HFMI groove which has no sharp or crack-like features and b an improper HFMI groove profile which shows the
prence of a crack-like feature due to plastic deformation of the material
