How To Treat Welded Joints

Transcription

1 The Revolution for Welded Constructions: 05/2009 HiFIT-treated as-welded EC Rupture weld toe Rupture basic material PFEIFER SEIL- UND HEBETECHNIK GMBH HiFIT Post-Weld Treatment DR.-KARL-LENZ-STRASSE 66 D MEMMINGEN TELEPHONE +49 (0) TELEFAX +49 (0) hifit@pfeifer.de INTERNET

2 Extended lifetime for Welded Constructions: the HiFIT Post-Weld Treatment The HiFIT process HiFIT High Frequency Impact Treatment is a high-frequency peening process. Thanks to targeted post-weld treatment it considerably increases the operational stability and the service life of dynamically loaded welded steel constructions. The HiFIT treatment is universally applicable, at a low cost of introduction. The HiFIT treatment delivers results every time that can be easily reproduced and offers the possibility of quality surveillance. Within the frame of a joint project promoted by the German Federal Ministry for Education and Research (BMBF) the HiFIT treatment samples have proved, through comprehensive fatigue tests, that the treatment is particularly efficient. The HiFIT device was designed by DYNATEC Gesellschaft für CAE und Dynamik mbh. 2 Contents Page Field of Application 4 5 Effectiveness of the Process 6 Process Suitability 7 Product Data, Spare-Parts & Accessories 8 Handling 9 The Scope of the PFEIFER Services 10 Application Examples 11

3 The advantages of the HiFIT post-weld treatment are impressive, and lead to an enormous increase in the cost-effectiveness of your welded constructions: An 80 % to 100 % increase in the weld fatigue strength Due to local reshaping the weld toe is plastically deformed and reinforced. Internal compressive stresses prevent the formation of cracks as well as the progression of cracks on the surface. 5-fold up to 15-fold increase in the service life of the weld More than 1000 tests have proven that the service life is increased. Equally effective for existing constructions In case of timely restoration of existing constructions there is almost no distinction from new treated welds. Hence the service life of existing construction is considerably increased. HiFIT is an ideal restoration tool as far as no macroscopically discernable cracks are evident. Use of high-quality steels becomes economically relevant Comprehensive experimental analysis on Notch Details and FEM-supported dimensioning processes show that the treatment is increasingly efficient with increasing tensile strength of fine-grained steels like S460N, S690QL, and of steels with even higher tensile strengths. For a same service life the weld is able to bear approx. 1.6-fold higher loads. Consequently the use of steels with higher strength becomes interesting for lighter construction types. Simple handling thanks to low weight and easy guidance Mobile compressors can also be used outside manufacturing plants. The compact construction and the low weight permits access to hard-to-reach spaces. The space required is only slightly larger than the space required by a welding torch. Robust LED lights on the head of the device provide for optimal light conditions also under difficult circumstances. Process reliability The treated zone can be visually inspected. The treatment line can be measured with a special calliper. A data log device is optional and available for recording. The working pressure can be monitored with a digital display on the handle. 3

4 Field of Application Welding is the most prevalent process used for joining steel elements. For the creation of a suitable weld numerous parameters must be complied with. Static loads can be tolerated up to a determined value. When the same load is cyclically applied local cracks form, gradually grow, and lead to failure. The replacement or repair of dynamically stressed steel constructions that suffer from fatigue give rise to expenditures amounting to billions of Euros each year. Weld toes are often the root cause of crack formation with later growth of the cracks. In many cases they are limiting the service life of the constructions. Additionally unforeseeable variations in the operating conditions which could not be taken into consideration during the design phase, e.g. longer operating times, higher loads, and the wish for longer use further limits the service life. On new welded constructions the steels with higher strength cannot efficiently be used, since the welded joint often is decisive for the service life. Well known mechanical processes like the internal grinding, the shot peening or the remelting-on indeed improve the fatigue resistance, however the results can not be proved and are less effective and almost non-reproducible. The high-frequency peening process HiFIT however is: efficient reproducible reliable 4 Applications: steel bridges HiFIT building machines cranes load suspension means wind power plants roller coasters etc.

5 80% 70% 60% 59% 67% Analyses made in the University of D-Braunschweig have shown that in the 20% building sector there is a strong shift in investment allocation from newer structures towards restoration and maintenance. The need for efficient and cost-effective restoration concepts becomes more urgent (Source: Institut für Bauwerkserhaltung und Tragwerk TU Braunschweig) New structure Restoration 30% 40% 41% %

6 Effectiveness of the Process Fig. 1 Fig. 2 Mode of operation of the high-frequency peening process The effectiveness of the peening results from the combination of the geometric (inside-rounding), and the mechanical (work hardening), and the strain (residual compressive stress) aspects. The HiFIT pin is ball-shaped with a defined radius. The defined impact leads to a reshaping and to an inside-rounding of the weld toe. The plastic reshaping of the surface causes a residual compressive stress in the border layer. This stress can be proved up to a depth of 2 mm. Superimposition of the residual compressive stress on the acting loads displaces the later into less critical areas. It prevents the formation or extension of micro cracks. As a result a uniform and continuous peening trace becomes visible on the weld toe. Verification procedure At present three different verification procedures are available: nominal stress concept structural stress concept notch stress concept Detailed descriptions in: FKM guideline (German Forschungskuratorium Maschinenbau (FKM) e.v.) IIW recommendations (International Institute of Welding) Eurocode The Research Project REFRESH The research project REFRESH was started on 01/01/2006 as a joint venture project among several well-known partners of the Industry and Scientific Institutes. The target of the project was the development of a holistic process for the extension of the service life of new and existing welded steel constructions. In doing so different aspects have been considered like optimization of the process quality assurance further development of the methods of calculation Experimental results about the fatigue strength More than 1000 analyses made on butt seams (Fig. 1), on transverse stiffeners, and on longitudinal stiffeners (Fig. 2) impressively prove the effectiveness of the high-frequency peening processes. The Wöhler lines of Fig. 3 present the results of dynamic analyses made on butt seam S690Q and show that the fatigue stability has almost been doubled. The notch class for this case of application gave 111 for the as-welded specimens and 201 for the treated specimens. Also the results obtained on longitudinal stiffeners S690Q were impressive (Fig. 4). Compared to the as-welded joints the course of the Wöhler lines could be improved from slope M = 3 to slope M = 4; we consequently obtained a manifold increase in the service life. Fig. 3: Measured Wöhler lines of a butt seam Stress oscillating width [N/mm²] Load cycles [ ] (Source: Institut für Bauwerkserhaltung und Tragwerk TU Braunschweig) Fig. 4: Measured Wöhler lines of a longitudinal stiffener on both sides Stress oscillating width [N/mm²] Notch class 201 m=3 Notch class 111 m=3 Notch class 90 m=3 Notch class 142 m=4 Notch class 82 Notch class 56 Buttseam S690QL Longitudinal stiffener S690QL m=3 m=3 HiFIT-treated as-welded EC Rupture weld toe Rupture basic material HiFIT-treated as-welded EC Rupture weld toe Rupture basic material Load cycles [ ] (Source: Institut für Bauwerkserhaltung und Tragwerk TU Braunschweig)

7 Suitability of the Process Not every construction is suitable for the application of the HiFIT process (Fig. 5). HiFIT improves the service life of professionally welded joints. Whereas HiFIT cannot remove production or quality deficiencies or operational stability problems caused by the weld root. Therefore prior to applying the process the task must be carefully examined and evaluated. Some examples are presented in the following figures. Case studies: Fig. 5: HiFIT unsuitable Fig. 6: HiFIT suitable a b a b c d c d Literature Weich, I. Ummenhofer, T. et. al.: Influence of treatment and loading conditions on the fatigue strength of welds improved by high-frequency peening IIW-Document XIII International Institute of Welding 2008 Telljohann, G. Dannemeyer, S.: HiFIT peening procedure for post-weld treatment of welded steel constructions Stahlbau Weich, I. Ummenhofer, T.: Post-weld treatment in practice Stahlbau Weich, I. Telljohann, G. Dannemeyer, S. Ummenhofer, T.: REFRESH-service-life extension of existing and of new welded steel constructions DVS Congress 2008 HiFIT 7

8 Product Data, Spare-Parts & Accessories HiFIT device Technical data of the HiFIT device: Pressure display Compressed-air supply : 6 up to 8 bar Power requirement (rechargeable battery): Dimensions (L x W x H): 3.7 V, 950 mah 288 x 46 x 170 mm Union nut Weight: 1.8 kg Storage temperature: up to + 60 C Metering range of pressure display: 0 up to 12 bar Peak Cylinder Display deviation: ± 0,2 bar Air demand: at least 400 l/min Subject to technical alterations. Properties of the HiFIT device: compact and robust construction mode powerful Peening hammer ON/OFF long lifetime Lighting low weight easily guidable Pin integrated pressure display and lighting integrated interface for recording the parameters (pressure, frequency, intensity) easily replaceable wearing parts welding spatters removed simultaneously and easily HiFIT device Lighting ON/OFF Intensity adjustment the working result is highly reproducible Product Weight Dimensions designation Order No. in kg L x W x H in mm HiFIT device ,8 288 x 46 x 170 HiFIT pin HiFIT peak HiFIT piston HiFIT guiding HiFIT circlip HiFIT pressure spring HiFIT O-ring HiFIT rechargeable battery HiFIT battery charger HiFIT data interface HiFIT compressed-air conditioning Rechargeable battery Interface Compressed-air connection (coupler plug, nominal width 7.2) HiFIT pin HiFIT piston HiFIT guiding HiFIT spring 8

9 Handling General / Basic aspects The HiFIT device is pneumatically operated and requires a compressed-air supply 6 up to 8 bar and an air volume at least 400 l/min. Acc. to the calibration the peening frequency will be between 180 and 300 Hz. The intensity will be adapted to the material to be treated by means of a special adjustment mechanism (not via the supply pressure!). A direct measurement of the impact intensity is integrated in the device. The intensity of the single impact is recorded and can be read via a serial interface that is obtainable as an accessory to the HiFIT device (order No HiFIT data interface, page 8). This permits on the one hand adjusting and calibrating of the device for the each case and on the other hand and the continuous monitoring and tracking of the peening process. Execution of the HiFIT treatment The high-frequency peening process like the welding work ranks among the "special processes". For this, the requirements to the manufacturer to the end user company to the qualification of the staff must be complied with. The following description is not a substitute for staff training. Course of the action: The impact intensity of the HiFIT device is to be calibrated acc. to the material and to the pressure of the air supply prior to use. The calibration is to be checked by means of a specimen, and to be corrected, if necessary. For the optimal effectiveness the device must be used with an angle = 60 up to 80 with regard to the basic material (see Fig. 3) and with an angle = 70 up to 90 in the direction of movement (see Fig. 4); be guided with a speed = 3 up to 5 mm/s along the weld. Fig. 1: before treatment Fig. 2: after treatment Inspection of the Treatment Visual check: A treatment trace must be evident on all defined weld toes. The weld toe identifiable as line ("undercut") may no longer be discernible (Fig. 2). Check by measurement: The impression depth must be approx. 0.2 mm (Figures 5 and 6). Check by means of specimen. Fig. 3 Fig. 4 3 _ 5 mm/s 70 _ _ 80 Abb. 5 Fig. 6 approx 0,2 mm 9

10 The Scope of the PFEIFER Services Sale Consulting Service Training Calculations/FEM-Analysis Technical Consulting Spare-Parts Service Check for Cracks 10 HiFIT is a holistic solution concept for the extension of the service life of welded constructions. Sale PFEIFER is the exclusive worldwide distributor of the HiFIT device, and of the related spare-parts. Consulting service Our consultants will gladly visit you and give you help analysing the existing task. Calculatory verification procedure It is possible to analyse by way of calculation the existing concrete situation with appropriate methods like special FEM programs, and to optimize the situation, if necessary. Technical consulting We propose to you the submission of improvements. Calculatory proof certificates and the consulting are furnished by DYNATEC Gesellschaft für CAE und Dynamik mbh. Training The operating of the HiFIT device should be reserved for experts. Consequently the training of the users and of the supervisory staff is part and parcel of our offer. Spare-parts service The rapid availability of spare-parts is of paramount importance for us. Check for cracks By taking advantage of HiFIT for existing constructions, the macroscopic check for evidence of cracks is absolutely necessary. We would be delighted in placing at your disposal our trained check service staff to carry out the inspection. HiFIT

11 Application Examples Fig. 1 Kranbau Köthen Foundry crane Use of the HiFIT process for increasing the fatigue strength in case of welds between bulkheads and chords of crane crossbeams. Maurer Söhne GmbH & Co. KG Schachtbau Nordhausen Bridge construction Maurer Söhne und Schachtbau Nordhausen use the HiFIT process among others for increasing the fatigue strength of steel bridge structures. In many cases the accessibility of the weld details to be treated is problematic (compare Fig. 2 and Fig. 3). The small dimensions of the HiFIT device also permit treating the welds on difficult to reach areas. Fig. 2 Fig. 4 Fig. 3 Fig. 5 Fig. 6 REPower Systems AG Wind power plant Use of the HiFIT process for increasing the fatigue strength in case of welds on the transition structure between the jacket area and the pipe way area of the offshore wind power plants (Fig. 5 and Fig. 6). 11

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