1、 GUIDE SPECIFICATION FOR HIGHWAY BRIDGE FABRICATION WITH HPS 70W (HPS 485W) STEEL 2ndEdition June 2003 GUIDE SPECIFICATION FOR HIGHWAY BRIDGE FABRICATION WITH HPS 70W (HPS 485W) STEEL 2ndEdition 1. INTRODUCTION3 1.1. Fabrication With HPS4 2. BASE METAL MATERIAL PROPERTIES4 2.1. Weathering.4 2.2. Mec
2、hanical Properties5 2.3. Weldability.5 3. WELDING6 3.1. Preheat and Interpass Temperature7 3.2. Consumables For Matching Strength Welds .7 3.2.1. Submerged Arc Welding (SAW).7 3.2.2. Flux Cored Arc Welding (FCAW) 8 3.2.3. Gas Metal Arc Welding (GMAW) 8 3.2.4. Shielded Metal Arc Welding (SMAW) .8 3.2
3、.5. Welding For Hybrid Designs.9 3.2.6. Qualification Test Requirements .9 3.3. Consumables for Undermatched Weld Strength9 3.4. Fillet Weld Applications10 3.5. Heat Input.10 3.6. Heating For Curving, Cambering or Straightening10 3.7. Backing 10 4. FABRICATION EXPERIENCES AND TECHNIQUES 11 5. REPAIR
4、S12 6. COST-EFFECTIVE HPS BRIDGES.12 6.1. Hybrid Designs 12 6.2. Plate Sizes 13 6.3. Butt Splices 13 6.4. Fillet Weld Sizes13 6.5. Superstructure Replacement 13 Table 1. Chemical Composition.14 Table 2 Mechanical Properties14 Table 3. Minimum Preheat and Interpass Temperature for HPS 70W (HPS 485W)
5、15 Figure 1. The Graville Welding Diagram .15 Appendix A Special Provisions: Fabrication with HPS 70W (HPS 485W) Steel.16 Appendix B Additional References19 2GUIDE SPECIFICATION FOR HIGHWAY BRIDGE FABRICATION WITH HPS 70W (HPS 485W) STEEL 2ndEdition 1. INTRODUCTION The intent of this Guide Specifica
6、tion for Highway Bridge Fabrication With HPS 70W Steel, 2nd Edition, hereafter referred to as the HPS Fab Guide is to provide owners, designers and fabricators with the latest recommended methodology to fabricate and weld structures using ASTM A709 or AASHTO M270, Grade HPS 70W (HPS 485W) steel, ref
7、erred to hereinafter as HPS 70W. The HPS Fab Guide is recommended for use until such time that other industry codes and specifications have included this product and have provided the necessary regulatory provisions to successfully fabricate bridges. The 2nd Edition is based on continued research an
8、d experience with fabrication and welding, and will be updated as additional research is conducted and additional experience is gained. The latest in research and experience with HPS 70W steel may be obtained by contacting the American Iron and Steel Institute (AISI) website at www.steel.org. HPS 70
9、W is now furnished in as-rolled or control-rolled condition, thermo-mechanical control processed (TMCP) or quenched and tempered (Q controlled soaking; cooling of ingots, slabs, or plates; or a combination thereof. Hardenability is much better controlled as a result of the tighter ranges for alloyin
10、g elements. 2.1 Weathering HPS 70W corrosion resistance is calculated using the heat analysis equation in ASTM G101, Estimating the Atmospheric Corrosion Resistance of Low-Alloy Steels. The higher the index, I, the more corrosion resistant the steel. The minimum Corrosion Index, I, for HPS 70W steel
11、 is a 6.5, compared to a minimum of 6.0 for 50W and former 70W steels. Therefore, it is assumed that HPS 70W steel will have superior corrosion resistance than 50W and former 70W, although this is unsubstantiated by tests at this time. Like other weathering steels, there is a potential for atmospher
12、ic corrosion rates to increase in applications that subject high performance steel to continuously wet environments for prolonged periods of time, or to corrosive chemicals, including deicing salts. 42.2 Mechanical Properties Table 2 compares the initial ASTM specification requirements of HPS 70W wi
13、th more recent revisions to the specification as HPS has developed. One of the most significant advantages of HPS 70W steels is its enhanced toughness. Minimum specified Charpy V-notch (CVN) values for HPS 70W steels with thicknesses up to 4 inches equal or exceeds Zone 3 requirements for both fract
14、ure critical and non-fracture critical applications. CVN values in excess of 100 ft-lb at -100F are consistently achieved for these steels. Contract plans and specifications must specify each component requiring CVN testing, the applicable test temperature zone, although the same CVN values are requ
15、ired for all three zones, and whether FCM requirements apply. Minimum Charpy V-notch toughness requirements should be specified as described in the AASHTO Standard Specifications for Transportation Materials and Methods of Sampling and Testing, 1999, or later. 2.3 Weldability Weldability of HPS 70W
16、may be improved when diffusible hydrogen is controlled to a maximum of H8based on current studies. The relative differences in weldability between former Grade 70W and HPS 70W are illustrated in Figure 1, which plots the carbon content and carbon equivalent of both steels using the Hydrogen Control
17、Method described in AWS D1.5, Annex VIII4. Note that in the majority of the cases, HPS 70W material is within Zone I, Safe Under Most Conditions field, while a significant amount of the former Grade 70W material is within Zone II and Zone III. However, be aware that HPS 70W can have certain conditio
18、ns that are within Zone II and especially Zone III where crack susceptibility is high under all conditions. (Note: the term zone used here is different than the AASHTO temperature zone for toughness requirements, i.e., Zone I is defined in AWS D1.5, Annex VIII5.2.1 as “Cracking is unlikely but may o
19、ccur with high hydrogen or high restraint.”) AASHTO Specification M-270M/M-270, Section 1.2, states, “All steels covered by this specification are weldable. Welding procedures must be selected that are suitable for the steel being welded and its intended use.” Note the emphasis on use of proper proc
20、edures. ASTM Standard Specification A709/A709M, Section 1.3, states, “When the steel is to be welded, it is presupposed that a welding procedure suitable for the grade of steel and intended use or service will be utilized. See Appendix X3 of Specification A6/A6M for information on weldability.” ASTM
21、 A6/A6M, Section X3, “Weldability of Steel,” states in part, “Difficulties arise in steel when the cooling rates associated with weld thermal cycles produce microstructures . that are susceptible to brittle fracture, or more commonly, hydrogen induced (or cold) cracking.” High restraint is uncommon
22、in properly detailed girder bridges. The primary concern is for hydrogen control during the welding of steels to prevent cold cracking. Appendix X3 broadly characterizes weldability as “the relative ease with which a metal can be welded using conventional practices.” Appendix X3 also notes that, oth
23、er than the chemical composition and carbon equivalent of a steel, cold cracking can be influenced by the following: (a) Joint restraint/base metal thickness, (b) Filler metal and base metal strength compatibility, 5(c) Diffusible hydrogen content of deposited weld metal, (d) Preheat and interpass t
24、emperatures, (e) Filler metal and base metal cleanliness, (f) Heat input. The time delay between successive weld passes is also a factor that can influence cold cracking. The safety of steel bridges includes resistance to brittle fracture. One way to minimize the potential for fracture is to elimina
25、te the conditions that cause hydrogen-induced cracks. Weld hardness and toughness may be controlled by selection of proper filler metal and welding variables, but the base metal and HAZ hardness are more dependent on the sensitivity of the base metal to high cooling rates that cause unacceptable har
26、dening. The chemical composition of HPS 70W steel was designed to protect against excessive hardness in both the HAZ and base metal during welding and subsequent cooling. Awareness and use of good hydrogen control practices, along with proper procedures, is absolutely essential to successful welding
27、 of HPS 70W steel. Fabrication in accordance with AWS D1.5 in combination with this HPS Fab Guide substantially increases the assurance that hydrogen levels will be controlled by emphasizing each factor listed previously. 3. WELDING Submerged arc welding (SAW) is the primary process used to join pla
28、tes for bridge components in the United States today. Other processes, including shielded metal arc welding (SMAW), flux cored arc welding (FCAW) and gas metal arc welding (GMAW), are used for certain applications. All consumables should be handled in accordance with AWS D1.5, including Section 4, f
29、or all HPS applications, except that the maximum allowable diffusible hydrogen (Hd) in the weld will be 8 ml/100g (H8), regardless of the weld process used. When the reduced preheats of Table 3 are used, all consumables must be handled in accordance with the procedures described in AWS D1.5, Section
30、s 12.6.5, 12.6.6 and 12.6.7 to ensure that diffusible hydrogen is controlled to a maximum level of 4 ml/100g (H4). Alternatively, consumables may be handled according to the consumable manufacturers recommendations if the consumable manufacturer recommends storage and handling procedures different t
31、han those of AWS D1.5 Sections 12.6.5, 12.6.6 and 12.6.7, and the consumable manufacturer will guarantee a maximum level of H4when their recommendations are used. For the SAW process, fluxes received in undamaged hermetically sealed pails may be used right from the pail without baking. Flux received
32、 in moisture resistant bags shall be rebaked prior to use. When ordering consumables, the diffusible hydrogen level, H2, H4or H8, should be specified. Regardless of the weld process used, consumables or fabrication practices that produce weld deposits with diffusible hydrogen levels in excess of H8s
33、hould never be allowed. Welding procedures for HPS 70W steels must be qualified in accordance with AWS D1.5, Chapter 5, except as modified herein. The Code specifies that only low-hydrogen welding practices be used. Procedure qualification tests should be based on the appropriate temperature zone fo
34、r the project site. HPS 70W steel meets AASHTO Zone 3 requirements, but welds need only meet the site requirements. 3.1 Preheat and Interpass Temperature Research and experience has demonstrated that control of diffusible hydrogen to H4or less using the procedures and consumables 6recommended herein
35、 can easily be achieved in fabrication shops under actual fabrication conditions. Therefore, controls must be implemented to ensure a maximum of H4for all matching strength submerged arc welding of HPS 70W steel when the reduced preheats of Table 3 are used, unless specific evidence is presented by
36、a fabricator that satisfactory welds can be produced at higher levels of diffusible hydrogen up to a maximum of H8. Diffusible hydrogen levels greater than H4to a maximum of H8must only be allowed when the higher preheat requirements of Table 3 for an Hdmaximum of 8 mL/100g are used. This conforms t
37、o the requirements of the current AWS D1.5, Table 4.4 for Grades 485W (70W), 690 (100), and 690W (100W). To summarize, the minimum preheat and interpass temperature may be in accordance with Table 3 when using matching strength consumables producing a diffusible hydrogen level of H4maximum. For a di
38、ffusible hydrogen level greater than H4up to a maximum of H8, the minimum preheat and interpass temperature must be in accordance with the higher preheat requirements of Table 3 for a Hdmaximum of 8 mL/100g. The maximum preheat and interpass temperature for welding HPS 70W steel is 4500F (2300C). 3.
39、2 Consumables for Matching Strength Welds Consumables used for matching strength welds are generically classified in AWS D1.5, Tables 4.1 and 4.2. However, research has suggested that when welding HPS 70W steel, consumables that would meet the generic specifications for Grade 70W steels may not prov
40、ide weldments with diffusible hydrogen levels low enough to avoid hydrogen cracking. As a result, continuing research has determined the consumables that would be expected to provide sound, crack free welds using conventional low hydrogen welding practice. The following sections list recommended, ma
41、nufacturer specific consumables for producing matching strength welds for each process. 3.2.1 Submerged Arc Welding (SAW) The SAW consumable combination LA85 electrode with Mil800HPNi flux, manufactured by the Lincoln Electric Company, has produced welds that meet all of the requirements specified i
42、n AWS D1.5 and this HPS Fab Guide using the minimum preheat and interpass temperatures as listed in Table 3. Alternate, matching strength, manufacturer specific SAW electrode/flux combinations will be allowed, subject to the provisions of HPS Fab Guide Section 3.2.5, providing they conform to AWS el
43、ectrode/flux Classification F9A4-EXXX-X, with optional diffusible hydrogen designator H8or less, as described in AWS A5.23, Specification for Low Alloy Steel Electrodes and Fluxes for Submerged Arc Welding, with 1% Nickel, minimum, in the weld deposit, using the minimum preheat and interpass tempera
44、tures appropriate for the diffusible hydrogen level as listed in Table 3. The owner should require the fabricator to satisfy the full range of weld tests required by Section 12.6, in addition to other WPSs required by Section 5 of AWS D1.5. Preheat and interpass temperatures may be in accordance wit
45、h Section 3.1. Alternately, fabricators may elect not to use the lower preheat and interpass temperatures allowed in Table 3, and to use the preheat and interpass temperatures specified in AWS D1.5, Table 4.4 when welding HPS 70W with any consumables, providing the WPS is clearly marked that Table 4
46、.4 preheat is 7required, and the lower allowable preheats specified in Table 3 of this HPS Fab Guide are not allowed. In addition, diffusible hydrogen testing must be conducted by the manufacturer in accordance with AWS A4.3, Standard Methods for Determination of the Diffusible Hydrogen Content of M
47、artensitic, Bainitic, and Ferritic Steel Weld Metal Produced by Arc Welding, to demonstrate that welds can be produced with a maximum diffusible hydrogen level of H4. Test results in excess of H4require a retest, with or without revised welding parameters. 3.2.2 Flux Cored Arc Welding (FCAW) Matchin
48、g strength FCAW consumables TM-95K2 (AWS Classification E90T5-K2) with a minimum heat input of 25 kJ/in, manufactured by ITW/Hobart, and DS II 101H4M with a minimum heat input of 40 kJ/in, manufactured by ESAB, have produced weldments in research and manufacturers studies that meet all of the requir
49、ements specified in AWS D1.5 and this HPS Fab Guide using the minimum preheat and interpass temperatures as listed in Table 3. It is further recommended that fabricators handle these consumables in accordance with AASHTO/AWS D1.5, Section 12.6.7, in addition to strictly following manufacturers more stringent recommendations. Alternate, matching strength, filler metals are not recommended at this time. Additional recommendations will be listed on the AISI website www.steel.org as research and experience progresses. 3.2.3 Gas Metal Arc Welding (GMAW) Matching strength GMAW M
