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1、G8. STRUCTURAL STEEL WORKSG8.L Reference StandardsParticular standards relevant for this chapter are listed below. If no standards exist, the work shall be performed according to recognized practice approved by the Engineer.American Society for Testing and Materials (ASTM) table8-lItemNameContent1AS
2、TM A 6/A 6MStandard Specification for General Requirements for Rolled Steel Plates, Shapes, Sheet Piling and Bars for Structural Use2ASTM A 36 /A 36 MStandard Specification for Structural Steel3ASTM A 108Standard Specification for Steel Bars, Carbon, Cold Finished, Standard Quality4ASTM A 153Standar
3、d Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware5ASTM A 325 /A325 MStandard Specification for High Strength Bolts for Structural St eel Joints6ASTM A 370Standard Test Methods and Definitions for Mechanical Testing of Steel Pro ducts7ASTM F 436 MSpecification for Hardened Steel W
4、as hers8ASTM A 563MStandard Specification for Carbon and Alloy Steel Nuts9ASTM A 607Standard Specification for Steel, Sheet and Strip, High-Strength, Low-Alloy, Columbium or Vanadium, or Bo th, Hot-Rolled and Cold-RolledDeutsche Norm (DIN)table8-2ItemNameContent1DIN 5 0049Materials Testing Certifica
5、tesAmerican Society of Mechanical Engineers (ASME) table8-3ItemNameContent1ASME Boiler and Pressure Vessel Code, Section IXQualification Standard for Welding and Brazing Procedures, Welders , Brazers and Welding and Brazing OperationsAmerican Institute of Steel Construction (AISC)table8-4ItemContent
6、1Specification for The Design of Cold-Formed Steel Structural MembersItemNameContent1AWS Dl.lStructural Welding Code - Steel2AWS Z49.1Safety in Welding and Cuttingtable8-5American Welding Society (AWS)G8.2. THE DESIGN OF STEELWORKWe shall design the steelwork to comply with the information given on
7、the Drawings. Loading and factors of safety shall comply with relevant codes and regulations. Shop drawings shall be prepared using welding symbols to AWS Dl.l where appropriate. Design calculations and shop drawings shall be submitted to the Engineer for his approval prior to fabrication of any mem
8、ber. We start the steel work after the Engineer approve it.Full information and specifications of all principal weld seams shall be a part of the design drawings. The Drawings shall indicate the type of weld, choice of electrodes, wires and welding powders to be employed. The number of welding passe
9、s shall be made in relation to the thickness of the plate, each pass shall be thoroughly de-scaled before the next pass is applied. For complicated parts, the sequence of welding shall be indicated clearly on the respective drawings.G8.3 MaterialsAll the materials should be qualified. And with the d
10、etail specification and the material characteristics. The materials should not crash severely so as to avoid that the materials are out of shape. After transporting to the site, the materials shall be placed properly to ensure the materials can be used without being damped.G8.4 Machining, Welding, B
11、olted and JointingG8.4.1 MachiningMachining of all parts shall be accurate and to specific dimensions so that replacements made as per design drawings may be readily installed. Like parts and spare parts shall be interchangeable.All machining shall be performed to secure proper matching of adjoining
12、 surfaces. If there are discrepancies between adjoining surfaces, these will be ground smooth, or machined, to proper alignment. Unfinished surfaces shall be true to the lines and dimensions shown on the drawings, and shall be ground to be free from projections and rough spots.The surface finish of
13、all parts and components shall conform with the respective strength and service requirements and as per approved drawings. Surface to be finished by machining shall be indicated on the shop drawings by corresponding standard symbols. G8.4.2 WeldingG8.4.2.1 Preparation for WeldingAll welds shall be p
14、erformed in such a manner that residual stresses will be reduced to a minimum. The weld seams shall, as far as possible, be positioned outside zones of stress concentration.Members and sections to be joined by welding shall be cut accurately to size, with their edges ground or machined to suit the r
15、equired type of welding and to allow full penetration and fusion of the weld with the base material.The surface of members or sections to be welded shall be free from rust, grease, mill scale, and other foreign matter for a distance of at least 30 mm back from the edge of weld. All painting material
16、s shall be removed well back of the heat-affected zones. Welding over zinc primers shall be avoided.G8.4.2.2 Welding ProcedureGeneralThe standard of welding works shall be in accordance with AWSAll welding shall be performed by the electric-arc (SMAW) method, and according to relevant standards unle
17、ss approved otherwise by the Engineer. The welding procedure shall be selected in consistence with the composition and properties of the base material, type of weld and working stresses of the welded joint. Whenever required, pre-heating and heat treatment of the welding seam shall be applied.The me
18、chanical properties of the weld shall conform to the base material as specified in the respective standards.All joining of plates in the principal stress direction shall be carried out using either single-welded or double-welded butt joints. Adjacent plates, carrying high stresses, shall in general
19、not differ more than 3 mm in thickness. If the difference is greater, the thicker plate shall be chamfered maxi mum 1: 4.Principal welds shall be ground as specified in the approved welding procedure. Cracked or defective tacks shall be removed before welding.For double welded butt joints, the root
20、must be completely removed by grinding or back-gauging before proceeding with the welding on the other side in order to prevent the presence of residues.Where auxiliary structural members are welded to components for the purpose of assembly and installation, the connecting welds shall be given parti
21、cular care. Once an installation has been completed, these auxiliary structural members shall be removed by burning them off, followed by grinding the affected areas flush with the plate, without introducing additional local thermal stresses. Knocking off of such members shall not be permitted.The e
22、lectrodes for arc-welding shall be classified on the basis of mechanical properties of the as-welded deposited weld metal, type of covering, hydrogen absorption, welding position of the electrodes and type of current.Electrodes shall be used only in the positions and under the conditions of intended
23、 use in accordance with instructions with each container. Electrodes for manual welding shall be suitable for welding in any position.During the welding operations the electrodes shall be stored and dried in electric heaters prior to welding, according to the instructions fro m the manufacturer.The
24、ignition of welding-electrodes shall not be initiated at the steel surface adjacent to the weld, but at the groove flanks to prevent detrimental increments of local hardness. Where ignition points of electrodes are discovered, they shall be ground appropriately.(1) Welding of Stainless SteelAll weld
25、ing of stainless steel shall be carried out using the inert gas method (TIG/MIG). Pipes shall be locally filled with inert gas during welding.Butt welds on thin walled pipes shall have a smooth, fully penetrated weld seam in- and outside. Partly penetrating, drops or metal sputter shall not be accep
26、ted.All welds and heat affected zones shall be carefully de-scaled and cleaned with a suitable cleaning paste and fresh water if inert gas has not been applied or if the inert-gas method has failed. Carbon steel tools shall not be used.G8.4.2.3 Heat TreatmentThe need for heat treatment shall be dete
27、rmined, taking into account the stress levels and design temperature, material properties including notch toughness, material thickness and forming, welding and inspection procedures according to internationally accepted standards . The shop heat treatment of welded components shall be performed on
28、the completed component prior to final machining.Procedures for heat treatment shall be submitted to the Engineer for approval.Heat treatment of site welding shall be performed according to the specifications for the welding procedure for the corresponding parts, which shall be submitted to the Engi
29、neer for approval.G8.4.2.4 Quality and Procedure ControlQuality testing and inspection methods, e.g. inspections by non-destructive testing (NDT) means, shall be carried out according to procedures approved by the Engineer. G8.4.2.5 Welders QualificationsFor welding of, or on, principal stress carry
30、ing parts, the standard of welding procedures, welders and welding operators qualifications shall conform to En-287 and EN-288. (ASM E Boiler and Pressure Vessel Code, Sections VIII and IX)All welders* and welding operators test certificates shall be submitted to the Engineer. G8.4.3 Bolted and Scre
31、wed JointsBolted joints shall be performed in accordance with good engineering practice and approved standards. All holes shall be made by drilling, reamed where required and otherwise made to fit the bolts with required accuracy. All bolts shall have washers and locks as required. Members to match
32、accurately shall be fitted with guide pins. Holes for bolts and screws shall in general have the same corrosion protection as the rest of the equipment.Bolts and screws shall have standard metric threads and be of high-quality steel.All standard-size bolts, studs, nuts and screws (including their wa
33、shers) shall be protected against corrosion, or made of stainless steel if so specified. Nuts and bolt-heads shall be hexagonal in shape and truly faced. Bolts and screws with sunk heads such as Hexagon Socket Head Cap Screws or Hexagon Socket Countersunk Head Cap Screws shall be made from stainless
34、 steel only, unless otherwise approved by the Engineer.G8.5 ErectionEach piece of steelwork shall be clearly marked before delivery, in accordance with assembly diagrams, and shall bear such other marks necessary to facilitate erection.The Contractor shall be responsible for the accurate positioning
35、, leveling and plumbing of all steelwork in accordance with the drawings and to the satisfaction o f the Engineer. The Contractor shall provide all necessary temporary braces or guys. Any material, which suffers damage and/or distortion during delivery, handling or erection shall be repaired or repl
36、aced to the approval of the Engineer.Site joints and connections shall not be finally bolted or welded until sufficient part of the structure is properly plumbed, leveled and aligned. No straining into position will be allowed.G8.6 TolerancesG8.6.1 GeneralIf not otherwise specified, the tolerances o
37、n measurements and shape shall be according to ISO 2768, class medium.In general, pipes, plates and profiled steel shall have tolerances in thickness, straightness etc. according to ISO 7452 or other approved standards. Unless otherwise specified, the following shall apply:G8.6.1.1 Straightness and
38、Flatness of Profiles and PlatesStraightness of profile s:L 12000 mm:Deviation from a straight line shall be within 0.002 LFlatness of plates:L = measured length, 1 L 3 mDeviation from a straight line shall be within 0.0 02 L.Pipe end planes shall be perpendicular to the pipe axis.G8.6.1.2 ThicknessP
39、late of thickness t 10 mm:toleranceis + 1.00 / - 0. 50 mmG8.6.2 Tolerances on ShapeDeviations from the theoretical shape on principal members shall not exceed the following, unless otherwise specified:Deviation of curved surfaces between measured and theoretical curvature shall not exceed 0.2 % of D
40、 over a chord length of 0.2 D. The pipes or shells shall throughout the entire circumference have a positive curvature with no dents.G8.6.2.1Fitting and alignment of plates:DefinitionPrincipal jointsSecondary jointsMaxi mum misalignment of centerlines of plates:0.1 t max. 3 mm0.1 x t maxm3.0 mmMaxi
41、mum misalignment on surfaces:0.1 t max. 3 mm0.1 x t + 1 mmmaxm4.0 mmPrincipal joints are perpendicular to main stresses, secondary joints parallel to main stressesG8.6.2.2Weld seam convexity:Plate thicknessConvexityt 12 mm1.5 mm13 t25 mm2.5 mm26 t 52 mm3.0 mmG8.6.2.3 Between the centre lines of prin
42、cipal members:+ 5 mm up to 15 m+ 10 mm over 15 mNote: the + 10 mm tolerance shall not be cumulative.G8.6.2.4In storey height: + 5 mm floor to floor.G8.6.2.5 In plumb ness of columns and walls:+ 10mm on any storey or over all the structure.G8.6.2.6 Symbols (units in mm):D = internal diameter of pipes
43、 or 2 x radius of curved plates t = thickness of the platesL = measured length of pipe, profile, plate.G8.7 Protective CoatingsProtective coatings of steelworks shall be applied in accordance with the manufacturers instructions. The requirements for such coatings shall comply with the appropriate cl
44、auses in B.S. 449 and B.S.C.P. 2 008.All surfaces which are to be painted, oiled or otherwise treated shall be dry and thoroughly cleaned to remove all loose scale and loose rust.Shop contact surfaces need not be painted unless so specified. If so specified, they shall be brought together while the
45、paint is still wet. Surfaces not in contact, but inaccessible after shop assembly, shall receive the full specified protective treatment before assembly. This does not apply to the interior of sealed hollow sections.In the case of surfaces to be welded, the steel shall not be painted or metal coated
46、 within a suitable distance of any edges to be welded if the paint specified or the metal coating would be harmful to welders or impair the quality of the welds.Welds and adjacent parent metal shall not be painted prior to de-slagging, inspection and approval. Parts to be encased in concrete shall n
47、ot be painted or oiled.The specified protective treatment shall be completed after erection. All rivet and bolt heads and site welds after de-slagging shall be cleaned. Damaged or deteriorated shop applied paint surfaces or metal coatings shall be made good with the same type of paint as the shop co
48、at and this coat shall be completed on site so as to be continuous over any welds and site rivets or bolts. Protection may be completed by painting on site subject to approval by the Engineer. Bolts, which have been galvanised or similarly treated, are exempted from this requirement. Site painting should not be done in very cold or misty weather or when humidity is such as to cause condensation on the surfaces to be painted.