1、AWS D10.18M/D10.18:2018An American National StandardGuide for WeldingFerritic/AusteniticDuplex StainlessSteel Piping andTubingAWS D10.18M/D10.18:2018An American National StandardApproved by theAmerican National Standards InstituteNovember 14, 2017Guide for WeldingFerritic/Austenitic DuplexStainless
2、Steel Piping and Tubing2nd EditionSupersedes D10.18M/D10.18:2008Prepared by theAmerican Welding Society (AWS) D10 Committee on Piping and TubingUnder the Direction of theAWS Technical Activities CommitteeApproved by theAWS Board of DirectorsAbstractThis standard presents a detailed discussion of the
3、 metallurgical and welding characteristics and weldability of duplexstainless steel used in piping and tubing. A number of tables and graphs are presented in order to illustrate the text.iiAWS D10.18M/D10.18:2018ISBN: 978-0-87171-930-0 2018 by American Welding SocietyAll rights reservedPrinted in th
4、e United States of AmericaPhotocopy Rights. No portion of this standard may be reproduced, stored in a retrieval system, or transmitted in anyform, including mechanical, photocopying, recording, or otherwise, without the prior written permission of the copyrightowner.Authorization to photocopy items
5、 for internal, personal, or educational classroom use only or the internal, personal, oreducational classroom use only of specific clients is granted by the American Welding Society provided that the appropriatefee is paid to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, tel
6、: (978) 750-8400; Internet:25 mm 1 in), it may be necessary to increase welding heat input to obtain a slower cooling rate and the nec-essary austenite-ferrite balance. Where both corrosion resistance and toughness are important issues, microprocessor orwaveform controlled pulse GMAW will typically
7、provide more reproducible and satisfactory results. SMAW may be achoice for field welding applications.In GMAW there are a number of proprietary welding shielding gases used in welding DSS and SDSS alloys. Most gasesare argon with various additions of helium, nitrogen, and CO2. The selection of shie
8、lding gases and welding parametersfor FCAW should reflect the filler metal manufacturers recommendations.Process modifications such as hot wire GTAW, welding wire manipulation or vibration, and GMAW power sourcewaveform control offer increased arc welding deposition over the nonmodified processes.10
9、. Welding Procedures10.1 General. The ferritic/austenitic duplex stainless steels have proven to have good weldability when the proper pro-cedures are followed. The same welding processes used for austenitic stainless steels are used for the duplex alloys.Since many welding characteristics of the tw
10、o types of stainless steels are quite similar, welders easily adapt to weldingeither family of alloy. However, a major difference between duplex and austenitic stainless steels lies in the fact that theDSS alloys respond differently to the heat of welding, a factor that is a part of the Welding Proc
11、edure Specification andnot related to the welders skill.10.2 Cleaning Before Welding. The weld area to be cleaned before welding includes the joint edges and about 50 mm2 in of adjacent surfaces on both the inside and outside of the pipe. The presence of surface contaminants can causeweld defects su
12、ch as cracks, porosity, and lack of fusion. The joints should be free of surface oxides such as might be leftafter thermal cutting. Grinding or other mechanical means should be used to remove all paint, scale, oxides, and dirt.There are a number of elements and compounds that if not removed can caus
13、e cracking, weld defects, or reduced corro-sion resistance resulting from the heat of welding. Sulfur, phosphorous, and low-melting metals may cause cracks in theweld or HAZ. These contaminants could be present in cutting fluids, marking materials, oil, grease, or any shop dirt.Carbon or carbonaceou
14、s material left on the surface during welding can result in a high carbon surface layer which inturn lowers corrosion resistance in certain environments. Hand tools, such as wire brushes, used in the fabrication ofduplex stainless steels should be made from stainless steel and should be used exclusi
15、vely on duplex stainless steel mate-rial.Oil and grease compounds can be removed by suitable solvent cleaning followed by a thorough rinse. A suitable solventis one that does not leave a residue and is not harmful to the welder or to the weldment. ASTM A380, Standard Recom-mended Practice for Cleani
16、ng, and Descaling Stainless Steel Parts, Equipment and Systems, is an excellent guide to use.10.3 Preheat. Preheating is not recommended with duplex stainless steels except to dry the surface or when the temper-ature is below 16C 60F, or when welding heavy sections (wall thickness 50 mm 2 in) where
17、a preheat of 50C122F may be appropriate.10.4 Interpass Temperature. The maximum interpass temperature control often used for 2205 and the leaner DSS is150C 300F while the maximum for SDSSs is 65C 150F. However, these temperatures are conservative andhigher temperatures of 200C 400F and 150C 300F, re
18、spectively, are often employed. Basically there is no singleinterpass temperature that covers all situations. The lower the maximum interpass temperature, the less time the HAZ isin the sigma formation range which may be a consideration for multipass weld joints or when maximum corrosion resis-tance
19、 is of primary concern. On the other hand, lower interpass temperatures introduce the economic constraint ofincreased welding times. Consequently, there is no single interpass temperature that covers all situations.1“Development of mechanized field girth welding of high-alloy corrosion-resistant pip
20、eline materials,” by R. E. Avery and C. M.Schillmoller, NiDI Technical Series, No. 10,1061.AWS D10.18M/D10.18:20181310.5 Heat Input. Heat input is often a compromise between a heat input high enough to avoid fast cooling with theresultant tendency to form excessive ferrite and heat input low enough
21、to avoid excessive time in the 700C to 980C1300F to 1800F sigma formation range. A heat input range commonly used for DSS is 0.5 kJ/mm to 2.5 kJ/mm12.5 kJ/in to 62.5 kJ/in. However, there are codes and user specifications that restrict the maximum heat input to1.75 kJ/mm 44.4 kJ/in for alloy 2205 an
22、d 1.5 kJ/mm 38 kJ/in for the SDSS. Lean duplex stainless steels have beensuccessfully welded with substantially higher heat inputs than those cited above. Special heat input guides for the rootpass and first fill pass of duplex and super duplex stainless steels are discussed in Annex A.10.6 Purging
23、(Backing) Gas. Nitrogen is the most suitable backing gas for DSS because it protects the root surfacefrom nitrogen loss, especially in GTAW. It is also less expensive than argon, although argon has been used successfully.Hydrogen addition, as is sometimes used with austenitic steels, is dangerous fo
24、r DSS because of the possibility of hydro-gen embrittlement and should be avoided. See AWS D10.11M/D10.11, Recommended Practices for Root Pass Welding ofPipe Without Backing, for guides in pipe purging techniques and purging gas specifications. When using an oxygen ana-lyzer, an oxygen content of le
25、ss than 0.2% is a good starting point to determine if the surface discoloration is satisfactory.The gas tungsten arc process is the most reliable process to make a quality root pass weld. A gas purge is essential inproviding a full penetration weld that is essentially free of oxidation. An extreme e
26、xample of root pass oxidation madewithout purging or with improper purging is a condition commonly referred to as a sugared weld. A heavily oxidized(sugared) weld often has weld defects, has poor corrosion resistance in many environments, and should be removed.More often the weld and HAZ may have va
27、rious degrees of heat-tint discoloration due to some level of oxygen in thepurge. Parts being purged should be clean and dry prior to assembly as excessive moisture can also contribute to tintingof the root side. Depending upon the service, the presence of heat-tint can significantly reduce pitting
28、or crevice corro-sion resistance or particles of oxide may be a source of product contamination. For applications where heat-tint discolor-ation could influence service performance, a weld discoloration level guide such as shown in AWS D18.1/D18.1M,Specification of Welding Austenitic Stainless Steel
29、 Tube and Pipe Systems in Sanitary (Hygienic) Applications, is moreuseful than specifying an oxygen level.Nitrogen may be included in the purge gas and/or the shielding gas to compensate for any loss of nitrogen during weld-ing. Nitrogen additions to the shielding (torch) gas are typically 1% to 2%.
30、 Nitrogen additions up to 100% have beenused in purge gas (back purge). A reduction of nitrogen in the weld will increase the amount of ferrite and in turn affectthe ferrite to austenite balance. Nitrogen additions for ferrite balance are often used in automatic welding operationswhere there is clos
31、er control of welding parameters than in manual welding.10.7 Postweld Heat Treatment. Localized postweld heat treatment is seldom performed or considered necessary forpiping assemblies. The as-welded structure is normally satisfactory when proper welding procedures are used. If a heattreatment is em
32、ployed after welding, it must be a full anneal. The correct annealing temperature depends upon whetheror not filler metal with higher nickel content than that of the base metal was used. If no filler metal was used, or if match-ing nickel filler metal was used, then an appropriate annealing temperat
33、ure is generally 1040C 1900F minimum.However, if enriched nickel filler metal, such as 2209, is used, then the annealing temperature needs to be higher(1150C 2100F) in order to dissolve all the intermetallic phases that form during heating to the annealing temperature.The higher nickel content makes
34、 sigma phase stable to higher temperatures. Water quenching directly from the anneal-ing temperature is necessary to avoid sigma formation on cooling after annealing.2As discussed previously, time in the315C to 980C 600F to 1800F range should be kept to a minimum to minimize the development of harmf
35、ul phases.Some situations where postweld or post fabrication heat treatment may be appropriate are:(1) When cold deformation exceeds 15% such as the U bending of tubes,(2) Welding with a process where heat input cannot be kept within the recommended range, and(3) After hot bending.If for some reason
36、 a postweld heat treatment is considered necessary, it is advisable to consult the base metal manufacturerfor heat treatment specifics.2Kotecki, D. J.; 1989; “Heat treatment of duplex stainless steel weld metals.” Welding Journal, 68(11): 431-s441-s.AWS D10.18M/D10.18:20181411. Weldment Quality Veri
37、fication11.1 Inspection Method. Because of the need for good inspection, this subclause briefly describes several inspectionand test methods that have proven satisfactory for stainless steel pipe welds. In addition to the usual final inspection, apreweld and in-process inspection program is of prime
38、 importance.A complete quality control program may include:(1) Visual inspection of finished bevels and all areas within 12 mm 1/2 in of the planned joint;(2) Review of welder training, qualification, and practice pipes;(3) Penetrant testing (PT) of root bead to examine questionable areas;(4) Check
39、that proper interpass temperature and heat input control are employed;(5) Removal of surface irregularities and undercut to prevent stress concentrations; and(6) Radiography (RT) of final welds on a 100% or spot basis, as required. If this is not possible due to joint locationor lack of adequate equ
40、ipment, the use of in-process PT or Ultrasonic Testing (UT) inspection should be considered.11.2 Visual Inspection. Visual inspection is of greatest importance and is the most versatile method of inspection avail-able. However, the inspection is only as good as the experience, knowledge, and judgmen
41、t of the inspector. The AWSpublication, Welding Inspection, is suggested as a guide for visual inspection.11.3 Hydrostatic Testing. A test with water under static pressure will generally reveal only fully penetrating defectsthat were overlooked during visual inspection. A water pressure test is usua
42、lly made at one and one-half times the oper-ating pressure or just below the yield strength of the weakest elements. With the weld under stress, near-penetrating andmicro-thin defects may enlarge sufficiently to seep water. Temperature of the water should be above that of the ambientair to avoid con
43、densation on the pipe which may interfere with the detection of seeping water. Particular care should betaken to avoid entrapment of air when testing. Test pressures for pipe are provided in applicable codes and specifica-tions. Water high in chlorides, such as sea water, should never be employed as
44、 the test water. A good rule is to employonly potable water. After the hydrostatic test, the water should be drained and the system dried to preclude the possibil-ity of corrosion such as microbiologically influenced corrosion.11.4 Liquid Penetrant Methods. Several methods of surface examination of
45、welds are available. Essentially, all utilizea suitable penetrating liquid and a developer to expose surface discontinuities by contrasting color. A few methods use afluorescent penetrant in the solution that is readily visible under ultraviolet light. A smooth, clean surface is preferable;however,
46、defects can be distinguished from surface roughness by experienced personnel. Since chloride can pit or causecracking of DSSs and SDSSs, chloride-free cleaners and penetrants should be employed.11.5 Radiography. Radiographic examination is a nondestructive inspection method that is frequently used t
47、o deter-mine surface as well as internal weld defects, such as slag and tungsten inclusions, porosity, cracks, incomplete fusion,and incomplete joint penetration. The acceptance criteria for such defects are covered by established radiographic stan-dards. Experience, knowledge, and good judgment are
48、 essential in the proper interpretation of radiographs. Rules, proce-dures, and standards are available from several sources, such as the AWS publications Welding Inspection and theWelding Handbook, ASTM standards, and ASME Boiler and Pressure Vessel Code, Sections I, III, V, and VIII.11.6 Ultrasoni
49、c Methods. These methods utilize equipment capable of propagating an electronically-timed ultrasonicbeam through the material under inspection. The signals reflected from the surfaces and interior structure of the metalare indicated on a cathode ray tube or digital display for comparison and interpretation. As sound reflection in DSSs andSDSSs is complex, the use of the equipment requires a special skill and experience. It is usually not practical to ultrason-ically inspect welds involving duplex castings because of their large gr
