1、PFI Standard ES-47 |Denotes Revision (Revised December 2013) WELDING OF INTERNALLY CLAD PIPING Prepared by Pipe Fabrication Institute Engineering Committee All PFI Standards are advisory only. There is no agreement to adhere to any PFI Standard and their use by anyone is entirely voluntary. Copyrigh
2、t by PIPE FABRICATION INSTITUTE Dedicated to Technical Advancements and Standardization in the Pipe Fabrication Industry Since 1913 USA 511 Avenue of Americas, # 601 New York, NY 10011 CANADA 655, 32ndAvenue, # 201 Lachine, QC H8T 3G6 WEB SITE www.pfi-institute.orgWelding of Internally Clad Piping P
3、FI Standard ES-47 |Denotes Revision (Revised December 2013) 1. Scope 1.1. This standard provides best practices for engineers, fabricators and installers for purchasing and assembly of pipe and fitting (piping components) that are internally clad with a corrosion-resistant or other metallic cladding
4、. 1.1.1. Piping components may consist of carbon or low alloy steel that has been manufactured by concentric forging of an internal liner made of stainless steel, nickel or nickel alloy or other metal in which the manufacturing process metallurgically bonds the cladding to the external piping compon
5、ent. Piping components may also be manufactured by the application of weld metal overlay by arc welding or other welding process such as explosion welding. 2. Cladding Material 2.1. The desired chemical analysis of the cladding must be established by the purchaser and stated in the specifications. W
6、hen cladding is applied by metallurgical bonding, identification of the grade or UNS number of the cladding material satisfies this need. When the cladding will be applied by welding, the fabricator will determine the welding filler metal that must be used to achieve the desired chemical composition
7、 of the cladding since this decision depends on the welding process that the fabricator will use; accordingly, owners and their engineers are generally discouraged from specifying the filler metal that is to be used when cladding is to be applied by welding. 2.2. If in situ verification of the compo
8、sition of weld buildup is required, the extent of such verification shall be specified by the customer. Verification shall be performed in accordance with PFI ES-42, Standard for Positive Material Identification of Piping Components using Portable X-Ray Emission Type Equipment. 3. Materials 3.1. The
9、 cladding thickness should be a minimum of 1/8 inch (3mm) thickness regardless of the thickness of the pipe components themselves. 3.2. When piping system components are supplied by the owner or someone other than the fabricator, those components should be purchased in accordance with this standard.
10、 If components do not meet this standard, the fabricator may have to add weld metal and machine the component ends to make the component suitable for shop and field welding; alternatively, the purchaser may wish to purchase components with square ends and have the fabricator prepare the ends. If cut
11、 lengths and fittings are supplied, the length of the fittings may not conform to standard B16 dimensions, and pipe will have to be trimmed to achieve the required assembly or system dimensions. 3.3. When the butt welds between clad pipe components are going to be radiographed or ultrasonically exam
12、ined by the fabricator or installing contractor, the ends of each component shall be radiographed or ultrasonically examined for a distance of not less than the greater of 3 inches or 1.5 times the thickness of the pipe from the end. Acceptance criteria shall be the same as will be required for the
13、butt weld that will be made between components. The internal surface of the cladding shall be sufficiently smooth that it does not interfere with proper interpretation or radiographs or ultrasonic examination signals. 3.4. For elevated temperature service, it should be recognized that differential t
14、hermal expansion will cause elevated stress at the transition between different types of materials (e.g., at carbon to stainless steel transitions). The customer shall be responsible for selection of filler metals to be used for welds joining clad pipe and fittings to each other and for overall suit
15、ability of such joints for the intended service conditions. 4. Weld End Preparation and Welding 4.1. Since pipe fittings that have been clad may not comply with the standard length dimensions shown in the applicable B16 standard, it may be necessary for the fabricator to measure each fitting prior t
16、o cutting pipe to achieve the correct dimensions in completed subassemblies. 4.2. For field welds and for pipe that is too small to weld from the cladding side, the weld end shall be machined as shown in Figure 1 and fit-up as shown in Figure 2. 4.3. Where ends to be welded together are available fo
17、r dimensional verification, the inside dimensions of both ends shall be measured and compared. Based on the measured dimensions, the fabricator shall determine the bore dimension PFI Standard ES-47 |Denotes Revision (Revised December 2013) so that the internal alignment of the ends to be joined will
18、 not exceed 1/16 in. 4.3.1. Where simply machining the weld end does not result in an extended root face (TIG lip) that consists of only the cladding material, the fabricator shall add weld metal to the end on the inside diameter and on the end of the pipe sufficient to ensure that the extended land
19、 is cladding material or suitable weld metal. The consumables and techniques used shall be such that the surfaces that will be exposed to the working fluid in the pipe in service are of the chemical analysis specified by the customer. On thin pipe, it may be possible to build up the ends sufficientl
20、y that a simple 35 to 40 bevel with a small root face will ensure that the wetted surfaces of the joint are of the required chemical analysis after the weld has been made. 4.3.2. Buildup of the weld end shall be made with filler metal that matches the corrosion-resistance or other critical propertie
21、s of the cladding material. 4.3.3. If the butt weld will be examined by radiography or ultrasonic methods, it is recommended that any weld buildup be similarly examined prior to making the weld or prior to shipping if the weld will be made in the field. When random radiography or ultrasonic examinat
22、ion is specified, it is not known which welds will be selected for examination prior to making the weld, therefore, it is recommended that 100% of any weld buildup should be examined. 4.3.4. If liquid penetrant examination is required for the cladding surface and weld buildup has been performed, the
23、 liquid penetrant examination shall be repeated on the final surfaces prior to fit-up. 4.3.5. Welds shall be made with the filler metal specified by the customer. The root pass will usually be welded using GTAW or GMAW. The balance of the weld can be competed using any suitable process. 4.4. Where e
24、nds to be welded together are not available for dimensional verification or where ends will match equipment or other parts, the engineer shall provide the bore dimension. It is recommended that the bore dimension be in accordance with PFI ES-21 less 0.25 inches. This will ensure that the minimum wal
25、l thickness of substrate is present and provide for approximately 1/8 inch (3mm) of cladding material. When this approach is used, it may be necessary for the cladding to be machined back from the substrate or it may be necessary to add sufficient cladding weld metal deposited to the weld end and in
26、side surface to ensure that the extended land is all cladding material or equivalent weld metal after machining. 4.5. Verification of the presence of stainless steel or nickel/nickel alloy cladding on the inside surface of the pipe can be verified by swabbing the surface with a solution of copper su
27、lfate in water. Any bare steel will quickly develop a copper deposit. Any copper deposits should be removed with a flapper wheel or aluminum oxide embedded in nylon wheels. Wire brushing is prohibited for removal of copper deposits since the wire brush simply smears the copper around instead of remo
28、ving it. The presence of cladding can also be verified using PMI in accordance with ES-42. PFI Standard ES-47 |Denotes Revision (Revised December 2013) 4.6. For shop welds where the pipe that is large enough to weld from both sides (i.e., it is large enough that a welder can climb inside and weld th
29、e cladding side comfortably, typically NPS 36 (DN 900) and larger), the following applies: 4.6.1. The cladding should be stripped back from the substrate material and beveled so that welding can be done from both sides of the joint. See Figure 3. Where cladding is stripped back, the remaining substr
30、ate wall thickness shall be measured to verify that the thickness satisfies the minimum design thickness requirements. Confirmed space precautions shall be observed whenever the cladding process requires personnel to enter pipe. 4.6.2. The inside of the joint is welded to flush with the end preparat
31、ion below the cladding level. After the outside has been backgouged to sound metal, the remainder of the inside weld should be completed using an appropriate filler metal to match the corrosion-resistance or other critical properties of the cladding material. See Figure 4. Any surface examinations s
32、uch as liquid penetrant examination that are required should be completed at this time. 4.6.3. The remainder of the weld should be completed from the outside if that has not already been completed. 4.6.4. After welding of the inside surface is completed, the inside surface should be cleaned using a
33、belt sander, abrasive-embedded nylon wheel or similar to remove any contamination from the internal welding operation. 5. Nozzles and Branch Connections 5.1. When nozzles and branch connections are used, the extent to which internal cladding is needed shall be established by the customer. 5.2. When
34、internal cladding of nozzles is required, it is preferred that clad tee fittings be used or that fittings be of a butt welding design that can be installed in a manner similar to that described above for circumferential butt welds. 5.3. The outlet size should be large enough that the inside diameter
35、 of the hole in the header can be overlaid with weld metal. See Figure 5. This is of particular concern for drain and instrument connections which are usually small-diameter connections. 5.3.1. Alternatively, the header can be beveled and the nozzle installed using a “set through” configuration in w
36、hich the corrosion-resistant alloy nozzle is welded to the lining at the inside surface of the header. This is a practical approach for pipe that is 1/2 inch (13 mm) thick or thinner. 5.3.2. Alternatively, the hole can be cut oversized and a sleeve of the appropriate corrosion-resistant alloy can be
37、 welded to the inner and outer surfaces and the fitting attached to both the sleeve and the header using the more conventional “set on” nozzle design. The inside surface of the pipe has to be sufficiently accessible that a welder can put a seal weld between the lining and the sleeve. Access limitati
38、ons make this approach practical when the branch connection is adjacent to a butt weld. 6. Tools 6.1. Tools such as grinding wheels and wire brushes that are used on cladding materials should be segregated and only used on those materials to avoid iron contamination of the clad surface. PFI Standard
39、 ES-47 |Denotes Revision (Revised December 2013) Figure 1 Weld end preparation details and fit-up for internally clad pipe that will be welded from the outside of the pipe Figure 2 Fit-up tolerance on internally clad pipe 20 to 30 R=1/8 min Bore dimension to match mating piece when mating piece is a
40、vailable to measure. When mating piece is not available, the bore dimension shall be in accordance with PFI ES-21 minus 0.25 inches. Other groove designs that use an extended root face (“TIG Lip”) joint design are also suitable. Where pipe is too thin or otherwise not suitable for machining it may b
41、e necessary to add weld metal to the root face using the filler metal to be used for the root pass to ensure that the root pass and any other wetted surfaces are of an appropriate chemical analysis. In this case, a simple v-groove joint design may be used. 0.075 to 0.090 in Substrate material Corros
42、ion-resistant Cladding 3/32 to 1/8” 1/16 in maxClass 2 or 3 Consumable insert may be used in lieu of open root welding. 0.06 to 0.10 in. Extended land (TIG lip) PFI Standard ES-47 |Denotes Revision (Revised December 2013) Figure 3 Machining details for weld ends of internally clad pipe where the pip
43、e can be welded from both sides. Successful removal of the cladding material may be verified by swabbing the inside surface of the weld end preparation with copper sulfate. This will result in deposition of a copper film where the clad material has been successfully removed. Copper film shall be rem
44、oved using a flapper wheel or equivalent prior to assembling the joint. Fit-up gap Substrate material Cladding Material Outer surface of pipeInner surface of pipe 1/16 to 3/16 in 1/4 in minimum 35 to 40 35 to 45 Lesser of t/3 or 3/8 in. 1/8 in max. 45 minimum PFI Standard ES-47 |Denotes Revision (Re
45、vised December 2013) Figure 4 Welding sequence for Clad Joints That are Welded from Both sides Step 1. Weld substrate root side with substrate matching filler metal Step 2: Backgouge to sound metal and reweld sufficiently to support members Step 3: Apply cladding weld metal on inside surface and com
46、plete the weld on the outside surface PFI Standard ES-47 |Denotes Revision (Revised December 2013) Figure 5 Branch Connection Options Opening too small to overlay the base metal Set-Through Nozzle Nozzle Opening with Liner 6.2. 6.3. 6.4. 6.5. Cladding15 Max Corrosion-Resistant alloy Welding electrod
47、e Cladding CladdingCorrosion-Resistant alloy Nozzle Corrosion-Resistant alloy tube Corrosion-Resistant alloy Nozzle Liner extends 1/16 in (1.5 mm) above flush minimum Seal weld nozzle liner to cladding. CURRENT INDEX OF 2014-2015 PFI STANDARDS A complete list of PFI members and available membership
48、CHARTER MEMBERS CONTRACTOR MEMBERS ASSOCIATE MEMBERS AFFILIATE MEMBERS HONORARY MEMBERS Associate and Affiliate member contributors Walter Sperko Sperko Engineering Services, Inc. Greensboro, NC Thomas Warrelmann Victaulic Company of America Easton, PA Sheryl Michalak Welding Outlets, Inc. Houston, TX PFI Standards and Technical Bulletins are published to serve proven needs of the
