RECENT CHANGES IN CODE REQUIREMENTS FOR REPAIR OF IN-SERVICE PIPELINES BY WELDING. William A. Bruce Materials Section, Edison Welding Institute

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1 IPC RECENT CHANGES IN CODE REQUIREMENTS FOR REPAIR OF IN-SERVICE PIPELINES BY WELDING William A. Bruce Materials Section, Edison Welding Institute ABSTRACT The API code requirements for repair of in-service pipelines by welding were recently up-dated. The 19 th edition of API Welding of Pipelines and Related Facilities - includes a new appendix (Appendix B) titled In-Service Welding, which is intended to eventually replace API Pipeline Maintenance Welding Practices. Work is also presently underway to up-date the requirements for weld deposition repair in ASME B Gas Transmission Systems. This paper reviews the rationale behind these changes and provides a brief summary of their primary features. INTRODUCTION Pipeline operators are often faced with opportunities to repair corrosion damage on pipelines, which is second only to mechanical damage as the primary cause of natural gas pipeline failures in the U.S. (Ref 0 ' To prevent an area of corrosion damage from causing a pipeline to rupture, the area containing the corrosion damage must be reinforced to prevent the pipeline from bulging. The most predominant method of reinforcing corrosion damage in cross-country pipelines is to install a fullencirclement repair sleeve. The application of this and other <Ref 2) repair methods are described in detail elsewhere. There are two basic types of full-encirclement sleeves; Type A and Type B (Figure 1). Type A sleeves are for repair of external corrosion only. While not necessary to prevent bulging, the ends of Type A sleeves are often welded to the pipeline to prevent further corrosion. Type B sleeves are for repair of leaking defects or defects that will eventually leak (e.g., internal corrosion). Therefore, the ends of Type B sleeves must be welded to the pipeline to contain the pressure. There are often significant incentives for avoiding interruption of pipeline service, therefore, this welding is often performed "in-service". There are two primary concerns with welding onto inservice pipelines, whether for installing repair sleeves or installing a branch connection prior to "hot tapping". The first is for "burnthrough", where the welding arc causes the pipe wall to be penetrated. The second concern is for hydrogen cracking, since welds made in-service cool at an accelerated rate as the result of the flowing contents' ability to remove heat from the pipe wall. An alternative method of repair for pipeline corrosion is deposited weld metal, or weld deposition repair (Figure 2). This method of in-service repair is attractive because it is simple and direct, and because it can be applied where the use of a full-encirclement sleeve is impossible, such as for the repair of fittings and field bends. In addition to the concerns for burnthrough and hydrogen cracking, there is concern for ensuring that the deposited weld metal has adequately restored both the static and fatigue strength of the pipeline. The results of a recent project at Edison Welding Institute (EWI) indicate that it is feasible to safely carry out weld deposition repair on corroded areas with a remaining wall thickness as thin as (Ref 3) in. (3.2 mm), provided that special precautions are taken. Properly made repairs were shown to have the ability to restore the strength of the pipeline and be resistant to pressure cycles. RECENT CHANGES TO API CODE REQUIREMENTS The 19 th edition of API Welding of Pipelines and Related Facilities - includes a new appendix that pertains to inservice welding. Appendix B - In-Service Welding - is intended to eventually replace API Pipeline Maintenance Welding Practices. Since its introduction in October 1966, the intent of API 1107 has been to provide a recommended practice for pipeline maintenance welding. This document is maintained by the API-AGA Joint Committee on Oil and Gas Pipeline Field Welding Practices, which also maintains API As the current Third Edition API 1107 approached its mandatory five year review in 1996, the committee recognized that it required updating to reflect updates that had been made to API 1104 and to reflect technological advances. To alleviate redundancy Copyright 2000 by ASME

2 between API 1104 and API 1107, and to alleviate time lag between updates, the committee approved a proposal to update and incorporate requirements of API 1107 into an appendix of API 1104 in In the mean time, the current edition of API 1107 was re-approved for another five year review cycle. An early draft of an appendix that was developed by the Maintenance Welding Sub-Committee was distributed to the committee in 1997 for review. Over the next two years, comments and suggestions that were received from the committee were reviewed and incorporated, as appropriate. In early 1999, the latest revision was approved by letter balloting of the main committee. Appendix B is included in the 19 th edition of API 1104, which was published in September The approach that was taken in the development of Appendix B was to first convert API 1107 into an appendix, to alleviate redundancy and time lag between updates, and then to make changes to reflect technological advances in the area of in-service welding. The "recommended practice" nature of API 1107 was maintained by using the non-mandatory "should" as opposed to "shall" throughout the appendix. The outline of the appendix follows that of the main body of API The title of Appendix B, "In-Service" Welding as opposed to "Maintenance" Welding, is intended to reflect the scope of the appendix, which is limited to only those welds made inservice (i.e., made onto carrier pipes that contain liquid petroleum or fuel gasses which may be pressurized and/or flowing). The appendix does not cover pipelines and piping systems which have been fully isolated and decommissioned, or have not been commissioned, since the requirements for these are the same as for new pipelines, to which the requirements in the main body of API 1104 should apply. The primary features of the appendix include an updated background section and alternative and/or additional requirements, most of which pertain to procedure and welder qualification, that should be applied to in-service welds. Updated Background Section The background section prominently indicates that the requirements for fillet welds in the main body of API 1104 should be applied to in-service welds that contact the carrier pipe, except for the alternative/additional requirements that are specified in the appendix. The updated background section clearly identifies the two primary concerns for in-service welding; bumthrough, where the welding arc causes the pipe wall to be penetrated, and hydrogen cracking, since welds made in-service tend to cool at an accelerated rate as the result of the flowing contents' ability to remove heat from the pipe wall. Some guidance on avoiding bumthrough is provided, although the majority of the appendix pertains to avoiding hydrogen cracking. Bumthrough guidance provided in the appendix includes a "rule of thumb" that resulted from early research by Battelle <Ref ' 4) indicating that bumthrough is unlikely if the wall thickness is inch (6.4 mm) or greater provided that low-hydrogen electrodes and normal welding practices are used, and reference to the use of the Battelle thermal analysis computer model (Ref 5) ' for predicting safe welding parameters. The three primary requirements for hydrogen cracking, all of which must be satisfied simultaneously, are identified in the appendix. These conditions are: hydrogen in the weld, the development of a crack-susceptible weld microstructure, and tensile stress acting on the weld. To prevent hydrogen cracking, at least one of the three conditions necessary for its occurrence must be minimized or eliminated. Like API 1107, the appendix indicates that, for welds made onto in-service pipelines, success has been achieved using low-hydrogen electrodes or a lowhydrogen process and, since low hydrogen levels cannot always be guaranteed, using procedures that minimize the formation of crack-susceptible microstructures. The appendix also indicates that the most commonly-used procedures rely on a sufficiently high heat input level to overcome the effect of the flowing contents. Methods for predicting required heat input levels are mentioned and a second reference is made to the Battelle thermal analysis computer model. The use of preheating, where practicable, and/or the use of a temper-bead deposition sequence (Figure 3) are also mentioned. Qualification of In-Service Welding Procedures As indicated throughout the document, the Qualification of In-Service Welding Procedures section of the appendix indicates that the welding procedure qualification requirements for fillet welds in the main body of the document should be applied to in-service welds, except for the alternative/additional requirements that are specified in the appendix. In the Specification Information section, the appendix indicates that the carbon equivalent of the material to which the in-service welding procedure applies should be identified in addition to the specified minimum yield strength (which is waived as an essential variable), and that carbon equivalent levels may be grouped. This provision for allowing in-service welding procedures to be qualified according to carbon equivalent groups as opposed to specified minimum yield strength groups was included because hydrogen cracking susceptibility is more a function of carbon equivalent level than it is to specified minimum yield strength, and carbon equivalent level can vary widely depending on pipe manufacturer and vintage. For example, a modern API 5LX-52 material that has been thermo-mechanically treated may have a low carbonequivalent value (and. therefore, a high resistance to hydrogen cracking); whereas, most 1950s-vintage X-52 materials have a high carbon-equivalent value. The appendix also indicates that the pipeline operating conditions (pipe contents, flow rate, etc.)

3 for which the procedure applies should be identified and that conditions may be grouped. For procedures intended to overcome the effect of the flowing contents by using a sufficiently high heat input level (heat input control procedures), the required heat input range should be specified. Similarly, for procedures intended to overcome the effect of the flowing contents by a using temper bead deposition sequence (temper bead procedures), the required weld deposition sequence should be specified. Footnotes pertaining to calculating carbon equivalent and heat input, like the ones shown below, are provided in the appendix. In addition to waiving essential variable requirement for specified minimum yield strength, the Essential Variables section also waives the essential variable requirement for pipe wall thickness. For in-service welds, the thermal severity (in terms of weld cooling rates) depends not only on wall thickness, but also on the pipeline operating conditions (pipe contents, flow rate, etc.). So instead of pipe wall thickness, the appendix indicates that an increase in the severity of the pipeline operating conditions above the group qualified constitutes an essential variable. Also, the appendix indicates that a change from a temper bead deposition sequence to some other deposition sequence constitutes an essential variable. The Welding of Test Joints section of the appendix indicates that the pipeline operating conditions that affect the ability of the flowing contents to remove heat from the pipe wall should be simulated while the test joints are being made. The purpose of qualifying a welding procedure is to demonstrate that the procedure is capable of producing sound welds under production conditions. Without simulating the ability of the in-service pipeline to remove heat from the pipe wall, unrealistically slow weld cooling rates can result, in addition to different solidification characteristics of the weld pool. A note in the appendix is provided that indicates that filling the test section with water and allowing water to flow through the test section while the test joint is being made has been shown to produce thermal conditions equivalent to or more severe than most typical in-service welding application, and that procedures qualified under these conditions are therefore suitable for most typical in-service application. The appendix also indicates that other media (e.g., motor oil) may be used to simulate less severe thermal conditions. A figure illustrating the use of this technique, which is a modification of an API 1107 figure, is provided, and is reproduced here as Figure 4. The use of this technique for simulating the ability of the flowing contents to remove heat from the pipe wall was (Ref 6) developed as part of research conducted at EWI. API 1107 includes a statement indicating that the cooling effects due to pipeline operating conditions should be considered, but gives no specific guidance. The Testing of Welded Joints section includes provisions for taking specimens from test welds made using either a sleeve weld or a branch weld configuration (as opposed to those for a sleeve weld only, as is the case with API 1107). A table listing the type and number of specimens that should be taken is included. A description of the Macro Section Test, which is included in API 1107 but does not appear in the main body of API 1104, is included in the appendix. Separate paragraphs for preparation, visual examination, hardness testing and acceptance requirements are provided. The purpose of the Macro Section Test is to reveal any significant discontinuities, including hydrogen cracking, that may be present. To facilitate this, the appendix indicates that at least one face should be ground to at least a 600 grit finish and etched with a suitable etchant prior to examination. The purpose of the hardness testing is to reveal the presence of hard heat-affected zone (HAZ) microstructures that may be present. The appendix indicates that procedures that produce HAZ hardness values in excess of 350 HV-lOkg should be evaluated with regard to hydrogen cracking risk. HAZ hardness values in excess of 350 HV are not necessarily unacceptable, but this is a level below which it is generally agreed that hydrogen cracking is not expected. A description of the Face Bend Test for branch and sleeve welds is also included in the appendix. The purpose of this test, which is taken from the Canadian code CSA Z Oil and Gas Pipeline Systems - is to reveal any hydrogen cracking at the weld toe areas. The test involves removing the sleeve or branch portion of the specimen, and the weld reinforcement, and bending the specimen so that the weld toe is placed in tension. An illustration of the test specimen is provided and is reproduced here as Figure 5. In-Service Welder Qualification The In-Service Welder Qualification section of the appendix indicates that the welder should be qualified to apply the specific procedure being used except for the alternative/additional requirements specified in the appendix. The Welding of Test Assembly section of the appendix indicates that the pipeline operating conditions that affect the ability of the flowing contents to remove heat from the pipe wall should be simulated while the test assembly is being made. The purpose of a welder qualification is to show that a particular welder is capable of executing a qualified procedure under production conditions. As with procedure qualification, without simulating the ability of the in-service pipeline to remove heat from the pipe wall, unrealistically slow weld cooling rates can result, in addition to different solidification characteristics of the weld pool. The same note pertaining to filling the test section with water or other media and providing flow while the test assembly is being made is included in this section. The appendix indicates that, for heat input control procedures, the welder should be able to demonstrate the ability to maintain a heat input level within the range specified. Similarly, for temper bead procedures, the welder should be able to demonstrate proper bead placement.

4 In the Records section, the appendix indicates that the pipeline operating conditions (pipe contents, flow rate, etc.) for which the welder is qualified should be identified, and that conditions may be grouped. Remaining Sections The remaining sections of the appendix include Suggested In-Service Welding Practices, Inspection and Testing of In- Service Welds, Standards of Acceptability, Repair and Removal of Defects. Much of the content of these sections is an updated version of those that appear in API 1107 which do not already appear in the main body of API In the Inspection and Testing of In-Service Welds section, the appendix indicates that, since in-service welds that contact the carrier pipe are particularly susceptible to hydrogen cracking, an inspection method that is capable of detecting these cracks, particularly at the carrier pipe weld toe, should be used. A note in the appendix is provided that indicates that magnetic particle testing, ultrasonic testing, or a combination of both, using properly developed, qualified, and approved procedures, have been shown to be effective at detecting hydrogen cracks at the toe of sleeve-, saddle-, and branch-tocarrier pipe welds. This guidance is based on the results of research conducted jointly between EWI and TWI. (Ref ' 7) In the Repair and Removal of Defects section, the appendix indicates that care should be taken during the removal of defects to ensure that the wall thickness is not reduced to less than that which is acceptable for the operating pressure of the carrier pipe. CODE REQUIREMENTS FOR WELD DEPOSITION REPAIR Until recently, weld deposition repair was prohibited in the US for gas transmission pipelines that operate at or above 40 percent of SMYS. 49 CFR Part Pipeline Safety Regulations - had required that damage either be cut out as a cylinder, repaired using a welded full-encirclement split sleeve, or that the pressure be reduced to a safe level. Several presentations were made to representatives of the US regulatory agencies in an effort to change these regulations to allow the use of weld deposition repair. A recently-adopted rulemaking by the USDOT OPS (Ref 8) allows both gas and hazardous liquid pipeline operators to make repairs using other methods, provided that reliable engineering tests and analyses show that the method can permanently restore the serviceability of the pipe. This rulemaking is intended to allow not only weld deposition repair, but other repair methods as well (e.g., ClockSpring repairs). Work is presently underway in the US to up-date the requirements for weld deposition repair in ASME B31.8. The proposed revisions indicate that small corroded areas may be repaired using weld deposition repair, provided that lowhydrogen electrodes are used. Repairs utilizing deposited weld metal require the use of a written maintenance procedure, an important factor of which is the selection of an appropriately qualified welding procedure and welder. The proposed revisions also indicate that in-service welding procedures and welders shall be qualified as described below, with specific regard for avoiding both burnthrough and hydrogen cracking. The maintenance procedure is to be based on demonstrated methods that assure permanent restoration of the piping system's pressure integrity. For background information on developing a weld deposition repair procedure, reference is made to guidelines previously developed at EWI. (Ref ' 9) For in-service welding, the proposed revisions to ASME B31.8 indicate that procedures and welders for carrying out weld deposition repair should be qualified under Appendix B of API The proposed revisions also indicate that procedures qualified under Appendix B for either branch or sleeve welds are suitable for weld deposition repair, provided the procedure is appropriate for the remaining wall thickness to which it is being applied. B31.8 allows repairs of other defects (i.e., other than corrosion, such as grooves and gouges) by grinding, provided that the defect is not dented. After grinding, if the ground area does not meet the remaining wall thickness requirement (i.e., enough wall thickness to meet either the B31G or the RSTRENG criterion), the proposed revisions allow the area to be repaired by filling it with deposited weld metal, provided that the area is small. SUMMARY A new appendix that pertains to in-service welding is included in the 19 th edition of API Welding of Pipelines and Related Facilities. Appendix B - In-Service Welding - is intended to alleviate redundancy between API 1104 and API 1107 and time lag between updates, and to address technological advances that have been made in the area of inservice welding. Work is also presently underway to up-date the requirements for weld deposition repair in ASME B31.8. REFERENCES 1. Eiber, R. J., Bubenik, T. A., and Leis, B.N. "Pipeline Failure Mechanisms and Characteristics of the Resulting Defects," Eighth Symposium on Line Pipe Research, Paper No. 7 (Houston, TX: American Gas Association, 1993). 2. Kiefner, J. F., Bruce, W. A. and Stephens, D. R., "Pipeline Repair Manual," Final Report to A.G.A. Line Pipe Research Supervisory Committee, Project PR , Kiefner and Associates, Inc., Columbus, OH, December 31,1994.

5 3. Bruce, W. A., Holdren, R. L., Mohr, W. C and Kiefner, J. F., "Repair of Pipelines by Direct Deposition of Weld Metal - Further Studies." PRCI Welding Supervisory Committee, Project PR , EWI, Columbus, OH, November Kiefner, J. F., and Fischer, R. D., "Repair and Hot Tap Welding on Pressurized Pipelines," Symposium during 11th Annual Energy Sources Technology Conference and Exhibition, New Orleans, LA, January 10-13, 1988 (New York, NY: American Society of Mechanical Engineers, PD-Vol. 14., 1987) pp Bubenik, T. A., Fischer, R. D., Whitacre, G. R., Jones, D. J., Kiefner, J. F., Cola, M. J., and Bruce, W. A., "Investigation and Prediction of Cooling Rates During Pipeline Maintenance Welding, and User's Manual for Battelle's Hot Tap Thermal-Analysis Models," Final Report to American Petroleum Institute, API Order No. D12750, December Bruce, W. A., and Threadgill, P. L., "Evaluation of the Effect of Procedure Qualification Variables for Welding onto In-Service Pipelines," Final Report to A.G.A. Pipeline Research Committee for PR , EWI Project No. J7141, Edison Welding Institute, Columbus, OH, July Bruce, W. A., and Kenzie, B. W., "Development of Optimized Non-Destructive Inspection Methods for Welds Made Onto In-Service Pipelines," ASNT International Chemistry and Petroleum Industry Inspection Technology III - Topical Conference (Houston), Federal Register, Vol. 64, No Department of Transportation, Research and Special Programs Administration, Pipeline Safety: Gas and Hazardous Liquid Pipeline Repair, Rules and Regulations, 64 FR 69660, December 14, Bruce, W, A. Guidelines for Weld Deposition Repair on Pipelines", PRCI Welding Supervisory Committee, Project PR , EWI, Columbus, OH, February End Fillet Weld End Fillet Side Seem (Butt Weld only, overtopping side strip not recommended) Type A Sleeve Figure 1. Type A and Type B sleeve Type B Sleeve

6 Figure 2. Example of weld deposition repair Weld metal buttering Grinding Completed weld Note 1 Note 1 - Toe of second buttering layer just consumes corner produced by grinding step. No new heat-affected zone in base material permitted. Figure 3. Example of temper-bead deposition sequence

7 H Figure 4. Note: This test position qualifies the procedure for all positions. Tests may be performed in other positions which will qualify the procedure for that position only. Suggested Procedure and Welder Qualification Test Assembly rfw~ /- See Note 1 /7 T I Appioximately 1" (25 mm) U-L * Approximately 9* (230 mm) Ve" (3 mm) max. R SLEEVE/ all comers BRANCH REMOVED Notes: 1. Test specimens may be machine cut or oxygen cut oversized and machined (see B ). 2. The sleeve or branch weld reinforcement should be removed flush with the surface of the test specimen. The branch weld test specimen is shown in the axial direction; specimens in the other direction are curved. Test specimens should not be flattened prior to testing. 3. Where wall thickness is greater than in. (12.7 mm), it may be reduced to in. (12.7 mm) by machining the inside surface. 4. In lieu of talcing separate specimens for the face bend test, the remaining portion of the nick break specimens may be used. Figure 5. Face-Bend Test Specimen