gtx rods

GTAW Flux-Cored Wires for Open Root SS Welding

1009718

GTAW Flux-Cored Wires for Open Root SS Welding

1009718

Technical Update, May 2004

EPRI Project Manager

Greg Frederick

Cosponsors

Ed Gerlach, PP&L

Jim Grewe, OPPD

EPRI-RRAC • 1300 W.T. Harris Blvd., Charlotte, NC 28262 • PO Box 217097, Charlotte, NC 28221 • USA 704.547.6100 • [email protected] • www.epri.com

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ORGANIZATION(S) THAT PREPARED THIS DOCUMENT

EPRI

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CITATIONS This document was prepared by

EPRI 1300 W.T. Harris Blvd Charlotte, NC 28262

Principal Investigator or Author G. Frederick

Omaha Public Power District P.O.Box 550 Fort Calhoun, NE 68023

Principal Investigator or Author J. Grewe PPL Susquehanna, LLC 769 Salem Blvd. Berwick, PA 18603 Principal Investigator or Author E. Gerlach

This document describes research sponsored by EPRI.

The publication is a corporate document that should be cited in the literature in the following manner:

GTAW Flux-Cored Wires for Open Root SS Welding, EPRI, Palo Alto, CA: 2004. 1009718.

iii

ABSTRACT Gas Tungsten Arc Welding (GTAW) procedures for stainless steel open root welding applications typically require purging or shielding with an inert gas (i.e. argon), during the root and subsequent hot passes, to assist with wetting and to prevent atmospheric contamination of the exposed surface. Lack of adequate purging or welding without a purge, typically results in weld defects both on the surface and within the weld deposit, such as porosity and poor bead profile. Poor root weld profile such as lack-of–fusion (LOF), undercut and underfill (concave bead profile), surface contamination (i.e sugaring, burn through, oxidation) and porosity can have detrimental effects on the material properties and corrosion resistance.

In many cases, inert gas purging is impractical due to complexity of system design, access limitations and increased procedure costs and schedule. To address open root GTAW welding without an inert gas purge, EPRI-RRAC has evaluated various welding filler materials (i.e. flux-cored, fluxed wires) and fluxing agents that assist or eliminate the need for purging, while maintaining acceptable weld quality.

The welding filler materials and products evaluated in this study are used with the manual GTAW process and are intended to eliminate the ID purge requirements typical of open root stainless steel welding applications. These products are typically used for the root pass weld only, subsequent weld passes including the hot pass are applied with standard solid wire products of similar chemistry. The products do not eliminate the need for shielding gas typical of the GTAW process.

The flux constituents provide various functions for the arc welding processes, including gas and slag formers for protection from the atmosphere and bead shaping, arc stabilizers for reduced spatter and penetration, deoxidizers and scavengers for decreasing impurities in the weld puddle and alloying elements for adjusting the deposited chemistry. For the products evaluated in this study the fluxes are primarily used to protect the surface from atmospheric contamination and are not used to alloy the weld deposit. The welding wire (i.e. sheath or core-wire) is typically selected to meet the alloy specification of the weld joint and to match the remainder of the weld deposit.

Three concerns of using a welding product with a flux with the GTAW process were identified:

Most fluxing products have some level of halogen (i.e. fluorides, chlorides) in the flux constituents and residuals in the slag remain in the system if slag is not completely removed. Pipe welding applications in the power industry, typically do not allow access for subsequent slag removal.

Fluxed welding wires (flux-cored and fluxed wires) for GTAW require a keyhole welding technique to maintain a constant flow of flux to the ID surface of the root weld. Keyhole welding requires additional welder skill and training.

Flux-cored wires and fluxed wires are not recognized by AWS, requiring the filler material to be qualified and maintained on site.

v

The purpose of this project was to evaluate the weldability and optimum welding parameters to successfully implement the use of flux cored and coated GTAW filler materials for root pass welding of austenitic stainless steel without back purging. The project was also aimed at providing verification that the material properties were not compromised by eliminating the conventional argon purge, and providing information to assist with material procurement.

To establish the acceptability of these welding products, weld test specimens were fabricated and subjected to a series of tests to verify the minimum mechanical and corrosion resistance properties are met. This report includes the Welding Specification and Guidelines and results of the test matrix including chemistry and metallographic analyses, corrosion tests and mechanical testing.

In summary, the flux type GTAW welding rods successfully deposited a root pass and subsequent hot pass without a back purge. The welds were free of surface sugaring and porosity, with the single or split hot pass technique. The welding rods provide acceptable mechanical and corrosion properties per ASTM and ASME requirement. The flux-type GTAW product requires an experienced welder and proper training/practice to achieve the required quality and test results. Due to the experience level of the welder required and the potential halogen content of the slag (based on individual utility requirements), use of the flux-type GTAW rods should be evaluated on a case-by-case basis.

vi

CONTENTS

1 INTRODUCTION ................................................................................1-1

Welding Products.................................................................................................... 1-1

2 MATERIAL AND EQUIPEMENT........................................................2-1

Welding Consumables ............................................................................................ 2-1 Base Material .......................................................................................................... 2-2 Welding Equipment................................................................................................. 2-2

3 WELDING PROCESS ........................................................................3-1

Welding Specifications ...................................................................................... 3-1 Welding Guidelines............................................................................................ 3-4

4 MATERIAL PROPERTY VERIFICATION ..........................................4-1

Material Acceptance Criteria................................................................................... 4-1 Chemistry Analysis ............................................................................................ 4-2 Delta Ferrite Determination ............................................................................... 4-5 Mechanical Properties ....................................................................................... 4-7 Corrosion Analyses ......................................................................................... 4-14 Flux - Slag Analysis ......................................................................................... 4-24

5 RECOMMENDATIONS ......................................................................5-1

vii

1 INTRODUCTION Gas Tungsten Arc Welding (GTAW) procedures for stainless steel open root welding applications typically require purging or shielding with an inert gas (i.e. argon), during the root and subsequent hot passes, to assist with wetting and to prevent atmospheric contamination of the exposed surface. Lack of adequate purging or welding without a purge, typically results in weld defects both on the surface and within the weld deposit, such as porosity and poor bead profile. Poor root weld profile such as lack-of–fusion (LOF), undercut and underfill (concave bead profile), surface contamination (i.e sugaring, burn through, oxidation) and porosity can have detrimental effects on the material properties and corrosion resistance.

In many cases, inert gas purging is impractical due to complexity of system design, access limitations and increased procedure costs and schedule. To address open root GTAW welding without an inert gas purge, EPRI-RRAC has evaluated various welding filler materials (i.e. flux-cored, fluxed wires) and fluxing agents that assist or eliminate the need for purging, while maintaining acceptable weld quality.

Welding Products

The welding filler materials and products evaluated in this study are used with the manual GTAW process and are intended to eliminate the ID purge requirements typical of open root stainless steel welding applications. These products are typically used for the root pass weld only, subsequent weld passes including the hot pass are applied with standard solid wire products of similar chemistry. The products do not eliminate the need for shielding gas typical of the GTAW process.

The flux constituents provide various functions for the arc welding processes, including gas and slag formers for protection from the atmosphere and bead shaping, arc stabilizers for reduced spatter and penetration, deoxidizers and scavengers for decreasing impurities in the weld puddle and alloying elements for adjusting the deposited chemistry. For the GTAW process the fluxes are primarily used to protect the surface from atmospheric contamination and are not used to alloy the weld deposit. The welding wire (i.e. sheath or core-wire) is typically selected to meet the alloy specification of the weld joint and to match the remainder of the weld deposit.

Three concerns of using a welding product with a flux with the GTAW process were identified:

Most fluxing products have some level of halogen (i.e. fluorides, chlorides) in the flux constituents and residuals in the slag remain in the system if slag is not completely removed. Pipe welding applications in the power industry, typically do not allow access for subsequent slag removal.

Fluxed welding wires (flux-cored and fluxed wires) for GTAW require a keyhole welding technique to maintain a constant flow of flux to the ID surface of the root weld. Keyhole welding requires additional welder skill and training.

1-1

Flux-cored wires and fluxed wires are not recognized by AWS, requiring the filler material to be qualified and maintained on site.

The purpose of this project was to evaluate the weldability and optimum welding parameters to successfully implement the use of flux cored and coated GTAW filler materials for root pass welding of austenitic stainless steel without back purging. The project was also aimed at providing verification that the material properties were not compromised by eliminating the conventional argon purge, and providing information to assist with material procurement.

To establish the acceptability of these welding products, weld test specimens were fabricated and subjected to a series of tests to verify the minimum mechanical and corrosion resistance properties are met. This report includes the Welding Specification and Guidelines and results of the test matrix including chemistry and metallographic analyses, corrosion tests and mechanical testing.

1-2

2 MATERIAL AND EQUIPEMENT

The EPRI RRAC evaluated flux cored and flux coated GTAW welding rods to provide welding parameters and specification, and to establish mechanical and corrosion properties. This section introduces the Welding Consumables evaluated and the Welding Equipment used the study.

Welding Consumables

Three GTAW filler materials were selected for evaluation; TGX, Stain Plus and FMI welding rods (Table 2-1). These electrodes were designed specifically for root welding applications and are not intended for use on the hot pass and fill pass welds.

The Kobelco TGX flux-cored GTAW consumable electrode consists of a tubular alloyed sheath, with gas and slag forming compounds inside the sheath. The sheath material is similar to the actual chemistry designation with additional alloying elements added to the flux inside the sheath. TGX is manufactured in a 3/32-inch diameter and comes in 36-inch lengths.

The FMI and Stain-Plus stainless steel flux coated GTAW consumable electrodes consist of an alloyed solid rod, coated with a gas and slag forming compound on the outer surface. The electrodes are manufactured in a 3/32-inch diameter and come in a 36-inch (Stain Plus) and 39-in. (FMI) lengths.

The product heat analysis for the welding materials evaluated in this program is shown in Table 2-2.

Table 2-1. Flux-cored and Flux coated GTAW Consumables.

Supplier X-Ergon Kobe, Koballoy Division Filler Metal Incorporated (FMI)

Product Type Flux-coated GTAW wire Flux-cored GTAW (manual wire)

Flux-coated GTAW (manual wire)

Trade Name 126-T StainPlus, ER316L TGX Wire FMI

Available Material Types

Type 316L (core wire) Type 308L, 309L, 316L and 347 chemistries

Type 308L

AWS/ASME Specification

Core wire meets SFA5.9-93, ER316L

TGX309L, AWS R309LT1-5 AWS A5.22, ASME SFA5.22

TGX308L, AWS R308LT1-5 AWS A5.22, ASME SFA5.22

ER 308L FC

Available Diameters/Length

3/32-in (2.2-mm) by 36-in. length



Applications Root Weld, GTAW Process Root Weld, GTAW Process Root Weld, GTAW Process

2-1

Table 2-2. Product Heat Chemistry for Flux-cored and Flux coated electrodes.

Mfg. Type Heat No. C Si Mn P S Cu Ni Cr Mo

TGX-308L B7B2015 0.02 0.75 1.44 0.018 0.004 0.08 10.05 19.59 0.06

TGX-308L B8J2035 0.02 0.70 1.56 0.020 0.007 0.06 10.33 19.87 0.05

TGX-308L B3F701 0.02 0.73 1.66 0.021 0.006 0.06 10.43 19.57 0.04

TGX-309L B8B9015 0.02 0.66 1.52 0.023 0.006 0.04 12.87 23.99 0.04

TGX-309L B3A921 0.02 0.79 1.57 0.021 0.008 0.06 13.71 24.42 0.03

Kobelco

TGX-316L B3A912 0.02 0.79 1.39 0.020 0.010 0.09 11.93 18.29 2.42

Filler Metal Inc.

ER-308L FC R9709056 0.02 0.35 2.11 0.018 0.003 0.00 9.93 19.84 0.00

Stain Plus 126T Stain Plus 316L

Base Material

Initial welder familiarization studies were performed on 3/8-in. and 1/2-in. thick SA-240 Type 304 stainless steel plate. Additional welding parameter evaluation and development work was performed on 5 and 6-inch Schedule 40, SA-312 Type 304L stainless steel pipe. The pipe chemical analysis is shown in Table 2-3.

Table 2-3. Typical Chemical Analysis of SA-312, Type 304L Pipe

Type Heat No. C Si Mn P S Cu Ni Cr Mo Co

304L 161693 .018 .51 1.80 .033 .015 0.27 8.98 18.16 0.28 0.18

Welding Equipment

Welding development was performed exclusively with manual GTAW process utilizing standard constant current welding power supplies. A Hobart Cyber-TIG (Figure 2-4) and a Miller Aerowave (Figure 2-5) power supply were utilized during the coarse of the project.

The flux type GTAW welding rods are not equipment dependant products. Standard constant current (CC) power supplies and GTAW welding torches are utilized with these consumables.

2-2

Figure 2-4. Hobart Cyber-TIG 350 Power Supply

Figure 2-5. Miller Aerowave Power Supply.

2-3

3 WELDING PROCESS The development of welding parameters and techniques, to allow implementation of the GTAW process for open root process, was one of the key objectives of this program. The root pass must exhibit good shape and tie-in (fusion) with an internal surface free of oxides (sugaring) and porosity. The integrity of the root surface must also be maintained during the subsequent hot passes.

Extensive testing was performed on both plate and pipe coupons, first evaluating the parameters provided by the weld electrode manufacturers and then with modifications developed by EPRI RRAC and utility personnel. The results of this evaluation and development effort were used to establish the Welding Specifications and Welding Guidelines for SS open root welding without a back purge.

Welding Specifications

Welding parameter evaluations were performed with the flux-assisted filler materials on Type 304L pipe and plate coupons. The objective of the parameter development phase was to establish welding parameters and techniques that yield defect free (i.e. sugar and porosity) and acceptable ID reinforcement geometry (i.e. undercut and suck-back) and to hot pass welding parameters and techniques that maintained ID surface integrity (i.e. sugaring) with standard solid stainless steel 308L filler material.

Since most welders are unfamiliar with the keyhole welding technique and flux-assisted filler products, training or practice time are necessary. Inconsistent weld appearance and overall poor weld quality was typical in the initial weld trials. An experienced welder should be able to produce acceptable root passes around the full diameter of the pipe in all positions after three to four days of becoming familiar with filler rod manipulation and keyhole welding techniques. Availability of welders familiar with the flux assisted filler materials should be considered before committing to open root welding application without a purge.

The welding specification for the flux-cored and flux-coated filler materials was similar in most cases. Both types used a keyhole technique for the root pass, although when excessive mismatch or root gap was present, a non-keyhole technique could be utilized with the flux-coated filler materials. When a non-keyhole technique is used the filler rod is held tight in the gap with a short arc length, and the arc is worked side to side (walking the cup). This method is effective with excessive pipe mismatch but results in a thin root pass deposit. Care must be taken when applying the hot pass, if the root thickness is not substantial.

The optimal welding parameters and joint geometry specifications established during the initial welding trials are listed in Table 3-1.

3-1

Table 3-1. Basic Welding Parameters for Flux-assisted SS filler materials.

Technique Gas Flow rates cfh (l/min)

Shielding Gas

Shielding Gas Cup

Tungsten stick-out length

Current/ Polarity

Volts Travel Speed (ipm)

Flux-cored Root Pass

Keyhole 30-35 (21-24)

Argon Size #4 3/32-in. to 1/8-in.

85 –90

Straight

12 1.5–2.0

Flux-coated Root Pass

Keyhole or Standard

30-35 (21-24)

Argon Size #4 3/32-in. to 1/8-in.

85 –90

Straight

12 3.0 to 3.5

Hot Pass Standard, split pass

30-35 (21-24)

Argon Size #5 90 –100

Straight

12 2.5-3.0

3-2

Bevel (1) (2)

(degrees) Root Gap (3)

(inch) Land (4) (7)

(inch) Joint

Geometry (5)

Thickness (6)

Mismatch (8)

35-40

(70-included)

1/16 to 1/8-in. (3/32-in. optimal)

0-1/16 (feathered

edge optimal)

Standard open root V-

Groove

Unlimited* .050-in.

* - Thickness is based on equipment accessibility into the joint geometry.

Figure 3-1. Weld joint geometry for Flux assisted SS Filler Materials.

3-3

Welding Guidelines

The manufacturers of the flux assisted filler materials recommend the use of a keyhole welding technique, which allows the flow of the molten flux to the backside of the weld (Figure 3-2), similar to the SMAW process. Without the keyhole technique the amount of slag reaching the backside would be insufficient to appropriately shield the exposed molten weld metal resulting in surface oxidation and poor wet out. A keyhole welding technique is commonly used for autogenous welding applications and automated processes, with a square butt weld joint configuration, but is not common for manual welding with a flux assisted filler material. A skilled welder and additional training will be required to perform acceptable SS root welds without a backing purge.

Weld Metal

Welding Direction

Key-hole Molten Pool

.020-.040-inch

Figure 3-2. Keyhole Welding Method for Flux Cored Filler Material

The welding technique for the flux-assisted electrodes is significantly different than the standard solid wire techniques. A summary of guidelines established from manufacturers recommendations, technique development during the coarse of this project, and from utility feedback is listed below. It is recommended that additional training and mockup welds be performed prior to implementation. Basic weld preparation is shown in Figure 3-1.

Fit up and Tack Welding

Root gap should be as wide as or slightly larger than the electrode diameter. A root gap of 1/16-in to 1/8-in. is acceptable and 3/32-in. was considered optimal.

• A less than optimal weld root gap resulted in insufficient flux transfer to the back of the root pass resulting in ID sugaring and lack of penetration and ID reinforcement.

• A greater than optimal root gap, resulted in a decreased root thickness. A thinner root pass could potentially cause hot pass problems (i.e. ID sugaring, blow through).

• Root Land: 0 to 1/16-in. land. A feathered edge (no land) was optimal.

The pipe should be laid out in segments such that

3-4

• Roots welds are continuous from tack to tack.

• The welding current is highest in the overhead position and lower in the vertical position.

• The last weld root connection should be at the 1:00 to 2:00 position for better weld root quality. Stops and starts should not be at the 12:00 and 6:00 positions.

Tacks should be large enough to assure the proper gap is maintained and is not allowed to close up during the welding process.

Tack welds should be made with solid filler material.

Root Welding Technique

The initial root pass should be started on a tack.

The flux-assisted filler should be used for root pass welding only and with a keyhole technique.

• Although not recommended a non-keyhole technique was found to be acceptable with the flux-coated filler products, with excessive pipe misalignment or root gap.

• When a non-keyhole technique is used the filler rod is held tight in the gap with a short arc length, and the arc is worked side to side (walking the cup).

• The non-keyhole technique with the excessive gap typically results in a thin root pass thickness. Care must be taken when applying the hot pass to maintain ID surface integrity.

Root pass welding must be performed in the vertical up position. Downhill welding inhibits the formation of the keyhole and allows slag to form ahead of the molten weld bead leading to lack of penetration.

Travel speed will be approximately 1.5 to 2 ipm for flux-cored and slightly faster (3.0 to 3.5 ipm ) with the flux-coated welding rods. The actual travel speed is difficult to maintain with the manual process and the welder will be required to maintain the appropriate puddle size and keyhole.

The keyhole size and shape directly affects the quality of the root pass.

• Maintain a sufficient and consistent molten pool size when dipping the filler rod into the keyhole.

• Maintain a tight arc while dipping the weld filler rod into the keyhole. The arc length should be as short as possible, with an aim of .080 to .120-inch. This can be achieved through proper electrode stick-out and contacting the nozzle/cup on in the groove faces/walls (walking the cup).

• Keep rod in leading edge of puddle while continually feeding.

3-5

• Use a slight oscillation to maintain the keyhole with constant dipping of the filler rod (every 1-2 sec.).

• The keyhole must be large enough such that the slag can be continuously flow to the back side of the root, but small enough to maintain a proper shape on the inside of the pipe.

• The filler rod must be manipulated quickly or filler metal will freeze without penetrating to the ID.

• Avoid penetrating the backside of the root with the filler material.

When cutting off the arc in the middle of welding, the crater should be moved back and toward the sidewall in order to avoid crater defects.

When restarting an arc, the arc should be struck approximately 3/8” from the end of the stop, on the existing bead, while the previous bead is still hot and without removing any slag. The slag must not be removed from the root side of the weld as this will lead to oxidation upon re-arcing.

When root pass welding reaches a tack weld, the tack must be removed by grinding prior to restarting the welding operation.

The proper weld puddle will appear orange as opposed to a clear puddle characteristic of GTAW welding.

• Torch angle 10-20-degrees max.

• Cleaning: Do not remove slag until the entire root pass is complete. Wire brush and chip prior to subsequent passes (hot pass).

Hot Pass Welding Technique

Travel speed increased to 2.5 to 3.0-ipm compared to root pass.

Wire brush between at stops and starts, at the toe of the root weld bead and between the weld beads if a split hot pass is utilized. Do not remove slag from ID surface.

o If scale or slag is not removed completely with a wire brush, power wire brush or grind to remove.

o The flux-coated products tend to have a more tenacious slag coverage and scale residue and may require a power brush prior to subsequent weld passes.

Larger cup size, #5 compared to root pass.

Amperage increased 5-10 amps compared to root weld.

Split pass reduced the potential for burn through and ID sugaring, and may be beneficial for less skilled welders. Figure 3-3 illustrates poor ID surface quality resulting from poorly applied single hot pass.

3-6

A conventional single hot pass can be performed by a skilled welder with acceptable results

• Require a split hot pass to eliminate sugaring of the ID surface (Figure 3-4) and to reduce potential blow through.

• Split hot pass incorporates two hot passes with the arc (weld heat) focused on the sidewall (bevel face) of the weld joint.

• The first hot pass is deposited on the bevel face and across the midpoint of the root weld centerline. The second hot pass is focused on the opposite sidewall and overlapped the first hot pass.

When the root pass is applied with a feathered edge (no land) thicker root reinforcement typically resulted. A single hot pass could be applied over the thicker root pass without jeopardizing the ID surface integrity (Figure 3-5).

Figure 3-3. Weld Root Pass with Gross Sugaring poor welding technique.

Figure 3-4. Weld Root Pass with Split Hot Pass Technique. ID surface (left), split hot pass surface

3-7

(right).

Figure 3-5. Weld Root id Surface with Single Hot Pass Utilizing the Feather Edge Weld Preparation

3-8

4 MATERIAL PROPERTY VERIFICATION

Flux-coated and flux-cored GTAW wires are not currently recognized by the American Welding Society (AWS), thus requiring Material and Procedural Qualifications to be performed prior to ASME applications. To assess the deposited weld material for ASME applications a series of test specimens were fabricated and evaluated to verify the flux material did not adversely affect the weld chemistry and mechanical properties. This section is divided into three categories; Material Acceptance Criteria, Mechanical Properties and Corrosion Evaluation.

Material Acceptance Criteria

The filler materials evaluated in this program were qualified per ASME Section II, Part C (SFA-5.22), ASME Section III, NB-2430 and Reg. Guide 1.31 specifications for deposited weld metal chemistry and delta ferrite number (FN) measurements.

SFA5.22, Table 4, specifies the required tests for each electrode classification (R3XXT1-X), although since the flux-cored and fluxed electrodes are only used for the root pass the list was reduced to chemical analysis and ferrite number (FN) determination in this section. Additional mechanical tests were performed in the Mechanical Properties Section, to assure material properties were not diminished. The acceptance criteria and procurement requirements are based off the following Code references:

ASME Section II, Part C (latest edition)

Mechanical Properties (SFA-5.22, Table 4) Chemistry Composition Requirements (SFA-5.22, Table 1 and Figure 1) Procurement Specification Ferrite Number (FN) Determination

ASME Section III, NB2430 (1989 edition)

Chemistry evaluation per NB-2432.2 and Table NB-2432.2(a)-1 Ferrite Number Determination

Regulatory Guide 1.31 Control of Ferrite Content in Stainless Steel Weld Metal (Rev. 3, April 1978)

Ferrite Number between 5-20 in undiluted weld metal. AWS A5.4, Specification for Corrosion-Resisting Chromium and Chromium-Nickel

Steel Covered Welding Electrodes. AWS A4.2-74, Procedures for Calibrating Magnetic Instruments to Measure the Delta-

Ferrite Content of Austenitic Stainless Steel Weld Metal.

4-1

Chemistry Analysis

Chemistry pads (Table 4-1) per ASME Section II, SFA5.22, 8.3 Weld Pad and Figure 1, ‘Pads for Chemical Analysis of Undiluted Weld Metal’ were performed. The weld specifications met the requirements of SFA5.22, A6.9 to allow FN to be measured on the same weld pad. Welding data and parameters are recorded in Table 4-2 for the overlay specimens. Welding specification for the chemistry pads include:

Preheat: Not less than 60F Cleaning: Interpass slag removal required Shielding Medium: 100% Argon (SFA5.22, Table 2) Base Material: Type 304L Weld Process: GTAW (manual) Weld position: Flat Weld Buildup: Minimum 4 layers and 3/8-in thickness Weld Technique: Alternating weld direction between weld passes. Stringer beads last two layers. Interpass Temperature: Maximum 300F for last two layers Quenching: Interpass quenching allowed 20 sec. after welding is complete. Last pass must air cool below 800F before quenching. Dimensions: 3-in. long by 2-in. wide (minimum .75-in. wide, top layer)

Results of the chemistry analyses is to comply with Table 1 of ASME B&PV Code, Section II, Part C, latest edition, SFA-5.22, under the corresponding AWS classification for welding rod.

Table 4-1. Overlay Weld Specimens and Test Matrix for GTAW Flux Type Rods

Identification Weld Configuration Weld Material Tests

309–TGX-03 1G, 1/2-in. Type 304L Plate, 9 layers

3/32-in. TGX 309L Chem. Pad CX

308–TGX-03 1G, 1/2-in. Type 304L Plate 9 layers


316–TGX-03 1G, 1/2-in. Type 304L Plate 9 layers


316-SP-03 1G, 1/2-in. Type 304L Plate 9 layers

3/32-in. Stain Plus 316L Chem. Pad CX

GPUN-308-99 1G, 1/2-in. Type 304L Plate Min. 4 layers, 3/8-in. min.

3/32-in. TGX 308L

Chem. Pad CX

GPUN-309-99 1G, 1/2-in. Type 304L Plate Min. 4 layers, 3/8-in. min.


316L Stain Plus 1G, BOP, Type 304L Plate 3/32-in. Stain Plus 316L Slag analyses

308L TGX 1G, BOP, Type 304L Plate 3/32-in. TGX 308L Slag analyses

308L FMI Slag analyses

4-2

Table 4-2. Welding Parameters for chemistry pads

Identification Weld Filler/ Diameter

Amps Volts Shielding Preheat Layers Travel Speed

Weld Technique

308-TGX-03 TGX 308L 3/32-in.

110 21-23 100% Argon

70F 9 layers Manual Stringer and weave

309-TGX-03 TGX 309L 3/32-in.

147 19 100% Argon


316-TGX-03 TGX 316L 3/32-in.

--- --- 100% Argon


316-SP-03 StainPlus316L 3/32-in.

110 23 100% Argon


GPUN-308-99 TGX308L 3/32-in.

80-90 --- 100% Argon

60F Min. 4 layers, 3/8-in. min.

Manual Stringer and weave

GPUN-309-99 TGX309L 3/32-in.

80-90 --- 100% Argon

60F Min. 4 layers, 3/8-in. min.

Manual Stringer and weave

Figure 4-1. Typical Overlay Buildup for Chemistry and Ferrite evaluation, TGX 308L Test Plate (left) and Stain Plus 316L Test Plate (right).

Each weld pad was ground to remove weld ripple (solidification lines), and not to exceed the minimum requirement for FN determination and chemical analyses. The prepared weld pads were analyzed to determine if the chemistry met specification for R308LT1-5, R309LT1-5 and R316LT1-5 per SFA-5.22, Table 1. Testing methods met ASTM Standard E 1086-94 for spectrographic analysis. Chemistry analyses for the welding rods are recorded in Table 4-3, 4-4 and 4-5 for R308LT1-5, R309LT1-5 and R316LT1-5, respectively.

4-3

All chemistries for the 308L and 316L weld deposits were within required composition ranges specified in each table. One of the 309L (309-TGX-03) weld deposits (Table 4-4) had a Chromium (Cr) level slightly higher than the acceptable range.

Table 4-3. Chemical Analyses of Undiluted Weld Metal (SFA-5.22, Table 1) for R308LT1-5.

Identification C Cr Ni Mo Mn Si P S Cu FN

AWS Classification R308LT1-5

UNS No. W30835

0.03 18.0-21.0

9.0-11.0

0.5 0.5-2.5

1.2 0.04 0.03 0.5 ---

TGX 308L Heat No. B7B2015

0.02 19.59 10.05 0.06 1.44 0.75 0.018 0.004 0.08

TGX 308L 308-TGX-03B 0.02 20.21 10.35 0.03 1.57 NM 0.003 0.001 NM

TGX 308L Heat No. B8J2035 (2)

0.02 19.87 10.33 0.05 1.56 0.70 0.020 0.007 0.06

TGX 308L GPUN 308-99 (2)

0.019

20.29 10.26 0.04 1.58 0.71 0.020 0.008 0.06 9.7 (3) 7.3 (4) 8-10 (5)

TGX 308L (certs)

B3F701 (1) 0.02 19.57 10.43 0.04 1.66 0.73 0.021 0.006 0.06

TGX 308L 308-TGX-03 (1) 0.01 20.3 10.6 0.01 1.53 0.77 0.023 0.012 0.06 9.4 (3)

FMI 308L (certs)

Heat No. R9709056

0.02 19.84 9.93 0.0 2.11 0.35 0.018 0.003 0.0 8.1 (5)

FMI 308L 308-FMI-99 (1) Dedication heat from OPPD. (2) Dedicated heat from GPUN. (3) Ferrite Scope. (4) Magna Gage. (5) FN from Chemistry NB2433.1.


Identification C Cr Ni Mo Mn Si P S Cu FN


UNS No. W30935

0.03 22.0-25.0

12.0-14.0

0.5 0.5-2.5

1.2 0.04 0.03 0.5 ---

TGX 309L (certs)

Heat No. B8B9015 (2)

0.02 23.99 12.87 0.04 1.52 0.66 0.023 0.006 0.04

TGX 309L GPUN 309-99 (2)

0.014 24.22 12.70 0.04 1.56 0.82 0.020 0.008 0.08 23-24 (5)18-20 (6)

TGX 309L (certs)

Heat No. B3A921 (1)

0.01 24.42 13.71 0.03 1.57 0.79 0.021 0.008 0.06

TGX 309L 309-TGX-03 (1)

0.02 25.4 (3)

13.3 <.002 1.5 0.76 0.024 0.012 0.06 22.8 (4)

(1) Dedication heat from OPPD. (2) Dedicated heat from GPUN. (3) Cr content above specification. (4) Ferrite Scope. (5) Magna Gage. (6) FN from Chemistry NB2433.1.

4-4


Identification C Cr Ni Mo Mn Si P S Cu FN (WRC)


UNS No. W31635

0.03 17.0-20.0

11.0-14.0

2.0-3.0

0.5-2.5

1.2 0.04 0.03 0.5 ---

Stain-Plus 316L

316-SP-03 0.01 19.52 11.94 2.14 1.15 NM 0.013 <.001 --- ---

TGX 316L (certs)

Heat No. B3A912 (1)

0.02 18.29 11.93 2.42 1.39 0.79 0.020 0.010 0.09 ---

TGX 316L 316-TGX-03 (1)

.01 18.5 12.7 2.31 1.48 0.90 0.024 0.012 0.05 8.0 (3)

(1) Dedication heat from OPPD. (2) Dedication heat from South Carolina Electric and Gas Company. (3) Ferrite Scope.

Delta Ferrite Determination

The same weld pads used for chemistry analysis were used for the ferrite number determination per SFA-5.22, A6.9. The FN based on chemistry analyses SFA-5.22 A6.10 and alternative ferrite scopes was also conducted for comparative reasons. Figure 4-2, shows the various ferrite measuring devices (magna gage, ferritescope). Calibration of magnetic instruments (Magne-Gage) is specified in AWS 4.2. A calibration chart for the Magne-gage is shown in Figure 4-3.

Figure 4-2. Ferrite measuring devices, Fisher Feritscope (left) and Magne-Gage (right).

4-5

DELTA FERRITE MEASUREMENTS

16

2.8

5.73.4

8.19.9

12

24

y = -3.7692x + 107.99

0

20

40

60

80

100

1200 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

FERRITE NUMBER

MA

GN

E-G

AG

E

MAGNE-GAGELinear (MAGNE-GAGE)

Figure 4-3. Magne Gage Calibration Chart

The FN measurements for the stainless steel fluxed type welding rods are listed in the corresponding chemistry tables (Table 4-4, 4-5 and 4-6). The delta ferrite value for stainless steel was required to be in excess of 5 FN and below 20 FN for Class 1 and 2 components, per Regulatory Guide 1.31 and ASME, Section III, NB2430. The FN for Type 308L and 316L met the FN requirements. Type 309L, was included in the matrix, but does not fall in the same restrictions as the 308L or 316L. The 309L resulted in a FN in excess of the 20FN when determined with the Magne-gage and the ferrite scope.

4-6

Mechanical Properties

Procedure qualification tests, per ASME Section IX, Subsection QW-451, were performed to validate the capabilities of the flux-type welding rods to perform open root stainless steel welding without a purge. In accordance with these requirements, test specimens were removed from weld coupons for tensile and bend tests as described below.

The flux type welding rods were used to weld the root pass on pipe and plate specimens with a standard V-groove configuration (Figure 3-1). The flux type welding rods were used to apply the root pass with the manual GTAW process and the remainder of the weld was performed with SMAW process or solid wire GTAW process (Table 4-6). Welding parameters for the V-groove test specimens are listed in Table 4-7.

Table 4-6. V-groove Weld Specimens and Test Matrix for GTAW Flux Type Rods

Identification Weld Configuration Weld Material Tests

308-TGX-03-1 1G, 1/2-in. Type 304L Plate 3/32-in. TGX-308L, root pass 3/32-in. Type 308L GTAW, hot pass 3/32-in. Type 308L GTAW, fill passes

Tensile Tests Side bends CX

308-TGX-03-2 1G, 3/8-in. Type 304L Plate 3/32-in. TGX-308L, root pass 3/32-in. Type 308L GTAW, hot pass 1/8-in. Type 308L GTAW, fill passes

CX Prac. C Prac. E

GPUN-308-99 5G, 5-in. Type 304L, Schedule 120 Pipe

3/32, TGX 308L, root pass 3/32-in. Type 308L GTAW, hot pass 308L SMAW, fill passes

Tensile Tests Side bends Prac. A

316-SP-03-1 1G, 1/2-in. Type 304L Plate 3/32-in. StainPlus 316L 3/32-in. Type 308L GTAW, hot pass 3/32 & 1/8-in. Type 308L GTAW fill passes

Tensile Tests Side bends CX

316-SP-03-2 1G, 3/8-in. Type 304L Plate 3/32-in. StainPlus 316L 3/32-in. Type 308L GTAW, hot pass 3/32-in. Type 308L GTAW fill passes

Prac. E Prac. C CX

TGX-308-98 6G, 5-in. Type 304L, Schedule 120 pipe

3/32-in. TGX-308L Type 308L GTAW, hot pass Type 308L GTAW, fill passes

Prac. E Side bends RT

TGX-308-S-98 6G, 5-in. Type 304L, Schedule 120 pipe

3/32-in. TGX-308L Type 308L GTAW, split hot pass Type 308L GTAW, fill passes

Prac. E Side bends RT

FMI-308-98 6G, 5-in. Type 304L, Schedule 120 pipe

3/32-in. FMI 308L, root pass Type 308L GTAW, hot pass Type 308L GTAW, fill passes

Prac. E Side bends Root bend RT

FMI-308-S-98 6G, 5-in. Type 304L, Schedule 120 pipe

3/32-in. FMI 308L, root pass Type 308L GTAW, split hot pass Type 308L GTAW, fill passes

Prac. E Side bends Root Bend RT

Table 4-7. Welding Parameters for V-groove test specimens

4-7

ID Pass Amps Volts Root/Land Travel Speed

Weld Technique

Root 85-95 12 3/32-in./feathered 1.7-2.0 ipm Keyhole, vertical up

Hot pass 90-100 12 --- 2-3 Stringer

TGX-308-98

Fill --- Manual Weave

Root 85-95 12 3/32-in./feathered 1.7-2.0 ipm Keyhole, vertical up

Hot pass 90-100 12 --- 2.5-3.5 Stringer

TGX-308-S-98


Root 85-95 12 3/32-in./feathered 3-3.5 Keyhole, vertical up

Hot pass 90-100 12 --- 2-3 Stringer

FMI-308-98


Root 85-95 12 3/32-in./feathered 3-3.5 Keyhole, vertical up

Hot pass 90-100 12 --- 2.5-3.5 Stringer

FMI-308-S-98


Root 122 23 .110/.050 Manual Keyhole, vertical up

Hot pass 115 22.4 --- Manual Stringer

308-TGX-03-1

Fill 110-121 23 --- Manual Weave


Hot pass 106 22 --- Manual Stringer

308-TGX-03-2

Fill 125 23-24 --- Manual Weave


Hot pass 106 22 --- Manual Stringer

316-SP-03-1

Fill 121-145 22-24 --- Manual Weave

Root 98 22.5 .111/.050 Manual Keyhole, vertical up

Hot pass 106 20 --- Manual Slight Weave

316-SP-03-2

Fill 115 22.5-23 --- Manual Weave

* Shielding gas - 100% argon for all passes. No back purge for root or hot pass.

Visual and RT Examination

A visual and RT examination was conducted on weld specimens to assure weld quality was acceptable prior to subjecting welds to further testing including mechanical and corrosion test.

After completing the weld root passes, the ID of the pipe was inspected to verify that there were no obvious defects (LOF, ID reinforcement) and slag coverage was acceptable. A typical ID and OD surface of a TGX root pass is shown in Figure 4-4. The ID surfaces were typically inspected again after the subsequent hot pass welds were completed with standard ER308L GTAW solid rod using a single and split hot pass. Specimens were inspected for typical defects associated with the hot pass (i.e. burn through, sugaring). Typical ID surfaces after single and split hot passes for TGX and FMI root welds are shown in Figure 4-5 and 4-6.

4-8

Figure 4-4. TGX 308L Root Pass, ID surface (right) and OD surface (left).

Figure 4-5. Photograph of Root Pass ID Surface, TGX308L with Single Hot Pass (left) and Split Hot Pass (right).

Figure 4-6. Photograph of Root Pass ID Surface, FMI 308L with Single Hot Pass (left) and Split Hot Pass (right).

4-9

After completing the hot passes, the test coupon were welded out and capped to support the post welding evaluation effort. Four of the pipe weld coupons were radiographically tested (RT) to verify rejectable indications were not present.

No rejectable indications, per the requirements of ASME Section III, were found about the full diameter of the four test coupons evaluated.

A number of test welds were cross-sectioned to permit visual inspection and light microscopy of the weld root and hot passes. There was no “suck back”, excessive penetration, porosity, or sugaring on the test welds evaluated. Cross sections of typical v-groove welds with TGX and StainPlus root passes are shown in Figure 4-7. The ID reinforcement for the flux-type welding rods was considered acceptable, and root pass welds could be made with no “suck back”, excessive penetration, porosity, or sugaring.

Figure 4-7. Typical Cross Section of V-groove welds with Stainplus 316L root pass (left) and TGX 308L (right).

Bend Tests

Full thickness transverse side bend and root bend tests were performed as required by ASME Section IX, QW-451.1. The transverse side bends were machined as illustrated in QW-462.2, and root bends per QW-462.3(a). Bend testing was performed in accordance with QW-466.

Four side bends were completed for each weldments and were typically removed from the 12:00 (flat) and 3:00 (vertical) positions for the pipe specimens. Root bend test specimens from the FMI single and split bead hot pass coupons were taken at the 3:00 position.

No indications were observed in the root area of the root bend specimens or in subsequent fill passes for the side bend specimens, as seen in Figure 4-8 and 4-9. Table 4-8 lists results of side and root bend tests.

4-10

Table 4-8. Bend Test Specimens

Weld Specifications Identification Test Results

TGX 308L, 5-in. Schedule 120 pipe

GPUN 308-99 (4) Side Bends Passed

TGX 308L, 1/2-in Plate

TGX-03-0.5 (4) Side Bends Passed

Stain Plus 316L, 1/2-in. Plate

SP-03-0.5 (4) Side Bends Passed

FMI 308, 5-in. Schedule 120 pipe

FMI-308-98 (4) Side Bends Passed


FMI-308-S-98 (4) Side Bends Passed

TGX 308, 5-in. Schedule 120 pipe

TGX-308-98 (4) Side Bends Passed

TGX 308, 5-in. Schedule 120 pipe

TGX-308-S-98 (4) Side Bends Passed


FMI-308-98 (1) Root Bend Passed


FMI-308-S-98 (1) Root Bend Passed

Figure 4-8. Typical Side Bend Test Specimens – 1/2-in. Plate Weldments, TGX 308L (308-TGX-03, left) and StainPlus 316L(316-SP-03, right).

4-11

Figure 4-9. Typical Root Bend Test Specimen, FMI (Single, FMI-308 and Split hot pass FMI-308-S).

Reduced Section Tensile Tests

Tensile specimens were removed from the each test coupon (pipe or plate) per QW-463.1. Reduced section tensile coupons were machined per ASME Section IX, QW-461.2(b). The test results shown in Table 4-9 indicate that all of the specimens were considered acceptable. The specimens ruptured in the weld at an ultimate stress exceeding 82 ksi, which is above the 75 ksi minimum allowable for the SA-312, Type 304L pipe. A photograph of a typical test coupon after testing is shown in Figure 4-10 and 4-11.

Two reduced section tensile tests (GPU-308-99 A & B) failed in the parent metal (Figure 4-10), although still met the minimum specified tensile strength (>75ksi) per Section IX, QW/QB-422.

Table 4-9. Reduced Section Tensile Results

Weld Material

Identification Dimensions Area Ultimate Strength Location of Fracture

Width & Thickness

In x in. Pounds Psi

GPU 308L-99A 0.754 x 0.465 0.3506 29,400 83,900 Parent Metal TGX 308L

GPU 308L-99B 0.752 x 0.483 0.3632 29,800 82,000 Parent Metal

TGX-308-98 (flat)

0.750 x 0.184 0.1380 11,600 84,100 Weld Metal TGX 308L

TGX-308-98 (vertical)

0.751 x 0.192 0.1442 11,840 82,100 Weld Metal

TGX-308-S-98 (flat)

0.748 x 0.173 0.1294 10,720 82,800 Weld Metal TGX 308L

TGX-308-S-98 (vertical)

0.748 x 0.193 0.1444 12,000 83,100 Weld Metal

4-12

FMI-308-98 (flat)

0.754 x 0.188 .1418 11,840 83,500 Weld Metal FMI 308L

FMI-308-98 (vertical)

0.754 x 0.189 .1425 11,760 82,500 Weld Metal

FMI-308-S-98 (flat)

0.754 x 0.187 .1410 11,760 83,400 Weld Metal FMI 308L

FMI-308-S-98 (vertical)

0.750 x 0.184 .1380 11,440 82,900 Weld Metal

Note: All samples prepared in accordance with ASME Section IX

Figure 4-10. Typical Tensile Test Specimen, FMI-308-S-98, vertical location.

Figure 4-11. Reduced Section Tensile Specimens – Kobe TGX 308L Weld specimen (GPUN-308-99). Failure location in Parents Metal.

4-13

Corrosion Analyses

To establish a basis for accepting the quality of stainless steel welds prepared without a back purge, ASTM A-262, Standard Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels, were used to evaluate austenitic stainless steel weld deposits. Three Practices were specified for this program including:

ASTM A-262, Practice A-Oxalic Acid Etch Test for Classification of Etch Structures of Austenitic Stainless Steels

ASTM A-262, Practice E-Copper-Copper Sulfate-Sulfuric Acid Test for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels

ASTM A-262, Practice C-Nitric Acid Test for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels

The slag remaining on the weld deposits were also collected and analyzed for halogens and low melting temperature elements.

Practice A-Oxalic Acid Etch Test

Practice A is an oxalic acid test for classification of etched structures of austenitic stainless steel materials and is used to determine acceptability of materials or weld deposits. Practice A is typically used as a rapid screening method to determine if the material is free of susceptibility to rapid intergranular attack in more aggressive tests (Practice B through E). If Practice A provided an acceptable etch structure (step or dual structure) the material is considered acceptable, although if an unacceptable ditched structure occurs additional testing is required. Further testing can provide a quantitative or verification of acceptability under specific test conditions.

Low carbon grades of stainless steel (i.e. Type 304L), are tested after sensitizing heat treatment (Sensitizing heat treatment, 1-h at 1250F) or in the as-welded condition. Specimens evaluated in this program were open root v-groove welds in the as-welded condition. The weld specimens are evaluated by cross-sectioning the weld and preparing the surface (polished, etched, etc.) according to the procedure specification of ASTM A 262, Practice A. The etched surface is typically evaluated at various locations along the HAZ at 250X and 500X magnification. Since the welding process being evaluated is primarily concerned with the quality of the root weld, acceptability of the etch structure at the toe of the root pass was used to determine acceptability. An acceptable etch structure for Type 304L austenitic stainless steel includes a step or dual structure, which consists of a structure with no grains completely surrounded by ditches.

Practice A testing was performed on a 5-in. Type 304 Schedule 120 pipe with a V-groove joint geometry to determine the degree of sensitization in the HAZ adjacent to the weld deposit. The weld deposit consisted of a root pass with flux type GTAW electrode (TGX-Type 308L), a single GTAW hot pass with solid Type 308L filler material, and intermediate and cap passes with Type 308L SMAW filler material.

4-14

Three locations along the HAZ were evaluated per ASTM A-262 Practice A (Figure 4-8). Location C is in the HAX at the toe of the root pass, location B is in the HAZ at the mid-section of the overall weld, and location A is in the HAZ at the toe of the cap passes. Photographs of the cross section at location C at 250x and 500x are shown in Figure 4-9. Photographs of the cross section at location B at 250x and 500x are shown in Figure 4-10. Photographs of the cross section at location A at 250x and 500x are shown in Figure 4-11.

No indication of ditching was observed at any of the location (A, B or C) at either 250X or 500X magnification. All weld locations were found to have an acceptable etch structure (step structure). Practice A test results are shown in Table 4-10.

A ditched structure for low carbon austenitic stainless steel materials (i.e. Type 304L) is not common when standard stainless steel welding procedures are followed. A ditched structure or sensitized structure can be produced if the base metal is overheated typically when the hot pass is applied or when the interpass temperature is not maintained (<350F) during subsequent fill passes. When back purge is not used, for example, with the Flux-cored GTAW root welding process, a split hot pass procedure is used to reduce the degree of sugaring and potential overheating of the previous weld pass and HAZ. Similarly, care should be taken when applying the hot pass and subsequent fill passes, when utilizing the flux type GTAW rods and no purge practice.

Figure 4-8. Cross section of TGX308L weld root and fill passes, Specimen GPU-308-99, with locations A, B, C identified.

4-15

Figure 4-9. Area C, HAZ at the toe area of the weld. Etch Structure shows no indication of ditching at 250x (left) and 500x (right) magnification.

Figure 4-10. Area B, HAZ at the mid section of the weld. Etch Structure shows no indication of ditching at 250x (left) and 500x (right) magnification.

Figure 4-11. Area A, HAZ at the top of the weld. Etch Structure shows no indication of ditching at 250x (left) and 500x (right) magnification.

4-16

Table 4-10. Practice A, Etch Structures for GTAW Weld Specimens

Specimen Weld Material Location Etch Structure Results

Location C (Root)

Step Structure Acceptable

Location B (center)


GPU-308-99

5G, 5-in. Schedule 120 Pipe (Type 304L)

3/32-in. 308L TGX rod – root

3/32-in. Type 308L GTAW – hot pass

308L SMAW - fill passes Location A (Top)


4-17

ASTM A 262 Practice E - Copper-Copper Sulfate-Sulfuric Acid Test

Since many of the potential repair applications for the FC-GTAW products are in a oxidizing environments, such as the BRW primary coolant systems, the root pass and associated heat affected zone was evaluated to determine susceptibility of the stainless steel weldments to intergranular attack. Root bend test coupons were removed from various test specimens and subjected to the ASTM A-262 Practice E Test, Copper-Copper Sulfate-Sulfuric Acid Test. This test does not detect susceptibility to sigma phase, nor does it provide a basis for predicting resistance to other forms of corrosion such as general corrosion, pitting, or stress corrosion cracking (i.e., IGSCC).

Full thickness transverse root bend coupons were removed from open root plate and pipe V-groove weld specimens (Table 4-2). The root bend coupons were placed in an acidified copper sulfate solution with copper shot, and boiled for 24-hours. Practice E test apparatus is shown in Figure 4-12. The test specimens were removed from the boiling solution and bent through 180° in a bend test fixture, in accordance with ASME Section IX and ASTM A 262 requirements.

Figure 4-12. ASTM A 262 Practice E Test Apparatus. The bend coupons from the plate welds consisted of four 1/2-in. wide by 6-in. long specimens. The four specimens consisted of two TGX 308L and two Stain Plus 316L root weld specimens (308-TGX-03-2 and 316-SP-03-2). Both specimens were welded with a single hot pass and the root reinforcement was ground flush with the substrate.

4-18

The bend coupon from the pipe welds consisted of four 5/8-inch wide by 3-inches long specimens. The four bend specimens consisted of two single hot pass and two split hot pass test specimens. One set was welded with TGX 308L flux cored rod (TGX-308-98 and TGX-308-S-98) and the other set was welded with the flux coated FMI 308L rod (FMI-308-98 and FMI-308-S-98). The root pass inner surfaces were left as welded with only the slag removed. Tabs were welded to each end of the test coupons after submerging in test solution for 24-hours, to extend the length to approximately 7-inches, to accommodate the bend fixture.

The bend test samples were examined by at 20x magnification. All specimens were free of intergranual fissures and cracks, which are indicative of intergranular attack, and were considered acceptable (Table 4-11). Photographs of the plate specimens are presented in Figures 4-13 and the pipe weld specimens are presented in Figures 4-14 and 4-15.

Table 4-11. Results of ASTM A262 Practice E Tests.

Specimen Weld material Location of Examination

Evaluation

308-TGX-03-2-A 308L TGX Root Acceptable

308-TGX-03-2-B 308L TGX Root Acceptable

316-SP-03-2-A 316L Stain Plus Root Acceptable

316-SP-03-2-B 316L Stain Plus Root Acceptable

TGX-308-98 308L TGX Root Acceptable

TGX-308-S-98 308L TGX Root Acceptable

FMI-308-98 308L FMI Root Acceptable

FMI-308-S-98 308L FMI Root Acceptable

4-19

Figure 4-13. TGX 308L (left) and Stain Plus 316L (right) Plate Weld Bend Specimens for Practice E Evaluations

Figure 4-14. TGX 308L single hot pass (left) and split hot pass (right) Pipe Weld Bend Specimens for Practice E Evaluations

4-20

Figure 4-15. FMI 308L single hot pass (left) and split hot pass (right) Pipe Weld Bend Specimens for Practice E Evaluations

4-21

Practice C – Nitric Acid Test

Practice C is a nitric acid test that provides a quantitative measurement that can be used to evaluate the performance of the material based on corresponding test specimen results. The test results are based on overall weight lose of test specimens over an extended exposure time. The test specimens are weighed after 48, 96 and 144-hours of exposure to the boiling nitric acid solution. The specimens are exposed in the as-welded or in-service condition for testing. Practice C, Boiling nitric acid test fixture and scientific scale are shown in Figure 4-16.

Two stainless open root weld specimens with 308L TGX and 316L Stain Plus root welds were prepared without an argon-backing purge. The weld specimens were sectioned into 1.5-in wide by 1.5-in. long by 3/16-in thick coupons containing 1.5-in. of weld length and a target mass of approximately 60 grams. The weld specimens were machined to a 3/16-in. overall thickness by removing material from the weld fill pass side and leaving the root ID surface in the as–welded condition. The final test coupon exposed 1.5-in. of as-welded root weld surface and 1.5-in. of intermediate weld passes (fill passes).

The weld specimens and associated mass loss after each exposure time (48-hours) are shown in Table 4-12.

A visual examination of the test coupons indicated that no localized wastage occurred on the exposed root surface. Weight loss was comparable to general base material weight loss of similar base metal coupons. Addition specimens (S3 and S4) produced with autogenous GTAW welds to simulate localized sugaring on ID surface are included in Table 4-12 for comparison. The sugared specimens were also considered to have minimal weight loss after 144-hours of exposure.

Figure 4-16. Practice C Test Apparatus and scientific scale.

4-22

Table 4-12. Practice C Mass Loss Measurements

308-TGX-03-2 308-SP-03-2 S3 S4

Original Mass 60.860 61.951 60.476 57.683

Mass after 48-hrs 60.790 61.873 60.406 57.605

Mass Loss 0.070 0.078 0.070 0.078

Mass after 96-hrs 60.745 61.832 60.362 57.565

Mass Loss 0.045 0.041 0.044 0.040

Mass after 144-hrs 60.703 61.794 60.318 57.529

Mass Loss 0.042 0.038 0.044 0.036

Overall 0.157 0.157 0.158 0.154

4-23

Flux - Slag Analysis

When utilizing the Flux type GTAW filler materials on closure welds, the ability to remove the layer of slag from the root pass surface is eliminated, thus leaving a foreign material inside the piping system. Since most welding slag formulations typically contain halogens (i.e. calcium fluoride), a potential concern arises regarding leaving the slag on the ID surface of the pipe system. Elements, or their compounds, such as chlorides, halogens, sulfur, and metal low melting point metals have been found to promote stress corrosion cracking (SCC) and intergranular attack (IGA) upon contact with austenitic stainless steels under certain conditions. The manufacturers of the FC-GTAW filler materials understand this concern and have formulated their fluxes to minimize the use of SCC and IGA promoting elements.

To address potential corrosion issues, the nuclear power industry and individual plant operators have established minimum requirements for non-metallic, nonpermanent products that come in contact with the surfaces of corrosion resistant materials of the reactor coolant system. Most utilities are concerned with water leachable halogens, although in some cases total halogen concentrations are specified.

Flux was collected from the ID surface and from bead on plate welds from test coupons welded with the flux type welding rods. The amount of slag per length of weld, typical of flux type GTAW welding rods) was calculated at <0.400 grams per 12-in. of weld. The flux samples were analyzed for total halogens and low melting point elements (dry testing) and water leachable halogens and sulfur at NSL Analytical Labs.

Water leachable concentrations for halogens and sulfur were performed with NSL procedure NSL1090 to obtain the aqueous layer. This solution was then analyzed with an Ion Chromatography procedure per ASTM D4329. The results of testing performed on the slag materials, and a range of allowable limits from industry surveys, are listed in Table 4-13. The water leachable test results indicate that both alloys exhibited very low and acceptable levels of halogens and sulfur. Analyses of the slag typically uses 1 gram of slag diluted into 100mL of deionized water. A total weld length of 30-in. would be required to produce one gram of slag for typical open root welding applications.

Table 4-13. Water Leachable Contaminate Concentrations From Slag Analysis Element 308L TGX

Actual 308L FMI

Actual 309L TGX

Actual Typical Utility

Allowables Water Leachable Chloride

<10 ppm <10 ppm <0.001 %

Water Leachable Fluoride)

44 ppm 110 ppm <0.0014 %

200–250 ppm (Cl + Fl)

Water Leachable Sulfur

<10 ppm <10 ppm <0.001 % 200–750 ppm

Water Leachable Iodine (1)

<10 ppm <10 ppm <0.001 % No Reported Limit

Water Leachable Bromine (1)

<10 ppm <10 ppm <0.001 % No Reported Limit

(1) Iodine and Bromine are halogens and are typically added to the measured chlorine and fluorine total to get total water leachable halogens.

4-24

Total concentrations for halogens, sulfur, and low melting point elements were performed using various analytical methods. Photographic Emission Spectroscopy was used to detect low melting point elements such as Pb, Sn, Sb and Cu, Ion Chromatography (ASTM D808) was used to detect Cl, F, Br and I and LECO furnace (ASTM D129) was used to detect Sulfur. The results for sulfur and low melting point metals appear to meet all industry and individual utility limits surveyed shown in Table 4-14. The fluorine content measured in slag exceeds all available standards for limits of total halogens. However, it should be noted that several utilities do not have established limits on total halogen, and only measure for water leachable halogens.

Table 4-14. Total Contaminate Concentrations From Slag Analysis Element/Compound TGX 308L

Actual (ppm) FMI 308L FC Actual (ppm)

Typical Utility Allowables (ppm)

Total Halogens Chlorine Flourine Bromine Iodine

160 25,000 <100 <100

150 44,000 <100 <100

1000

Total Sulfur

240

200

1000

Other Low Melting Point Element Pb Sn Sb

<10 <5

<10

<10 <5

<10

No intentional additions of low melting point elements (1)

(1) If no statement is available from manufacturer, limits and 250 ppm maximum for all low melting point metals except mercury. Mercury is typically limited to less than 10 ppm. As a result of the high total halogen measurement due to fluoride content in the slag, and the acceptable water leachable halogen measurement, the use of these materials will have to be evaluated on an individual utility basis.

4-25

5 RECOMMENDATIONS Welding evaluations were performed with the flux type stainless steel GTAW welding rods without the use of back purging. The welding evaluations substantiated welding parameters, weld prep configuration and welding techniques that would provide an acceptable root and hot pass without incorporating the standard argon back purge for stainless steel open root welds. The study documents welding guidelines and a test matrix to verify weld integrity, mechanical property, and corrosion data for each filler material type and welding practice.

Basic results of the welding development concluded:

Experienced GTAW stainless welders after several days of practice could develop the necessary skills and technique to perform successful root and hot passes with the flux type filler materials.

Welding without a back purge did not diminish mechanical properties.

o Tensile, side bend, and root bend specimens tested in accordance with the requirements of ASME Section IX were acceptable with no visible weld defects.

o RT and cross sectioned weld specimens revealed no rejectable weld defects.

o Visual examinations of root surfaces showed acceptable ID reinforcement with no lack of fusion or rejectable oxidation/sugaring.

Weld chemistry and ferrite measurements met minimum requirements specified by ASME specifications

Corrosion testing showed acceptable resistance to IG attack

o ASTM A-262 Practice E revealed no rejectable flaws at 20x magnification

o ASTM A-262 Practice A revealed an acceptable etch structure.

o ASTM A-262 Practice C revealed minimal wastage (weight loss).

o Analyses of residual slag indicated an acceptable level of water leachable halogens (chlorine + fluorine + bromine + iodine) and sulfur was detected in the slag

o An unacceptable levels of total halogens was detected in the slag

o Less than 0.4 grams of slag are formed on 12-in. length of weld

In summary, the flux type GTAW welding rods can be successfully deposited with root passes which are oxidation and porosity free with the single or split hot pass. The welding rods provide acceptable mechanical and corrosion properties. With proper training and practice these alloys can be used to perform weld root passes on stainless steel pipe without the use of a back purge.

5-1

Due to the experience level of the welder required and the potential halogen content of the slag, use of the flux-type GTAW rods should be evaluated on a case-by-case basis.

5-2

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