By Duane K. Miller, Jeff Hietpas, And Rich DePue
Reproduced with the permission of Welding Journal and the American Welding Society
No matter what branch of the welding industry you're in, no doubt there are questions that come up time and time again. The Welding Journal recently asked three active members of the welding community to provide answers to some of the questions they are most often asked. The questions and answers from each contributor follow some short biographical information.
DUANE K. MILLER, Sc.D., P.E., is manager, Welding Technology Center, and welding design consultant, The Lincoln Electric Co., Cleveland, Ohio. Miller is a recognized authority on the design of welded connections. In 1994, he was selected to chair the American Welding Society's Presidential Task Group on Northridge earthquake issues. He also served on the Project Oversight Committee of SAC, a consortium sponsored by the Federal Emergency Management Agency (FEMA) to provide understanding of connection behavior in the wake of Northridge. Miller currently serves as first vice chair of the AWS D1 Committee on Structural Welding and chairs the Seismic Welding Subcommittee.
Q: What is undermatched weld metal? Where can I use it? What are the advantages of undermatched weld metal?
A: When weld metal strength is compared to the base metal strength, one of three relationships may exist: the weld metal may be stronger than the base metal ("overmatched"), generally equivalent to the base metal ("matching"), or lower than the base metal ("undermatching"). AWS D1.1, Structural Welding Code -Steel, defines matching and undermatching in the table in Section 3.3.
In D1.1, overmatching is never required. Matching strength is required for some connections and loading types: complete joint penetration (CJP) groove welds in tension are the most common example. All partial joint penetration (PJP) groove welds, all fillet welds, and all plug and slot welds can be made with undermatching weld metal. D1.1 Table 2.3 defines where matching and undermatching weld metal is required or permitted.
When undermatching weld metal can be used, the weld is typically more resistant to fabrication-related cracking. The increased ductility of the lower strength weld metal and the reduction in residual stresses can reduce lamellar tearing tendencies as well. Undermatching is typically considered only when the base metal yield strength is 70 ksi (485 MPa) or greater. A typical application where undermatching may be considered is when fillet welds are used to join A514 or A517 steel (minimum specified yield strength of 100 ksi [690 MPa]).
It is important the weld size reflect the use of undermatching weld metal. Depending on the particular loads involved, it may be necessary to increase the specified weld size when undermatching welds, as opposed to matching strength welds, are used.
Q: We are a structural steel fabricator. On a recent job, FEMA-353 was specified in the contract documents. What is FEMA-353 and how will it affect us?
A: FEMA-353, Recommended Specifications and Quality Assurance Guidelines for Steel Moment-Frame Construction for Seismic Applications, provides supplemental design and fabrication recommendations and supplemental quality control and quality assurance recommendations for the construction of steel moment frame structures designed for seismic applications. FEMA-353 is designed to supplement other welding codes, such as AWS D1.1, Structural Welding Code -Steel, or AISC Manual of Steel Construction LRFD.
FEMA 353 contains provisions that affect welder qualification, filler metals that can be used, welding procedure specifications (WPSs), inspection practices, and other issues.
Unfortunately, there is not enough space here to discuss the numerous recommendations in FEMA-353. The Lincoln Electric Company has prepared an easy-to-read brochure, FEMA 353 Welding Manual (C1.60), that summarizes many of the main welding recommendations in FEMA-353. This manual may be downloaded or ordered free of charge at www.lincolnelectric.com/products/litre quest/
Q: Why is aluminum alloy 7075 not listed in AWS D1.2, Structural Welding Code - Aluminum?
A: Most aluminum alloys are weldable, but a fair number of them are not, including 7075 aluminum. When designers and welders look for an aluminum alloy to use, many will start by reviewing a table that lists all of the aluminum alloys and their strengths. Alloy 7075 is often selected because it is one of the highest strength aluminum alloys. But, few of the higher strength aluminum alloys are weldable, especially those in the 7000 and 2000 series, and they should not be used.
The one exception to the rule of never using 7075 for welded applications is in the injection molding industry, which uses 7075 dies and will repair them with welding. However, 7075 should not be used for structural work.
When you need to design something of high-strength aluminum, look to a 5000 series high-magnesium alloy instead of a 2000 or 7000 series. The 5000 series alloys are weldable and will produce the best results.
Q: Why is my aluminum welded connection so much weaker than the base material?
A: In steel weldments, a welded connection can be made as strong as the base material, but this is typically not the case with aluminum. In almost all instances, the welded connection will be weaker than the base material.
To understand why this occurs, consider the two classifications of aluminum alloys: heat treatable and nonheat treatable. The latter category is hardened only by cold working, which causes physical changes in the metal. The more the alloy is cold worked, the stronger it gets. When you weld an alloy that has been cold worked, you locally anneal the material around the weld so it goes back to its zero-tempered (or annealed) condition and it becomes "soft." Therefore, the only time you can make a weld as strong as the base material with a nonheat-treatable alloy is when you start with zero-tempered material.
With heat-treatable aluminum alloys, the last heat treatment step heats the metal to approximately 400°F (200°C). When welding, the material around the weld (the heat-affected zone) becomes much hotter than 400°F so the material tends to lose some of its strength. Unless a postweld heat treatment is applied, the area around the weld will become significantly weaker than the rest of the aluminum - by as much as 30 to 40%. Post-weld heat treatment can restore this loss in strength if a heat-treatable aluminum is used.
Table 1 is a guide as to which series of aluminum alloys are heat treatable and which are not.
Table 1 - Guide to Heat-Treatable Aluminum Alloys
Q: Section 12 of AWS D1.5, Bridge Welding Code, addresses fracture control. Shouldn't this apply to all structures since fracture avoidance is so important?
A: The Engineer responsible for a product or structure must determine what codes apply to a project. Further, the Engineer must develop job specifications that address the specific requirement for specific projects. The Engineer must also determine whether D1.5 Section 12 is appropriate or not.
The scope and intent of Section 12 should be understood before it is invoked on a project. It is intended to apply to "fracture critical members" (FCMs), which are defined in D1.5, paragraph 12.2.2. It states: "Fracture critical members or member components are tension members or tension components of bending members (including those subject to reversal of stress), the failure of which would be expected to result in collapse of the bridge." Two elements are important in this definition: tension and collapse. FCMs must be tension members or tension components. Columns that see only compressional loading cannot be FCMs.
The collapse component of this definition has to do with the overall performance of the bridge should a FCM fracture. Most bridges are redundant, that is, there are multiple load paths available should a single member fail. However, a two-girder bridge is likely to be fracture critical in that the fracture of a single member will likely cause the collapse of the bridge.
Bridge designers need to determine whether the bridge member is fracture critical or not, and specify such on design drawings (see D1.5, paragraph 12.3.1). For nonbridge applications, the Engineer responsible for the project needs to determine whether D1.5 Section 12 is applicable. The Engineer should know it was not the intent of D1.5 to cover nonbridge applications (see D1.5, paragraph 1.1.1), although it may be appropriate for certain situations. When applied to nonbridge applications, the Engineer should realize the materials and product forms (plate, sheet, shapes, tubes) that will be employed on the nonbridge project may not be covered by D1.5. Job specifications must address these situations.
Q: New wording has been added to AWS D1.1, Structural Welding Code - Steel, that addresses "original equipment manufac- turers" (OEMs). Why was this done and what does this mean?
A: The section to which you refer is 1.3.4, which states: "'OEM' shall be defined as the single Contractor that assumes some or all of the responsibilities assigned by this code to the Engineer." Historically, D1.1 has outlined the responsibilities of the parties involved with the typical building construction process: the Engineer, who acts on behalf of the owner; the Contractor, the entity that performs the welding; and the various types of Inspectors. In the typical building construction process, the Engineer and the Contractor are separate entities. Thus, code responsibilities assigned to the Engineer are intended to be executed by a different party than the one doing the fabrication.
Many users of the D1.1 Code do not fit into this traditional building construction pattern. For example, the purchaser (owner) of a piece of construction equipment may require the product be built to D1.1. The manufacturer of this equipment may have a whole staff of engineers, but in D1.1 terms, these "engineers" are not the same as the D1.1 "Engineer" who represents the owner. In this situation, the engineers represent the manufacturer of the equipment. Thus, application of D1.1 to these situations can cause a variety of points of confusion.
To address this situation, the D1 Committee has introduced the OEM concept. The commentary to D1.1-2002, paragraph 1.3.4, describes this situation in more detail. Provision 1.4(8) requires contract documents outline the responsibilities of all the parties involved for OEM applications. The commentary provides some examples of possible relationships for these applications.
By providing these new code provisions, it is hoped implementation of D1.1 for applications other than the typical building construction practice will be simplified.
Q: AWS D 1.3, Structural Welding Code - Sheet Steel, says in its scope that it covers sheet metal applications "which are equal to or less than 3Ž16 in. (0.188 in./4.8 mm) in nominal thickness" (para. 1.1). AWS D1.1, Structural Welding Code - Steel, says it is not intended to be used for applications involving "steels less than 1Ž8 in. (3 mm) thick." This leaves an overlap between 1Ž8 in. (3 mm) and 3Ž16 in. (4.8 mm) where (apparently) both codes apply. Which one should I use for applications where the steel is in this thickness range?
A: The Engineer responsible for the project must determine which code is applicable. Applicable codes may be spelled out in contract documents or in building codes.
The overlap in thickness between the two codes has several advantages, despite the confusion created with such overlap. If a project primarily involves structural steel, and some of those thicknesses drop below 3Ž16 in. (4.8 mm), D1.1 can be used to address all aspects of the project, providing no materials are less than 1Ž8 in. (3 mm). Conversely, if a project involves primarily sheet steel, and some materials are heavier than 1Ž8 in. (3mm), D1.3 can be used to govern all the project, provided no materials are thicker than 3Ž16 in. (4.8 mm).
One applicable code on a project has several advantages. Welders need to be qualified to only one code. Welding Procedure Specifications need only comply with one code. Inspectors need to refer to only one code. By creating an overlap in the scope of the two documents, the D1 Committee has eliminated some of the duplication that would have necessarily resulted if there were no overlap in coverage.
Consider, for example, the implications of no overlap. Assume the cut-off point was 1Ž8 in. (3 mm). Assume D1.1 governed 1Ž8 in. and greater, and D1.3 addressed less than 1Ž8 in. Gauge material of number 10 or thicker (0.1345 in. [3.416 mm]) would need to be welded to D1.1, but number 11 (0.1196 in. [3.038 mm]) would be governed by D1.3. Two applicable codes would create unnecessary confusion. By creating the overlap, the Engineer can select the most applicable code and, in many situations, one code can be used to govern all the work being performed.
Jeff Hietpas has been involved with the welding industry for 29 years. Currently, he is Product Manager for the Three-Phase Industrial Product Group at Miller Electric Mfg. Co., Appleton, Wis.
Q: How does a wire feeder with a four drive roll system affect wire feedability compared to two drive roll systems?
A: If you're running your wire feeder on a full-time basis and are using a variety of wire diameters, it's important to consider a wire feeder with a four drive roll system. Feeders featuring a two drive roll system have proven effective, but on anything above 0.045 (and ideally 0.035 and above), a four drive roll system will assist with a smoother feed. With larger diameter wires, there is often a great deal of cast that causes stiffening in the wire. The four drive roll system grips and straightens the wire, making for an easier feed.
However, in light fabrication shops where you're set up to run one type of wire all day and you don't need a lot of flexibility or range in wire (anything 0.035 and below), a two drive roll system will suffice.
Q: What's being done with wire feeders today to help improve productivity, weld quality, and overall ease of use?
A: In recent years, wire feeders have evolved so that they provide a great number of options that either didn't exist in the past or were not as easy to use. Some of these options include the following:
- Autodetection systems are being implemented that can tell if a feeder is hooked up to a power source with a 14-pin connection for current and voltage feedback. Newer feeders can now disregard the run-in sequence when attached to power sources without feedback, eliminating the need to remove covers and manipulate dip switches, making them ready to use out of the box, even with older power sources.
- New auxiliary menus on some machines allow welding supervisors to set locks without having to toggle dip switches. Locks are protected by codes, making it nearly impossible for individual operators to toy with settings and weld at levels not recommended or forbidden on certain applications. This is a common problem in shops where operators are welding three shifts a day and you have different welders with different tastes operating on each machine.
- Today's wire feeder can be a source of remote amperage and voltage control that can clear your work space, allowing closer work cells, added productivity, and less clutter.
We see a lot of shops still relying on older wire feeders, mostly because they don't know this technology exists and can greatly improve their productivity and weld quality. By simply upgrading your wire feeder, you can turn an older power source into a more productive welding unit.
Q: Why should I upgrade my wire feeder and when?
A: Wire feeders are designed to push wire. If they're not pushing wire, it's time to change to a newer model. It's time to upgrade when weld quality begins to deteriorate and you begin to have other performance issues (feeding, for example). That's the simple answer.
In reality, the evolution of wire feeding technology over the past few years has been such that a feeder implemented today can drastically outperform a feeder you purchased five years ago. Newer models allow for a greater number of programs to be stored and to be regulated within a matter of ±0 to 10 volts or 0 to 150 in./min. The enhancement of preflow/postflow conditions (the shielding gas dispersed before and after a welding sequence) ensures a stronger weld and drastically reduces instances of crater cracking. Remote control capabilities, locks, connection systems, and simplified menus greatly improve productivity, weld quality, and consistency. New options make many older models obsolete.
If you are in a situation where you run one wire every day, all day, upgrading is not as critical. If you're comfortable with that feeder and don't need it to be more flexible, by all means continue to use what works - there's no need to complicate proven practices by adding features beyond your required functions.
Q: How do I combat "dirty power" (the voltage fluctuations that hamper my arc stability and weld quality)?
A: Whether it be other workers running tools and equipment off of the same primary power line, brownouts, power spikes, or generators that don't regulate auxiliary power voltage, voltage fluctuations can cause havoc with welding parameters.
New technologies are ensuring that operators never experience a fluctuation in the welding arc. Line voltage compensation devices have been implemented on units to help curtail such fluctuations. Manufacturers are also creating new technology that makes sure the primary power remains within certain parameters. One of the newest multiprocess units available promises no arc fluctuation or wandering as long as the primary power remains within a 185 to 635-V range. That covers a "low line" 208-V primary all the way through a "high line" 575-V primary. This system takes primary power and converts it to a buss voltage, then using that buss voltage to drive the control part of the inverter mechanism.
This technology is ideal for job sites where many workers run tools off of the same power and where line transients cause voltage fluctuations.
Q: Why am I being told my current engine drive may not be sufficient for flux cored welding on structural steel?
A: In the past, engine-driven welding generators with a constant current (CC) output have dominated the rental and construction markets. Many contractors outfit these engine drives with a voltage-sensing wire feeder to enable flux cored welding. If you're looking to buy a new engine drive, save the future headache and go straight for an engine drive that also features constant voltage (CV).
Many engineering firms, construction companies, and building codes no longer allow flux cored welding with a CC power source. It does not provide adequate assurance the weld is being made with the proper voltage. For this reason, CV power sources are being required, especially for nickel-alloy flux cored wires used for structural welds on buildings and bridges. Some of the self-shielded wires are particularly voltage sensitive. A wide variety of multiprocess machines are available that feature both CC and CV capabilities.
Q: Why do I care about circuit boards in my engine drive?
A: Because they can be a giant hassle when not protected. The reality of all work areas is that they're dirty. Between dirt, dust, humidity, and other intrusive elements of construction work, there are many things that can cause circuit board failure. While you'll find some constant current (CC) machines that completely eliminate circuit boards, you can't escape them entirely.
Constant voltage (CV) engine drives require at least one circuit board to control the arc and are necessary for many flux cored and gas metal arc welding (GMAW) jobs. Many new engine-drive models are implementing a single circuit board and encasing it in a "vault" of sorts. Since this practice has been implemented, circuit boards with that added protection have had a 99.71% durability rating, which is important because repairing circuit boards can cost upward of $1,000. Tip one would be to look for a machine with the fewest amount of circuit boards that still offers the welding processes you require. Since you can't entirely get rid of them, it's equally as important to find an engine drive that protects its circuit boards.
Q: I have a dependable GMAW unit and need to weld aluminum. Can I do that or should I look into other options?
A: The aluminum material thicknesses that can be welded with the GMAW process are 14 gauge and heavier. How heavy depends on the output capacity of the welding machine being used. To GMA weld aluminum thinner than 14 gauge (0.074 in.), either specialized pulsed gas metal arc or AC gas tungsten arc welding equipment may be necessary.
Q: What is the most dependable method for welding aluminum with a GMAW machine?
A: Spray transfer is the desired mode of metal transfer for welding aluminum. Spray transfer offers a smooth transfer of molten metal droplets from the end of the electrode to the molten pool. The droplets crossing the arc are smaller in diameter than the electrode. There is no short circuiting. The deposition rate and efficiency are relatively high and the arc is smooth, stable, and stiff. The weld bead has a nice appearance and a good wash into the sides. In spray transfer mode, a large amount of heat is involved, which creates a large weld pool with good penetration that can be difficult to control and cannot be used on materials thinner than 14 gauge. This transfer will produce a hissing sound and no spatter.
Q: I'm getting a lot of melt- through. What am I doing wrong?
A: There are a number of remedies for this, one of which might be switching to the gas tungsten arc welding (GTAW) process.
You're getting the melt-through due to excessive heating of the base material. This can be dealt with by increasing the travel speed and making shorter welds. Moving the arc around on the part and spreading the heat will also help. Eliminating and reducing any gaps will also prove effective, but you may have to consider switching to a thicker material or going with an AC GTAW or pulsed GMAW machine.
Rich DePue has more than 21 years' experience in the welding industry beginning with 11 years as a welder specialist at West Valley Nuclear Services. He is currently a Weld Inspection/NDE Manager for Industrial Training Consultants, Wellsville, N.Y. He is an AWS Certified Welding Inspector (CWI) and Certified Welding Educator and a New York State Department of Education Certified Welding Instructor. He also holds ASNT NDE Level III certification.
Q: In taking the AWS CWI exam, is it easier to use API 1104 or AWS D1.1 for the code portion of the exam?
A: Many people feel API 1104 is easier to use than D1.1 because it is a much smaller document. I will agree it may be easier to answer questions from a 70-page code than a 500-page code; however, the AWS CWI exam has a D1.1 flavor throughout the exam aside from the code portion. Many exam candidates choosing API 1104 as the code of choice do poorly because they did not prepare themselves for Part B, which resembles D1.1.
While the CWI candidate should be generally familiar with all major codes, the advantage to using D1.1 as the code of choice on the exam is that little or no attention would have to be paid to 1104 or any other code. Whereas in using 1104, the candidate must be familiar with 1104 and with several of the charts and footnotes found in D1.1.
Regardless of the choice of the code used, to be successful the prospective CWI must be familiar with AWS D1.1. In my opinion, the best way to prepare for the CWI exam is to take the week long AWS CWI seminar with the D1.1 Code Clinic.
Q: How can I obtain welder certification?
A: In general, a welder can get certified in three ways.
1) Company certification. A welder can get certified to his or her company's procedures. Welding Procedure Specifications (WPSs) can be developed by a company in accordance with the requirements of codes, standards, or in-house contract requirements. With the development and qualification of a WPS, an individual can be administered a test that will qualify his or her welding skills.
2) National certification by exam. A welder can enroll in a school or attend an institution that is an approved or certified testing facility. At this facility, a test will be administered and the welder's skills evaluated and certified.
3) National, state, or municipal certification. Welder certification can be obtained by the issuance of a test by a national-, state-, or municipal-affiliated entity. A state department of transportation, utility, or public works can issue certification to national, building, or municipal codes. The military also offers certification to its codes and standards.
To summarize, to be certified means, in the eye of a qualified entity, an individual has met the requirements of a recognized code or standard. There is also up-to-date, written documentation to represent this activity.
Q: How concerned should I be about the long-term risk of illness caused by welding fumes?
A: It is best to treat all welding smoke and fume as potentially harmful and utilize the best possible techniques and equipment to reduce exposure. Because of the melting of base and filler metal, the fumes from welding contain solid particles that can cause temporary dizziness, eye irritation, nausea, and fever. Fumes can be more serious with the welding of alloy metals such as stainless steel, manganese, and zinc, and exposure to these fumes should be kept to a minimum.
Many of the gases used in welding such as argon, helium, and carbon dioxide are nontoxic; however, their release during welding displaces oxygen. This displacement, especially in confined and poorly ventilated areas, can cause dizziness, unconsciousness, and death.
The long-term risk of health conditions because of welding has to be taken seriously. Any injurious conditions encountered will be the result of a lifetime of exposure to smoke and fumes without adequate air filtration or ventilation. Therefore, a welder must be cognizant of air quality every working day. Some tips to reduce exposure to fumes include keeping your head out of the fume plume, getting as close to the source of fume as possible with ventilation or making sure there is adequate air movement throughout the room, and properly cleaning metals prior to welding.
Q: What is a PQR?
A: PQR is an abbreviation for Procedure Qualification Record. A PQR is a document that represents the qualification of a welding procedure. Three ways a Welding Procedure Specification (WPS) can be qualified include
1) Utilizing a prequalified welding procedure. Some AWS codes offer prequalified welding procedure specification data to be used for the development of a welding procedure specification that does not require testing.
2) Qualify a welding procedure by testing. Welding codes and standards usually have a specific chapter or section that addresses welding procedure qualification testing. Testing can include tensile, guided bend, radiography, ultrasonic, impact, or any combination of these.
3) Utilize noncode company procedural qualification testing. When acceptable in contract documents, a procedure can be qualified by unconventional means as required by individual company requirements providing that good engineering judgment is not compromised. Testing should be compatible with product design and intended service.
Regardless of the type of testing used to qualify a procedure, the development of a WPS and PQR should always be performed by qualified personnel such as a welding engineer or CWI.
Q: What causes porosity during welding?
A: In any welding process, porosity can be caused by the presence of contaminants or moisture in the welding zone, which includes the base metal, filler metal, shielding gas, and the surrounding atmosphere. Contaminants can include oil, dirt, grease, or cutting fluids. Concurrently, moisture can collect in the flux, shielding gas, or on the base metal, or come from the atmosphere.
Porosity occurring in a welding process that utilizes an external shielding gas can occur from using too much or too little gas flow, poor gas quality, or a defective welding torch, gun, or hose.
Operator technique can also cause porosity. Electrode, torch, or gun angle can lead to porosity, as can excessive arc length, electrode extension, or travel speeds.
Q: How can I obtain NDE certification?
A: The certification of personnel performing nondestructive inspection can be accomplished by the following methods:
1) Obtain certification through training and testing by the American Society of Nondestructive Testing (ASNT). Providing the candidate has the required experience and training, ASNT has exams for all levels and all NDE methods. An inspector can participate in NDE training and testing at several schools and institutions nationwide in order to obtain ASNT certification as an NDE trainee or levels I, II, or III.
2) Utilize the requirements of ASNT-SNT-TC-1A. A company can certify its own personnel using the requirements set forth in the Recommended Practice SNT-TC-1A. These requirements include the proper number of training hours, experience hours, and written and practical testing. Such training and testing should be performed by a Level III or duly designated company party or approved third party.