1. Design 2

2. Design 2 Learning Activities Read Handbook pp 149-158
View Slides;
Read Notes,
Listen to lecture
Do on-line workbook
Do homework
Lesson Objectives
When you finish this lesson you will understand:
Joint Design Terminology
Prequalified Joint Selection
Statically & Dynamically loaded Joints
Keywords
Joint Design, Butt Joint, T Joint, Lap Joint, Corner Joint, Edge Joint, Square Weld, Fillet Weld, Bevel Groove, V Groove, J Groove, U Groove, Groove Angle, Bevel Angle, Root, Root Face, Land, Root Opening, Throat, Leg Length, Weld Face, Weld Toe, Flat, Horizontal, Vertical, Overhead, Tension, Compression, Bending, Torsion, Shear

3. Introduction
Welding Design
Welding design involves consideration of strength requirements, cost, and service conditions
Mechanical & Physical properties
Joint Design
Welding stress and distortion
Previously we examined the mechanical and physical properties of materials as part of the design function. Once we have knowledge of these properties we can then being to design the weld joints which will be manufactured, keeping in mind that the joints must maintain the integrity of the mechanical and physical properties expected in the final part. We will start looking at joint designs. T

4. Welding Design Types of joints and welds Joint selection - AWS D1.1
Introduction
Welding Design
Types of joints and welds
Joint selection - AWS D1.1
Fatigue design
Residual stress and distortion
We will start our discussion with a listing of the types of joints and the types of welds to accommodate these joints. We should not loose site of the fact that the more conventional joint designs have been adequately documented by the American Welding Society and can be found in many of their codes and specifications. One of the most useful AWS D1.1 Structural Welding Code. This code list a whole series of “Pre-Qualified Joints”. These pre-qualified joints are joint designs which have been used so successfully over the years that engineers are convinced they will continue to be effective in applications. The code not only lists these joints but specifies all the pertinent welding conditions needed to make acceptable high quality weldments using these joint designs which will not compromise the mechanical property across the joint.
A word of caution however is appropriate. Not all manufactured items will find applications in statically loaded service. Some will experience cyclic loading where fatigue becomes an issue. Cautions or modifications of joint designs must be followed in these cases. Also, we should not loose sight of the fact that the process of making a weld invariably results in the formation of some residual stresses within the part being manufactured. In some cases these residual stresses can over shadow the original design stresses of the part. Thus these also must be considered in the original design calculations. We will look at each of these factors below.

5. Joint Types Butt joint T joint Lap joint Corner joint Edge joint
Joint Design
Butt joint
Continuity of section
T joint
Flanges or stiffeners
Lap joint
No joint preparation
Corner joint
Edge joint
Two or more parallel, or nearly parallel members
Butt joints are noted for their continuity of section, with the two welded members lying in the same plane. For a plate thickness above approximately 3/8-inch, the joint is typically grooved to ensure complete penetration.
Fillet welds are often made on T-joints.
Lap joints do not require edge preparation. Unlike the butt weld, the load does not transfer directly across the joint. For this reason, lap joints are not preferred for fatigue service. Overlap of five times the material thickness is recommended for double fillet welds in order to limit rotation under load. Resistance spot and resistance seam welding require lap joints.
Corner joints are often arc-welded with fillet, J-groove or V-grooves.
Two essentially parallel plates come together at an edge joint. It may be possible to weld this joint without additional filler material.

6. Weld Types Fillet weld Square Weld Approximately triangular
Joint Design
Weld Types
Fillet weld
Approximately triangular
No joint preparation required
Most common weld in structural work
Square Weld
Penetration difficult with single; double used to ensure strength
Sometimes root is opened and a backing bar is used
Single fillet welds should not be used when an in-service bending moment loads the root of the weld in tension due to the stress concentration at the weld root. The use of single fillet welds should be limited in fatigue service.
Double fillet welds limit the rotation of T-joints and corner joints during service and thereby reduce stress at the weld root.
Penetration is a major concern with the square weld. As such, a double weld is often used to ensure full penetration. If a root gap is used, a backing bar will keep the molten weld metal in place.

7. Weld Types Bevel groove V-groove
Joint Design
Weld Types
Bevel groove
Single bevel is widely used
Double preferred if metal thickness >3/4
V-groove
Both members beveled
Butt joints for plate thickness greater than 1/4 inch
Double welds reduce distortion and require 1/2 the weld metal for a given plate thickness
Only one member is beveled in a bevel-groove. The bevel angle is measured between the beveled edge and a plane perpendicular to the surface of the non-beveled member.
Joint preparation for beveled welds are easily prepared and work well with corner-joints and T-joints. Double-bevel welds should be used when plate thickness is greater than 3/4-inch, if welding can be accomplished from both sides. The double bevel produces less distortion because the stresses on opposite sides of the plate offset each other. Also, the double bevel uses approximately half the weld metal of a single bevel for a given angle.
Both members are beveled in a V-groove. The groove angle is measured from one beveled surface to the other. Joint preparation is relatively easy, as in the bevel-groove weld. Double V-groove welds enjoy the same advantages as double-bevel groove welds, including less weld metal and reduced distortion. Full penetration is required to ensure the strength of the joint.

8. Weld Types J-groove U-groove
Joint Design
J-groove
Single well suited for butted corner and T joints
Machined or carbon arc gouged preparation
U-groove
Rounded base allows larger electrodes for narrower groove angles
The J-groove weld is well suited for butted corner joints and T-joints. It requires a minimum of 1/8-inch root face and 1/4-inch root radius. Therefore, the plate material must be greater than 3/8-inch thick.
Joint preparation for the J-groove weld is more complicated than for the bevel-groove or V-groove. The edge must be machined, and this increases cost. The double J-groove has the same advantages as other double welds.
The U-groove comes into play in the welding of thicker plates. It allows access to the weld root while using less weld metal than a V-groove. As with the J-groove, plate thickness must be greater than 3/8-inch.
Edge preparation costs are higher than the bevel-groove or V-groove. The edges may be machined or arc gouged. The double U-groove enjoys the advantages of all double grooved welds.

9. Parts of a Weld Joint 1 - groove angle 2 - bevel angle
Joint Design
Parts of a Weld Joint 1 2 5 3 4 1 2 3 6 4 5
1 - groove angle
2 - bevel angle
3 - root face (land)
4 - root opening (root gap)
5 - groove face
1 - throat
2 - weld face
3 - depth of fusion
4 - root
5 - fillet leg length
6 - weld toe
A proper welding procedure specification calls out details such as root opening, groove angle and root face. For the design of a fillet weld, the stress calculation will involve the throat thickness and fillet length. The weld toe is the region where the weld metal meets the surface of the base plate. The weld toe is often discussed in terms of hardness variations and discontinuities, such as undercut, which are associated with this region.

10. Welding Positions 1 - flat 2 - horizontal 3 - vertical 4 - overhead
Joint Design
Welding Positions 2F
horizontal
1 - flat
2 - horizontal
3 - vertical
4 - overhead
F - fillet weld
G - groove weld
A welding position is designated by a letter-number combination. G1 refers to a groove weld in the flat position. Welding in the flat position whenever practical can help to improve productivity. The horizontal position is also preferred to overhead and vertical welding; horizontal welding is, however, more prone to overlap and undercut defects than in the flat position.
In pipe welds, these letter-number combinations indicate welding positions unique to pipes. Pipe welds are designated with the letter “G” because they normally involve groove welds. The 1G position specifies the pipe axis to be approximately horizontal; welding is done in the flat position as the pipe is rotated under the arc. The 2G position indicates that the pipe axis is in a vertical position. The 3G and 4G positions do not exist for pipes. The 5G is also referred to as “multiple position;” the pipe axis is flat and stationary while the welder moves the arc around the pipe. For the 6G position, the axis of the pipe is near 45°, and the welder welds around the stationary pipe. The pipe axis can vary ±45° for the G1, G2 and G5 pipe welding positions but only ±5° for 6G. A 6G restricted position is often used for qualification. This position, designated 6GR has a restricting ring placed around the pipe near the weld. 1F
flat

11. Questions?
Turn to the person sitting next to you and discuss (1 min.):
Do a calculation to prove that a double V groove requires ½ the weld metal than a single V groove with the same groove angel on the same thickness plate.

12. Loading of Joints
Blodgett “Design of Weldments” James F. Lincoln Arc Welding Floundation, 1976

13. AWS D1.1 Structural Welding Code - Steel
Guidelines for design of welded joints, prequalified joint geometries
Statically loaded structures
Dynamically loaded structures
Tubular sections
Details the processes used with particular joints
How to qualify welding procedures and personnel
Outlines quality and inspection in welded construction
ANSI/AWS D1.1 is “An American National Standard” published by the American Welding Society and accepted by the American National Standards Institute. The abstract to the 1996 version of the standard states that,
“This code covers the welding requirements for any type of welded structure made from the commonly used carbon and low-alloy constructional steels. Sections 1 through 8 constitute a body of rules for the regulation of welding in steel construction.”
Section outline
1. General requirements
2. Design of welded connections: common requirements of nontubular and tubular connections; specific requirements for nontubular connections (statically or cyclically loaded); specific requirements for cyclically loaded nontubular connections; specific requirements for tubular connections
3. Prequalification of WPSs
4. Qualification: general requirements; welding procedure specification (WPS); performance qualification
5. Fabrication:
6. Inspection: general requirements; contractor responsibilities; acceptance criteria; nondestructive testing procedures; radiographic testing; ultrasonic testing of groove welds; other examination methods
7. Stud welding
8. Strengthening and repairing existing structures
12 Mandatory annexes: e.g., effective throat, requirements for impact testing, flatness of girder webs, guideline on alternate method for determining preheat
12 Nonmandatory annexes: e.g., guide for specification writers, sample welding forms, contents of prequalified WPS, safe practices
The simplest form of joint design is that for the statically loaded structures. Calculation for the stress and strain as noted previously becomes the driving factor and the major goal is to provide sufficient defect free joint cross sectional area so that the load can be successfully transmitted across the welded joint.

14. AWS D1.1 Prequalified Joint Geometry
Welding Code
AWS D1.1 Prequalified Joint Geometry
ANSI/AWS D1.1 provides prequalified joint designs (example above), as well as filler metal and preheat selection guidelines. Prequalified joints, as given in Section 3 of D1.1, are exempt from the WPS testing required under Section 4 of the code, provided the written WPS conforms to all provision of Section 3 of the code. This exemption can save considerable time in the structural design. However, the engineer should still evaluate the appropriateness of the joint selection. The welders that use prequalified joints are required to be qualified themselves in conformance with Section 4, Part C.

15. And of course the penetration and other requirements specified in the prequalified procedure should be rigidly followed. In this case, if a full penetration joint was called for, the weld is undersize so the cross sectional area is insufficient and this joint would not be able to carry the design load.

16. Questions?
Turn to the person sitting next to you and discuss (1 min.):
We have already seen that some materials suffer mechanical property loss in the heat affected zone. How is this taken into account in the prequlified procedures?

17. AWS D1.1 Structural Welding Code - Steel
Guidelines for design of welded joints, prequalified joint geometries
Statically loaded structures
Dynamically loaded structures
Tubular sections
Details the processes used with particular joints
How to qualify welding procedures and personnel
Outlines quality and inspection in welded construction
The D1.1 code also deals with dynamically loaded structures. These require significantly more care in design and execution.

18. Class E - base metal at ends of weld
Fatigue Design
AWS D1.1 Fatigue Design
Class B
Class F - weld metal
Class E - base metal at ends of weld
ANSI/AWS D1.1 provides fatigue design guidelines for six stress categories. General fatigue guidelines include the following:
1) Partial penetration groove welds loaded in tension transverse to the longitudinal axis of the weld cannot be used where design criteria indicate that cyclic loading could produce failure.
2) Groove welds made from one side only cannot be used if the welds are made with backing (other than steel) that has not been qualified to Section 4. There are exceptions for secondary or non-stress carrying members, and for corner joints meeting certain criteria.
3) Intermittent groove welds are prohibited.
4) Intermittent fillet welds are prohibited, with a given exception.
5) Bevel grooves and J-grooves in butt joints for other than the horizontal position are prohibited.
6) Plug and slot welds on primary tension members are prohibited.
7) Fillet welds < 3/16-inch are prohibited.
AWS D1.1 provides fatigue design guidelines for different weld types and loading configurations

19. AWS D1.1 Fatigue Design Lines
The weld stress category is determined by matching the weld to a series of examples given in ANSI/AWS D1.1. The stress range is determined by subtracting the minimum design stress from the maximum design stress. The fatigue life of a welded joint is located by matching the stress range to the stress category and then reading the cycle life value for that point. The design curves reflect a safety factor below the mean as determined through fatigue testing.
Example 1: A category D weld joint, designed for a stress range of 5 ksi has a fatigue life of 7 million cycles.
Example 2: A category B weld joint, designed for a stress range of 10 ksi should not fail in fatigue. This assumes a properly qualified weld with no defects.
An important note on weld design
Welds are generally designed to ensure that the strength of the metal across a given throat thickness can support the maximum stress. Fatigue, however, occurs independent of metal strength. Changing the base metal to a higher strength will not result in longer fatigue life. Fatigue is often noted to occur at the toe of the weld, although it can still occur through the throat of the weld. In fact, there are different stress categories for stress on the weld metal as opposed to stress on the base metal at the weld toe, as was pointed out on the previous page.

20. Questions?
Turn to the person sitting next to you and discuss (1 min.):
The previous slide showed some fatigue design curves for a non-redundant structure design, that is if this part fails the structure fails. What might the chart look like for a part that is a redundant part?

21. Case Study: Solidification Cracking
Weld metal shrinks as it solidifies
Shrinkage causes stress
Stress on hot weld metal
Metals have lower strength at high temperatures
Weld metal cracks
Affected by
Joint geometry
Impurity elements (S, P)
The next series of slides illustrates a case study of a company which did not use the code and found themselves in some trouble. We will go over this case study in class.

22. “Cocktail Napkin” Welding Procedure
Case Study
“Cocktail Napkin” Welding Procedure
Submerged arc welding
Corner joint, 30° bevel angle
1025 steel
Saw-cut parts
amps
35-36 volts
20-22 inches/minute
risers
30°
30°
base plate

23. “The Weld Looked Great!”
Case Study
“The Weld Looked Great!”
Weld cap before machining
Internal crack wasn’t visible after welding
Weld cap removed during final machining
Crack “appeared”

24. “The Welding Supplier Said Change the Wire/Flux”
Case Study
“The Welding Supplier Said Change the Wire/Flux”
Weld metal strength is increased by adding more manganese
Select a wire/flux combination that adds manganese to the weld metal
Stronger weld metal is less susceptible to cracking
Manganese scavenges out excess sulfur
Sulfur in steel can exacerbate solidification cracking

25. “Let’s Look It Up in the Handbook”
Case Study
“Let’s Look It Up in the Handbook”
Solidification cracking in submerged arc welds occurs when the depth-to-width ratio exceeds 1.25 W D
< 1.25 D W
to prevent cracking

26. “Check With AWS D1.1” Joint angle 60°-70°
Case Study
“Check With AWS D1.1”
Joint angle 60°-70°
Extra width reduces D/W ratio to below 1.25
Cracking disappears
To consider:
More weld metal to deposit leads to lower productivity
Could weld in 2 passes at high speed; good depth/width ratio on each pass
60° (+10°/ - 0°)
¼” min

27. Welding Economics Amount of weld metal Joint preparation Accessibility
Joint Design
Welding Economics
Amount of weld metal
Cost of weld metal
Time required to deposit
Joint preparation
Grooves are prepared by machining, grinding, gas cutting, gouging
Accessibility
Poor access to joint adds to weld time
The cost of making a weld includes many factors. Among these are plate preparation, weld metal, flux, shielding gas, power, operator time, and any post-weld heat treatment.
Operator time includes not only the amount of time spent actually welding the plate, but also positioning, changing electrodes, etc. A joint with good accessibility for the operator will allow for greater efficiency and reduced costs.
A properly designed joint is one that meets strength and service requirements at the lowest cost. Reduction in the amount of filler metal is one way to reduce cost. Avoid joints with deep grooves. Deep penetrating processes such as SAW require less weld metal and may eliminate the need for joint preparation in thinner materials.
Joints should not be overdesigned; strength is always based on the thinnest member. The use of excessive filler metal increases not only material costs but also the amount of time required to complete a weld.
Double-groove welds should be employed when possible. As plates become thicker, weld selection will move from V-groove to J-groove to U-groove. Root openings and included angles should always be kept to a minimum. T

28. Homework