AWS WHC1.06

INTRODUCTION

All types of welded structures—from steel bridges to jet components—serve a function. Likewise, the welded joints in these structures and components are designed for service-related capabilities and properties. Predicting service performance on the basis of laboratory testing presents a complex problem because weld size, configuration, and the environment as well as the types of loading to which weldments are subjected differ from structure to structure. This complexity is further increased because welded joints—consisting of unaffected base metal, weld metal, and a heat-affected zone (HAZ)—are metallurgically and chemically heterogeneous. In turn, each of these regions is composed of many different metallurgical structures as well as chemical heterogeneities.

Testing is usually performed to ensure that welded joints can fulfill their intended function. The ideal test, of course, involves observing the structure in actual or simulated service. An example of such “mock-up” testing is that done to validate new designs of moment frame and similar connections for large buildings in strong seismic areas.¹ Unfortunately, mock-up and actual service tests are expensive, time consuming, and potentially hazardous. Therefore, standardized tests and testing procedures are performed in the laboratory to compare a specimen’s results with those of metals and structures that have performed satisfactorily in service. Standardized testing provides a bridge between the properties assumed by designers and analysts and those exhibited by the actual structure.

Mechanical testing provides information on the mechanical or physical properties of a small sample of welds or metals to infer the properties of the remaining material within a lot, heat range, or welding procedure. Standardized procedures are used to sample, orient, prepare, test, and evaluate the specimens in order to provide results that can be compared to design criteria. For example, virtually all design codes are based on a minimum tensile strength that must be achieved not only in the base metal but also in the weldment.

When selecting a test method, the test’s purpose must be considered and balanced against the amount of time and the resources available. For example, tension and hardness tests both provide a measure of strength, but the latter are simpler and more economical to perform. Hardness tests can be used to confirm that adequate strength has been achieved in some heat-treated components. Although they can verify that a maximum heat-affected-zone hardness has not been exceeded, hardness tests cannot adequately establish the strength of a welded joint because of the heterogeneous nature of welds. Regardless of the differences between test methods, all testing procedures measure either a composite average or a “weak-link” component of the property of interest within the area sampled. Thus, an understanding of the test details is necessary to interpret the results.

When testing a welded or brazed joint, the investigator must not only relate the test to the intended service of the actual structure but also determine whether true properties are measured by the limited region tested.

Test results must therefore be carefully interpreted and applied. As each laboratory test provides only a limited amount of information on the properties of welded joints, most weldments are evaluated using several tests. Each test provides specific data on the serviceability of the weldment. The properties evaluated by testing include strength (e.g., ultimate tensile strength, yield strength, shear strength), tensile ductility (e.g., elongation and reduction of area), bend test ductility, toughness (e.g., fracture toughness, crack arrest toughness, and Charpy V-notch toughness), fatigue, corrosion, and creep. The scope of the testing is either defined as part of the investigation or specified in the relevant code or standard, depending on the application.

Testing should be performed on samples that reflect the heat treatment condition used in service. However, the topic of the aging of steel specimens often arises in testing welded joints. In this context, aging is a degassing treatment at room temperature or a slightly elevated temperature. For example, the American Welding Society’s filler metal specification for carbon steel flux cored arc welding electrodes,² as well as some welding codes such as Structural Welding Code—Steel, AWS D1.1:2000,^{3, 4} permit the aging of tension test specimens at 200°F to 220°F (93°C to 104°C) before testing. However, other codes such as the Bridge Welding Code, ANSI/AASHTO/AWS D1.5-96,⁵ do not permit aging for weld procedure qualification tests.

The welding process can introduce hydrogen into the weld metal, mostly from water that is disassociated under the high temperature of the arc. The hydrogen diffuses out over time but may introduce anomalies into tensile test results. These can sometimes be seen as “fisheyes” (small pores surrounded by a round, bright area on the fracture surface of tension tests of steel welds) even though normal cup-and-cone fracture may be observed, if tested only days later, and the yield strength, ultimate strength, and impact test results will remain unchanged. Such low-temperature aging is permitted because it does not change the metallurgical structure; it simply quickens the diffusion of hydrogen from the weldment. With this one exception, weldment testing is typically performed using specimens that represent the heat treatment condition of the weldment as it will be used in service.

The various testing methods used to evaluate the expected performance of welded and brazed joints and thermal spray applications are examined in this chapter. The description of each method includes a discussion of the property being tested, the test methods used, the application of results, and, most importantly, the manner in which these results relate to welded joints. An overview of weldability testing is also presented.⁶

This chapter makes frequent reference to the Standard Methods for Mechanical Testing of Welds, ANSI/ AWS B4.0 and AWS B4.0M,⁷ and Standard Methods and Definitions for Mechanical Testing of Steel Products, ASTM A 370.⁸ The latest edition of these standards should be consulted for more information on the testing and evaluation of welded joints. In addition, the American National Standard Safety in Welding, Cutting, and Allied Processes, ANSI Z49.1,⁹ should be consulted for rules regarding health and safety precautions.

1. American Institute for Steel Construction (AISC), Seismic Provisions for Structural Steel Buildings, Chicago: American Institute for Steel Construction.

2. American Welding Society (AWS) Committee on Filler Metals, Specification for Carbon Steel Electrodes for Flux Cored Arc Welding, ANSI/AWS A5.20, Miami: American Welding Society.

3. American Welding Society (AWS) Committee on Structural Welding, 2000, Structural Welding Code—Steel, AWS D1.1:2000, Miami: American Welding Society.

4. At the time of the preparation of this chapter, the referenced codes and other standards were valid. If a code or other standard is cited without a date of publication, it is understood that the latest edition of the document referred to applies. If a code or other standard is cited with the date of publication, the citation refers to that edition only, and it is understood that any future revisions or amendments to the code or standard are not included; however, as codes and standards undergo frequent revision, the reader is encouraged to consult the most recent edition.

5. American Welding Society (AWS) Committee on Structural Welding, 1996, Bridge Welding Code, ANSI/AASHTO/AWS D1.5-96, Miami: American Welding Society.

6. Weld soundness is evaluated using the nondestructive examination methods described in Chapter 14, Vol. 1 of the Welding Handbook, 9th ed., Miami: American Welding Society.

7. American Welding Society (AWS) Committee on Mechanical Testing of Welds, Standard Methods for Mechanical Testing of Welds, ANSI/AWS B4.0, Miami: American Welding Society; American Welding Society (AWS) Committee on Mechanical Testing of Welds, Standard Methods for Mechanical Testing of Welds, AWS B4.0M, Miami: American Welding Society.

8. American Society for Testing and Materials (ASTM) Subcommittee A01.13, Standard Test Methods and Definitions for Mechanical Testing of Steel Products, ASTM A 370, West Conshohocken, Pennsylvania: American Society for Testing and Materials.

9. American National Standards Institute (ANSI) Accredited Standards Committee Z49, Safety in Welding, Cutting, and Allied Processes, ANSI Z49.1, Miami: American Welding Society.

Edition:

01

Published:

01/01/2001

Number of Pages:

58

File Size:

1 file , 4.5 MB