WELD QUALITY Level 1 Chap 6 Objectives When

WELD QUALITY Level 1 -Chap 6

Objectives When we have finished this chapter, you should be able to : Identify and explain codes governing welding Identify and explain weld imperfections and their causes Identify and explain nondestructive examinations Identify and explain welder qualifications Perform a visual inspection of fillet welds

1. 0. 0 Introduction Quality is an important aspect of the welder’s job. Acceptable welding criteria have been established in codes and standards. Several codes govern welding activities, qualification requirements, and tests.

2. 0. 0 codes governing welding A code is a set of requirements covering: Permissible materials Service limitations Fabrication Inspection Testing procedures Qualification of welders

2. 0. 0 codes governing welding Welding codes ensure that safe and reliable welded products will be produced. Clients specify in the contract which codes will be used on the project. All welding must then be performed following the guidelines and specifications outlined in that code. Agencies and societies that have established codes include: American Society of Mechanical Engineers (ASME) American Welding Society (AWS) American Petroleum Institute (API) American National Standards Institute (ANSI)

2. 1. 0 American Society of Mechanical Engineers (ASME) ASME has two codes: ASME boiler and Pressure Vessel Code ASME B 31, Code for Pressure Piping ASME Boiler and Pressure Vessel Code contains eleven sections. The sections most referenced are: �Section II – Material Specifications �This sections contains specifications for acceptable ferrous material (part A) and non-ferrous (part B) base metals and for acceptable welding and brazing filler metals and fluxes (part C).

2. 1. 0 American Society of Mechanical Engineers (ASME) The sections most referenced are: Section V - Nondestructive Examination �This sections covers the methods and standards for nondestructive examination of boilers and pressure vessels. Section IX – Welding and Brazing Qualifications �This section covers the qualification of welders, welding operations, brazers, and brazing operations.

2. 1. 0 American Society of Mechanical Engineers (Asme) ASME B 31 – Code for Pressure Piping Consists of eight sections. Each section gives the minimum requirements for the design, materials, fabrication, erection, testing , and inspection of a particular type of piping. Section B 31. 1 – Power Piping covers power and auxiliary service systems for electrical generation stations Section B 31. 3 covers chemical plant and petroleum refining piping. All sections of ASME B 31 -Code for Pressure Piping, require qualification of the welding procedure and testing of welders.

2. 2. 0 American Welding Society (AWS) The American Welding Society publishes numerous documents covering welding. AWS D 1. 1 – Structural Welding Code –Steel Most frequently referenced code book It covers welding and qualification requirements for welded structures of carbon and low-alloy steels.

2. 3. 0 American Petroleum Institute (API) The American Petroleum Institute publishes documents in all areas related to petroleum production. API 1104 – Standard for Welding of Pipelines and Related Facilities - applies to arc and oxyfuel welding of piping , pumping, transmission, and distribution system for petroleum. API 1104 also presents suitable methods to ensure proper analysis of weld quality.

2. 4. 0 American National Standards Institute (ANSI) The American National Standards Institute is a private organization that does not actually prepare standards. Instead, it adopts standards that it feels are of value to the public interest. ANSI standards deal with dimensions, ratings, terminology and symbols, test methods, safety specifications.

3. 0. 0 Basic Elements of Welding Codes All welding codes provide detailed information about qualification in three general areas. These are: Welding procedure qualification Welder performance qualification Welding operator qualification Machine welding is covered in some codes but is not common to all codes.

3. 1. 0 Welding Procedure Qualification A welding procedure is a written document that contains: Materials Methods Processes Electrode Type All other relevant information Welding procedures must be qualified before they can be used. Procedure qualification has nothing to do with the skills of the individual welder.

3. 1. 0 Welding Procedure Qualification Welding procedure qualification are limiting instructions written to explain how welding will be done. These limiting instructions are listed in a document known as a welding procedure specification (WPS).

3. 1. 0 Welding Procedure Qualification The purpose of the WPS is to define and document in detail the variables involved in welding a certain base metal. The WPS lists the following in detail: Base metals to be joined Filler metal to be used Range of preheat and postheat treatment Thickness of material and other variables described for each welding process

3. 1. 0 Welding Procedure Qualification WPS variables are identified either as essential or nonessential variables. Essential variables are item in the welding procedure specification that cannot be changed without requalifying the welding procedure. Nonessential variables are items in the WPS that ay be changed within a range identified by the code.

3. 1. 0 Welding Procedure Qualification The following can be considered essential variable in a welding procedure: Filler metal classification Material thickness Joint design Type of base metal Welding process Amperage Travel speed Shielding gas Electrode and filler wire size

3. 1. 0 Welding Procedure Qualification The WPS is qualified for use by welding test coupons and by testing the coupons in accordance with the code. The test coupons are used to make: Tensile test Root bends Face bends The test results are then recorded on a document known as a procedure qualification record (PQR).

3. 3. 0 Welder Operator Qualification When fully automatic welding equipment is used, the operators of the equipment must demonstrate their ability to set up and monitor the equipment. The codes also contain qualification test for these operators.

4. 0. 0 Weld Discontinuities and Their Causes Codes and standards define the quality necessary to achieve the integrity and reliability of the weldment. Weld discontinuities can prevent a weld from meeting the minimum quality requirements. AWS defines a discontinuity as an interruption of the typical structure of a weldment.

4. 0. 0 Weld Discontinuities and Their Causes A discontinuity in not necessarily a defect. A defect found during inspection will require the weld to be rejected. A weld can have one or more discontinuities and still be acceptable.

4. 0. 0 Weld Discontinuities and Their Causes The welder should be able to identify discontinuities. The most common weld discontinuities are: Porosity Inclusions Incomplete joint penetration Incomplete fusion Undercut Arc strikes Unacceptable weld profile

4. 1. 0 Porosity is the presence of voids or empty spots in the weld metal. Porosity is the result of gas pockets being trapped in the weld as it is being made. Porosity can be grouped into four major groups: Uniformly scattered porosity – located evenly through out a weld Cluster porosity – a localized grouping of pores that results from improper starting or stopping the weld Linear porosity – aligned along a weld face, the root, or a boundary between beads Piping porosity – normally extends from the root of the weld toward the face Most porosity is caused by improper welding techniques or contamination.

4. 1. 0 Porosity

4. 2. 0 Inclusions are foreign matter trapped in the weld metal, between weld beads, or between the weld metal and the base metal. Inclusions generally result from faulty welding techniques, improper access to the joint for welding or both. A typical example of an inclusion is slag. Inclusions are more likely to occur in out-ofposition welds.

4. 2. 0 Inclusions

Break Time 15 minute break

4. 3. 0 Cracks are narrow breaks that occur in the weld metal, in the base metal, or in the crater formed at the end of a weld bead. They are caused when localized stress exceed the ultimate strength of the metal. Cracks are generally located near other weld discontinuities.

4. 3. 0 Cracks

4. 3. 1 Weld Metal Cracks Three basic types of cracks can occur in weld metal: Transverse Longitudinal Crater Transverse cracks run across the face of the weld and may extend into the base metal. Longitudinal cracks are usually located in the center of the weld. Crater cracks have a tendency to form in the crater whenever welding is interrupted.

4. 3. 1 Weld Metal Cracks

4. 3. 1 Weld Metal Cracks Weld metal cracking can usually be reduced by taking one or more of the following actions: Changing the electrode manipulation Increase thickness of the deposit to resist the stresses by decreasing the travel speed Preheating Using low-hydrogen electrodes Avoiding rapid cooling conditions

4. 3. 2 Base Metal Cracks Base metal cracking usually occurs within the heat-affected zone of the metal being welded. These cracks usually occur along the edges of the weld and through the heat-affected zone into the base metal. Weld toe cracks are generally the result of strains caused by thermal shrinkage acting on a heat-affected zone.

4. 3. 2 Base Metal Cracks Base metal cracking can usually be reduced or eliminated by one of the following: Controlling the cooling rate by preheating Controlling heat input Using the correct electrode

4. 4. 0 Incomplete joint Penetration Incomplete joint penetration occurs when the filler metal fails to penetrate and fuse with an area of the weld joint. Insufficient heat at the root of the joint is a frequent cause of the incomplete joint penetration. Improper joint design is another cause of incomplete joint penetration.

4. 4. 0 Incomplete joint Penetration

4. 5. 0 Incomplete Fusion Incomplete fusion is the failure of a welding process to fuse layers of weld metal or weld metal and base metal. Incomplete fusion may occur at any point in a groove or fillet weld. Causes for incomplete fusion include: Insufficient heat as a result of low welding current Wrong size or type of electrode Contamination Improper joint design Inadequate gas shielding

4. 5. 0 Incomplete Fusion

4. 6. 0 Undercut is a groove melted into the base metal beside the weld. It is the result of the arc removing more metal from the joint face than is replaced by weld metal. Some causes of undercut are: Too high weld current Arc gap that is too long Failing to fill up the crater completely with weld metal

Weld Flaws

4. 7. 0 Arc Strikes Arc strikes are small, localized points where surface melting occurs away from the joint. Arc strikes can cause hardness zones in the base metal and can become the starting for cracking. Arc strikes can cause a weld to be rejected.

4. 8. 0 Spatter is made up of very fine particles of metal on the plate surface adjoining the weld area. It usually caused by high current, a long arc, or improper shielding.

4. 9. 0 Acceptable and Unacceptable Weld Profiles The profile of a finished weld can affect the performance of the joint under load as much as other discontinuities. An unacceptable profile could lead to the formation of discontinuities such as incomplete fusion or slag inclusions.

4. 9. 1 Fillet Welds A fillet weld is a weld that is approximately triangular in cross section and is used with T, lap, and corner joints. The size and locations of fillet welds are given as welding symbols. The following terms are used to describe a fillet weld: Weld face – the exposed surface of the weld Leg – the distance from the root of the joint to the toe of a fillet weld

4. 9. 1 Fillet Welds Fillet weld terms continued: Weld toe – the junction between the face of a weld and the base metal Weld root – the point shown in cross section at which the weld metal intersects with the base metal and extends farthest into the weld joint Size – the leg lengths of the largest right triangle that can be drawn within the cross section of a filler weld

4. 9. 1 Fillet Welds Welding codes require that filler welds have a uniform concave or convex face. The convexity of a fillet weld or individual surface bead will be approximately 0. 07 times the actual face width or the width of the individual surface bead, plus 1/16”.

4. 9. 1 Fillet Welds

4. 9. 2 Butt Welds Butt welds should be made: with slight reinforcement (not exceeding 1/8”) A gradual transition to the base metal at each toe Butt welds should not have: Excessive reinforcement Insufficient throat Excessive undercut overlap

5. 0. 0 Nondestructive Examination Nondestructive examination (NDE) is a term used for those inspection methods that allow materials to be examined without changing or destroying them. Inspectors are trained in the proper test methods to conduct the examinations. Welders should be familiar with basic nondestructive examination practices.

5. 0. 0 Nondestructive Examination Some common nondestructive examinations methods are: Visual inspection Liquid penetrant inspection Magnetic particle inspection Radiograph inspection (x-ray) Ultrasonic inspection Eddy current Leak testing

5. 1. 0 Visual Inspection In visual inspection, the surface of the weld and the base metal are observed for visual imperfections. Visual inspection is the examination method most commonly used by welders and inspectors. It is the fastest and least expensive method of examination. Visual inspection can detect more than 75% of discontinuities.

5. 1. 0 Visual Inspection Prior to welding, the base metal should be examined for conditions that may cause weld defects. Dimensions, including edge preparation, should be confirmed by measurements. Some of the more common welding gauges used in visual inspections are: Undercut gauge Butt weld gauge Fillet weld gauge

5. 1. 1 Undercut Gauge An undercut gauge is used to measure the amount of undercut on the base metal. Most codes allow for undercut to be no more than. 010” deep (1/32”). Two types of undercut gauges currently used are: Bridge cam gauge V-WAC gauge

5. 1. 1 Undercut Gauge

5. 1. 2 Butt Weld Reinforcement Gauge Is used to measure the size of a fillet weld or the reinforcement of a butt weld. Be sure to read the correct scale for the measurement being taken.

5. 1. 3 Fillet Weld Blade Gauge Set The fillet weld blade gauge set has seven individual blade gauges for measuring convex and concave fillet welds. The seven blades can measure eleven weld sizes: 1/8”, 3/16”, ¼”, 5/16”, 3/8”, 7/16”, ½”, 5/8”, ¾”, 7/8” and 1”

5. 1. 3 Fillet Weld Blade Gauge Set

Answer review questions 1 - 9 END OF SESSION 1

5. 2. 0 Liquid Penetrate Inspection Liquid penetrant inspection (PT) is a nondestructive method for locating defects that are open to the surface. A penetrating liquid, usually red in color, is applied to the surface of the weld. Any discontinuity will draw the liquid into it. A developer, usually white, is then applied over the weld. If the discontinuity is significant, the red penetrant will bleed through the developer. The most common defects found using this process are surface cracks.

5. 2. 0 Liquid Penetrate Inspection (pg. 4. 17)

5. 3. 0 Magnetic Particle Inspection (MT) uses electricity to magnetize the weld. Metal particles are sprinkled onto the weld surface. If there are defects, the metal particles will group into a pattern around the defect. The defect can be identified by the shape , width, and height of the particle pattern.

5. 3. 0 Magnetic Particle Inspection

5. 3. 0 Magnetic Particle Inspection The disadvantage is that the material has to be capable of being magnetized. Also, the inspector must be skilled in interpreting indications. A rough surface can interfere with the results. Defects can only be detected near the surface.

5. 4. 0 Radiograph (RT) is a nondestructive examination method that uses radiation (x-rays or gamma rays) to penetrate the weld and produce an image on film. When a joint is radiographed, the radiation source is placed on one side of the weld and the film on the other. Radiograph should only be used and interpreted by a trained, qualified personnel. Radiograph can produce a visible image of weld discontinuities, both surface and subsurface.

5. 4. 0 Radiograph

5. 4. 1 Radiograph The advantages of radiograph are: The film gives a permanent record of the weld quality The entire thickness can be examined Can be used on all types of metal The disadvantages are: It is slow Expensive Radiation is a type of hazard Some joints are inaccessible

5. 5. 0 Ultrasonic Inspection The term ultrasonic indicates that these frequencies are above those heard by human ear. Ultrasonic inspection (UT) is a nondestructive examination method that uses soundwave vibrations to find defects in the weld material. The waves are passed through the material being tested and are reflected back by any density change caused by a defect.

5. 5. 0 Ultrasonic Inspection Ultrasonic examination can be used to detect: Cracks Laminations Pores Slag inclusions Incomplete fusion Incomplete joint penetration

5. 5. 0 Ultrasonic Inspection Advantages of Ultrasonic inspection are: Finds defects throughout the material Used on material that cannot be radiographed Nonhazardous to personnel and equipment Disadvantages of Ultrasonic inspection are: Requires a high degree of skill to interpret Very small or thin weldments are difficult to inspect

5. 6. 0 Electromagnetic Inspection (Eddy Current) Eddy current used electromagnetic energy to detect defects in the joint. An alternating current coil is placed on or around the part being tested. The coil produces a current in the metal through induction. A discontinuity in the test joint will interrupt the flow of the eddy current. The eddy current change can be observed on a oscilloscope.

5. 6. 0 Electromagnetic Inspection (Eddy Current) Advantages of Eddy Current are: Very useful in inspecting circular parts, such as pipe and tubing Disadvantages of Eddy Current are: The current decrease with depth, so defects farther from the surface may go undetected Accuracy depends on calibration of equipment and the inspector’s skill

5. 7. 0 Leak Test Leak test is used to determine the ability of a pipe or vessel to contain gas or liquid. Test methods vary depending on the application of the weldment. A method called vacuum box test is used to test a vessel where only one side of the weld is accessible. A leak is detected by the presence of bubbles.

6. 0. 0 Destructive Testing Destructive testing is so called because the test sample is destroyed or damaged in the testing process. Examples of destructive test commonly used are: Tensile test Hardiness test Impact test Soundness test

6. 0. 0 Destructive Testing Tensile test A sample weld is placed in a tensile test machine and pulled until it breaks The test is performed to determine specific characteristics of the weldment �Such as strength and ductility Hardness test Is done by using a penetrating device that leaves an indention in the weld sample The indention is measured to determine hardness

6. 0. 0 Destructive Testing Impact test The ability of a weld to withstand in impact, or toughness, is measured by this test. A notch of a specified size is made on the sample weld Then the weld is struck by a pendulum-type machine that simulates a heavy hammer blow.

6. 0. 0 Destructive Testing

6. 0. 0 Destructive Testing Soundness test Three types of soundness test – bend, nick break, and fillet weld Bend test Is the most commonly used test to determine the qualification of a welder or welding procedure The sample weld is bent into a U-shape with a device called a jig. The bending action places stress on the weld metal and reveals any discontinuities. The bend is then inspected for weld defects. Guided bend test are used to evaluate groove welds on plate and pipe. Three type of test performed on the jig: root, face, and side

6. 0. 0 Destructive Testing

6. 0. 0 Destructive Testing Nick-break test Used primarily in the pipeline industry The specimen is saw-cut so it will break in a specific place. Then it is broken, and the weld is examined for defects. Fillet weld break test A fillet weld is made on one side of a T joint Stress is then applied to the T joint until the weld breaks The weld is then examined for defects.

Break Time Take a 15 min. break

7. 0. 0 Welder Performance Qualification Tests The purpose of the welder performance qualification test is to measure the proficiency of individual welders. Codes require that welders take a test to qualify to perform a welding procedure.

7. 1. 0 Welding Positions Qualifications The welder is qualified by welding positions. The qualification tests are designed to measure the welder’s ability to make groove or fillet welds in different positions in accordance with the applicable code. Each welding position is designated by a number and a letter. (1 G, 2 G, 3 G, 4 G, 5 G, 6 G, 1 F, 2 F, 3 F, 4 F) This system is standard for all codes.

7. 1. 0 Welding Positions Qualifications Plate Weld Positions

7. 1. 0 Welding Positions Qualifications Pipe Welding Positions

7. 1. 0 Welding Positions Qualifications A welder who qualifies in one position does not automatically qualify to weld in all positions. Qualifying for pipe will qualify a welder for plate in certain codes. Qualifying under one code does not qualify a welder under another code.

7. 2. 0 AWS Structural Steel Code AWS D 1. 1 code provides information concerning the qualification of weld procedures, welders, and welding operation for the fabrication in building and bridge construction. The mild steel electrodes used in SMAW are classified by F numbers (F 1, F 2, F 3, &F 4). Qualification with and electrode in a particular Fnumber will qualify the welder with all electrodes in that classification and in lower F-number groups. (table 1, pg. 6. 26)

7. 2. 0 AWS Structural Steel Code Material thickness is an essential variable in qualification test under AWS code. Plate test qualify the welder only up to twice thickness of the test piece or unlimited thickness depending of the material thickness of the test plate. A typical AWS welder qualification test is a Vgroove weld with metal backing in the 3 G and 4 G positions using an F 4 electrode (7018). Passing this test qualifies the welder to weld with F 4 or lower electrodes and make groove and fillet welds in all positions.

7. 2. 0 AWS Structural Steel Code Typical AWS Plate Test

7. 3. 0 ASME Code Welders who are required to weld to ASME code must qualify in accordance with Section IX of the ASME Boiler and Pressure Vessel Code The typical ASME welder qualification test is to weld pipe in the 6 G position using an open root. Passing a 6 G pipe test qualifies the welder to weld pipe in all positions and plate in all positions (fillet and groove).

7. 3. 0 ASME Code Typical ASME Pipe Test – 6 G

7. 4. 0 Welder Qualification Test A welder becomes qualified by successfully completing a weld made in accordance with a WPS. Passing a groove weld test permits a welder to weld groove welds and fillet welds.

7. 4. 1 Making the Test Weld Qualifications tests are designed to determine the capability of welders, but some welders have failed for reasons not related to their welding ability. This is due to carelessness in the application of the weld and in the preparation of the test specimen. It is important to note prior to welding where the test strips will be cut from the weld coupon.

7. 4. 2 Removing Test Specimens There are specific locations where test strips are cut from the test pipe or plate. For material 3/8” thick and under, a face bend a root bend are required. For material over 3/8”, two side bends are required. For pipe welded in the 5 G or 6 G positions , four specimens are required. Two face bends Two root bends

7. 4. 2 Removing Test Specimens

7. 4. 2 Removing Test Specimens

7. 4. 3 Preparing the Specimens for Testing Poor specimen preparation cause a sound weld to fail. To properly prepare the test strip: Grind the surface to a smooth finish. �All grinding marks must be lengthwise on the sample. Remove any face or root reinforcement from the weldment. Round the edges to at smooth 1/16” radius. Do not water quench test strips when grinding. �Quenching may create small surface cracks to become larger during the bend test.

7. 4. 3 Preparing the Specimens for Testing

7. 4. 3 Preparing the Specimens for Testing The criteria for acceptance by AWS D 1. 1 is that the surface shall contain no discontinuities that exceed: 1/8” measured in any direction 3/8”-the sum of all discontinuities exceeding 1/32”, but less than 1/8” ¼”-maximum corner crack, except when the corner crack results from visible slag inclusions A corner crack exceeding ¼” with no slag inclusions or fusion discontinuities can be discarded and a replacement strip cut from the original weld test

7. 4. 4 Welder Qualification Limits Welders may retest if they initially fail the test. An immediate retest consists of two welds for each type failed. All test specimen must pass this retest A welder may have to retest if they have not used the specific weld process for a certain time period A welder may be required to retest if there is reason to question the welder’s ability to make weld that meet code.

8. 2. 0 Chain of Command A welder should follow the chain of command Some examples when a welder should bypass the chain of command: When you are directed to perform an unsafe act When you are directed to perform a weld that you are not qualified for Always try to resolve problems with your immediate supervisor before bypassing the chain of command. (note pg. 6. 32)

Summary Quality is everyone’s responsibility. Keeping quality in mind as you perform each step of your job will help you identify and correct small problems before they become large problems Weld codes set the standard for what is a quality weld A weld, good or bad, will be seen long after the job is done.

Review Questions Answer review questions 10 – 15 Answer trade terms 1 - 11