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Overview of Welding

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Welding is the process of joining separate metals together using extreme heat. Welding can be used for a number of different purposes. For example, repair welds are minor welds that are applied to structures to repair areas of minor surface damage. Weld overlay, on the other hand, is a process that is used to add an outer layer to a piece of equipment.

There are multiple different welding processes. Some of the more common types of welding are shielded metal arc welding, CO2 welding, Metal Inert Gas (MIG) welding, Submerged arc welding, and Plasma Transferred Arc (PTA) welding.

After performing any weld. it is important to perform a post weld heat treatment (PWHT) on the weld area to reduce residual stresses. If this is not done, then the weld is more likely to experience brittle fracture. PWHT is also able to reduce the chances of hydrogen induced cracking (HIC) in the weld as well.

Hot Work

Hot work refers to any work involving electric or gas welding, cutting, brazing, or similar flame or spark-producing operations. In many oil and gas or chemical processing enviroments, hot work has the potential to ignite a combustible material and cause significant process safety incidents. Extreme caution must be used whenever planning and performing any hot work.

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Articles about Welding
  • In Case You Missed It: Here's a Look at Some of Our Most Popular Content from the Past 6 Months
    Blog
    June 6, 2019 By Alyssa Hatton at Inspectioneering

    Over the last six months, Inspectioneering has released a plethora of interesting and educational content that has been read more than 150,000 times online. In case you missed it, here's a recap.

  • Assuring Pressure Part Manufacturing & Repair Quality - Has ticking the box become more important than the end product?
    March/April 2019 Inspectioneering Journal
    By Andreas Fabricius at Tetra Engineering, James Malloy at Tetra Engineering, and Mark Taylor at Tetra Engineering

    The quality of the thousands of factory and field welds present in pressure part modules is critical for assuring reliable operation over the life of a plant. Companies should be doing more than paying lip service to quality. Don't just tick a box.

  • Impact of Welding Defects on Integrity of Equipment & Piping
    January/February 2019 Inspectioneering Journal
    By Qasem Fandem at Saudi Aramco

    Welding imperfections vary in impact from being acceptable to requiring repair. It is important to ensure the quality of welds using NDT and to ensure the strength of the entire piping system with hydrotesting.

  • Observations on Flaw Tolerance and Brittle Fracture: The Effect of Post Weld Heat Treatment
    January/February 2018 Inspectioneering Journal
    By Phillip E. Prueter at The Equity Engineering Group, Inc.

    Given the concern throughout industry regarding the potential for brittle fracture failures, PWHT guidance to address potential issues arising from the recent changes in PWHT code requirements for carbon steel is examined in this article, and commentary on the potential reduction in fracture toughness due to PWHT is provided based on a review of published literature.

  • The Power of Proper Post-Weld Heat Treatment
    May/June 2017 Inspectioneering Journal

    The "simple" process of PWHT is more complicated than it may appear at first glance. Knowledge of the procedures, attention to details, and actual experience are indispensable in preventing failures caused by improper PWHT.

  • Vanta XRF Analyzer: Redefining PMI, Ruggedness, and Ease of Use
    Partner Content

    The Vanta handheld XRF is Olympus’ first full spectrum PMI analyzer that is IP65 rated and drop tested. The analyzer provides accurate, repeatable material chemistry and alloy grade matching in as little as 1–2 seconds. Operation is simple with an intuitive touch screen and swipe interface. Optional Wi-Fi, with the Olympus Scientific Cloud, provides seamless connectivity for efficient data and fleet management.

  • Digital Radiography of Welds Using Flat Panel Detector Base Image Sensors
    July/August 2016 Inspectioneering Journal
    By Sanjoy Das at Bhabha Atomic Research Centre, and D. Mukherjee at Bhabha Atomic Research Centre

    The structural integrity of components is controlled by material properties, the presence of flaws, and levels of applied stress. Several factors such as temperature, type of loading, toughness, corrosion resistance, micro-structural stability, cost etc. dictate the suitable material for the desired application.

  • Remaining Life Sensitivity to Longitudinal Weld Seam Peaking in High-temperature Low Chrome Piping
    July/August 2016 Inspectioneering Journal
    By Mark Geisenhoff at Flint Hills Resources, Jonathan D. Dobis at The Equity Engineering Group, Inc., Phillip E. Prueter at The Equity Engineering Group, Inc., and Dr. Michael S. Cayard at Flint Hills Resources

    This article summarizes a recent finite element analysis (FEA)-based study that employs creep simulation techniques to investigate the elevated temperature response of piping with peaked longitudinal weld seams.

  • The Benefits of Laser-Based Inspection
    March/April 2015 Inspectioneering Journal
    By Connie LaMorte at EWI, and Jon Jennings at EWI

    Weld inspection using lasers is not new, but doing it 75 meters inside a pipe or streaming inspection data wirelessly is new. As laser technology has improved, more industries such as oil & gas are beginning to require laser inspection as part of their specifications. This non-contact method can help catch an unacceptable condition before it becomes too late to remedy the weld.

  • To Test or Not to Test: A Comparison of the Pressure Testing Requirements between ASME B31.3 and ASME Section VIII, Division 1
    January/February 2015 Inspectioneering Journal
    By Hugo Julien, P.E. at GCM Consultants, and Serge Bisson at GCM Consultants

    Are you still hitting the welded joints of pressure vessels with a hammer during hydrostatic testing? If yes, then you’re due for a refresher on the pressure testing requirements of ASME Section VIII Division 1 since this requirement was for pressure vessels back in the mid 1940’s. This article will help you by highlighting the main requirements of, and differences between, the hydrostatic test for new pressure vessels fabricated according to ASME Section VIII, Division 1 and the hydrostatic leak test for new piping systems made under ASME B31.3.

  • The Hydrogen bake-out process: an introduction and helpful resources
    Blog
    November 10, 2014 By Nick Schmoyer at Inspectioneering

    One of the more insidious problems within the industry is the issue of atomic hydrogen dissolving into steel equipment. This can happen to some steel components under certain circumstances and can cause weld failure, or what is known as “hydrogen cracking.” These cracks can occur during the welding process itself, but sometimes they can occur up to 48 hours later.

  • Global, simultaneous inspection with Acoustic Emission Testing
    Partner Content

    AET is a powerful, non-intrusive inspection technique to verify the structural integrity of pressure vessels, spheres, high-temperature reactors and piping, coke drums, above-ground storage tanks, cryogenic storage tanks, and more.

  • Abnormal Cracks Led to Premature Decommissioning of Boiler Feed Water Exchanger – What Happened and Why?
    September/October 2014 Inspectioneering Journal
    By Ana Benz at IRISNDT, Dr. Donald H. Timbres at D. & E. Consulting, Inc. , and Matt Stroh

    A small leak from top tubesheet-to-tube welds prompted further inspection of the 1¼Cr- ½Mo Ammonia Converter Boiler Feed Water (BFW) Exchanger during a planned shutdown. Further cracks were identified in the top channel to tubesheet butt weld that operated at 700 °F.

  • The Pathway to ASME PCC-1 2013 Appendix A Compliance and its Critical Importance
    May/June 2014 Inspectioneering Journal
    By Neil Ferguson at Hydratight

    In November 2013, ASME released its updated PCC-1 guidelines for pressure boundary bolted flange joint assemblies. Contained within the document is Appendix A, which represents a major change from the previous 2010 release and is considered to be one of the most critically important changes for BFJA technicians, operators, and other industry professionals.

  • A Discussion on Hydrogen Bake-Outs
    January/February 2014 Inspectioneering Journal
    By Marc McConnell, P.E. at Pro-Surve Technical Services, Josh Yoakam at Holly Refining and Marketing - Tulsa, LLC, and Frank Dean at Ion Science, Ltd.

    This is the second of two articles published in Inspectioneering Journal discussing the value of hydrogen bake-outs. Our first article was published in the May/June 2013 issue and received a great response from the Inspectioneering community. In this piece, we will continue the discussion and touch on some new technologies used to enhance the bake-out process.

  • New Standards for Quality Control and Assurance of Bolted Flanges
    January/February 2014 Inspectioneering Journal
    By Neil Ferguson at Hydratight

    If necessity is the mother of invention, then the American Society of Mechanical Engineers (ASME), the Occupational Safety and Health Administration (OSHA), and the Environmental Protection Agency (EPA) are the parents of guidelines, standards, and regulations that help keep industrial operations safe for humans and the environment.

  • Leaking Dryers and Scrubbers Located at Natural Gas Well Facilities
    January/February 2013 Inspectioneering Journal
    By Ana Benz at IRISNDT

    In this article you will find the failure investigations of six 0.094 inch thick carbon steel vessels. These vessels were in service in natural gas well facilities; some functioned as dryers and were subjected to cyclic loads. Metallographic tests, hardness tests, and fracture surface scanning electron microscopy (SEM) examination results are presented for each of the vessels.

  • The New Acronym You Need to Know: FPI
    Partner Content

    Facilities are facing increasing challenges, including justifying inflated budgets, managing contractor hours, ensuring regulatory compliance and qualifying the work being completed. To help facilities manage evolving inspection requirements, PinnacleART offers Fixed-Price Inspection (FPI), meaning we will develop and execute a comprehensive Risk-Based Inspection plan for one fixed-price. Yes, you read that right – one fixed-price.

  • Welding Research Council (WRC) Bulletins Now Available
    September/October 2010 Inspectioneering Journal

    For years the WRC has provided the documented technical basis for many decisions made regarding design, repair, remaining life estimation, and fitness for service of pressure equipment in our industries. Many codes and industry recommended practices are based on the information found in these bulletins, globally.

  • Tangential Radiography Technique for Special Weld Joints Configuration
    January/February 2008 Inspectioneering Journal
    By Sanjoy Das at Bhabha Atomic Research Centre, P.R. Vaidya at BARC, and B.K. Shah at BARC

    Most common radiographic practices for circumferential weld testing are single wall and double wall techniques with certain variations in technique details. Different Codes deal with the number of exposures required and applicability of the technique for different combinations of pipe diameter and wall thickness. However, there are certain geometries where these conventional radiography techniques are not applicable, mainly because the weld is superimposed on some structural material inside the tube or pipe.

  • 99 Diseases of Pressure Equipment: Stabilization Heat Treatment of Austenitic Stainless Steel Weldments
    March/April 2007 Inspectioneering Journal
    By John Reynolds at Intertek

    In the welded condition many stainless steels are susceptible to rapid intergranular corrosion or stress corrosion cracking. This is because the heat from welding sensitizes the base metal heat affected zone (HAZ) and the weld.

  • 99 Diseases of Pressure Equipment: Welding to Weld Overlayed or Clad Equipment
    March/April 2007 Inspectioneering Journal
    By John Reynolds at Intertek

    A myriad of issues need to be considered before welding to or repairing weld overlayed or clad equipment. (By clad we mean roll-bonded or explosion bonded, i.e. basically 100% metallurgically bonded, and not a loose or seam-welded liner, e.g., not strip lining.)

  • 99 Diseases of Pressure Equipment: Practical/Communication Issues That Can Lead to Welding Flaws
    March/April 2007 Inspectioneering Journal
    By John Reynolds at Intertek

    When we talk about welding QA/QC we typically focus on the technical requirements and what QA/QC is needed to assure that the technical requirements are met. Examples include the preheat, interpass, and PWHT temperatures and how to assure that the correct temperatures and hold times are used.

  • Conventional, Digital and Computer Radiography
    Partner Content

    ProSource Radiography Services, a sister company and subsidiary of Pro-Surve is ready to tackle your radiography needs. Should you need a small bore piping survey or other need for computed radiography. ProSource can take conventional film, and convert them to digital files for easy naming and storage. ProSource is ready to be your Sole-Point-Of-Contact (SPOC) for your radiography needs.

  • 99 Diseases of Pressure Equipment: Hydrogen Bake-out
    May/June 2006 Inspectioneering Journal
    By John Reynolds at Intertek

    As noted in the discussion on delayed cracking, when the steel contains hydrogen as a result of service exposure (or corrosion, or high temperature - high pressure hydrogen processing) then a hydrogen bake out may be needed to avoid cracking problems during or after welding.

  • 99 Diseases of Pressure Equipment: Welding Flaws and Defects
    January/February 2006 Inspectioneering Journal
    By John Reynolds at Intertek

    After a pressure equipment or piping failure, it’s not uncommon to find out during the failure analysis part of the investigation that the failure initiated at a welding flaw of some sort.

  • 99 Diseases of Pressure Equipment: Welding QA/QC
    January/February 2006 Inspectioneering Journal
    By John Reynolds at Intertek

    Among other things, a welding QA/QC program needs to ensure that only qualified welders, utilizing qualified procedures are allowed to weld on any pressurized equipment, including storage tanks and piping.

  • Damage Mechanisms Affecting Fixed Equipment in the Fossil Electric Power Industry
    July/August 2005 Inspectioneering Journal
    By Jonathan D. Dobis at The Equity Engineering Group, Inc., and David N. French

    This bulletin is part of a series of WRC Bulletins that contain the technical background and other information to evaluate damage mechanisms in various industries to facilitate the use of API 579. These bulletins, shown below, will be updated based on the latest knowledge and technology developed for identification of damage mechanisms.

  • Avoiding PWHT - Can It Be Justified?
    May/June 2005 Inspectioneering Journal
    By Julian Speck at TWI Ltd., and Amin Muhammed at TWI

    Current BSI and ASME codes for the construction of pressure vessels, boilers and piping specify that post-weld heat treatment is required if the thickness of the components being welded exceeds a specified value. This value depends on the type of material being used, and varies from code to code. An alternative procedure is available for deciding whether or not PWHT is necessary to avoid the risk of failure by fracture. This involves conducting a fracture mechanics assessment using procedures such as those in BSI 7910, or API 579. The use of these procedures is permitted in the British pressure vessel standard BS PD 5500:2003.

  • Avoid Flange Leaks with In-Service Face Raised Flange Inspection
    Partner Content

    Let Pro-Surve identify corrosion on your flange raised faces while your unit remains in operation. Using phased array TFM, custom transducers and proven procedures Pro-Surve technicians identify corrosion on flange raised faces from the flange outside diameter. Identify scope for pipe spools for turnaround pre-fabrication using this technique. Identify flanges needing replacement or re-machining.

  • 99 Diseases of Pressure Equipment: Repair Welds
    January/February 2004 Inspectioneering Journal
    By John Reynolds at Intertek

    Repair welds can be another undetected and insidious "fabrication defect" that eventually results in equipment failure. Any experienced metallurgist that has completed numerous failure analyses over the years will tell you that periodically they see failures that initiated at the site of a repair weld. Sometimes those repair welds are field repairs, but not infrequently they occurred during original fabrication and were unknown to the purchaser. Typically our standards and specifications do not cover repairs completed by the fabricator, so they believe they are free to do whatever they want to repair a manufacturing or fabrication defect, then grind it flush, finish the fabrication and ship the product.

  • 99 Diseases of Pressure Equipment: Inadequate Overlay Weld Thickness and Chemistry
    January/February 2004 Inspectioneering Journal

    When we specify that some equipment (vessels, flanges, fittings, etc.) be overlaid with a corrosion resistant alloy, we need to pay attention to making sure that the chemistry of the top layer of alloy welding, that will be exposed directly to the process fluid, is sufficient to resist degradation from the process environment. This may sound logical, but I’m aware of several cases where weld overlaid surfaces are ground or machined to meet specification tolerances, and in so doing the most resistant part of the alloy overlay is removed.

  • 99 Diseases of Pressure Equipment: Dissimilar Weld Metal (DMW) Cracking and Other Spec Breaks
    January/February 2004 Inspectioneering Journal

    DMW cracking is another fabrication issue that can and does result in equipment failure. It usually occurs at the weld juncture where carbon steel or low alloy steels are welded to austenitic (300 series) stainless steels in high temperature applications. The large difference in coefficient of expansion of the two steels, sometimes exacerbated by thermal cycling, results in cracking at the toe (HAZ) of the weld joining the two materials. Using an austenitic stainless filler material for the DMW junction also increases the stress intensification on the toe of the weld on the ferritic side of the weldment. This type of cracking is most common when temperatures above 800F (425C) are involved, such as in FCCU reactor/regenerations systems, superheaters, reheaters, fired heaters, and hydroprocess equipment. Use of bolted joints, if possible, or nickel base filler materials helps to avoid the DMW cracking problem.

  • 99 Diseases of Pressure Equipment: Weld Heat Affected Zone Cracking
    January/February 2004 Inspectioneering Journal
    By John Reynolds at Intertek

    Cracks along the toe of a weld are not uncommon during fabrication, and can occur for a wide variety of reasons involving the metallurgy and process control of the the same issues covered above on repair welds can apply to repair welds on castings; especially if you are unaware that the foundry or fabricator is trying to salvage a defective casting by covering up porosity and shrinkage cracking with a big glob of weld metal.

  • 99 Diseases of Pressure Equipment: Inadequate Postweld Heat Treatment (PWHT)
    January/February 2004 Inspectioneering Journal
    By John Reynolds at Intertek

    Inadequate PWHT is one of our pressure equipment nemeses. We normally specify PWHT for a variety of pressure equipment integrity reasons including when we need to lower residual stresses, increase resistance to cracking or soften weld hardness. All for the purpose of prolonging the service life of our equipment and preventing unexpected failures. But this issue is clearly where those old sayings of "Buyer beware" and "You don't get what you expect, you get what you inspect" apply quite often.

  • InVista™ In-Line Inspection for Unpiggable Pipelines
    Partner Content

    InVista is a lightweight, hand-held ultrasonic in-line inspection tool (intelligent pig) capable of detecting pipeline wall loss and corrosion in unpiggable or difficult-to-inspect pipelines. The pipeline geometry inspection data captured by the InVista tool is exceptionally powerful when combined with the LifeQuest™ Pipeline fitness-for-service capabilities, providing an integrated solution set for the pipeline industry.

  • A New API Recommended Practice, API RP 577
    May/June 2003 Inspectioneering Journal
    By John Reynolds at Intertek

    A new recommended practice from the API is in the final stages of preparation before publications. It is API RP 577 on Welding Inspection and Metallurgy.

  • 101 Essential Elements in a Pressure Equipment Integrity Management Program for the Hydrocarbon Process Industry Part 4
    November/December 2000 Inspectioneering Journal
    By John Reynolds at Intertek

    Part 4 of this article continues to outline the 101 essential elements that need to be in place, and functioning well, to effectively and efficiently, preserve and protect the reliability and integrity of pressure equipment (vessels, exchangers, furnaces, boilers, piping, tanks, relief systems) in the refining and petrochemical industry.

  • UT Inspection for Cracking in Heat Exchanger Tube-to-Tubesheet Welds and Tube Corrosion
    September/October 1999 Inspectioneering Journal
    By Reggie Cross at ND Tech

    This paper describes use of a UT fixture for detection of stress corrosion cracking in ferrous heat exchanger tube-to-tubesheet welds and external tube corrosion or pitting near the tubesheets including crevice OD corrosion of the tube in the tubesheets.

  • Post-weld Inspection Using Laser Vision
    July/August 1998 Inspectioneering Journal
    By Constance Reichert at Edison Welding Institute

    Visual inspection is the most common nondestructive testing method. For critical applications, machine vision technology provides advantages over visual inspection.

  • Can TOFD Replace Conventional UT for Weld Inspection?
    July/August 1998 Inspectioneering Journal
    By H. Wuestenberg

    The debate about advantages and drawbacks of the application of the TOFD (time of flight diffraction) approach for ultrasonic weld inspection should not forget the original reasons for its introduction in the 1960s. The major advantage at that time had been the better crack detection in comparison to x-ray techniques, especially in view of an increased use of steels and welding technologies with a the presence of diverse cracking phenomena (e.g. cold cracking, transverse cracks etc.).

  • Results of Degassing of Refinery Steel Components Prior to Welding
    May/June 1997 Inspectioneering Journal

    Case 1: Fuel Gas to Boilers in boiler house: in 1992 two flanges were installed for installation of knock blinds. No degassing was completed. Both welds were radiographed and noted as acceptable. Case 2: Alky Unit Flare Header: No degassing completed in 1993 on multiple tie-ins. All of these tie-ins were radiographed and noted as acceptable. Case 3: Alky Unit flare Header: No degassing completed in 1993 on multiple tie-ins, all of these tie-ins were radiographed and noted as acceptable.

  • Automatic Flaw Detection in TOFD Images for NDT During Welding
    November/December 1996 Inspectioneering Journal
    By Shaun W. Lawson at Mechatronic Systems and Robotics Research Group, University of Surrey

    The basic approach to the inspection and repair procedure for welding has barely altered for three decades. The normal practice has continued to be to inspect a weld only after the welding programme is complete. Thus by the time a defect is detected, considerable time and money has been spent on completing the welding of a rejectable component. Furthermore, a large number of additional weld runs will generally have been deposited over the defect, thus increasing the cost of repair and decreasing the quality of the component.

  • Addressing Gusset Problems: Pipe Cracking Part 3
    May/June 1996 Inspectioneering Journal
    By Del Underwood at Det Norske Veritas

    This final issue on gusset problems will discuss why gussets are "stiffeners" rather than "strengtheners." The effective load bearing capacity of a member of given strength is based upon how large a cross-sectional area is carrying the load. Gussets are commonly welded to tubular members to reduce their flexure under a bending load.

  • Addressing Gusset Problems: Pipe Cracking Part 2
    January/February 1996 Inspectioneering Journal
    By Del Underwood at Det Norske Veritas, and Tim Munsterman at Det Norske Veritas

    Last issue, in keeping with the evaluation that "gussets are stiffeners, not strengtheners," we discussed welding around the ends of the gusset plate instead of just along the sides in order to reduce the stress concentration. A further improvement in the gusset life can be obtained by welding it to a reinforcing plate and/or a fitting instead of directly to the pipe.

  • Addressing Gusset Problems: Pipe Cracking Part 1
    September/October 1995 Inspectioneering Journal
    By Del Underwood at Det Norske Veritas

    A key to any piping evaluation program is to understand where problems can occur. Vibrating piping can propagate a crack relatively quickly. Have you ever installed gussets to stabilize a vibrating pipe situation only to find, shortly thereafter, that the gussets have cracked the pipe? If so, you've got lots of company.

  • Considerations in the Assessments of Welded Hot Reheat Pipework
    May/June 1995 Inspectioneering Journal
    By Bob Browne at ERA Technology

    For reason of economy, the hot reheat pipework in many US power plants is fabricated from seam-welded low chrome-moly carbon steel spools. Unlike girth butt welds, where the critical weldment microstructures can off-load stress to the stronger parent material, seam welds are subject to the full pressure hoop stress. A number of failures have occurred, some of which have been evidenced by fast fracture over extended lengths of the seam weld with a massive and violent steam release.

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