Stress-relieving is a form of post-weld heat treatment. In stress-relieving we heat a material to a specific temperature; hold it at this temperature for a specified amount of time in order to reduce or eliminate residual stresses, and then cool it at a slow enough rate to prevent these stresses from redeveloping. In most cases, stress relieving is done to regain dimensional tolerance and to reduce distortion. Distortion occurs due to the rapid and uneven heating and cooling of the weld metal and the surrounding base metal.  As the molten weld metal cools it contracts and does so at a … Continue reading PWHT weld stress relieve concept

We recently helped out a customer in determining why some of their welds were cracking.  It was determined that cracking on their parts was due to rapid cooling and improperly sized welds. The discussions we had before and after determining the cause were quite interesting.  We went over the typical causes of cracking with our customers.  Here is a brief summary of our meetings.  Please note that these are not all the causes for cracks. Generally speaking, we can separate cracks in two groups, which have to do with the timing of the cracks: hot cracking and cold cracking.  Essentially … Continue reading Weld Hot Crack vs Cold Crack

Stainless steels are iron-based alloys that contain a minimum of 10.5% chromium.  This chromium reacts with the air and forms a very thin but very tenacious chromium oxide layer which is what prevents stainless from rusting. There are 5 types of stainless steels that are categorized depending on additional alloying elements.  One thing they all have in common is the minimum chromium content of 10.5%. The five types are: Austenitic Stainless Steels Ferritic Stainless Steels Martensitic Stainless Steels Duplex Stainless Steels Precipitation Hardening Stainless Steels Out of these five, austenitic stainless are the most common and familiar types of stainless steels. They exhibit … Continue reading Stainless steel welding and sensitiztion

Hydrogen Induced Cracking (HIC), also called hydrogen assisted cracking (HAC) and cold cracking, is a common welding defect when welding heavy steel sections and steels with high carbon content. In the above mentioned article we explained that you need three things in order to have cold cracking: source of hydrogen, susceptible microstructure and a certain level of stress.  If you can eliminate one you eliminate the potential for cold cracking.  When we ignore this, whether by choice or by ignorance, we are in trouble.  However, many weldments fail due to hydrogen induced cracking even when good welding procedures are in … Continue reading Hydrogen Induced Cracking (HIC) in welding

Today we’ll cover 5 more very important concepts that are governed by the AWS D1.1 Structural Welding Code (Steel).  These concepts can show up as questions in the Certified Welding Inspector (CWI) Exam. As stated in our article from last week, in this exam you don’t have to explain your answers, you simply have to choose the right answer (multiple choice exam). As long as you can find the answer in the codebook you are good. However, it is very important to know why the code imposes certain limits and requirements. Below are 5 more fundamental principles that must be … Continue reading CWI welding inspector notes