Construction work and construction workers are both regulated closely, to help ensure that the finished structures are safe and meet the appropriate legal codes. For example, welders can earn certification from multiple organizations including the American Welding Society, American Petroleum Institute or the American Society of Mechanical Engineers. Each has its own focus. For example, ASME certification is centered around the construction of boilers and other pressurized vessels.
Mechanical engineering is the branch of the profession that designs and builds physical objects, ranging from the tiniest computer components to the largest of construction machinery. Large pieces of equipment such as boilers and other pressurized tanks sometimes need to be fabricated on-site by skilled tradespeople, so since 1916 the American Society of Mechanical Engineers has provided certification for both the manufacturing companies and individual welders. Certification ensures that both the manufacturing process and the welder's skills meet objective standards set by the ASME.
This type of large, pressurized storage vessel is usually constructed for a specific purpose, so the fabrication process also has to be individualized. Contracting companies in the business of making large pressurized tanks must submit their designs to the ASME for evaluation, along with a detailed description of the welding processes that will be used in their fabrication. The ASME evaluates the processes as described in the application, and verifies that they meet appropriate standards for materials, thicknesses and fabrication methods. To do the actual work, the contractor or manufacturer then has its welders certified.
Welding certifications are very specific, applying to a given type or thickness of material and a given welding technology. Employers hiring new welders, regardless of their prior experience or certifications, usually have them certified in the specific processes required for a given job. For example, union welders can usually be certified at the nearest United Association test center. ASME-approved examiners will supervise a series of test welds, using the appropriate materials and technology. Some workplaces or complex projects might require welders to take several tests, to demonstrate competence in the full range of necessary skills.
Part of the evaluation process takes place during the test, as the examiner monitors the welder's work habits, including the use of appropriate procedures and safety precautions. Once completed, the welds must be tested for soundness. In some cases, the test is as simple as flexing the weld and observing how well it holds up. ASME standards are more exacting, and require each weld to pass radiographic testing. That means the weld is examined with X-rays, to detect flaws or fissures that would compromise the integrity of a pressurized vessel. Welders who pass are considered certified for that process and welding apparatus.