Welding inspection involves much more than simply checking the accuracy of welds after they are made. Inspectors must know codes, standards, materials, and other fabricating processes.
Welding inspection is not something to be taken lightly. Lives can depend on the accuracy of the inspection. Failed welds that cause the loss of life or property make the news and technical journals. Unfortunately, these failures sometimes are blamed on the welding inspector. However, the harmful event could have been avoided if the inspector had done it correctly.
In some cases, this claim is justifiable; inspectors make mistakes like any other person in the fabrication chain. However, an inspector cannot inspect the quality of the product. The quality of a weldment must be established at the beginning of the project and followed through to the end. If any step in the job is not established and carried out with quality as the top priority, the possibility of failure exists.
In years past, poor welds caused many more catastrophic failures than today. Boilers exploded, ships sank, buildings and bridges collapsed, and pipelines blew up frequently. These disasters became far less frequent as codes and standards were established.
Which Code or Standard?
The American Society of Mechanical Engineers (ASME) worked diligently to establish rules for fabricating boilers, pressure vessels, and piping. The American Welding Society (AWS) established structural fabrication and erection rules. The American Petroleum Institute (API) continually is quality and safe for pipelines and related facilities.
An inspector must know which code or standard should be used for the inspection criteria—both the code of construction and the code to qualify the welding procedures and welders. These requirements must be outlined in the job specifications. The inspector should not make assumptions or rely on his judgment to set the standard. The inspector should not proceed without clarification if it is not written in the specifications or on the drawings.
It must be noted that the ASME Section IX is only for welding procedures and welder qualification. It may not be used as a code of construction. The AWS D1.1 code may be used for welding procedures and welder qualification and as a construction code. The API 1104 is for welding and nondestructive testing of pipelines and related facilities.
Before welding begins, the inspector must verify that the welding procedures comply with the applicable code or standard. Sometimes a customer establishes a standard not referenced to a particular code. This is often the case with substantial companies, such as Siemens and General Electric. In these cases, the customer standard prevails.
Each contractor or company is responsible for establishing welding procedures. No code that I am aware of allows a company to outsource a test for welding procedures. However, prequalified welding procedures are available from the AWS. The user must demonstrate that the company can perform these procedures. Most companies require fabricators to establish and test their procedures. The API 1104 code does not recognize prequalified procedures. All codes require destructive tests for the qualification of procedures, and each code has different procedure testing requirements (Figure 1)
The welding inspector must verify that the welders are qualified and certified to the proper code or standard. Welder qualification is established by testing. A welder who successfully performs a test and receives a certification document is called a certified welder.
Essential and nonessential variables are listed in each of the codes. Some essential variables common to all the codes are position, vertical progression, weld deposit thickness, and others related to the specific process. Nonessential variables do not require requalification, but essential variables do. For example, the inspector may need a welder to perform a demonstration for a reasonable cause, such as multiple failures and poor workmanship.
The inspector must observe the joint design to ensure that the procedures cover the type of weld specified on the drawing. For example, if the procedures and welders are qualified only for welds with backing, no open-root welds are permitted. On the other hand, if the procedures and welders are qualified for welds without backing, then welds with or without backing can be used. This variable is common to all the codes (Figure 2).
Material traceability is an absolute necessity for all jobs. If a failure occurs and liability is involved, proof of material quality can hold the key to the cause of the failure. The inspector can only recommend specific additional tests to ensure that the material is of sufficient quality for use. For example, I advise a client to require an ultrasonic examination on any material that is 1-inch thick or thicker.
A plate with lamellar inclusions should be detected and reported before any work is done to the material. Material suppliers must replace defective material, but convincing a supplier to pay for any work done before flaws are discovered is complicated.
The inspector must check the material test report (MTR) to ensure it meets the code requirements. Usually, the ASTM is referenced for AWS work, and the ASME Section II, Parts A and B, are referenced for ASME fabrications. Even when low-carbon materials are being welded, care must be taken to compare the chemical, physical, and mechanical properties to the proper standard. For example, the API piping standard is API 5L.
The inspector may question the material selection but accept the material if it meets the job specifications. The specification for material type is to be determined by the customer (usually the engineering department or an outsourced engineering firm).
Tracking the Job
The inspector should request a shop traveler—a step-by-step guide that begins when the job is designed by engineering and proceeds through packaging and shipping. The guide enables the inspector to establish hold points when necessary for tracking inspections in the process. An inspector should sign off on each step of the fabrication. If a part is cut, bent, or rolled incorrectly, the condition must be recorded and held as nonconforming until the customer decides. The decision may be to rework, use as is, or scrap. This decision is not to be made by the inspector, but the inspector must record the matter and secure it in the permanent job records.
Inspectors use tools such as these recommended and assembled in a kit by AWS. These tools and the inspector’s knowledge of codes, standards, materials, and processes help determine welded products and structures’ quality, durability, and safety.