Weld time is money. Money spent on poor structural/pipe weld execution and poor weld quality/nondestructive examination (NDE) failures is wasted money. Costly welds equal lost time and money. Consequently, without the availability of qualified personnel that are responsible for weld execution planning, process troubleshooting and overseeing fabrication operations, the likelihood for costly weld problems arises.
For example, a company was experiencing porosity and NDE-ultrasonic testing (NDE-UT) rejections in submerged arc welding (SAW) welds for an extended period of time. Subsequent weld equipment inspections revealed a high degree of rust on spooled SAW high-strength/low-alloy weld filler metal mounted on tractor wire feeders (see Figure 1).
In response, the company hired a welding engineer and implemented a new policy to store weld filler material in accordance with the manufacturer’s guidelines. Regrettably, the company had already lost money due to the issue. Prior to the decision to bring in the welding engineer, recurrent weld rework and repairs and weldment shipping delays had been incurred by the company. And, there was the expense of replacing spools of rusted filler metal with new ones.
Although the situation greatly improved with the introduction of a welding engineer, costly welds are a common occurrence in many shops. Presented here are further examples of structural/pipe fabrication situations that resulted in costly welds and how to avoid them.
The cost of poor weld execution and poor weld quality is the accumulated expense of not meeting drawing, code, contract or customer specification requirements. Unqualified decisions result in unacceptable outcomes. The following reflects actual fabrication events where unqualified decisions resulted in costly welds.
1) Assigning inexperienced flux-cored arc welding (FCAW) welders to perform out-of-position complete joint penetration (CJP) welding on 3-in.-thick structural steel plates where weld joints required NDE-UT inspection. Decision result: incomplete fusion and slag inclusion weld defects.
2) Welding duplex and austenitic stainless steel pipes without an adequate argon purge/backing gas environment (i.e., the internal pipe oxygen content was too high) where GTAW CJP girth welds required NDE-PAUT/TOFD (phased array ultrasonic testing/time of flight diffraction) inspection. Decision result: pervasive incomplete root fusion weld defects due to severe oxidation/“sugaring.”
3) Carrying out a GMAW-P (pulsed) circumferential CJP groove weld on a 45-ft.-dia., 2-in.-thick HY100 steel cylinder without first conducting a soaking through thickness preheat. Decision result: widespread weld metal/heat-affected zone.
Evolution of weld cost
Performing out-of-position welding process work is challenging especially when there are stringent NDE-UT inspection requirements per the AWS D1.1 Code. Take, for example, a 2 1/2-in.-thick structural steel plate with a CJP double-bevel groove weld joint design that was welded in the 2G horizontal position. A decision was made to employ inexperienced welders and a weld joint with no root opening/gap (see Figure 2). The weld joint was 55 ft. long and was welded using FCAW.
The thought process of shop management was that after the first side bevel was completely welded, the first side root weld would then be backgouged from the second side to sound weld metal prior to the second side bevel welding. However, after both sides were completely welded, the entire length of the weld joint failed NDE-UT inspection due to incomplete joint penetration, incomplete root fusion and slag inclusion weld defects. Extensive backgouging, grinding, GTAW repair welding and NDE-UT inspection iterations were required to obtain an acceptable weld joint. Weldment shipping was delayed and production costs increased by more than threefold.
In another example, structural steel weldments containing a variety of internal gussets, bulkhead plates and cross members were being fabricated. The procedure qualification records (PQRs)/welding procedure specifications (WPSs) were qualified per the AWS D1.1 Code employing FCAW, GTAW, GMAW and SAW processes where flat, vertical, horizontal and overhead welding was required.
During the project, overhead fillet welding (4F) was performed on more than 4,000 fillet weld joints employing a CJP vertical qualified FCAW PQR/WPS as opposed to an overhead qualified FCAW PQR/WPS. Company shop management, inspectors, welders and fitters did not understand AWS D1.1 Code, Figure 4.2 – Positions of Fillet Welds. The shop consensus was that if a weld “looks” vertical, it must, therefore, be a vertical weld (see Figure 3).
In analyzing weld positions, there are two major areas of consideration: the inclination of axis and the rotation of face. The welders had been qualified/certified for overhead welding. However, as predicated by the customer’s nonconformance report (NCR) that was issued for the as-welded overhead fillet welds, corrective actions had to be completed by the company. All shop floor employees (i.e., supervisors, inspectors, welders, fitters) were required to attend mandatory training classes relative to AWS D1.1 Code and visual inspection criteria.
Additionally, a new AWS D1.1 Code, overhead FCAW PQR/WPS had to be qualified based on the essential/supplementary essential variables of the respective vertical FCAW PQR/WPS that was utilized in error for overhead welding. In all, on top of a tarnished business reputation, more than 900 hours were expended by the company to disposition the customer’s NCR.
Weld execution planning
The cost of weld execution and quality is directly proportional to the competency of a production execution plan. A well-formulated weld execution plan mitigates welding and fabrication risks. That is, via diligent planning and preparation/research, the secret to welding success lies in the development of a comprehensive, production weld execution plan that identifies and outlines required actions and resources, including the right personnel, specialized tooling/equipment, PQRs/WPSs and optimal welding processes based on welding engineering analysis. Without a competent plan, the risk increases for production cost and time overruns.
For instance, the SMAW process was utilized for out-of-position recessed rebar welding (complete depth fill) of #14 rebar into 3-in.-thick vertical structural steel plates. Each individual plate consisted of more than 200 welds where there were more than 100 plates. All weld joints and rebar ends were shot blasted prior to welding.
Welds required visual inspection per the AWS D1.1 Code. During production, enough welds were failing visual weld inspection (see Figure 4) that a decision was made to 100 percent “flat top” each SMAW weld after welding and then perform a GTAW weld repair/“TIG cap.” That is, after each SMAW weld was completed, the weld was ground flush to the base metal surface, and then a GTAW weld repair/“TIG cap” was performed.
Unfortunately, a weld execution plan that would have identified the optimum welding process for the job (i.e., GMAW-P) and the optimal fabrication/fit-up practices and weld bead sequence/tie-in techniques was not developed. Whereby, due to an extraordinary amount of unplanned grinding and GTAW weld repair efforts, fabrication costs increased by more than 20 fold during the tenure of the project.
Escalated costs transpire due to an absence of qualified personnel to provide requisite engineering expertise, technical leadership and skilled technique, such as welding and synergic engineers, CSWIP (certification scheme for welding inspection personnel) inspectors, AWS senior certified welding instructors (SCWIs)/CWIs, American Petroleum Institute inspectors and coded welders/operators. Costs skyrocket when pertinent knowledge, proficiency and understanding are unavailable to plan, oversee and resolve problems and issues relevant to welding engineering, design/fabrication engineering, quality assurance/quality control, NDE inspection, metallurgy/heat treatment, code criteria and so on.
Causes that result in escalated weld costs include:
- Failure to develop a comprehensive, production weld execution plan.
- Failure of management by creating an environment of complacency/lack of continuous improvement initiatives and a shortfall of workplace accountability. Accountability matters; management needs to select the right person for the job and provide pertinent training.
- Making unqualified decisions based on lack of qualified personnel where ineffectual responses to questions, poor quality and low production performance are entwined (see Figure 5, AWS D1.6 Code application).
- Not spending requisite money on tooling, modular fixturing, equipment and so on.
- Personnel not possessing the fundamental skills to perform tasks such as reading, writing, math or language comprehension.
- Personnel using the wrong tools for the job. For example, utilizing 90-degree T-joint template-type fillet weld gauges to measure the leg length on skewed T-joint fillet welds.
- Disgruntled/disengaged/underperforming employees equal low workforce morale.
- Poor weldment/weld joint designs.
- Poor heat-treatment practices, such as dehydrogenation heat treatment and post-weld heat treatment.
- Failure of shop floor supervision and quality assurance/quality control to verify the correct PQR/WPS is being used for the job prior to welding. Also, failing to perform diligent operations oversight/surveillance, welder auditing, and in-process visual weld and weldment dimensional inspections.
- Poorly written WPSs, which are error traps for craft personnel. Ambiguous language or missing process specifics such as purge/backing gas details, power supply waveform settings, a weld bead sequence map and so on.
- Poor weld joint fit-up/alignment; large gaps, non-uniform root openings, mismatch (high/low).
- Placing a higher emphasis on production scheduling as opposed to the quality of workmanship, including failing to develop build strategies so the installation of permanent structural/pipe members or process equipment doesn’t obstruct weld joint accessibility of nearby weld joints yet to be.
- No open communication to resolve drawing or process questions. Thereby, personnel resort to “tribal knowledge.” They make assumptions or use the “that’s the way we have always done it” reasoning.
- NCR welds as the result of welders not following the qualified WPS; welders not being qualified/certified for the specific job; utilization of the wrong WPS for the job; and welding without having a qualified PQR/WPS for the job.
- Failure to employ weldment positioning equipment or employing mechanized or automatic equipment where applicable and utilizing improperly operating or uncalibrated equipment.
- Lost weld traceability due to poor weld joint maps, WPS maps, project weld log and so on.
- Ineffectual peer reviews/not employing a questioning attitude. For example, not pointing out an error or a discrepancy on a drawing when reviewing a WPS or during a design review.
- Insufficient welder training/technique competency where additional hands-on/practical training and classroom instruction is required via apprenticeship programs, professional welding schools, technical schools, vocational schools and so on.
Optimizing weld time
Weld time comprises all the required action times plus the actual arc-on, beam-on or solid-state joining time to complete an acceptable weld. That is, the execution phase of the weld execution plan, which will vary depending upon the scope of the application. These actions may include chamber pump down time, weld joint preparation/fit-up time, purge/backing gas time, heat-treatment time and NDE inspection time. Effectively managing weld time is crucial. To achieve the highest value for the dollar and to avoid costly welds, adhere to the weld execution plan – plan the work and work the plan.
As the criticality of a welding application increases (seismic protection weldments, for example), weld time cost increases as well as the subsequent cost to rectify poor weld execution and poor weld quality. Therefore, optimizing weld time is vital.
Weld time is money. Poor structural/pipe weld execution and poor weld quality/NDE failures result in costly welds – lost time and money. In addition, costly welds increase the level of concern respective to operational safety, in-service performance and increased warranty cost exposure/liabilities. Without qualified personnel to provide essential engineering expertise, technical leadership and skilled technique, the prospect for costly welds increases.