then calculated using the measured data: • Travel speed (in./min) calculated by welding length (in.) ÷ welding time (min) • Heat input (KJ/in.) calculated by V A 60 ÷ travel speed (in./min). Values were then reviewed to ensure no welding passes were made that violated the parameters set forth in the WPS, particularly heat input. This required close monitoring by a quality control (QC) representative to collect the data, accurately perform the calculations, review the results, and ensure compliance. In addition, these data were retained as a record document. Figure 9 shows a welder performing a weld with the QC monitor nearby recording the required data. Data collection for the welds and welding process on the SMO 254 alloy was an extensive undertaking by the quality control and quality assurance departments, but it was absolutely critical to mitigate potential shutdowns in the plant for repairs, as well as ensuring a long design life. Due to the SMO 254 alloy’s sensitivity to heat input, common defects found were cracks, incomplete fusion (particularly at the sidewall), and lack of penetration. Radiographic inspection lends itself well to detect these types of defects and was the nondestructive examination of choice. All welds on the SMO 254 piping were 100% radiographic inspected. Conclusion Desalination has the potential for huge growth within the United States, and the Carlsbad Desalination Plant is at the forefront of that progression. Understanding the weldabilty and essential variables in Alloy SMO 254 is critical if one hopes to withstand the highly corrosive properties of seawater and the osmotic pressures that must be overcome during the RO process. SMO 254 has the ability to resist corrosion in the seawater process, as well as handle the high pressures. It has superior weldability characteristics compared to other alloy options, such as duplex, but it is imperative that the risk of heat-induced cracking is considered, and measures are taken to mitigate this risk through careful monitoring and planning of the welds and weld sequence. In addition, providing training and obtaining a skilled workforce is also imperative to ensure success when working with fully austenitic stainless steels like Alloy SMO 254. Last, a carefully controlled and documented QC program is crucial to producing sound welds, ensuring long service life, and avoiding weld failures and costly repairs in the future. Successfully welding corrosion-resistant alloys like SMO 254, utilizing the measures mentioned previously, leaves desalination poised to quench the drought and spawn a new industry within the United States. Works Consulted 1. smt.sandvik.com/en/materialscenter/ material-datasheets/tube-andpipe seamless/sandvik-254-smo/. 2. carlsbaddesal.com/. 3. weldersuniverse.com/welding_ beads.html. 4. lincolnelectric.com/en-us/ support/process-and-theory/Pages/understanding polarity-detail.aspx. 5. rjsales.com/techdata/alloys/ 254smo.html. 64 WELDING JOURNAL / JUNE 2016 WJ Fig. 9 — A welder makes an in-place weld on SMO 254 pipe on the reverse osmosis train at the Carlsbad Desalination Plant. Each of the 14 RO trains produces roughly 2000 g/min of fresh water. Fig. 10 — A completed weld on the SMO 254 alloy pipe at the Carlsbad Desalination Plant. Stringer beads were used per the pipe manufacturer’s recommendation and the WPS. Matthew Sternisha (Matthew.Sternisha@kiewit.com) is a project manager with Kiewit Corp., Santa Fe Springs, Calif.
Welding Journal | June 2016
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