Gone are the days when most companies retain their own materials engineers/metallurgists or fabrication savvy personnel on staff. With the swings in the process industries over the past two decades, a number of companies have elected to dispense with their materials/metallurgy group and instead rely on a process engineer or a consulting metallurgist to specify materials of construction. Process engineers are specifying welded equipment more and more, and often with a lack of fabrication/materials know-how. Their approach is to rely on a fabricator to guide them through the materials decisions and to point out any oversights. Furthermore, with the widespread use of sophisticated vessel design software, many small- to mid-sized fabricators no longer employ engineers. Instead they depend on technicians to design vessels, many of whom lack the technical insight or materials background often required. In today’s market, fabricators often do not have the time to challenge material/fabrication datasheet abnormalities and merely add these additional costs to their bid or choose not to bid, putting the engineer in a less competitive position. As a result, if the engineer receives a quote from the fabricator, it’s weeks later, higher than expected, and with exceptions, deviations and surprises, all of which must be reconciled before proceeding. In the end, the project will have incurred unnecessary schedule delays, higher equipment costs, and then finds itself over budget and behind schedule before it gets off the ground.
You can pre-empt such problems with a bit of guidance. So, in this first article in our three-part series, we’ll look at a dozen important factors to consider in materials selection. We won’t get deep into the technical weeds but will provide pointers gleaned from our first-hand experiences that can help you avoid costly mistakes and delays.
1. Select the right material. For non-corrosive service, use design temperature to choose a readily available, cost-effective material. Table 1 offers a general guide [1, 2]. For corrosive or hydrogen service, consult a materials engineer.
2. Avoid specifying materials by trade name. Many projects involve replacement-in-kind of existing or similar equipment. The original design may have specified a particular brand or trade name alloy such as Hastelloy C276, Carpenter 20-Cb3, Monel or Inconel 600, and so these words are used throughout project development. Citing brand or trade name materials was necessary in the 1970s because many were unique and protected by patents. Today however, most major metals manufacturers produce their own and competitors’ alloys. So, unless sticking with an exact proprietary alloy is mandated, using generic names, such as Alloy C276, Alloy 20, Alloy 400, or specifying the trade name “or equal” on the data sheet is more appropriate.
3. Take your bid expiration date seriously. Prices for commodity metals change daily on world metal exchanges. There was a time when mills/suppliers only adjusted their prices once per month and you could hold onto a firm quote for two to four weeks while it was evaluated. However, in recent years, metal pricing has become more sensitive to world events and more frequent and dramatic pricing swings occur. A fabricator recently reported that its quote for several large heat exchangers had to be adjusted upward $300,000 when the order was placed two months later — solely because of increases in stainless-steel tube cost due to a surge in nickel and molybdenum prices. In today’s market, fabricators must contend with material pricing from suppliers that can expire at the end of day. So, take your bid expiration date seriously. On the other hand, carbon-steel costs, while rising, tend to be less volatile than those of alloy steels; so it’s safe to assume normal escalation during the project development/estimating phase.