Engineers hate doing original work. If you do original work you have to work shit out from first principles, you have to experiment and build scale models and calculate forces and bending moments and see if they exceed your material strengths. This is lame and boring and takes up valuable time you could be using to drink whiskey or oppress the native Indian population or whatever engineers used to do back in the 1800's.
Fortunately, engineers somehow developed exactly one ounce of professional solidarity and poured it into the writing of handbooks. Handbooks are lovely: if your boss hands you a requirement document, you can haul out your copy of the CRC Handbook "Selection of Engineering Materials and Adhesivesâ and look up the appropriate material for the forces and torques involved in your design, which unfortunately still requires you to avoid day drinking and do some maths. Here, letâs look at the CRC handbookâs documentation on some materials. Iâm gonna avoid the equation stuff for now and stick to flowcharts and tables.
Letâs say weâre looking for a metal that we want to use for something on a boat. Maybe this is some steam piping or something. Boats insist on getting wet, often in seawater. Thatâs a huge pain in the ass but you work for a naval contractor so you knew what you were getting into, youâd best get started.
(disclaimer: if youâre a real engineer you need to be a bit more careful than this I am skipping the boring steps)
At first you think âfuck Iâm gonna have to look at reactivity series.â but fortunately to your rescue comes this handbook thatâs hopefully on a bookshelf at your office. You open to the section on metals:
Alright cool letâs say we need a medium strength material and we canât post-process it because we donât have passivation equipment in the factory and theyâre not buying it just for this. Looks like stainless steel then. The machine shop guys arenât gonna be happy about this but they havenât updated your phone number on the corporate directory so you can probably get this one in under the wire. Cool, what do I know about Stainless Steel. Thatâs right, nothing, Iâm an electrical engineer, we donât even have a material science class to fall asleep in, Iâll be right back.
Ugh, thatâs like 30 pages. Fine, Iâll read it. At least I donât have to get out the strength testing hydraulic stretch thing. Last time I used that a chunk of steel almost got me in the neck.
Looks like we want Austenitic steel. Duplex sounds expensive and this part isnât that important, itâs probably fine. I donât know what Austenitic steel is, what does the book say about that.
Man I hate it when I pick a chart and it just sends me to a bigger chart. The more specific this gets the more expensive itâs probably gonna be so letâs just pick something that sounds good. Weâre gonna weld this so we donât have to worry about machining, letâs try 316L stainless, and if the maths doesnât work out then I guess we just cry about it. 316L comes in pipe according to the book, so weâre fine there. If itâs bad for pipe then itâs the manufacturerâs fault for making it pipe shaped.
Alright hopefully at this point youâve already designed your item and calculated what the forces and minimum tolerances could be. If you havenât done that, I guess go look if what you want to make is on McMaster Carr and just copy it. Now take those minimums you calculated and see if it exceeds these:
(aw damn I did end up with a couple equations in here I lied earlier sorry)
If something doesnât meet your requirements, go back up the list and pick a new material, you messed up. If itâs fine, I mean, probably check the data sheet for actual 316L steel, youâre an adult with a job and youâre signing off on this, do it right. But if thatâs all good, congratulations, you managed to choose the appropriate material for a job and you didnât have to look up what âgrain structureâ or âgalvanic seriesâ means once.
Now itâs just a matter of making sure you replace all your âTODO FIND MATERIALâ notes in the drawing with 316L Stainless Steel, hand off to the fabrication department and hope to god they don't come to your office you over frivolous matters like âunheard of screw thread dimensionsâ or âimpossible weld geometries.â
Handbooks are a way to offload a lot of the mathematics, design and testing youâd otherwise have had to do yourself to a Boeing machine shop with a team of women in a room somewhere performing dozens of strain calculations for eight hours a day in the 1940â˛s.