We use ALS Global for most of our equipment (Power generation, Cogen and Hydro). Mostly Turbine/Generators, pumps, air compressors, cooling tower fans, and hydraulic systems. We have a few service trucks as well. We get pretty good value from them: Quick turnaround, a human technician writing up the lab comments, and an actual human lab manager will talk to you if you call the number on your report.
We also use SGS for our wind turbines. Similar to ALS but no hand holding and no detailed lab comments. But it's cheaper. Still, human technical service comes at a price; I think it's worth it.