If you are thinking of hiring a consultant, here are some things to consider.
First, consider whether you need a consultant at all. It is entirely possible that you do not need a consultant. Consider all of your resources and whether the manpower and time needed to achieve your goals are within your means.
If you do decide you need a consultant, research a few of them, and start at their websites. Does the consultant have a website that has more than just a phone number? Some companies have a website with phone and email, but no physical address. This isn't definitively a bad thing, but it also does nothing to show the depth that an office location and staff roster can.
"One-man-bands" have flooded the consultant industry in recent years. There is nothing inherently wrong with an expert in a particular field putting his knowledge to work, mind you. Working out of one's home office can keep costs low and pricing more agreeable to fabricators. However, when considering the metal fabrication industry, there is demand for expertise that a larger staff is better equipped to accommodate.
Larger companies in particular might need CWIs who know how to create and review WPSs and determine if they are applicable to AWS welding codes like D1.1 or D1.5. Or they might need engineers who know how to establish a fracture critical program and answer questions on how their company might do bridgework. The demand for the creation of a quality system and that system's subsequent consultation audit may pose a problem. How can a "One-man-band" write a manual and then perform an internal audit on the manual's implementation? There are no checks and balances! A deeper company can offer someone to write a manual and implement the system, and then can offer a different person (a new set of eyes) to audit. The auditor might see things the author did not.
A consulting company in structural steel with depth would have the staff and resources to accommodate these needs.
Lastly, you should consider what "stripes" the consultant boasts. Does the consultant have a degree from a mining a school? Or do they have accolades of the industry? Does the consultant have only a 10-20 year-old graduate degree? Or do they have industry certifications with professional development, continuing education, and recertification requirements? For steel fabrication consulting, Certified Weld Inspectors, Certified Weld Engineers, and Certified Manufacturing Engineers (to name a few) all require the regeneration of knowledge in the industry to get recertified. Depth in consulting should include stripes like this, and should be more than one person.
So when choosing a consultant, it's less about how deep you want to go, but more about how deep want the consultant to go.