Hot Bolting / Single Stud Replacement:
What is it, why is it done, and what are other options?
What is Hot Bolting (AKA – Single Stud Replacement), anyway?
Hot bolting, or single stud replacement, is used as a technique to prevent galling – in other words, to ensure the asset comes apart once it cools down. During operation, the flange will typically see both high bolt loads and high temperature.
Furthermore, the studs have usually been sitting there under this load and heat for a long time. Creep starts settling in and they are primed to start the galling process. The galling typically occurs once it cools down as creep settles in and asperities become permanently embedded. The key message here: the galling occurs once existing studs cool down – and that is why hot bolting is done.
When performing hot bolting, field technicians will go in and replace one stud at a time while it is still hot – as the stud will likely not gall and everything has lower load.
But why put in a new stud? It is because fresher studs are easier to remove when it is time for breakout. They will have less creep, less embedment, and fresher lubricants. This is conventional wisdom and, at the end of the day, it produces the result that is needed.
Tl;dr – Hot Bolting is done to prevent galling.
Let’s take a step back – why?
However, let’s think about this for a moment. Operations is not waking up in the morning and saying “Hey, let’s go take some bolts off for fun today”. They are doing it because galling and stuck studs are such a pain that hot bolting seems like the only feasible option. Hot bolting results in:
- Doing the same job twice (assembly + breakout x 2)
- Safety issues (working on a hot unit)
- Permitting (time sink)
- Buying two sets of hardware to hold one flange ($$$)
Tl;dr – Hot Bolting feels like the only option.
Another preventive option (that is much easier and cheaper)
Instead of buying two sets of bolts, two washers, two crews – you can just use Velocity Washers™.
Velocity Washer™ eliminates the galling. When we say the bolts are primed for galling, it is not like they have galled already. They have not melted together – nothing is getting 2,500f – there is never a liquid phase. They are primed to start the process.
Galling is not an event, it is a process. Velocity Washer™ will take your bolts off before the process is able to complete.
At the end of the day, it is not like our industry experts are crazy. They are doing hot bolting because it is their best option vs. dealing with the consequences of a galled asset (open flames, cutting, flange damage). Hot bolting is an option because it is eliminating the problem rather than the symptom. However, hot bolting is very labour intensive, dangerous – and frankly a pain in the rear end.
Velocity Washer™ is a prevention, just like hot bolting / single stud replacement, but it is a lot easier and inexpensive. As the adage goes: work smarter, not harder.
Tl;dr – Use Velocity Washer™ instead of Hot Bolting to drive down cost and lower complexity
Written in collaboration by: Michael Psimas PhD, General Manager – INTEGRA Engineered Products, and Ryder Britton, Manager of Technology
velocitywasher.com | 800-779-2658