Please advise me when should we use bolt torque wrench (torquing) and bolt tensioning ?
when we want to joint flange 26" #900, should we use bolt tensioner ?
thanks for advise

Regards

A bolt torque is a very inaccurate method of determining the gasket loading. The friction in the bolt/nut threads depends upon bolt tolerance, lubrication and good luck.

For high pressure flanges I suggest you use a tensioner to get the correct gasket loading.

“The beautiful thing about learning is that no one can take it away from you.”
---B.B. Kinghttp://waterhammer.hopout.com.au/

Of course, both methods of tightening will eventualy get the job done. However, on large flanges such as this one, tensioning is advantageous not only because of the reason outlined above but also because it is a faster process. When tensioning, one is able to tighten at least 50% of the stud population at the same time. In some cases it's even possible to tighten 100% simultaneoulsy. This is important because it ensures consistent gasket compression and thus reduces the risk of damage before the joint is even pressurized.

Torquing, as implied above, can also be utilized. However, then one foregoes the previously-described benefits. Furthermore, in order to deal with the inherent innacuracies of any torque-tightening procedure of critical flanges, the bolt bolt stress MUST be verified after tightening. This is imperative since it will enable the operator to "tune" the applied torque at each fastener so that it applies the necessary clamp load. In so doing, one will usually find that it's necessary to apply a different torque to each fastener in oredr to ensure that they are all equally "tight".

There are many benefits to bolt/stud tensioning instead of torquing.

Among these benefits are:

- Assurance of uniform bolt loading and gasket compression
- Quicker assembly, disassembly of the joint
- Safety, prevention of accidents
- Prevention of fastener damage

The disadvantages, as I see them are:

- Cost, training, maintenance of tensioning equipment
- Need for adequate thread length above the nut for device engagement

IMO studs larger than 1.5", use tensioning (esp if you've a design pressure that's near the upper end of the flange pressure range). Studs 1.5" or smaller, torque is OK (if you know what you are doing).

Conventional torque wrenches are limited to 250 ft-lb. Some larger torque wrenches will take you up to 600 ft-lb. In addition to the inaccuracies of torque, it's gets to be a safety risk pulling on wrenches to develop 600 ft-lb. I suggest using hydraulic torquing or tensioning at torques >250 ft-lb.