Removing seized bolts is a frustrating and time consuming process and is fraught with risks to both the machine operator and the components surrounding the bolts. By their very nature, flange joints in the oil, gas and power generation industries are tight, stubborn and difficult to dismantle. But with the right equipment the job can be carried out efficiently and safely.
Here we look at two very different methods of bolt removal and give an insight into the portable machine tools available to carry out the job.
Solution 1: Drilling
When there’s no other option but bolt removal, the commonest solution is to carefully drill out each of the offending bolts using a heavy duty portable drilling machine.When part of a maintenance project, obviously the flange or valve body should not be damaged in any way. Simply attempting to drill out a bolt in one drilling operation is not advisable. Each job varies and needs careful consideration, but some common steps are as follows.
- First, the machine should be mounted securely to the flange body. A mounting plate may need to be created to suit each particular problem. A heavy duty portable drill should then be bolted in position or secured using switch magnets.
- Seized studs are often cut, leaving approximately 10mm proud of the flange surface.
- Each is then carefully drilled to within 3 to 4mm inside the stud’s core size.
- Following this, using a single point boring bar is recommended, as they provide more visibility inside the bore and deliver greater accuracy. Boring bar attachments can simply be added to the HT drill unit used for the initial drilling operation.
- When the boring operation is complete it will be possible to remove the remaining thread, which should be able to be pulled out, looking very much like a ‘coiled bed spring’.
What drill should I use?
Removing seized bolts by drilling requires a machine that is both robust and also delivers accuracy. One machine that fits the bill perfectly is the Mirage HT50 (0 - 5") Portable Drill, which can be attached in position using the four 12.5 mm diameter holes in the footplate, or using an optional switch magnet base. The machine’s construction incorporates linear rails & guides, providing both accuracy and a high load carrying capacity.
The feed of the HT50 can be controlled manually at a rate of 2.5mm per revolution, or automatic at anything between 0 – 32 mm per minute. RPM is between 5 and 60 (air 3.5hp or 5.0hp hydraulic). Other technical details of the HT50 include:
- Drilling diameter range from 0 - 5”
- Stroke of 0 -16”
- ISO 50 spindle accepts standard tooling
- High torque geared spindle
- Auto feed and hand feed gearbox and motor
You can watch the HT50 in action on our YouTube channel here.
Solution 2: Using a bolt slitting saw
One Mirage customer needed a solution for cutting seized bolts used in pipeline flange joints for maintenance and decommissioning projects. The method previously being employed was the using hand held reciprocating saws, which were slow, inefficient and uncomfortable for the operator.
The resulting product that Mirage created was the MBS-355-H Bolt saw, which uses a 355mm diameter blade fed into the gap between the 2 flanges and provides a “spark free” cutting solution. When compared with drilling and cutting using a hand held reciprocating saw, bolt removal using this machine is rapid as the cutting duration for each M36 bolt is just 3 minutes.
The saw is designed to allow fast installation and can be used in either a conventional or upside-down orientation. The unit is positioned using ‘rough locators’ supported by adjustable height setting straps which locate on the top face of the flange and is then locked in place using either a chain clamp or lightweight and easier to handle ratchet straps. The blade is fed manually and following each cut the machine is easily moved around to the next cut utilising the mounting rollers which sit on the flange diameter.
Technical details of the MBS-355-H Bolt Saw
- Cutting stroke: 110mm 4.3”
- Feed type – manual
- Cut duration for an M36 bolt is 3 minutes.
- Available with either hydraulic or air drive
- API 16 3/4” or API 13 5/8” flanges.
- Weight: 85 kilos (187 lbs) with 4 lifting points
You can download the Drilling & Tapping Buyers Guide guide here, or if you have a potential project needing one of these products right now please click here to get in touch.