Square Head Machine Bolts for Pipe Bolting?

They will work fine, I would think. The advantage of using hex bolts is that you can use sockets and a ratchet with them, much easier in tight spaces and faster. Also they cover more surface of any washers or lock washers being used, if your using lock washers the square head can catch the split in the washer rendering it useless. Square heads are also more likely to become rounded. If the flanges are round and the holes are close to the pipe or whatever you're flanging, they can bind up. That said, as long as the grade of the bolts are what is specified for the application, I don't see why not.

You do not say what your job is so we do not know why you would question what is being done.

1. The Hex Head Machine bolts and the Hex Nut w/Stud is common for the Process Plant industry.

2. Square Head bolts are not normally as strong as the Hex Head Machine Bolt

3. The Square Head bolts might be fine for assembling a wood frame structure for a kids swing set but may not be able to supply the Torque required for Flanged Joints in pressurized process systems.

4. If you use Square Head Bolts in your process piping systems you may get a lot of flack from the Maintenance Department. Some places have pretty tight fits and the 1/8th turn of a hex wrench is easier than the 1/4 turn of an open end wrench.

5. Maintenance possibly already has a warehouse supply of spare Hex Bolts and Nuts.

I'm a consulting engineer. I question what is being done because it is a variance being requested by the contractor, not coming up from a plant department - that being said, this is not the contractor's first time at the plant. We're bolting up a piping system - not exceptional pressures, but pressures, certainly. I'll have to ask our man on site what sort of bolts Maintenance has on hand. I don't know. If a bolt craps out, Maintenance can replace it with a hex head at any rate.

What I'm understanding from this post and the one above it is that there is no standing, blanket condemnation of square headed bolts in bolting piping flanges together, but that hex heads do the job better. That jibes pretty well with what I've seen in the plants I've been in - lots of hex, very little (if any) square.

Thank you, guys.

Have a Great Day,

Gary

As other posters have said, I'd be surprised if you could get hold of square-headed bolts even if you wanted to use them, which most people wouldn't.

You don't mention nuts. If it's a through-bolt, it should be possible to keep the bolt from turning as the (hexagon) nut is tightened, so some of the possible problems raised don't apply. Different if it's into a threaded hole.

Cheers......Codey

Square headed bolts were manufactured from mild steel.

The adoption of hex heads spurned the development of higher tensile steels for greater loads. SAE hex grades 5, 8, 12, etc, (metric equivalents) as the resistance to tension rises.

I mostly spec grade 8 or better on med to high pressure pipe flanges.

Composition of gasket is one of the factors, as is pipe/flange composition.

Be nothing wrong with using square headed bolts, and square nuts on pipework which is 'low' pressure, but you'd have to watch the tightening torques, or they'll strip 'em. No point using HT hex nuts on low grade bolts.

Sorry! Not trying to be smart. You did ask.

Cheers,

Stu. (PE)

I can't remember the last time I saw square heads on anything. Maybe on an old Ford tractor?

Chances are very high, IMHO, that there are presently no square heads in repair inventory. So, you'd have to stock them, in addition to all the modern bolts you already have.

Can the contractor produce any justification for square heads?

For connecting a flanges, all codes and standards like ASME state that we have to use Stud Bolt with two Hexagonal Nuts. Where using stud bolt with 2 hex nuts will facilitates tightening from both connected flanges, and equality of stresses on both flanges.

The only pressure piping I have seen with square head hardware is in the Texaco (now Equilon) refinery in Wilmington, and dates to WWII. This is not current practice.

From the theoretical point of view, if your square head bolt has the same holding strength as a so-called "regular" bolt... such as tensile strength, percentage of thread depth engagement... yes, it will hold your pipe together, no problem. For maintenance convenience in tight corners, now that could be another story.

There are a few issues

- ASME normally specifically calls for Hex bolts and nuts (I wonder why, though in a few cases it talks about socket too, so likely the hex Soc Hd screws are permitted.)

- The most likely reason for this is that it is dealing in flange joints and there instead of reducing number of bolts and going for higher grade bolts (Soc heads of 12 point heads are usually 10.9-12.9 grade whereas the Hex Hd stops at 8.8, a few do go upto 10.9 but I have not seen farther than that).

- The reason for the less strength and more number is, as I can make out (i can't of course look into the brain of ASME ), the pressure on joint. Though theoritically the pressure can be maintained by less number of bolts stressed to higher level, but then another critical factor of leak free joint- the pressure cones overlap can not be acieved. So overall tensile Force is balanced by the number of compressive force exerted by the bolts with the required stiffness thrown in.

- To increase the pressure cone, the flange thicknesses has to be increased, and that will build up the cost as well as create some other hurdles in the rigidity too.

- So this limits us to Hex Bolts as far as economics is concerned- why pay for high-tensile fasteners when the lower tensile ones will do the job.

- As far as the sjapes are concerend

for the grade the Hex Hd are the most common, and the required spanners are universally available.

Soc hd - higher tensile (ruled out as per above)

12 point (or star head) - in fact more suitable, but as on now the ASME has not covered it, I wonder why. Anyway these are specific application oriented and a bit costlier.

Square head- Usualy much lower grade. Though available upto 12.9 (officially). The usual problem will be the locus of corners, that will most likely not clear the flange walls.

For Example for say a A/F of 100, the washer will be just below 100 and the locus of the corner will be a circle of dia 115.5 for the same features, for square head it will be 141.4 ie you will need about 22% extra space- that will move PCD away from the joint, increase flange OD (to accommodate PCD) , may need more fasteners,...

In fact by the Hex Soc head Screws or 12 point screws, the PCD could have been brought nearer.

For tight places, the hex head is better suited where incremental turns are the most possible. Whereas a Square head may not afford such luxury.

I'd like to add more but, I can't; you've received some very astute comments to your question ! Nevertheless, my curiosity is piqued: why does the contractor want to use Square Head bolts (assuming that he can find the proper grade)? Does he have a bucket of them left over from a wood trestle bridge contract ? Please let us know.

Dear Mr.Gary,

Hex.bolts are generally preferred for connecting and clamping flanges mainly because of the fact that while using a normal open ended spanner, we have more available space for manipulating leverage because of three flats as against less space because of two flats in a sq.bolt. Besides that , the clamping area occupied by a hex.head area is more by about 17% whether one is using a washer or not.

I suggest you go in for Hex.bolts.

Gangadharan.P

NET EFFECT IS--> IT MAKES NO DIFFERENCE, HEX OR SQUARE HEAD

It mostly depends on what industry and/or location you are talking about. A flange pair with the appropriate bolts, be it hex or square, torqued to the stated tightness is more than sufficient to hold the flanges together. If proper hangers are used and there are no extraordinary stresses, the flanged piping system will probably outlast anyone involved with the system.

Very important is that the gasket used is of a compatible material with the right compression properties and the alignment of the flanges.

Studs with hex nuts are usually specified where clearance for inserting or removing the bolt might be a problem, such as adjacent to an elbow, tee, pump, etc.

The ultimate choice is up to the pipefitter and the usual determining factor is usually what is most convenient to get at the stock room or what is on hand.

"The ultimate choice is up to the pipefitter and the usual determining factor is usually what is most convenient to get at the stock room or what is on hand"

Absolutely not! There have been a number of catastrophic failures where this has happened. Lives have been lost because bolts have been pulled off the shelves just because they were the right size. Notwithstanding whether a bolt has a hex or square head, there are reasons why there are different material choices. Everybody down from the Owner, the Division VP, to the Plant Manager should be sacked and strung up if they allow people to be hired who don't understand this.

My statement still stands true, if you had read the complete statement and taken it all into consideration when posting your comment

"The ultimate choice is up to the pipefitter and the usual determining factor is usually what is most convenient to get at the stock room or what is on hand"

The "appropriate bolts" is one of the correct diameter, length, materials, strength, etc. not just one of the correct diameter.

Any pipefitter worth his salt when facing up a flange set doesn't worry about the type of head shape, hex or square, unless there are wrench clearance situations, because he knows that the wrench on the bolt head is held back (reverse torque) while he tightens the hex nut. This is done so that the bolt stem does not move while the bolt is being tightened jepordizing alignment.

Of much greater concern is that the bolts are tightened incrementally in several steps in the proper sequence to the specified torque. This is commonly referred to as "star tightening".

After 40yrs as a Chem Eng designing, building, operating, and very involved with safety and environmental issues I have never seen any bolt failures because the wrong head, hex or square, was used. As a member of the AICHE safety group and safety experience I have investigated (and prevented) numerous incidents and know that doing it right the 1st time is the best preventative too.

I have suggested in other forums and will on this one, that posters read and comprehend the full original posting that they are replying to before making statements. Many of the people reading these postings take them as the gospel truth while in reality many of them are only unverified opinions or wild guesses. There are many people on this earth but none to spare because of dumb answers on this forum.

It would have been more productive to the readers of the forum if you had posted a reply question concerning my original posting instead of making a presumptive posting that is tangential to the original posting. I would have gladly answered any questions just as most others would.

Posters watch what you post, you never know how they may be taken!

Salty,

Thank you for your clarification. Since your most recent comments were nowhere to be seen in your original post I felt that it was important to strongly voice my opinion against what you had advocated - lest someone take this for face value.

One additional comment that I'd like to make concerning your "Of much greater concern is that the bolts are tightened incrementally in several steps in the proper sequence to the specified torque" is the following:

If we get down to brass tacks, "of much greater concern" is actually that the bolts have been tightened to the proper preload regardless of the applied torque. After all, torque isn't a measurement of how tight a bolt is but rather how much force was applied to a nut or bolt head when trying to turn it. Any "specified torque" should only be considered as a rough target. A "specified preload" is the actual goal. Torquing without considering the effects on preload is a guessing game at best. Unfortunately, it's what we are most often left to do because the design engineer didn't understand this basic fact and thus couldn't/didn't provide a preload figure .

Indeed, on pipe flanges the tightening process can be done in an incremental "star" pattern as you suggest (if using conventional wrenches of some sort) or, simultaneously (if using bolt tensioners -thereby producing even gasket crush rather than possibly cocking it). Verification that the applied load has actually resulted in the required preload is achieved by measuring the elongation of the tightened fasteners and "tuning" (a little more torque, a little less torque, a little more tensioner pressure, a little less tensioner pressure etc) as necessary. This crucial measurement step is much more important in critical flanges that have been "torqued" compared to those that have been "tensioned".

Thanks for your input.

Really though, in my 20 years as a Steamfitter, all that was supplied was B7 studs and Heavy Hex nuts. I'm really suspicious of square heads representing soft bolts. Get the right stuff and save trouble later!

Thank you all for your help. Evidently, what Maintenance was looking for was CS plated (in one case) and B7 CS bolts (in another), with heavy hex heads. Somebody made an I-don't-know-what-or-why error and called out the appropriate materials but an inappropriate head shape.

At least we are on hex heads, which is good.

Thank You Again,

Gary

Square-headed bolts and nuts are still used on railway permanent way in the UK. The advantages over a hex are:

• The maintenance operative spends less time tightening-up a square-headed bolt/nut compared to a hexagonal-headed one, reducing exposure to traffic and the risks associated with being struck by passing trains.
• The greater ratio of the head across the corners compared to across the flat faces compared to a hex bolt/nut gives longer life while it is exposed to the demands of its job in this particular environment. It also gives greater opportunity to fit the range of spanners that may be encountered in this environment. A particular spanner may fit only one size of bolt if the bolt is hex-headed and not fit smaller ones. The same spanner may fit a range of square bolt head sizes, meaning that the maintenance operative needs to carry fewer tools to sustain integrity, which is a distinct advantage on account of their length, weight and the distance needed to be travelled to the next stock of spanners.

Despite the advent of the Huck fasterner for certain applications, the square-headed bolt is here to stay!

This is true in the US also. The round bolt "head" has a square shoulder below it that fits into a square hole in the hardware and the nut is square. This requires only one spanner to secure a bolt in place.

Cheers.

Dear Gary,

square head bolt can be used but for heavy pipes flange joint, hexa head bolt is more suitable and easy to tight and lose by using the ring spanner.square head having less strenght instead of hexagonal head and if we use the ring spanner for square head,head can slip and head be damaged.

hexagonal having more grip or strenghtful instrad of square.

rcmandal

C.E.(INDIA)