Vulcan’s Blow Count Specifications

The durability and longevity of Vulcan pile hammer is something that is seldom replicated in just about any other manufactured product.  Since pile driving is self-destructive on the equipment, this is a remarkable achievement, but it should be tempered by the fact that it’s possible to render a Vulcan hammer inoperable by the way it’s used.  There are many things that can make this happen–inadequate or nonexistent hammer cushion material or lubrication to mention two–but the one thing that Vulcan decided to include in its warranty was the blow count specification.

Recording the blow count–the number of hammer blows per inch, foot or metre of pile advance–is virtually universal on pile driving jobs.  The dynamic formulae basically translated blow count into pile capacity.  While anyone familiar with pile dynamics understands that blow count is a crude measure of the response of a pile to impact, including a blow count specification is a good first measure of both the advance of the hammer and also how much energy is being returned to the hammer, which is a case of hammer damage.

BLOWCNT
Blow count-resistance graph, developed by Vulcan in the early 1990’s as part of its effort to educate state and federal agencies on the basics of pile driving. As the blow count increases, the amount of SRD (soil resistance to driving) increases, but at a progressively slower rate. This indicates that simply increasing the blow count is a “diminishing returns” proposition, destructive for hammer and pile alike.

High blow counts indicate that more and more of the energy was going back into the hammer rather than into the pile, thus increasing the danger of hammer damage.  They also indicate that pile top stresses increase with higher blow counts, as the movement of the pile to mitigate the maximum impact force decreases.  Thus high blow counts just to get the pile to tip elevation without considering changes in hammer or basic drivability considerations is a losing proposition.

Starting in the late 1970’s, Vulcan voided the warranty on its hammers if the blow count exceeded 120 blows/foot.  It’s interesting to note that Vulcan never made its specification in blows/inch.  This was true for its onshore hammers; however, for its offshore hammers it was forced by circumstance to increase the hammer refusal criterion as follows:

BLOW COUNT SPECIFICATION 1

Vulcan hammers are designed to withstand a continuous driving resistance of 120 blows/foot (400 blows/meter). In addition to this, Vulcan hammers will withstand refusal driving resistance of 300 blows/foot (1000 blows/meter) for five (5) consecutive feet (1500mm) of penetration. Any resistances experienced in excess of these are beyond rated capacity and will void the warranty. This definition is not an exclusive definition of excess of rated capacity and other criteria may apply.

1 Specification applies to all Vulcan offshore hammers, not just those listed in this catalog.

This was drawn from the API RP 2A specification, which was discussed relative to pile stick-up.  An elevated refusal blow count specification was justified by two things.  First, the offshore hammers were more robustly built than the Warrington-Vulcan hammers which made the company famous, as they were derived from the Super-Vulcan hammers.  Second, the remoteness of offshore job sites made high blow counts a necessity, as bringing a larger hammer to the job was frequently impractical.  (Improved methods of drivability predictability lessened the possibility of this happening.)

Blow count limiting warranty specifications are not an absolute method to prevent hammer abuse, but they’re a good start, and Vulcan used them to the advantage of itself, its end users and the owners of the projects where Vulcan hammers were used.

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Driving Piles with Stub Leaders and a Template

The best known setup for pile driving equipment is a crane and a set of full-length (of the pile and hammer) leaders, attached to the crane in a variety of ways.  But another alternative is to use a “stub” leader, i.e., one that is very short, and a template to align, position and guide the pile.  This is traditionally associated with steel piling, so we’ll look at this first.

For these hammers the platform itself is the template, the piles are driven from the top through the legs.  Most conventional platforms had angled legs so the hammers almost invariably drove on a batter, which gave rise to the “stick-up” problem, more about that below.

But using stub leaders and a template isn’t restricted to steel piles; it has also been done on concrete piles, as can be seen below.

From a contractor’s standpoint, handing hammers in stub leaders requires a considerable level of skill from the crane operator, but the weight savings and ability to handle the hammer in difficult situations makes the use of stub leaders, when possible, a very attractive option.

Engineering Aspects of Stub Leaders

From the photos above, you can see that piles can be driven with stub leaders either plumb or on a batter.  Plumb piles are not much different with stub leaders than with conventional leaders: the key is to have the hammer straight and square on the pile, which means that the leader setup should be balanced to hang straight and side forces on the hammer be avoided.

With batter piles, since the offshore industry used them (and still does) intensively, the most complete specification for such piles is the American Petroleum Institute’s RP2A specification.  With stub leaders the pile basically supports the hammer during driving, and the hammer in turn loads the pile with both the impact loads and the static load of the hammer assembly, which in turn acts both parallel and perpendicular to the axis of the pile.  Basically there are two important engineering aspects to configuring driving batter piles with stub leaders on a template:

  1. Column buckling due to the weight of the hammer acting on the axis of the pile.
  2. Beam loading of the hammer due to the component of the weight which acts perpendicular to the axis of the pile.  This creates a cantilever beam with a maximum bending moment at the template.  Obviously the weight of the hammer assembly (along with the weight of the pile) will induce bending stresses.  These stresses are both tensile and compressive, and both are important to the structural integrity of the pile during driving.  The template must also be designed to handle the loads and moments on its structure.

With steel piling, the combined weights of hammer assembly and pile limit the permissible length of the “stick-up” of the pile.  Steel piles are easily spliced and added on to, so piles which are much longer than the stick-up can be drive.  (Piles which are much longer than practical lengths of conventional leaders can be driven as well.)  With concrete piles, these can be splices but there is less flexibility and less resistance to bending moment with splices, which limit the possibilities of driving these with stub leads on a batter.  (The ability or lack thereof of concrete to withstand bending stresses also complicates the situation.)

One more important point: the weight of the hammer assembly cannot generally be assumed to be at the pile head, but above it.  That’s why the center of gravity information is so important for offshore driving, which led to Vulcan tips such as this.

Stub leaders combined with templates is an attractive option for driving piles, but proper engineering and construction procedures must be followed for successful results.

 

Vulcan’s Most Famous Sheet Piling/Extractor Photo

The photo above, dating from 1949, shows a worker tightening the bolts on the connecting links of a Vulcan extractor to the top of a prepared sheet piling in preparation to impact the sheeting upwards and take it out.  This photo was used for many years in Vulcan literature, including Vulcan Bulletin 71B.  (Note: don’t try this now without a safety belt and other safety equipment for the worker!)

The project it was on was in familiar country to Vulcan: it was for the Calcasieu River Bridge between Westlake and Lake Charles, LA.  The owner was the State of Louisiana Department of Highways.  The contractors were Kansas City Bridge and Massman Construction, still a user of Vulcan and Conmaco equipment.

It’s also interesting because it’s similar to the “sheet pile setter” logo that Pile Buck has used for many years in its own logo and advertising.

Parts Diagram for DGH-900 Hammer

Above is a parts diagram for the Vulcan DGH-900 hammer, from the late 1950’s.  It’s similar to the DGH-100 hammer.  More information about these hammers is here.  The complete Field Service Manual for both DGH series hammers is in the vulcanhammer.info Guide to Pile Driving Equipment.

An Overview of Tapered Pipe Threads, and Their Application at Vulcan

It’s hard to imagine that much of our technology is underpinned by very old, basic standards that year after year simply “do their job” without much regard.  One of those is tapered pipe threads.  This is a brief overview of same, and specifically the “National Pipe Taper” or NPT threads.  Much of this material comes from the American Machinists’ Handbook by Fred Colvin and Frank Stanley, Second Edition (1914).

Most screw threads are “straight threads,” i.e., the diameters of the threads (outside, pitch, inside) are constant along the length of the threads.  Tapered threads by definition can only work for a limited length, but when pipes are connected, that’s fine.  Like any other taper lock, tapered threads have an additional wedge effect, which means that they can seal fluids in the pipe (or outside of it.)

Originally these pipe threads were referred to as “Briggs standard threads” after Robert Briggs who came up with them.  In 1886 these were adopted as a standard by the American Society of Mechanical Engineers and various manufacturers.  They have varied little since that time.  They have been a durable standard for leak-resistant, permanent (and semi-permanent) connections ever since.

An overview of the “Briggs standard thread” is below.

americanmachini00stangoog

As noted above, only the “perfect” threads (in one way or another) contribute to the sealing/joining of the pipe thread.

The overall dimensions of the various sizes of tapered pipe threads are shown below, with a diagram showing the types of gauges used to check the threads.

americanmachini00stangoog5americanmachini00stangoog6americanmachini00stangoog7

The tapered reamer was one item Vulcan seldom used; the usual procedure was to tap drill the hole and then use a tap for the threads in question to put the threads in the hole.  Below are some tap sizes for NPT (National Pipe Taper, or Briggs) threads.

americanmachini00stangoog4
Tap drills for National Pipe Taper threads.  The “Briggs” values are for the NPT threads; the Whitworth are for their UK counterpart, which were never as popular as the NPT/Briggs threads.  The drill size for the 2″ pipe tap should read 2 3/16″.  In reality there is a little “wiggle room” for the tap drill size, as is the case with straight threads.
americanmachini00stangoog2
When threading a pipe, a die is generally used. The “actual inside diameter” can vary; the table here is closely related to Schedule 40 pipe. It can obviously be smaller for higher pressure applications and those where the mechanical strength of the connection needs to be larger (as with pressure gauges.)

A more detailed treatment of the threads as the pipe and hole threads interface is shown below.

Crane_Valve_World
Theoretical standards for the NPT/Briggs standard pipe threads, with a more complete treatment of the perfect and imperfect threads, which is important in the design of pipe threaded holes, specifically how deep they need to be.  This comes from “The Crane World” magazine, January 1919, from the Crane Company, a leading manufacturer of valves.  When the Crane Company was established in 1855, it was near Vulcan’s facility and in fact Vulcan’s founder, Henry Warrington, was Crane’s first customer, placing an order for box castings (a notoriously difficult shape to cast) and other parts for locomotives, which Warrington was making at the Vulcan Foundry.  In his later years, after his sons were active at Vulcan and their other activities, Warrington worked at the Crane Company.

The pipe taper standard was wildly successful, and is used in everything from home plumbing to high-pressure hydraulics.  In the oilfield the standard was so successful that it’s widely used even in places where metric standards are the norm

As far as Vulcan is concerned, Vulcan used the standard in many of its products, both the air/steam hammers and later the hydraulic vibratory hammers, where they were used for pressures up to 5000 psi.  This was due to their durability, ability to resist vibration (a must with any Vulcan product) and their flexibility in radial orientation.  With a pipe thread there is a point where it’s “tight” but it can generally be tightened a little further, thus allowing some flexibility in the orientation of parts.  One thing Vulcan learned with pipe threads was, although they are designed to seal with their taper, the use of some kind of “pipe dope” or sealant is very important.

Below are some applications of pipe threads in Vulcan hammers.

D11450-2
A Vulcan drawing “callout” for pipe threads, in this case small ones for the grease fittings on the Hydra-Nut.
hydra-nut-out
The “outside” of the Hydra-Nut (U.S. Patent 3,938,427.) Introduced in the 1970’s to directly replace the cable nuts (as shown above,) the Hydra-Nut simplified the process of tensioning the cables. The Hydra-Nut was screwed on without the cast thread protector cap on the top, the cable was lightly tensioned with a “manual jack,” the threaded sleeve was screwed down on the cable fitting and tightened against the jack body, the manual jack removed and thread protector cap replaced (aligning the flats on the cable fitting with those on the cap,) then the chamber was pressurised through the grease fittings to the pressure where the cables would have their proper, full tension. The weakness of the Hydra-Nut was in the grease fittings; should dirt or paint get in them, the chamber would depressurise and the cables would be loose. This was more probable when Zerck fittings were used than with the button head fittings as shown. Vulcan addressed this issue in the 1980’s with the Auto-Jack, which altered the Hydra-Nut by adding an internal cable nut with the integral jacking cylinder, which was then depressurised when the cable achieved proper tension.
D11284
A call out for a pipe flange on a Vulcan offshore hammer. Note that now, instead of tap “drilling,” we’re forced to bore the hole before putting the pipe tap in.
Vulcan-040-Close-Up-Cylinder-Prestressed-Job-2
A close-up of the 040 cylinder during exhaust. The large hose is the steam hose that powers the hammer, the small hoses are the Vari-Cycle hoses that shift the trip shifter one way or the other to vary the stroke. The hose is connected to the hammer through a connector which is screwed in the large pipe caps on the double pipe flange in the front of the hammer.
85c-cta-13-jan-1969
Vulcan 85C Hammer.  Note that, towards the top of the cylinder are two pipe plugs.  These are installed into tapped tapered pipe fitting holes.  (There are actually four of these, two are covered by the plate referred to as a “belly band.”)  Behind them is a cored passageway between the valve and the top of the cylinder.  These holes helped to support this core during casting but had to be plugged for use, and the pipe plugs were the ideal way of doing this.

Pile Buck Ads 5: Vulcan 530 in Offshore Leaders — vulcanhammer.net

For the last of the “Pile Buck Ads,” a photo of the Vulcan 530 hammer is featured in offshore stub-type leaders. The 530, introduced in 1978 for driving pipe piles offshore in the Gulf of Mexico, was and is used in a wide variety of pile driving projects. In this case it’s shown to be […]

via Pile Buck Ads 5: Vulcan 530 in Offshore Leaders — vulcanhammer.net

Pile Buck Ads 4: Link Belt Diesel with a Mandrel — vulcanhammer.net

The fourth in our series on the ads which Pile Buck allowed vulcanhammer.net to run was this shot of a Link Belt 520 driving shell piles using the Vulcan Expanding Mandrel. The mandrel’s history and shell piles in general are discussed here. The Link Belt 520 is an interesting story in itself. The diesel […]

via Pile Buck Ads 4: Link Belt Diesel with a Mandrel — vulcanhammer.net

The Pile Buck Ads 2: Vulcan #1 Hammer in Action — vulcanhammer.net

On this, the twenty-second anniversary of the beginning of this site, we present another of the ads which Pile Buck allowed us to run in their books. It shows the Vulcan #1 hammer on the South Side of Chicago. It also features the URL of the vulcanhammer.info site, which is dedicated to Vulcan hammers and […]

via The Pile Buck Ads 2: Vulcan #1 Hammer in Action — vulcanhammer.net

Vulcan 014 and 016 Valve Gear Assembly

Above is a valve gear diagram for the Vulcan 014 and 016 hammers.  It shows the workings of the valve, its positioning during operation and other details.  Although Vulcan made improvements after this drawing (valve liners and Vari-Cycle, for example) it shows the basics of the valve which has done well in Vulcan hammers for more than a century.

More details on the 014 and 016 hammers are here.