GASKETS-A little bit of theory

Gaskets are needed to create a seal between two (usually Stationary, well-bedded, and dimensionally stable) parts of a piping assembly. 

This gasket is called upon to maintain that seal over a wide range of operating conditions, which can vary with water chemistry, temperature, pressure and position (pipe movement), as well as over time,  meaning many decades in the case of a water distribution system. 

If it were possible to perfectly mate two pieces of pipe and hold them in that position, a gasket would not be needed.    This is usually impossible however, due to:

-Size of the piping
-Maintaining the perfect finish through installation and transport procedures
-Corrosion/erosion of the surfaces during operational life
-Expansion/contraction/settlement of the pipe changing the orientation of the  mating surfaces.  (thermal, axial, angular, parallel)

Gaskets usually provide a seal by flowing into and filling the                                   flaws/imperfections in the surfaces that are to be joined.  This flow is usually caused by external forces, such as clamping (flange bolts), wedging (MJ or Dresser Couplings, or a hydrant ball rubber), by internal pressure (Victaulic couplings or Straubs) or combination of any or all of the above.

wamco clww2ww

Gaskets and seals must be designed to meet the following conditions:

-They must be able to flow into the imperfections that are anticipated in a given joint. This can be thought of as compressibility to take up large imperfections, and micro-conformability for the small ones.

-Sufficient force must be available to make the gaskets flow as required, and  for our purposes, this means bolt loading for the most part.

-Sufficient force must be available to maintain a load or residual stress on the gasket to maintain contact with the mating surfaces under expected pressures.  This is necessary to prevent blow-by or leakage, under variant pressures and pipe/joint flexing.

-The gasket will not contaminate the system fluid by leaching or dissolving.

-The material should be able to withstand the medium in the pipe, ie be impervious or resistant to corrosion, disinfectants, etc in the water. 

-Is resilient, yet creep resistant enough to maintain an adequate portion of the applied load.  It should not flow out of its assembly or collapse.

-should possess adequate recovery to follow the expansions, contractions and movements of the joint and the pipe.

-Has sufficient strength to resist crushing under the applied load, and maintain its integrity when being handled and installed. 

-should have minimal or no leakage through or around the gasket

There is no such thing as "Zero" leakage through a gasketed joint.  Whether or not a joint is apparently "tight" depends on the sophistication of the methods used to measure leakage. In certain applications the degree of leakage may be perfectly acceptable if one drop of water per minute is noted at the gasketed joint. (This is the assumption behind the concept of “Allowable Leak Loss” over many joints when watermain is pressure tested.)

Other requirements are that no bubbles would be observed if the gasketed joint was subjected to an air or gas test underwater. A very stringent inspection would require passing a mass spectrometer test, but this would not be practical for potable water.

The rigidity of the test method would be determined by:

    * The hazard of the material being confined (ie Nuclear)
    * Loss of critical materials in a process flow (expensive Product)
    * Impact on the environment should a particular fluid escape into the 	atmosphere (Oil and Gas, sewage)
    * Danger of fire or of personnel injury (Nuclear, oil, gas, steam, chlorine)

Materials

Some gasket materials in the water works industry:

Natural Rubber-NR-Good mechanical Properties, impervious to water and air

Nitrile-NBR-Excellent resistance to oils and weak acids

Styrene Butadiene-SBR-Similar to natural rubber, can break down in sunlight

Ethylene Propylene-EPDM-excellent resistance to water, acids and bases.

Polyurethane-PU-excellent resistance to oils, ozone,

The above materials are rubbers and synthetic rubbers which are well suited to water supplies.  Rubber in general is able to stretch and move a large amount, and recover rapidly.  It has good memory and stores the energy that is used to deform it within itself.  By judicious blending of polymers, fibres, and substrates, gaskets can be made to suit many applications.   When chloramines are used as a disinfectant, standard rubber formulations can degrade, and the AWWA research Foundation has investigated this at some length.  If chloramine conversion is anticipated, special formulations of Nitrile or EPDM should be used.

Rubber is virually incompressible, and therefore displaces or flows to provide a seal.  Under a compressive load, it will flow, and if over-compressed can shear or creep.  (Creep means a further deformation, after the initial load.)

The mouldability of rubber is a distinct advantage to the water industry, because flat flange faces have had limited use in distribution systems.   Rubbers can be shaped to various cross sections and geometries to fill gaps between different pipe surfaces and shapes.  (O-rings, MJ gaskets)

Maintenance of the seal 

The seal in most repair clamps and couplings is clamped and loaded by bolts, for the most part.   The amount of claping force on the seal is related to the torque applied to the bolts and nuts.

Not all torque goes into tension
The standard rule of thumb is that torque is divided up into 50-40-10. The amount of torque used in overcoming thread friction (mating threads) is about 50% of what is applied. About 40% of the torque goes into overcoming bearing face friction (the rubbing of the nuts or bolt faces against what ever it is that they are being tightened against). And only 10% of the applied torque is actually used to tighten the parts together.
A small amount of change (i.e., oiling a bolt) can affect the tension greatly. For example, reducing thread friction by 2% (50% to 48%) will increase the clamping load from 10% to 12% (a change of 20% in value.)	

GALLING-A problem with stainless steel bolts and studs

Tightening and Galling

As with all fasteners the proper installation of stainless steel products is critical to its performance; this is particularly so with respect to tightening and galling.

Galling occurs when the stainless steel oxide surface film breaks down as a result of direct metal contact. Solid-phase welding can then take place (whereby material is transferred from one surface to another). The symptoms of galling include surface damage and seizing and freezing up of equipment. Galling commonly occurs when using stainless steel nuts and bolts together, where the contact points are subjected to high tightening torques.  It can happen when other soft metals are used as part of a fastening system also, for example, aluminum or brass.

Fasteners made in accordance with internationally recognized standards should ensure the uniformity of threaded products. Reasonable care should be taken when handling stainless steel fasteners to avoid any thread damage and keep the threads clean and free from dirt, coarse grime or sand. If the threads are tightened on sand or dirt the possibility of galling or seizing is increased.

Ways to reduce galling include:

Rolled Threads:
Rolled threads are less susceptible to galling than machined ones as they have a smoother surface and the grain lines follow the thread rather than cut across it, which is the case with machined threads.

Tightening Torque:
Bolts should be tightened to the correct torque using a torque wrench as overtightening will promote galling.

Lubrication:

It is often recommended that some form of lubrication be applied to threads prior to assembly. Proprietary grease-type lubricants, containing tenacious metals, oils, etc are available. Some commonly used lubricants contain molybdenum disulphide or nickel powder (sometimes with graphite materials).  Newer fasteners incorporate a mechanical zinc coating which serves as a lubricant that is fixed to the fastener.

Hardness Modification

Galling can also be reduced by using two different stainless steels, of significantly different hardnesses, on the mating surfaces. A Brinell hardness difference of 50HB may overcome galling.

A common belief that the use of grade 316 studs with grade 304 nuts (or vice versa) will avoid galling is a myth (there is no notable difference in galling).

Stress relaxation is a reduction in stress over time.  Creep is a change in strain.   These two factors cause a loss of torque over time and therefore a loss of seal, potentially.  Therefore proper loading of the gasket is necessary to ensure that there is room for the gasket to recover.

Proper loading is also necessary to counteract the pressure from inside the seal. 

Unfortunately there are many things in the joint and its installation that can affect the torque and its resultant clamp load. Obviously, friction and those things that affect it (oils, finishes, surface roughness), as well as hardness, dimensional fit, tool speed and type of tooling need to be considered. As could be expected with many variables, the tension produced by a specific torque will not be the same for every bolt or nut tightened. Plotting the results of torque vs. tension will not produce a single line but rather a band of readings. This is what is known as "torque scatter," the plus and minus values around the calculated average. 

Unless a torque wrench is used the tendency is to under tighten large bolts and over tighten small ones.

Torque wrenches are accurate within 10% or better with care, dial down the clicker types after use so the spring does take a compression set
Tension tests-ultra sonics-give one microsecond delay and relate to length of the bolt

When a torque problem is addressed the questions to be asked are: 
•	What are the torque values specified? 
•	What are the conditions of the assembly? This is the mating parts, [their grade, thread tolerance, hardness]. What finish are they both? Many times the presenter thinks that it is a fault of a part (bolt/nut, etc.) when it is almost always due to an interaction of factors. 
•	What tools and speeds are being used? 
•	How close to the limits of the material of the parts is the torque specification? The old fastener saying that "If tight is good, tighter is better" has been our albatross for years. If the joint appears to be loose let's just increase the torque specification. 
The correct and exact torque value is best determined by laboratory testing. In the case of a critical joint, it is probably safer to suggest that a laboratory and fastener expert examine the problem than risk making a judgment call. 

Corrosion Considerations

Where corrosion is a possibility, an inexpensive solution is to specify steel fasteners with some form of plating or coating rather than to use products manufactured from corrosion resistant materials. Although painted, plated or galvanised fasteners are usually adequate in applications where corrosive conditions are not severe, consideration should also be given to the cost of possible failure when the protective coating becomes damaged or compromised, in comparison to the cost of stainless steel product. Damage to the coating on steel products can be easily caused by the wrench or driver used for tightening, poor plating practices or simply from the turning action of one thread against another in assembly.

MATERIALS

 Stainless steels are iron based alloys that contain a minimum of approximately
11% chromium by weight. It is this addition of chromium that gives stainless steel
its unique corrosion resistant properties through the formation of an invisible and
adherent chromium-rich oxide surface film.
The vast majority of chromium in stainless and other specialty steels is in the
metallic/elemental form. A small amount of chromium (oxide) is formed on the surface of specialty steels and is crucial for protecting the alloy from corrosion. 

18-8 Stainless Steel This is the most popular type of stainless used in the production of fasteners. Its composition is approximately 18% Chromium and 8% Nickel, thus the name 18-8. Several grades of stainless are included in this classification including 302, 303, 304 and 305. These all have good strength and corrosion resistance. 
316 Stainless Steel This is more corrosion resistant than 18-8, but also more expensive. It is composed of approximately 18% Chromium and 12% Nickel with the addition of 2% to 4% Molybdenum. It also maintains its strength at higher temperatures than 18-8. 

SSINA.com   Specialty steel industry of North America-information on stainless steel and its properties
Bolt Science .com for info about nuts and bolts in general
TPS.US  Hymax couplings and EZ Max Clamps
Romac.com

   

    

Why is scatter important? Let's look at a typical torque tension band (see chart at right). The average value looks fine as a single line. However, the factors that we mentioned produce a scatter band that is very wide (A'–A). So wide in fact that at the torque value chosen (X) which was to generate the correct clamp load (Y) the scatter band could now give us so much loading that it could exceed the tensile strength of the metal of either the bolt or nut at one side (Point A) or it could cause the part to become loose due to too little clamp load at the other end (Point A'). In this example, the engineer had determined that any load below line B will cause the part to vibrate loose. 
What is the right torque? 
The correct method to determine the right torque is to run actual tests in a laboratory using production parts and production tooling. Except for all but the most critical of joints, this is neither practical nor inexpensive. Torque tables, derived from hundreds of joints with various conditions of finish, are often used. While not accurate to the ninth degree, they offer a good ballpark guess at where the torque value should be. When a torque problem occurs the first thing is to check the value being used. If it is near the value given in the table, then the problem is probably due to another cause.
When looking at some other causes, you should consider how much the tool affects the clamp up. All installation tooling has variation, the amount being controlled by the type, speed of operation, conditions of assembly, etc. For this reason, all specifications are given as a range (X-Y or a value ± %). Ordinary air powered tooling is accurate to ± 15-25%. Electric tooling is a bit more accurate (more in the range of ± 12-20%) but the cost of tooling and energy charges makes assembly with DC nut runners unprofitable in some shops. Tools are adjusted by increasing or decreasing air (electric) pressure until the "gun" stalls at the torque set on test stand. This type of tool is used for joints that do not require any great accuracy. 
Impact guns are about the worst, with accuracy being anyone's guess (probably in the range of ± 30-40%). Most major OEMs do not allow the use of impact guns in their assembly plants. 
The next step in accuracy is torque-control tooling. These tools monitor the torque via an adjustment (set screw, etc.) that is turned to meet an adjustment factor determined by the tooling department. Accuracy is in the area of ±5-15%. The tools offer better control of the torque but at a higher cost. 
Torque monitoring tools are as accurate as torque control tools, except that they have the capacity to record the actual torque values delivered on the line. They are used in areas where records of the actual values are needed (critical joints such as steering and suspension systems) for legal or other reasons. Many times this kind of tooling will be tied in with a "Green/Red light" system for further control in the assembly operation.
The most expensive and accurate tightening system is torque control system tooling. This torque operation is a complete system with gun, electronic transducer readouts, controllers, and data bank recorders that measure the torque as the joint is being tightened and feeds the information back into the control panel. The system will estimate where the proper turn off point is (as set by the specification) and stop the tightening process within ± 3-5% of the set value. This type of torque control tooling is the most expensive and is used for critical attachments such as wheel lugs. The operator simply pulls the "trigger" and holds on until the tool turns off (usually with a green light to indicate "Good Joint").
Hand torqueing, often used for inspection after the assembly, is not very good either. The best of operators has been estimated to be about 8 percent off when fresh on the job. When coupled with most hand wrenches (±2-3%) the amount of variation is quite a problem. 
Tool speed contributes to inaccurate torque answers. The coefficient of friction is different between a bolt run at 15 RPM in a laboratory test stand and one run at 600 RPM on the assembly line. It is a common mistake for engineers to base their assembly torque values upon laboratory tests run with hand tools and slow laboratory speeds. The use of a new type of tooling, the Hydropulse gun, has caused some concerns with speed of run down. The tool consists of a very rapid (up to 8,000 RPM) rundown that changes to a pulsed slower impact-type tightening after a certain set point of torque is reached. The very high rundown, especially in situations of frictional resistance, can cause meltdowns as well as jamming and seizure of overheated parts. 
Other factors that can change the tension produced by a specific torque are those that change the surface condition of the mating surfaces. One is the hardness of the parts and mating surfaces. If too hard, the surface is smoother, and smoother means less friction. As mentioned above, less friction in one area increases the loading in tension. Likewise, surface roughness is the same case. Rougher is more frictional to parts sliding (threading) over each other. The material of the joint should be an obvious factor but is often overlooked. Aluminum and soft metal are more frictional. Enough said? Dimensional differences (loose fit, tight fit) will obviously affect the way the parts go together.
Finish and tension 
Finish is a major contributor to torque problems. On one hand, the thickness contributes to tighter fits by filling up what little interspace there is between male and female threads. On the other hand, many of the new finishes today (used for higher corrosion resistance) are multi-element chemicals that may contain lubricants, Teflon-like compounds and torque modifiers for decreased driving torques and ergonomic considerations on the plants. This would work to decrease friction and raise tension loads. Conversely, some finishes show increased friction when used against each other. 
Lubrication, both wanted and unspecified, causes torque tension problems. Many parts are tested without lubes and then cause concern when the assembly plants cannot meet values. Also, the line operators often think that the parts "go in faster and easier" when they are dipped into a can of oil/grease on line. Good, except this is not the value that was used to calculate the specification on.

410 Stainless Steel It has approximately 12% Chromium with no Nickel. It is not very corrosion resistant and is magnetic, but it can be heat treated to become harder. 
Alloy 20 This alloy has approximately 20% Chromium and 34% Nickel plus 3% to 4% Molybdenum. It is very corrosion resistant and is especially popular when in contact with sulfuric acid. 
Brass This metal is approximately 65% Copper and 35% Zinc. It offers a good combination of strength, corrosion resistance and workability. 
Nickel Copper 400 This alloy is approximately 70% Nickel and 30% Copper. It has excellent strength and corrosion resistance and is used in salt water marine and other chemical environments. 
Titanium This has a very high strength to weight ratio, as well as good corrosion resistance. 
Inconel Registered Trademark of Inco Ltd. Composed of approximately 77% Nickel and 15% Chromium. It offers superior strength and good corrosion at high temperatures. 

Silicon Bronze It is composed of approximately 96% Copper, 3% Silicon, and 1% Manganese. It is more corrosion resistant and tougher than brass. It is widely used in the electrical industry. 

"i need help on the steps to pouring a lead joint"
Then you need a oldtime plumber that cut his teeth on lead and oakum joints. Hey! That would be me! Let me explain about lead and oakum joints. I'm going to assume that you have a basic knowledge of the tools needed to pour and caulk a joint. A short course: It's not the lead that makes the joint water tight. It's okum, a hemp like material that swells up when water hits it. The lead is just to make sure the okum is packed in tight enough to seal. You should also know what special tools are needed to yarn and pour a joint from scratch. A lead ladle and a gas torch hot enough to melt lead in it. Then you need lead and okum. Next you will need a , yarning iron to push the okum down in the joint. A packing iron to pack the okum down tight. If the joint is a horzontal one you will need a well oiled running rope to hold the lead in the joint untill it cools. And last you will need inside and outside caulking irons plus a ball peen hammer. 
Take a length of oakum and run it around the inside of the bell/hub and tamp it down with a yearning iron. Do this untill the oakum is almost to the top. Now take the packing iron and ball-peen hanner and pack the oakum tightly in the bell. You should be left with a 3/8 to 1/2" of space for the lead.
Too much oakum? Take some out and repack it.
Now melt lead into the ladle and pour the joint to the top of the bell in one pour. Let the lead cool and set uo. Now take the inside caulking iron, ( the one with the bevel looking out) and caulk the inside of the pipe using enough strength to mark the lead well, but not strong enough to crack the cast iron bell. Do the same with a outside iron, ( the one with the bevel looking in.) and you've just poured and caulked a lead joint. ( And here you thought the only definition of a joint was one you rolled and smoked, LOL.) Good luck on your test, Tom