Hydrostatic & Pneumatic Procedure

Hydrostatic testing is most often preferred over pneumatic testing because of safety considerations. Water is the preferred fluid medium for hydrostatic testing. In addition to its relatively incompressible nature, it is also the safest fluid because it is nontoxic and nonflammable and it remains in liquid form down to atmospheric pressure unless heated above the boiling point. Water is readily and economically
available. ASME B31.1, section 137.4.3, specifies water as the test fluid for hydrostatic tests unless otherwise specified. ASME B31.3, section 345.4.1, also specifies water as the test fluid for hydrostatic test unless there is the possibility of freezing or damage from adverse effects of water on the piping or the process for which the piping system is designed. This section provides for other uses of other nontoxic liquids as long as the flash point exceeds 120F (49C). If hydrostatic testing is being considered for a system that was designed for use of a gaseous medium as the process fluid, it must first be determined that the piping system will support the weight of the test liquid or that the piping can be safely supported during the hydrostatic test.

There are some cases where water cannot be employed as a fluid test medium. Traces of water left in the piping may react adversely with the process; for example, in piping for liquid sodium or a cryogenic process. If the test is to be run at temperature conditions which would make freezing likely, antifreeze may be added to the water as long as the antifreeze is not harmful to the piping or the process and the disposal of large amounts of antifreeze is not environmentally unacceptable. If water cannot be employed as the fluid test medium and another liquid is not practical, or if it is not practical to support the weight of a test liquid with piping supports, a pneumatic test may be the next best choice

Checklist for Hydrotest:

● Completed and torqued flanges with no missing bolts or gaskets
● All gravity supports installed
● Proper pipe routing
● Correct valve type and orientation
● Vents and drains installed to allow proper filling and draining

● Proper material type verified using color codes or markings, and heat numbers
   recorded if required by the codes
● All required piping stress relief, weld examinations, and welding documentation
   completed and acceptable
● Before the test is to be run, make certain, by reviewing the piping against the
   P&ID and valve line-up sheet, that
● All equipment not to be tested is disconnected from the test or isolated by closed
   valves or testing blinds
● Tagging and lockout of any valves used to isolate the test boundaries is in place
    to protect both the testing personnel and any others who may be on site
● All non boundary valves in the test boundary are in the open position
● Expansion joints, if any, have required restraints to protect against damage from
   the test pressure
● All springs have travel stops to protect against the weight of the test medium
● All test equipment is checked and all test connections are tight
   For gas systems, additional gravity supports may be required temporarily to support the weight of the test liquid. Since requirements vary from project to project, the person responsible for the test will need to make a specific checklist of items for each project before testing can begin.

Hydrostatic Testing Preparation

All joints, including welds and flanges, of the portions of the system to be tested are left uninsulated and exposed for examination during the test. Some insulation may be installed on the straight runs or previously tested piping. If the system is to include jacketed piping, the leak tests should be run before any jacketing is installed.

A flow water pump is substituted for the pressurizing water pump during the filling of the piping. The water source should provide clean chloride-free water. The system is filled from the bottom to facilitate the venting of all air in the portion of the piping system under test. For sloped piping systems, filling should be done against the slope. Vents must be located at all high points in the piping and should be open during the filling stage. Once it is determined the system is completely liquid filled the vents may be closed and a pressurizing water pump connected to the system in place of the flow pump. The pressurizing pump must have a capacity greater than the allowable leakage of the system. Leakage at the packing glands of valves and pumps is permissible by the codes and is necessary to preserve the life of the packing. However, if this leakage is so great that the test pressure cannot be controlled by being trapped, there will be a problem in running the test. It is not very practical to turn the pressurizing pump on and off to maintain the pressure close to the required level. One solution is to temporarily tighten all the packings to a greater compression than is normally used during regular operation of the system. It may also be necessary to tighten flanges, screwed connections, and other mechanical or gland-type joints to eliminate leakage.

Test and Examination Pressures

Test pressure minimum	Test pressure maximum	Test pressure hold time	Examination pressure	Code	Test type
ASME B31.1	Hydrostatic1	1.5 times design	Max allowable test pressure any component or 90 percent of yield	10 minutes	Design pressure
ASME B31.1	Pneumatic	1.2 times design	1.5 times design or max allowable test pressure any component	10 minutes	Lower of 100 psig or design pressure
ASME B31.1	Initial service	Normal operating pressure	Normal operating pressure	10 minutes or time to complete leak examination	Normal operating pressure
ASME B31.3	Hydrostatic	1.5 times design	Not to exceed yield stress	Time to complete leak examination but at least 10 minutes	1.5 times design
ASME B31.3	Pneumatic	1.1 times design	1.1 times design plus the lesser of 50 psi or 10 percent of test pressure	10 minutes	Design pressure
ASME B31.3	Initial service3	Design pressure	Design pressure	Time to complete leak examination	Design pressure
ASME I	Hydrostatic	1.5 times max allowable working pressure4	Not to exceed 90 per- cent yield stress	Not specified, typically 1 hr	Max allow able working pressure4
ASME III Division 1 Subsection NB	Hydrostatic	1.25 times system design pressure5	Not to exceed stress limits of design section NB-3226 or maximum test pressure of any system component5	10 minutes	Greater of design pressure or .75 times test pressure
ASME III Division 1 Subsection NB	Pneumatic	1.2 times system design pressure6	Not to exceed stress limits of design section NB-3226 or maximum test pressure of any system com	10 minutes	Greater of design pressure or .75 times test pressure
ASME III Division 1 Subsection NC	Hydrostatic	1.5 times system design pressure	If minimum test pressure exceeded by 6 percent establish limit by the lower of analysis of all test loadings or maxi- mum test pressure of any component	10 minutes or 15 minutes per inch of design mini- mum wall thickness for pumps and valves	Greater of design pressure or .75 times test pressure
ASME III Division 1 Subsection NC	Pneumatic	1.25 times system design pressure	If minimum test pressure exceeded by 6 percent establish limit by the lower of analysis of all test loadings or maxi mum test pressure of any component	10 minutes	Greater of design pressure or .75 times test pressure
ASME III Division 1 Subsection ND	Hydrostatic	1.5 times system design pressure for completed components, 1.25 times system design pressure for piping systems	If minimum test pressure exceeded by 6 percent establish limit by the lower of analysis of all test loadings or maxi mum test pressure of any component	10 minutes	Greater of design pressure or .75 times test pressure
ASME III Division 1 Subsection ND	Pneumatic	1.25 times system design pressure	If minimum test pressure exceeded by 6 percent establish limit by the lower of analysis of all test loadings or maxi mum test pressure of any component	10 minutes	Greater of design pressure or .75 times test pressure

                                                                                                                                                              

                                                                                                                                                              

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 PIPE JOINTS

Pipe Joints are used to couple runs of piping, to provide branches from Main Header  , change the direction , connection to Valves & Equipment .The common types of joints are :

• Butt welds
• Socket welds
• Threaded Joints
• Bolted Flanges
• Mechanical couplings.

1) Butt welds: 

Butt welded joints are most common types of joints used for 2 inch and higher dia Piping.This type of joint is not normally used on below 2 inch & below, except when High stress , corrosion or other conditions that would affect joint. The end preparations are designated by welding codes and standards.

2) Socket welds:

Socket welds joints are almost used in joining small bore piping. The joint is fit up by slipping the plain end into the Socket connection.A gap of 1/16 inch at the bottom of the socket is normally required to allow expansion between the fitting and pipe.This prevents the weld from possibly Cracking due to thermal Stress during welding or High temperature services.

3) Threaded Joints:

Threaded joints are normally used on low pressure system. Pipes & Fittings for threaded joints in low pressure system usually have National Pipe Taper (NPT) threads.A pipe joints compound or thread sealant must be used to prevent leakage around threads joints.

4) Flanged joints:

Bolted Flanged Joints are required where Pipe , Piping Components , or Equipment must be disassembled for maintenance. The are required when Joining Glass , High Density polypropylene , or other lined piping.Sometimes they are used to join Prefabricated shop spools.

Flange Bolting Procedure:

Flanges have equally spaced Bolts in multiple of four , so that valve or fittings can be positioned to face in any quadrant . Identification symbols are used for flange Bolting.All bolting must be long enough to ensure that the bolt will have one or two threads showing beyond the nut when joint is complete.

Both excessive or inadequate initial bolt stress can cause leakage at the joint. Accurate prestressing of the connection is required for proper operation. Prestressing Methods include :

- Tightening by Hand Wrench 

- Tightening by Calibrated power torque wrench 

- Hydraulic tensioning 

Before prestressing , all bolts should be thoroughly coated with an antiseize compound to allow removal .Bolting sequence is not performed in clockwise rotation , but across the face to properly draw the flanges together .Also stress on bolting should be increased in a step manner to bring the bolt up equally to prevent from rolling the gasket. Both of these two actions helps in stopping  poor gasket setting , which can cause leakage.

To assemble Bolted Flange Connection :

- Thoroughly clean the flange faces prior to fitup 

- Rig the flanges into position with the bolt holes aligned & check flange Faces for parallelism using a dial indicator or other means.

- Provide coating on Flange bolts & install gasket , bolts ,nuts.

- Tighten Flange bolts in sequence as shown in figure 

Step - 1: 25% of minimum required stress or torque 

Step - 2 : 50% of minimum required stress or torque 

Step - 3 : 100% of minimum required stress or torque 

 Note : Minimum required stress or torque Values to be determine from Project Technical specifications.

                                                                                                                               

                                                                                                                               

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 PIPE SIZES AND MATERIALS

STANDARD PIPING SIZES

Piping is divided into three major categories:

• LARGE BORE PIPE generally includes piping which is greater than two inches in diameter
• SMALL BORE PIPE generally includes piping which is two inches and smaller in diameter
• TUBING is supplied in sizes up to four inches in diameter but has a wall thickness less than that of either large bore or small bore piping and is typically joined by compression fittings

The term diameter for piping sizes is identified by nominal size. The manufacture of nominal sizes of 1/8inch through 12 inches inclusive is based on a standardized outside diameter (OD). This OD was originally selected so that pipe with a standard wall thickness will have the inside diameter (ID) of the size stated. The 14 inch and larger sizes have the OD equal to the nominal pipe size. Pipe sizes ⅜ inch, 1 1⁄4 inches, 3 1⁄2 inches, 41⁄2 inches, and 5 inches are considered to be nonstandard and should not be used except to connect to equipment having these sizes. In these cases the line is normally increased to a standard size as soon as it leaves the equipment. Tubing is sized to the outside diameter for all applications and pressure rating is dependent on varying wall thicknesses.

Schedule (Wall Thickness)
Pipes are manufactured in a multitude of wall thicknesses, these have been
standardized so that a series of specific thicknesses applies to each size of piping. Each thickness is designated by a schedule number or descriptive classification, rather than the actual wall thickness. The original thicknesses were referred to as standard (STD), extra strong (XS), and double extra strong (XXS). These designations or weight classes have now either been replaced or supplemented by schedule numbers in most cases. Schedules begin with 5 and 5S, followed by 10and 10S, then progress in increments of ten through Schedule 40(20,30,40) and finally by increments of twenty to Schedule 160( 60,80,100,120,140,160). Wall thickness for schedule 40 and STD are the same
for sizes 1⁄8 to 10 inches. Schedule 80 and XS also have the same wall thickness for 1⁄8 inch through 8 inch diameter pipe.

Pipe ends

Pipe may be obtained with plain, beveled, or threaded ends. Plain ends (PE) are cut square and reamed to remove burrs. This type of end is needed when being joined by mechanical couplings, socket weld fittings, or slip-on flanges. Beveled ends (BE) are required for most butt-weld applications. Threaded ends (TE) are used with screwed joints and are ordered noting threads on both ends or one end (TBE or TOE).

1) PIPE MANUFACTURING

• SEAM LESS PIPES  MANUFACTURING PROCESS

• SPIRAL PIPES  MANUFACTURING PROCESS

STANDARD PIPING MATERIALS

Carbon Steel Pipe

Carbon Steel is one of the most commonly used pipe materials. The specifications that cover most of the pipe used are published by the American Society for Testing and Materials (ASTM) and American Society of Mechanical Engineers (ASME). Carbon Steel Material specification ASTM A106 is available in grades, A, B, and C. These grades refer to the tensile strength of the steel, with grade C having the highest strength. Common practice is to manufacture the pipe as A106 Grade B.

ASTM A53 is also commonly specified for galvanized or lined pipe or as an alternate to A106 . The testing requirements for A53 are less stringent than for A106. Three types of carbon steel pipe are covered by A53. These are type E or electric resistance welded, type F or furnace-butt welded, and type S or seamless. Type E and S are available in grade A and B, comparable to grades A and B of A106 .

Stainless Steel Pipe

Austenitic Stainless Steel pipe commonly referred to as "stainless steel" is virtually nonmagnetic. Stainless steel is manufactured in accordance with ASTM A312 when  8-inch or smaller sizes are needed. There are eighteen different grades, of which type 304 L is the most widely used. Grade 316 L has high resistance to chemical and salt water corrosion, and is therefore used in applications where this characteristic is needed. The "L" denotes low carbon content and is best suited for welding. Larger sizes (8 inches and up) of stainless steel pipe are covered by ASTM A358. Extra light wall thickness (Schedule 5S) and light wall (Schedule 10S) stainless steel pipe is covered by ASTM A409 .

Chrome-Moly Pipe

Chromium-Molybdenum Alloy Pipe is commonly referred to as "chrome-moly". Ten grades of this type pipe material are covered by ASTM A335. Appropriate grades of chrome-moly pipe are sometimes used in power plants applications requiring good tensile property retention at high temperatures, especially when the added corrosion resistance of stainless steel is not required. Chrome-moly pipe is used extensively in heat exchangers. Special care must be exercised when fabricating or welding this material, since it must be annealed (stress relieved) after being joined.

Plastic Pipe

Thermoplastic Pipe is commonly referred to plastic pipe and is categorized into two principal groups.

Thermoplastic pipe is available in a great variety of plastic compositions including:
• Polyvinyl chloride (PVC)
• Polyethylene (PE)
• Acrylonitrile-butadiene-styrene (ABS)
• Polyamide (nylon)
• Polypropylene

Concrete Pipe

Concrete Pipe is made from a mixture of portland cement, sand, gravel, and water. It is manufactured as:

• Plain (unreinforced)
• Reinforced concrete pipe
• Prestressed concrete pressure pipe

The usual method for joining this pipe is by bell and spigot ends. The spigot end of one pipe is inserted into the bell of the mating piece, then the joint is sealed with mortar or a joint compound. It may also have a provision for a rubber gasket to seal the joint.

Nickel and Nickel Alloy Piping

Nickel and Nickel Alloy Pipe has a great resistance to alkalis such as caustic soda and potash. Nickel and nickel alloys are sometimes used for high temperature applications. Inconel, Incoloy, and Monel are commonly used nickel alloys.

Special Piping Applications

Other piping materials such as plastic lined, glass lined, concrete lined, and steam jacketed are utilized in special project applications.

                                                                                                                                                          

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