Now we entering the new chapter of this blog, which is Piping & Fabrication blog and I wish this information will be useful to all of us and thanks for every support to this blog.
FABRICATION AND INSTALLATION OF PIPING SYSTEMS
INTRODUCTION
Background
The term fabrication applies to the cutting, bending, forming, and welding of individual pipe components to each other and their subsequent heat treatment and nondestructive examination (NDE) to form a unit (piping subassembly) for installation.
The term installation refers to the physical placement of piping subassemblics, valves, and other specialty items in their required final location relative to pumps, heat exchangers, turbines, boilers, and other equipment; assembly thereto by welding or mechanical methods; final NDE; heat treatment; leak testing; and cleaning and flushing of the completed installation.
Depending on the economics of the particular situation, fabrication may be accomplished in a commercial pipe fabrication shop, or a site fabrication shop, where portions of the piping system are fabricated into subassemblies or modules for transfer to the location of the final installation.
Commercial pipe shops have specialized equipment for bending and heat treatment which is not normally available at installation sites. They also have certain types of automatic welding equipment which permits welding to be performed more efficiently and economically than in field locations where fixed position, manual arc welding is most often employed.
As a general rule piping NPS 21⁄₂ (DN 65) and larger for nuclear and fossil power plants, chemical plants, refineries, industrial plants, resource recovery, and cogeneration units are most often shop fabricated. Piping NPS 2 (DN 50) and smaller is often shop fabricated where special heat treatment or cleaning practices may be required; otherwise it is field fabricated. Pipelines and other systems involving long runs of essentially straight pipe sections welded together are usually field assembled.
In recent years, the infusion of new bending technologies, new welding processes, new alloys, fracture toughness limitations, and mandatory quality assurance (QA) programs have made piping fabrication and installation much more complex than in the past. Greater emphasis is being placed on written procedures for QA and quality control (QC) programs, special processes, and qualification and certificationof procedures and personnel.
Improper selection of fabrication or installation practices can result in a system which will not function properly or will fail before its expected life span. Accordingly, fabrication and installation contractors must work closely with the designer and be aware of the mandatory requirements of the applicable codes, the unique requirements and limitations of the materials, and those of the fabrication and installation techniques being applied.
Codes and Standards Considerations
A great many codes and standards apply to piping. These are discussed in detail in Chap. A4. It is incumbent on the fabricator and/or installer to be familiar with the details of these codes and standards since some codes have the force of law. As an example, the ASME B31.1 Power Piping Code1 is referenced by ASME Section I Power Boilers2 for piping classed as Boiler External Piping. The latter, which is law in most states and Canadian provinces, contains rules for code stamping, data reports, and third-party inspection. Piping under ASME Section III3 also has legal standing.
Most other piping codes are used for contractual agreements. Most codes reference ASME SectionV4 for nondestructive examination methodology and ASME Section IX5 for welding requirements. Each of the codes covers a different piping application, and each has evolved in a different way over the years. For specific practices, some have mandatory requirements, while others only have recommendations. Heat treatment requirements may vary from one to another. The manner in which the code-writing bodies have perceived the hazardous nature of different applications has led to differing NDE requirements.
Generally, the codes are reasonably similar, but the owner, designer, fabricator, and installer must meet the specifics of the applicable code to ensure a satisfactory installation. It is essential that the designer be very familiar with the code being used and that purchasing specifications for material, fabrication, and installation be very specific. Reference to the code alone is not sufficient. In the design, a particular allowable stress for a specific material, grade, type, product form, and/or heat-treated condition was selected. The specifications issued for material purchase and fabrication must reflect these specifies to assure that the proper materials and fabrication practices are used.
As an example: Type 304 stainless steel has a specified carbon content of 0.08 percent maximum. There is no specified minimum. Footnotes in the B31.1 Code Allowable Stress Tables for Type 304 indicate that for use over 1000°F (538°C), the allowable stresses apply only when the carbon content is 0.04 percent or higher.
It is essential that this requirement be put in the purchasing specification if the design temperature exceeds 1000°F (538°C). Similarly, in the B31.1 Code, low chrome alloy electric fusion welded pipe has
differing allowable stresses depending upon whether the plate from which it was made was annealed or normalized and tempered. If this material is to be heated above the lower critical temperature during fabrication by hot bending or forming, the designer should specify a postbending heat treatment appropriate for the allowable stress level used in the design.
It is also incumbent upon the fabricator and/or installer to be very familiar with the applicable code. Each project should be reviewed in detail. ‘‘Standard shop practices’’ may not always produce the desired result. Communication between the designer, fabricator, and installer is essential. All should be familiar with the various standards used in piping design. Most piping systems are composed of items which conform to some dimensional standards such as ASME B36.10M6 and ASME B36.19M for pipe, B16.57 for flanges, etc. Other dimensional standards are issued by the Manufacturers Standardization Society (MSS)8 and the American Petroleum Institute (API).
The Pipe Fabrication Institute (PFI)10 publishes a series of Engineering Standards which outline suggested practices for various fabrication processes. These standards give excellent guidance for many aspects of piping fabrication not covered by the codes.
The American Welding Society (AWS)11 publishes a number of recommended practices for welding of pipe in various materials.
INTRODUCTION
Background
The term fabrication applies to the cutting, bending, forming, and welding of individual pipe components to each other and their subsequent heat treatment and nondestructive examination (NDE) to form a unit (piping subassembly) for installation.
The term installation refers to the physical placement of piping subassemblics, valves, and other specialty items in their required final location relative to pumps, heat exchangers, turbines, boilers, and other equipment; assembly thereto by welding or mechanical methods; final NDE; heat treatment; leak testing; and cleaning and flushing of the completed installation.
Depending on the economics of the particular situation, fabrication may be accomplished in a commercial pipe fabrication shop, or a site fabrication shop, where portions of the piping system are fabricated into subassemblies or modules for transfer to the location of the final installation.
Commercial pipe shops have specialized equipment for bending and heat treatment which is not normally available at installation sites. They also have certain types of automatic welding equipment which permits welding to be performed more efficiently and economically than in field locations where fixed position, manual arc welding is most often employed.
As a general rule piping NPS 21⁄₂ (DN 65) and larger for nuclear and fossil power plants, chemical plants, refineries, industrial plants, resource recovery, and cogeneration units are most often shop fabricated. Piping NPS 2 (DN 50) and smaller is often shop fabricated where special heat treatment or cleaning practices may be required; otherwise it is field fabricated. Pipelines and other systems involving long runs of essentially straight pipe sections welded together are usually field assembled.
In recent years, the infusion of new bending technologies, new welding processes, new alloys, fracture toughness limitations, and mandatory quality assurance (QA) programs have made piping fabrication and installation much more complex than in the past. Greater emphasis is being placed on written procedures for QA and quality control (QC) programs, special processes, and qualification and certificationof procedures and personnel.
Improper selection of fabrication or installation practices can result in a system which will not function properly or will fail before its expected life span. Accordingly, fabrication and installation contractors must work closely with the designer and be aware of the mandatory requirements of the applicable codes, the unique requirements and limitations of the materials, and those of the fabrication and installation techniques being applied.
Codes and Standards Considerations
A great many codes and standards apply to piping. These are discussed in detail in Chap. A4. It is incumbent on the fabricator and/or installer to be familiar with the details of these codes and standards since some codes have the force of law. As an example, the ASME B31.1 Power Piping Code1 is referenced by ASME Section I Power Boilers2 for piping classed as Boiler External Piping. The latter, which is law in most states and Canadian provinces, contains rules for code stamping, data reports, and third-party inspection. Piping under ASME Section III3 also has legal standing.
Most other piping codes are used for contractual agreements. Most codes reference ASME SectionV4 for nondestructive examination methodology and ASME Section IX5 for welding requirements. Each of the codes covers a different piping application, and each has evolved in a different way over the years. For specific practices, some have mandatory requirements, while others only have recommendations. Heat treatment requirements may vary from one to another. The manner in which the code-writing bodies have perceived the hazardous nature of different applications has led to differing NDE requirements.
Generally, the codes are reasonably similar, but the owner, designer, fabricator, and installer must meet the specifics of the applicable code to ensure a satisfactory installation. It is essential that the designer be very familiar with the code being used and that purchasing specifications for material, fabrication, and installation be very specific. Reference to the code alone is not sufficient. In the design, a particular allowable stress for a specific material, grade, type, product form, and/or heat-treated condition was selected. The specifications issued for material purchase and fabrication must reflect these specifies to assure that the proper materials and fabrication practices are used.
As an example: Type 304 stainless steel has a specified carbon content of 0.08 percent maximum. There is no specified minimum. Footnotes in the B31.1 Code Allowable Stress Tables for Type 304 indicate that for use over 1000°F (538°C), the allowable stresses apply only when the carbon content is 0.04 percent or higher.
It is essential that this requirement be put in the purchasing specification if the design temperature exceeds 1000°F (538°C). Similarly, in the B31.1 Code, low chrome alloy electric fusion welded pipe has
differing allowable stresses depending upon whether the plate from which it was made was annealed or normalized and tempered. If this material is to be heated above the lower critical temperature during fabrication by hot bending or forming, the designer should specify a postbending heat treatment appropriate for the allowable stress level used in the design.
It is also incumbent upon the fabricator and/or installer to be very familiar with the applicable code. Each project should be reviewed in detail. ‘‘Standard shop practices’’ may not always produce the desired result. Communication between the designer, fabricator, and installer is essential. All should be familiar with the various standards used in piping design. Most piping systems are composed of items which conform to some dimensional standards such as ASME B36.10M6 and ASME B36.19M for pipe, B16.57 for flanges, etc. Other dimensional standards are issued by the Manufacturers Standardization Society (MSS)8 and the American Petroleum Institute (API).
The Pipe Fabrication Institute (PFI)10 publishes a series of Engineering Standards which outline suggested practices for various fabrication processes. These standards give excellent guidance for many aspects of piping fabrication not covered by the codes.
The American Welding Society (AWS)11 publishes a number of recommended practices for welding of pipe in various materials.
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