ASME B31.4

ASME B31.4 prescribes requirements for the design, materials, construction, assembly, inspection, testing, operation, and maintenance of liquid pipeline systems between production fields or facilities, tank farms, above- or belowground storage facilities, natural gas processing plants, refineries, pump stations, ammonia plants, terminals (marine, rail, and truck), and other delivery and receiving points, as well as pipelines transporting liquids within pump stations, tank farms, and terminals associated with liquid pipeline systems. This Code also prescribes requirements for the design, materials, construction, assembly, inspection, testing, operation, and maintenance of piping transporting aqueous slurries of nonhazardous materials such as coal, mineral ores, concentrates, and other solid materials, between a slurry processing plant or terminal and a receiving plant or terminal.

Piping here consists of pipe, flanges, bolting, gaskets, valves, relief devices, fittings, and the pressure containing parts of other piping components. It also includes hangers and supports, and other equipment items necessary to prevent overstressing the pressure containing parts. It does not include support structures such as frames of buildings, stanchions, or foundations, or any equipment

Also included within the scope of this Code are:

(a) primary and associated auxiliary liquid petroleum and liquid anhydrous ammonia piping at pipeline terminals (marine, rail, and truck), tank farms, pump stations, pressure-reducing stations, and metering stations, including scraper traps, strainers, and prover loops

(b) storage and working tanks, including pipe-type storage fabricated from pipe and fittings, and piping interconnecting these facilities

(c) liquid petroleum and liquid anhydrous ammonia piping located on property that has been set aside for such piping within petroleum refinery, natural gasoline, gas processing, ammonia, and bulk plants

(d) those aspects of operation and maintenance of liquid pipeline systems relating to the safety and protection of the general public, operating company personnel, environment, property, and the piping systems

Key changes to this revision include a revised scope and updates to the stress section in Chapter II. A new paragraph has been added in Chapter III for material requirements in low-temperature applications. In addition, changes have been included throughout to reference minimum wall thickness requirements as permitted by manufacturing specifications.

The stress analysis of a pipeline is quite different from that of plant piping. The most fundamental difference between pipeline and plant piping is the very long length of the pipeline. A pipeline with kilometres in length has the potential of producing a very large amount of expansion. A reasonable estimate of the movement and its interaction with the end resistance force afforded by connecting piping and equipment are very important aspects in designing a pipeline. The salient points for stress analysis I feel are as follows:

• B 31.4 code addresses analysis of lines within temperature range starting from -20 degree centigrade till 120 degree centigrade.
• There are no Sh values similar to B 31.3. A pipeline normally runs for several kilometres without any fittings attached. Because of such simplicity, the stress in the majority portion of a pipeline is quite predictable. Taking advantage of this characteristic, the code’s allowable stress for a pipeline is greatly increased, as compared to that for plant piping. All allowable values are linked with Sy (Specified Minimum Yield Strength) as the allowable stress of a pipeline is mainly to protect the pipe from gross deformation. Whenever you select B 31.4 in Caesar II all Sh value fields become grey.
• The following equations are used to calculate various stress allowable:

o Expansion Allowable=(0.72) (Sy)

o Sustained Allowable=(0.75) (0.72) (Sy)

o Occasional Allowable=(0.8) (Sy)

o Operating Allowable=(0.9) (Sy)

• Pressure elongation of pipe line is also important along with expansion elongation and need to be taken care. Caesar II automatically does this whenever you select B 31.4 code.
• There is nothing like liberal stress in B 31.4
• The modelling procedure is similar. Whenever material is selected the Sy value automatically filled from Caesar database. However you have to input the Design multiplication factor (Fac) value additionally. Fac value indicates whether the pipe is restrained, such as long or buried, or unrestrained. Fac should be 1.0, 0.0, or 0.001.

o This value should be one for pipe under complete axial restraint. This value should be one when the pipe is fully restrained, such as buried for a long distance.

o The default value for Fac is 0.0.

o When Fac is 0.001, this indicates to CAESAR II that the pipe is buried but that the soil supports have been modelled. This causes the hoop stress component, rather than the longitudinal stress, to be added to the operating stresses if the axial stress is compressive.

• Some parts of the lines are buried or underground and some parts are aboveground. So you need to understand the soil pipe interaction for buried parts. Soil properties need to be taken from Civil/Geotechnical team while performing stress analysis of underground piping.

For underground piping there should be some minimum depth of cover as per B 31.4 depending on location of pipeline.