Design Detail Considerations for Piping Supports

ASME Code for Pressure Piping

Specific design requirements for piping support are included in the sections of ASME B31, Code for Pressure Piping, listed below:

● B31.1, Power Piping

● B31.2, Fuel Gas Piping

● B31.3, Process Piping

● B31.4, Liquid Transportation Systems for Hydrocarbons, Liquid Petroleum Gas, Anhydrous Ammonia, and Alcohols

● B31.5, Refrigeration Piping

● B31.8, Gas Transmission and Distribution Piping Systems

● B31.9, Building Services Piping

● B31.11, Slurry Transportation Piping Systems

In addition, ASME Boiler and Pressure Vessel Code, Section III, defines rules for piping supports used in nuclear power plants.

These requirements must be adhered to on piping installations when piping must conform to these codes. In most cases, supports conforming to MSS-SP-58 are acceptable for these installations.

Government Specifications

The Federal Specification WWH-171, of the latest issue and entitled ‘‘Hangers and Supports, Pipe,’’ is the governing specification for all federal agencies. This specification illustrates types of pipe hangers and supports and lists the requirements of certain applications.

Design Temperature

Design temperatures for parts of hangers and supports in direct contact with pipe shall be the temperature of the fluid contained in the pipe. Parts of hangers and supports not in direct contact with pipe may be designed to a temperature reduced by 100 F per 1 in (55 C per 25 mm) away from the pipe wall. Allowable stresses
for materials commonly used in the design of pipe hangers and supports are listed in applicable codes and standards.

Welded Fabrication

Welded fabrication shall be accomplished with good engineering practice as prescribed by the appropriate welding code. In the United States, the American Welding Society (AWS) and the American Society of Mechanical Engineers, Section IX, are the governing codes. In Germany, DIN EN 288 controls welding, and in Britain it is BS 5135. Attachments welded directly to the pipe must be of appropriate (compatible) chemical composition, and the process of attachment must conform to the requirements for fabrication of the pipe regarding preheating, welding, and stress relieving.

Cold Spring

The cold-springing procedure for piping systems involves, basically, the cutting short of each segment of piping in an amount equal to some specific percentage of the normal thermal growth of the segment, with proper allowance to compensate for possible terminal connection movements. The cumulative effect results in an offset gap between the piping ends at the point of final field closure. The drawing together and alignment of the piping ends by the application of required forces and moments are called cold pull and result in a slight relocation of all points along the entire piping system.

This relocation is the only effect that cold springing has on supports. The piping is then considered to be in the cold-sprung position, which is equivalent to the cold operating position. The movement at all support points from the erected to the cold-sprung position must be calculated, and provision made for this movement in the form of hanger rod adjustment.

Adjustment

It is necessary to provide vertical adjustment to attain the desired elevation of the piping system. On piping supported from above, it may suffice to adjust an MSSSP-58 Type 1, 5, 6, 9, or 10 support through the yoke portion by raising or lowering the nut on the rod. For larger ranges of adjustments, it is necessary to provide a turnbuckle, MSS-SP-58 Type 13 or 15, in the hanger rod. It is also practical to select a top attachment whereby adjustment can be made at the top of the hanger rod.

On piping which is supported from below, provision for adjustment can be made with screw thread stanchions, MSS-SP-58 Type 38, or by shims or grout.

Protective Coatings

Protective coatings are normally applied to pipe supports for corrosion resistance. Metallic coatings may be applied by either the electroplating or the hot-dip process. Nonmetallic coatings, if selected for specific purposes, should be applied as recommended by the manufacturer. Consideration must be given to coatings used on threaded parts that are to be assembled after coating.

Get Notified for new Tutorials: *Check your email to confirm your subscription*