Transportation Of Pressure Vessels

The transportation of a pressure vessel by ship, barge, road, or rail will subject the vessel to one-time-only stresses that can bend or permanently deform the vessel if it is not adequately supported or tied down in the right locations. The shipping forces must be accounted for to ensure that the vessel arrives at its destination without damage.

It is very frustrating for all the parties involved to have a load damaged in transit and to have to return it to the factory for repairs. The cost and schedule impacts can be devastating if a vessel is damaged in transit. Certain minimal precautions can avoid the costly mistakes that often lead to problems. Even when all precautions are made, however, there is still the potential for damage due to unforseen circumstances involved in the shipping and handling process.

Care should be taken to ensure that the size and location of the shipping saddles, tie-downs, or lashing are adequate to hold the vessel but not deform the vessel. Long, thin-walled vessels, such as traved columns, are especially vulnerable to these shipping forces. The important thing to remember is that someone must take the responsibility. The barge and rail people have their own concerns with regard to loading and lashing. These may or may not coincide with the concerns of the vessel designer.

The shipping forces for ships, barges, trucks, and rail are contained in this procedure. Each method of transportation has its own unique load schemes and resulting forces. Barge shipping forces will differ from rail due to the rocking motion of the seas. Rail shipments, however, go around corners at high speed. In addition, rail forces must allow for the "humping" of rail cars when they are joined with the rest of the train. Ocean shipments have to resist storms and waves without breaking free of their lashings.

Whereas horizontal vessels 011 saddles are designed for some degree of loading in that position, vertical vessels are not. The forces and moments that are used for the design of a vertical vessel assume the vessel is in its operating position. Vertical vessels should generally be designed to be put on two saddles, in a horizontal position, and transported by various means. That is the purpose of this procedure. Too often the details of transportation and erection are left in the hands of people who, though well versed in their particular field, are not pressure vessel specialists.

Often vessels are transported by multiple means. Thus there will be handling operations between each successive mode of transportation. Often a vessel must be moved by road to the harbor and then transferred to a barge or ship. Once it reaches its destination, it must be reloaded onto road or rail transport to the job site. There it will be offloaded and either stored or immediately erected. A final transport may be necessary to move the vessel to the location where it will be finally erected. At each handling and transport phase there are different sets of forces exerted on the vessel that must be accounted for.

Shipping Saddles

The primary concern of the vessel designer is the location and construction of the shipping saddles to take these forces without overstressing or damaging the vessel. If saddles are to be relocated by the transporter, it is important that the new locations be reviewed. Generally only two shipping saddles should be used. However, this may not always be possible. Remember that the reason for using two saddles is that more than two saddles creates a statically indeterminate structure. You are never assured that any given saddle is going to take more than its apportioned load.

Here are some circumstances that would allow for more than two saddles to be used or for a special location of two saddles:

• Transporter objects due to load on tires.

• Transporter objects due to load 011 barge or ship.

• Heavy-walled vessels for spreading load on ship or transporters.

Shipping saddles can be constructed of wood or steel or combinations. The saddles should be attached to the vessel with straps or bolts so that the vessel can be moved without having to reattach the saddle. Horizontal vessels may be moved on their permanent saddles but should be checked for the loadings due to shipping forces and clearances for boots and nozzles. Shipping saddles should have a minimum contact angle of 120°, just like permanent saddles. Provisions for jacking can be incorporated into the design of the saddles to allow loading and handling operations without a crane(s).

Shipping saddles should be designed with the vessel and not left up to the transport company. In general, transportation and erection contractors do not have the capability to design shipping saddles or to check the corresponding vessel stresses for the various load cases.

Whenever possible, shipping saddles should be located adjacent to some major stiffening element. Some common stiffening elements include stiffening rings, heads (both internal and external), or cones. If necessary, temporary internal spiders can be used and removed after shipment is complete.

Key factors for shipping saddles to consider:

• Type of construction.

• Jacking pockets.

• Method of attachment to the vessel.

• Overall shipping height allowable—check with shipper.

The stresses in the vessel shell should be determined by standard Zick's analysis. The location of shipping saddles should be determined such that the bending at the midspan and saddles is not excessive. Also, the stresses due to bending at the horn of the saddle is critical. If this stress is exceeded, the saddle angle and width of saddle should be increased. Also, move the saddle closer to the head or a major stiffening element.


Vessels are lashed to the deck of ships and barges. In like manner they must be temporarily fixed to railcars, trailers, and transporters. Lashing should be restricted to the area of the saddle locations. Vessels are held in place with longitudinal and transverse lashings. Lashings should never be attached to small nozzles or ladder or platform clips. In some cases, lashing may be attached to lifting lugs and base rings. Lashings should not exceed 45° from the horizontal plane.

Other Key Factors to Consider

• Shipping clearances.

• Shipping orientation—pay close attention to lift lugs and nozzles.

• Lifting orientation.

• Watertight shipment for all water transportation.

• Escorts and permits.

• Abnormal loads—size and weight restrictions.

• Vessels shipped with a nitrogen purge.

• Shipping/handling plan.

Organizations That Have a Part in the Transportation and Handling of Pressure Vessels

• Vessel fabricator.

• Transport company.

• Engineering contractor.

• Railway authorities.

• Port authorities.

• Erection/construction company.

• Trailer/transporter manufacturer.

• Crane company/operator.

Special Considerations for Rail Shipments

1. Any shipment may be subject to advance railroad approval.

2. Any shipment over 10ft-6in. wide must have railroad approval.

3. A shipping arrangement drawing is required for the following:

a. All multiple carloads (pivot bolster required).

b. All single carloads over 10ft-6in. wide.

Recommended contact angle and saddle width:

Vessel Diameter

Contact Angle

Minimum Saddle Width



11 in.

13 ft-0 in. < D<24 ft-0in.


17 in.




Vessel Stresses c. All single carloads over 15 ft-0 in. ATR (above top of rail).

d. All single carloads that overhang the end(s) of the car and are over Sft-Oin. ATR.

4. Clearances must be checked for the following:

a. Vessels greater than 9 ft in width.

b. Vessels greater than 40 ft overall length.

c. Vessels greater than 50 tons.

5. The railroad will need the following specific data as a minimum:

a. Weight.

1). Overall length.

c. Method of loading.

d. Loadpoint locations.

e. Overhang lengths.

g. Height.

h. Routing/route survevs.

i. Center of gravity.

6. A swivel (pivot) bolster is required whenever the following conditions exist:

a. Two or more cars are required.

h. The capacity for a single car is exceeded.

c. The overhang of a single car exceeds 15 ft.

7. Rated capacities of railcars are based on a uniformly distributed load over the entire length of the car. The capacity of a car lor a concentrated load will only be a percentage of the rated capacity.

8. Rules for loads, loading, and capacities vary by carrier. Other variables include the types of cars the carrier runs, the availability, and the ultimate destination. Verify' all information with the specific carrier before proceeding with the design of shipping saddles or locations.

9. F'or vessels that require pivot bolsters, the shipping saddles shall be adequately braced by diagonal tension/compression rods between the vessel and the saddle. The rods and clips attached to the vessel shell should be designed by the vessel fabricator to suit the specific requirements of the carrier.

10. If requested, rail bolsters can be returned to the manufacturer.

11. Loading arrangement and tie-downs will have to pass inspection by a representative of the railways and sometimes bv an insurance underwriter prior to shipment.

12. Accelerometers can be installed on the vessel to monitor shipping forces during transit.

13. A rail expediter who accompanies the load should be considered for critical shipments.

14. The railroad will allow a fixed time for the cars to be offloaded, cleaned, and returned. Demurrage charges for late return can be substantial.

Outline of Methods of Vessel Shipping and Transportation

a. Truck/tractor and trailer.

b. Transporters—single or multiple, self-propelled or towed.

c. Special—bulldozer.

d. Frame adapters.

e. Beams to span trailers or transporters.

f. Rollers.

g. Special.

a. Single car.

b. Multiple cars.

c. Special cars.

d. Types of cars.

• Fishbelly flatear.

a. River barge.

b. Ocean-going barge.

c. Lakes and canals.

b. Loading and off-loading capabilities.

d. Floating cranes.

b. Helicopter.

c. Bulldozer.

Rail—Types of Cars


1. Allowable vessel weight ranges and limits are subject to reductions under certain conditions and as noted herein.

2. Dimension A = ATR, above top of rail.

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Renewable Energy 101

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