Underwater Piping Contractor Chicago

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Pipe delivery Fabrication yard

Pipe delivery Fabrication yard

Operational Life

Moderate

Moderate

Moderate

N/A

Moderate

Not practical for this pipe material

PredictionRisk

Low

Low

High

Moderate

63.7.2 Cast Iron Pipe. Cast iron (or ductile iron) pipe is suitable for low pressure water transmission lines. Cast iron pipe contains low carbon and high silicon contents which give this material superior corrosion resistance. However, cast iron is a britde material which is subject to failure from thermal strains or impact damage. It is normally supplied with bell and spigot type joints which can deflect up to 15 degrees for submarine pipeline installations. It is also available with flange ends. It is generally ordered in lengths of 12 or 18 feet.

6.3.7.3 Polyvinyl Chloride (PVC). Polyvinyl chloride pipes provide excellent corrosion resistance and are suitable for the transmission of water and chemical products. PVC pipe can be furnished in continuous lengths for small diameter applications (3 to 4 inches in diameter). Larger diameters are furnished with plain end, flanged end, or mechanical couplings. It is normally furnished in 20-foot lengths when ordered as individual sections. Plain end pipe sections are joined in the field using solvent weld pipe couplings.

63.7.4 High Density Polyethylene (HDP). High density polyethylene pipe provides excellent corrosion resistance and is suitable for the transmission of water, gas, and chemical products. Polyethylene (PE) pipe can be obtained in continuous lengths (3 to 4 inches in diameter), plain end, flanged end, or mechanical couplings. It is normally furnished in 20- or 40-foot lengths when ordered as individual sections. Plain end pipe sections must be joined in the field using a carefully controlled heat fusion process.

A unique property of PE pipe is that it will attempt to regain its original shape after deformation. Repairs to low pressure transmission line are accomplished by pinching the pipeline to stop the flow while repairs are made. After the repair is complete, the pipe will return to its original shape with no permanent deformation. This property is also used to install PVC liners inside steel pipe products. The PE pipe is compressed and pulled through a steel pipe. After die pulling operation, the PE pipe expands to fill the annular space between the PVC and steel pipe walls.

6.3.7.5 Fiberglass. Fiberglass pipe is suitable for water or chemical products and is generally furnished in 20-foot lengths. Flanges and threaded couplings are standard joint types. Field welded joints are also possible using layers of fiberglass impregnated with resin.

While fiberglass is suitable for submarine pipelines, it is seldom employed in practice due to its relative price position. It is much more expensive than PVC or HDD and only slighdy less expensive than steel. For a small increase in cost, most projects benefit from the superior strength and performance of steel pipelines.

The advantage of fiberglass is its high strength-to-weight ratio and resistance to chemical and corrosive attacks. It is most suitable in a submarine environment for large diameter pipelines where the ability to limit weight or installation stress is a controlling factor in the material selection process.

6.3.7.6 Flexible Pipe. Flexible pipe (see Section 5.3.4.5) is a special product manufactured by a select few manufacturers (e.g., Coflexip, Wellstream, and Simplex) to meet the specific requirements of each particular project. The pipe consists of concentric layers of spiral wound steel reinforcing and HDP extruded coating. The pipe is manufactured in a continuous length and gener ally furnished with an end fitting. Interior coatings can be provided to suit any product requirement.

6.3.7.7 Collapsible Hose. Collapsible hose is'manufactured from neoprene or other rubber-type synthetics. It is most commonly used in military applications for temporary POL and water pipelines such as the Amphibious Assault Bulk Fuel System (AABFS).

6.3.7.8 Oil Suction and Discharge Hose. Oil suction and discharge hose is heavy-walled hose manufactured from reinforced rubber or rubber-type synthetics. The hose body is reinforced with high strength textiles and/or steel wire spirals. Oil suction and discharge hose for offshore applications is manufactured in accordance with the Oil Companies International Marine Forum (OCIMF), Hose Standards.

Oil suction and discharge hose is a specialty product manufactured by a few manufacturers (Dunlop, Bridgestone, Uniroyal, Yokohama, Pirelli, Kleber, and Hewitt). Hose sections are manufactured in standard lengths of 30 and 35 feet. It is commonly employed for floating and submarine hose strings at both Navy and commercial offshore oil tanker terminals.

6.3.7.9 Concrete. Concrete is traditionally employed for low pressure, shallow water, large diameter (greater than 36-inch) submarine pipelines, primarily for water intake and discharge lines. Concrete pipe sections are normally supplied in 16-foot lengths (up to 34 inches in diameter) or 16-and 32-foot lengths (greater than 34 inches in diameter). All concrete pipe sections use a bell and spigot-type joint.

6.3.7.10 POL Pipelines. Suitable materials for submarine pipelines carrying fuel or tanker ballast water include:

• Carbon steel piping material, ASTM A-53-93a, Grade B or API 5L-92, Grade B or superior grades. Pressure temperature rating for all piping valves and fittings shall conform to ANSI B31.3A-93 or B31.4-92 as appropriate. This includes:

- line pipe

- coiled tubing

- tubing and casing

• Heavy duty oil and gas hose conforming to OCIMF, Hose Standards

• Flexible pipe conforming to API RP 17B-88

The collapsible hose system such as that used by the Military Sealift Command's prepositioned ships is considered a temporary system and should not be employed for permanent construction or when the life expectancy exceeds 30 days.

6.3.7.11 Lined Pipe. Pipeline materials may also be combined to produce a composite pipe construction. For example, thin-walled polyethylene liners may be pulled through steel well casing to construct a potable water pipeline. In this situation, the steel casing provides strength to withstand high installation and operational stress levels while the polyethylene liner ensures product quality and protects the pipeline against internal corrosion.

6.3.7.12 Pipe Bundles. If several pipelines are to be installed as part of the same facility (i.e., separate fuel offloading and ballast water pipelines at a tanker terminal), the individual pipelines may be bundled to allow a simultaneous installation. Figure 6-25 depicts a pipe bundle for

Figure 6-25. Pipe bundle.

Figure 6-25. Pipe bundle.

a fuel offloading terminal which also includes a hydraulic control line.

6.3.8 Pipe Joint Types

The vast majority of submarine pipelines are commercial oil and gas lines and utilize welded steel joints. However, other joint types have also been employed for submarine pipelines. These include:

• Threaded coupling

• Rigid bell and spigot

• Flexible bell and spigot (ball and socket)

A comparison of common pipe joints for military applications was included in Pannell and Cevasco (1978) and is reprinted as Table 6-7. Illustrations of common mechanical joints employed for submarine pipelines are shown in Figure 6-26. Additional comments are provided below.

6.3.8.1 Pipe Flange. The flanged joint is a very reliable jointing technique but is seldom used for joining individual pipe sections due to (real or imagined) difficulties created by the protruding flanges. The flange projections have a tendency to "hang" on installation equipment and increase passive soil resistance for bottom pull techniques.

Flanged connections are commonly employed for tie-ins of long sections of pipe as well as connecting individual sections of heavy duty (OCIMF) oil and gas hose.

6.3.8.2 Threaded Coupling. The threaded coupling is a reliable jointing technique which is ideally suited to military applications. It is rapidly assembled and requires minimal personnel training. However, a utvucnvvM / en //wo / mllm / iUi\l fttui,cuutic^

Wash Pipe Installation Table Oil Wells

Pipe Flange

Uni Flange With Retainer Glands
Basic power tight makeup Hand tight makeup

Threaded Coupling

Figure 6-26. Common mechanical joints used for submarine pipelines.

Undersea Construction

Bolt

Rubber ring gasket

Cast iron retainer ring Pipe wall

Bolt

Split Gland Follower
Split cast iron follower gland

Flexible Bell and Spigot (ball and socket)

Figure 6-26. Common mechanical joints used for submarine pipelines (continued).

Table 6-7. Pipe Joining Methods

Joint

Suitability for Use Offshore in Military Applications

Suitability for Troop Use

Extent of Training Required

Adaptability* to Training

Indicated Dependability in Offshore Applications

State-of-Art

Reliability and Performance

Electricb Welded

Excellent

Poor

Extensive

Poor

Excellent

Advanced

Excellent

Explosive0 Weld

Good

Excellent

Intermediate

Poor

Good development

Primarily in

Unknown

Threaded"1 Coupling

Good

Excellent

Intermediate

Excellent

Good

Advanced

Good

Zap-Lock

Good Questionable

Good -

Intermediate

Poort

Good development

In use and

Unknown

Bolted Flange

Poor

Good

Minimum

Excellent

Good

Advanced

Good

Coupled Sleeve (Victaulic)

Unsatisfactory

Excellent

Minimum

Excellent

Very poor

Advanced

Unsatisfactory

Other Mechanized Coupling

Unsatisfactory

Excellent

Minimum

Excellent

Poor

Advanced and development

Unsatisfactory

8 All methods listed as poor require expenditure of materials and complete removal of joint area at completion of training and for retrieval of pipeline for reuse at another location.

b Electric welded pipeline would require extensive training and practice to maintain proficiency. As such, they are poorly adapted to training. c Explosively welded joints have been under development by industry for some time but have not found widespread use. Therefore, reliability and performance cannot be assessed accurately.

d Threaded coupling joints are proven joints. In 4- and 6-inch sizes they have been demonstrated by the Army and Navy as being fully satisfactory for troop use and appear to be satisfactory in 8-inch size. Subitability of threaded couplings in sites greate than 8-inch diameters appear questionable because of the requirement for larger sizes, more powerful equipment, and handling problems.

horizontally-mounted rotary pipe tong is required to assemble the pipe sections in the field. This equipment was previously developed as part of the Navy BLPS and is no longer maintained in inventory. New tongs must be custom designed prior to using this joint for a submarine pipeline project.

Leak prevention in a threaded coupling is also dependent upon pipe dope, a high density compound used to seal the threads in the coupling. Thread compounds should conform to API Bulletin 5 A2, Thread Compounds for Casing, Tubing, and Line Pipe. Pipe compounds are subject to aging, however, and this can reduce the useful life of the pipeline from 5 to 10 years.

6.3.8.3 Rigid Bell and Spigot. The bell and spigot joint is traditionally employed only for concrete pipelines and is suitable for low pressure, large diameter intake and outfall pipelines. It has limited flexibility and typically can accommodate only 1 to 2 degrees of deflection at the joint. Steel bolts or other longitudinal reinforcement is generally required to increase the resistance of the joint to longitudinal pull-out.

63.8.4 Flexible Bell and Spigot (Ball and Socket). This joint is traditionally employed for submarine pipelines constructed of cast iron. It provides a reliable seal which can sustain pressures up to 250 psi. The flexible joint allows deflection up to 15 degrees in any direction.

6.3.9 Pipeline Stabilization Techniques

In deep water, it is common practice to design the pipeline such that the submerged weight of the pipeline is sufficient to prevent the pipeline from moving when sub jected to hydrodynamic loads. In shallow water, the hydrodynamic forces are generally so large that it is impractical to rely stricdy on pipeline submerged weight and an additional form of stabilization must be employed to restrain the pipeline. Submarine oil and gas pipeline are traditionally 44 weight coated" with a layer of high density (up to 200 lb/ft3) concrete when additional submerged weight is required. If additional stabilization is required beyond the weight coating, common techniques include:

• Anchoring: -Clump weights -Mechanical anchors

• Trenching: -Fluidization train -Air lift

-Mechanical trenchers -Submarine plow

Anchoring methods are employed only to increase the resistance of the pipeline to motion due to hydrodynamic forces. Trenching methods may be employed either to reduce hydrodynamic loads on the pipe (and thereby increase stability) or as a means of protecting the pipe against impact damage from dragging anchors or fishing gear.

Selecting a stabilization method is done on a case-by-case basis and depends on soil type, hazard type, length of pipeline to be protected, equipment requirements, and cost. Evaluation criteria to be considered when selecting a stabilization method are summarized in Table 6-8. Illustrations of typical stabilization equipment are shown in Figure 6-27.

Table 6-8. Stabilization Method Evaluation Factors

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