Technical FAQs

1. Sizes and Wall Thicknesses

Is there such a thing as standard dimensions for steel pipe outside diameters?
We have tabulated standard OD's for steel pipe as shown in Section Two of our manual; however, in many instances spiral weld steel pipe offers the flexibility to be manufactured to any specified OD.

What wall thicknesses and yield strengths are available from American SpiralWeld?
Generally, ASWP is capable of forming spiral weld-seam pipe with wall thicknesses up to 1.00-inch with specified minimum yield strengths up to 70,000 psi. However, this maximum thickness is difficult to form in smaller diameters; therefore, consult your AMERICAN Sales Engineer.

2. Field Welding

Do you have a standard procedure for the field welding of a lap-welded joint?
AWWA C206 should be utilized as a guide for field welding. It is typically the responsibility of the welding contractor/subcontractor to design the weld for a given set of performance parameters.

3. Joints and Joint Assembly

What are the standard joints offered by American SpiralWeld?
ASWP offers lap weld, butt weld, and rubber-gasketed joints, including O-ring and Carnegie joints. Additionally, various joint configurations are available to accommodate other connections. These include flange, Victaulic Depend-O-Lok ends, mechanical joint, et al.

Which way do I lay the bell end of the pipe when I am laying lap-welded joint pipe?
When laying lap-welded joint pipe, the spigots should be laid ahead. With this type of joint the bell is used as a hinge to assist in the assembly of the joint. Contact AMERICAN for details on this installation method.

Are special tools needed for a lap-welded joint?
As steel pipe is a flexible conduit, many contractors choose to have a hydraulic "porta-power" on site to occasionally assist in the jointing of two pipes. Others utilize a "spatula" type tool to assist in assembling the bell onto the spigot or plain-end. Finally, the welding personnel should have an adequate supply of small wedges to equalize the gap in the lap-welded bell immediately after assembly.

Do you have a standard procedure for the field welding of a rubber-gasketed joint?
When it becomes necessary to weld an O-ring gasketed joint for joints not within areas of restraint, after proper authorization, the contractor should place a 1-inch mild steel rod on the lead edge of the bell and apply two (2) circumferential welds of appropriate size. These welds should be applied between the lead edge of the bell and the 1-inch rod, and the spigot (or plain-end) and the 1-inch rod. This should effectively seal the joint. ASWP should be consulted when conditions require field welding of an O-ring joint.

Which way do I lay the bell end of the pipe when I am laying rubber-gasketed joint pipe?
Bells should be laid ahead when installing rubber-gasketed joint pipe. This method will allow for the centering of the spigot as it is engaged into the bell.

What special tools are needed for a rubber-gasketed joint?
Good practice should include a rounded-end screwdriver that should be used just prior to engagement of the spigot into the bell by passing the screwdriver under the gasket around the entire circumference. Additionally and most important, utilizing a feeler gauge to ensure complete penetration of the spigot, verify gasket placement, and verify "metal-to-metal" contact, is a requirement on all joints.

4. Installation - Deflection

What is the allowable deflection for various pipe linings and coatings?
As mentioned in AWWA M11, flexible coating and mortar lining has a deflection limit of 3%, flexible coating and lining has a deflection limit of 5%.

What is the best method for predicting pipe deflection due to external loading?
The Marston theory, taking a prism of soil above the pipe, should be used to calculate earth load, utilizing additional live loads from trucks, equipment and railway cars as necessary.

What is the standard procedure for re-rounding?
For pipe not yet bedded and backfilled: Pipe requiring and suitable for re-rounding (within the deflection limits) should be accomplished by blocking and jacking the pipe from the inside, taking caution to prevent lining damage. The jacking mechanism should remain in place until the joint is complete.

For pipe that is bedded and backfilled: It is suggested that the backfill material (overburden) be removed to about spring line to unload the pipe. Then the pipe needs to be rounded as noted above. After the pipe is properly re-rounded, it is recommended that the backfill be consolidated and compacted in the haunch area, and properly placed and compacted to at least 0.7D, as measured from the bottom of the pipe.

What is stulling, and how is it beneficial to steel pipe?
Stulling is usually made up of a single timber for smaller diameter pipe, or combination of multiple timbers or other rigid supports for larger diameter pipe. Stulling is generally installed in multiple sets, each set being placed at a strategic position along the pipes' interior. With the stulling tightly engaged, radially against the interior of a pipe section, the roundness of the pipe section can be maintained during transportation and handling.

Can I reinstall stulling once it has been removed?
Yes. Stulling can be replaced at any time; in fact, any pipe not yet laid that is observed without stulling should have them replaced prior to installation. In some instances where buried pipe has deflected, reinstallation of the stulling may not be easily accomplished, or possible at all.

When can I remove stulling from the pipe?
It is recommended that the stulling be removed after the backfill requirements have been met.

Is stulling designed to accommodate installation, compaction and backfill?
No, stulling is designed to maintain roundness during handling and transportation, and facilitate joint completion.

5. Buckling

How is the allowable buckling pressure for steel pipe calculated?
For unburied pipe in a fluid environment, the Stewart formula is utilized to determine buckling pressure (refer to M11, Section 4). Although history has shown that a properly installed and backfilled pipe will not buckle at full vacuum, industry standards for analysis of buckling conditions is defined in Section 6 of AWWA M11.

6. Installation - Bedding

Is there a standard for material and dimensions for bedding and backfilling a trench for steel pipe?
There are minimum recommendations outlined in Section 12.3 of M11. Care should always be taken to ensure backfill material and compaction efforts maintain the integrity of the pipe coating.

7. Linings and Coatings

What linings and coatings are available from ASWP?
Currently, ASWP offers cement-mortar lining and tape, polyurethane and various epoxy coatings.

How should cement-mortar-lined, tape-wrapped pipe be handled and stored on the job site?
Care should be taken to prevent damage to the tape coating. Good practice would include small dirt mounds between the pipe and ground to keep the lifting area of the pipe accessible. Furthermore, nylon straps should be utilized, and handling equipment should be sufficiently padded.

8. Lining and Coating Repair

What is the standard procedure for cement-mortar lining repair?
The procedure is outlined in section 4.4.6 of AWWA C205.

What defines coating damage that must be repaired?
There are two types of coating damage: superficial and that which results in a coating holiday. Analysis and subsequent repair of damage should be performed in accordance with the tape manufacturer's guidelines and repair procedure. Typically, this procedure would include cutting out only the damaged layer(s), applying a primer and replacing tape conforming to C209 with a 4" minimum overlap.

Do you have a written procedure for field tape repair?
We would furnish a written procedure obtained from the tape manufacturer.

9. Joint Lengths

What are the standard lengths offered by American SpiralWeld?
ASWP can furnish hydrostatically tested pipe in lengths up to 50', un-hydrostatically tested pipe in lengths up to 80'.

What determines the maximum joint length that can be laid in the field?
The maximum joint length should be determined by considering field limitations for installation such as trench box length and equipment-handling capacities.

10. Corrosion

Is there a standard or recommendation for corrosion control or monitoring for steel pipe?
All steel pipelines constructed with lap-welded joints are inherently electrically continuous, and those constructed with rubber-gasketed joints should have the joints bonded to facilitate pipeline monitoring. We would recommend that, if the Owner and Engineer have determined, through field testing and/or experience, that in addition to the specific coating system, electrically continuous pipeline, and monitoring system, that cathodic protection will be needed, then a corrosion engineer should be secured. This corrosion engineer would be responsible for the design of both the monitoring system and the recommended testing program with the necessary protocol, and also the cathodic protection system.