Section Three: Joints

SP IRALWELD P IPE

AMERICAN offers a variety of steel pipe joints to meet the designers needs, allowing the designer to select the most effective joint type(s) for the projects installation and performance requirements. The joint type is generally identified as one of the following: field welded, bell and spigot O-ring gasket, flange, or coupling.

Field Welded JointsField welded joints are available for all diameters and wall thicknesses of AMERICAN pipe. These joints are generally used where restraint of longitudinal thrust is required for buried pipe. In addition, some specifiers prefer to use field welded joints throughout an entire piping system in lieu of a system including both gasketed and welded joints.

Field welded joints do not allow for in-service flexibility, but they can accommodate, during installation, deflections that are generally larger than those for O-ring gasket joints. Field welded joints can be supplied as bell and spigot lap type, butt strap type, and butt weld type. Requirements for field welded joints are defined in the AWWA standard for field welding, C206.

Although each joint type employs welding in some manner, the manufacturing process, assembly, and performance limitations differ.

Lap Weld (24 - 144) The bell and spigot lap weld joint has a proven performance history in steel pipe. It is an economical method for restraining longitudinal thrust in buried pipes. Lap weld joints can be configured for welding inside only, outside only, or both when design conditions dictate. A single full fillet weld is adequate for restraint of longitudinal thrust forces due to internal pressure. Conditions involving other longitudinal forces such as from thermal stress, Poissons ratio of hoop stress, or bending stress require additional consideration. Consult an AMERICAN representative when presented with such conditions.

The joint can be configured for welding after backfill of the installed pipe. This configuration is generally used for joints employing a single inside fillet weld. The installation of pipe, exterior joint wrapping, and trench backfilling can progress uninterrupted by the welding process, which takes place after consolidated fill has been placed to at least one foot over the top of the pipe. This process improves installation efficiency and reduces project costs. It also significantly reduces the level of longitudinal thermal stress in the steel cylinder, as the steel can achieve thermal equilibrium

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with the surrounding soil prior to welding. The weld after backfill method can be employed on joints requiring a fillet weld both inside and outside, but the cost benefit is less significant and the reduction in thermal stress would not be achieved.

Lap weld joints offer flexibility for varying installation conditions. Alignment correction can be achieved by providing field trim at strategic locations such as major horizontal or vertical alignment changes, connections to existing pipes, specific appurtenance placements, connections to pipes at structures, and closures. In areas where post-installation access is difficult or undesirable, such as inside casings, tunnels, or encasements, the joint can be configured for the application of one full structural fillet weld, one seal weld, and an air test hole. The joint can then be tested to assure that the structural weld is watertight prior to installation. When required, the joint also can be configured to function as a temperature control joint. Refer to AMERICANs Field Service guide for assembly recommendations for a lap weld joint.

ManufactureA lap weld joint consists of a bell and spigot integrally formed into the parent cylinder, without the use of separate, welded-on joint rings. The parent cylinder steel is formed beyond its elastic limit to exacting tolerances to form the bell, and, when necessary, to size the spigot. The tolerances are small to maintain a tight fit between the outside of the spigot and the inside of the bell to minimize the weld and eccentricity of the joint. The joint is configured to provide a minimum engagement equal to the smaller of 1 plus the design joint pull, or 3 times the thickness of the bell plus the design joint pull. Additional engagement can be accommodated in instances where the joint will be used as a temperature control joint. The bell and spigot are generally formed prior to hydrostatic testing. When expansion takes place after the parent cylinder has been hydrostatically tested, the weld seams in the formed section of a bell or spigot are nondestructively examined visually (VT) and by the magnetic particle method (MT).

Angular Joint DeflectionA lap weld joint can be disengaged on one side, commonly referred to as deflecting or pulling, to accommodate small alignment changes and curves required for installation. AMERICAN recommends a maximum design pull of 1 for all pipe sizes. Where additional deflection is required, weld bell pipe ends can be miter-cut prior to expansion. Such miter-cut ends are generally limited to approximately 5. Consult an AMERICAN representative regarding specific miter-cut bell limitations. The angular deflection for a 1 joint pull and the resulting minimum radius for a pulled joint curve installation are computed as follows:

Angular Deflection, Q = tan-1(joint pull/pipe O.D.) Minimum curve radius = [(pipe length)/2]/sin(Q/2)

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NominalDiameter

(in.)

Angular Deflection

Q(degree)

JointPull(in.)

Offset per50 Length

(in.)

Radius ofCurve*

(ft)

Max. MiteredDeflectionAngle** (degree)

Max. Offset per 50 Length

(in.)

Radius ofCurve*

(ft)

24 2.26 1.00 23.65 1270 5.00 52.23 570

30 1.83 1.00 19.12 1570 5.00 52.23 570

36 1.53 1.00 16.00 1880 5.00 52.23 570

42 1.31 1.00 13.71 2190 5.00 52.23 570

48 1.15 1.00 12.06 2,49 5.00 52.23 570

54 1.03 1.00 10.76 2790 5.00 52.23 570

60 0.93 1.00 9.72 3090 5.00 52.23 570

64 0.87 1.00 9.11 3290 5.00 52.23 570

66 0.84 1.00 8.84 3390 5.00 52.23 570

72 0.77 1.00 8.08 3710 5.00 52.23 570

78 0.72 1.00 7.50 4000 5.00 52.23 570

84 0.66 1.00 6.96 4310 5.00 52.23 570

90 0.62 1.00 6.50 4610 5.00 52.23 570

96 0.58 1.00 6.09 4930 5.00 52.23 570

102 0.55 1.00 5.74 5230 5.00 52.23 570

108 0.52 1.00 5.43 5530 5.00 52.23 570

114 0.49 1.00 5.14 5830 5.00 52.23 570

120 0.47 1.00 4.89 6130 5.00 52.23 570

126 0.45 1.00 4.66 6440 5.00 52.23 570

132 0.43 1.00 4.45 6740 5.00 52.23 570

138 0.41 1.00 4.26 7040 5.00 52.23 570

144 0.39 1.00 4.09 7340 5.00 52.23 570

Based on a 1 pull, the resultant angular deflections and associated minimum curve radii based on these angular deflections are as shown below.

Lap Weld JointDeflection Table

* Curve radius shown is directly proportional to pipe length. Use of shorter pipe lengths will result in a proportionally smaller radius. For example, if the radius using 50 long pipes is 1690, then the radius using 25 long pipes will be approximately 845.** Angle shown is the maximum possible as a combination of miter cut and joint deflection. Mitered lap joints can be furnished at resultant angles between approximately 0.5 and 5.0 .

Butt Strap (4 - 144) The butt strap joint is an economical method for connecting two butting pipe ends at closures, post-installation access points, and repair areas. The straps are generally furnished in two halves that are assembled around the butting pipe ends and fillet welded in place. The strap can be fillet welded inside only, outside only, or both inside and outside. In instances where butt straps are to be welded both inside and outside, each half of the strap can be furnished with air test holes to facilitate pneumatic testing of the finished fillet welds. This is especially beneficial at closures completed after the installed pipe has been hydrostatically tested. In addition to the circumferential fillet welds, this configuration requires two longitudinal complete-joint penetration welds where the two strap halves meet.

Angular Joint Deflection

Butt strap joints are typically located in areas where the two butting pipes are on the same slope. Designed deflections in this type joint are rare, but are acceptable, as are installed joint deflections, as long as gap tolerances between the strap and the pipes are maintained in accordance with the requirements for bell and spigot lap weld joints as defined in AWWA C200 and AWWA C206.

Butt Joint (4 144) The welded butt joint can be furnished in any diameter or wall thickness and is suggested for exposed joints that will be subject to excessive bending, in-service thermal cycling, or vibration. Most steel pipe installed using horizontal directional drilling (HDD) methods are furnished with butt joints.

The joint can be welded from either the inside or outside, or from both sides. Single welded butt joints can be furnished with or without backing. Backing assists in placement of a sound root pass. Backing also aids in aligning pipe ends during assembly and welding, although it limits joint deflection. Design joint deflections are accomplished by miter cutting one or both ends of the mating pipes. Miter cutting only one pipe end is acceptable as long as the assembled joint between the resulting ellipse of the cut end and the mati