Filler passes that are deposited on heavy-wall pipes used in cross­country pipelines are welded by using stringer bead sequences. On the next page the diagram shows that the first three passes are single layer deposits, each extending across the bevel. The second diagram shows all the completed sequences.

Pipeline welds that use the stringer sequences often lack fusion on the bevel surface, Actually, this is often because welders fail to maintain the interpass temperature, which assists in having a fluid puddle.

However, the direction is downwards, and the puddle has the tenden­cy to run or sag in a downward direction. Therefore, welders have to use their wrists, not their entire arms. They should turn their wrists so that they are pointing the electrode as shown in Fig. 8-33A. Then they will be able to have the puddle wash-up on the face of the bevel more effec­tively each time the stringer bead is deposited, as shown in Fig. 8-34B.

This technique also removes any possibilities of having deep crevices. Such crevices are not easily corrected, even by depositing a bead with a very high current. The proper method for correcting such a problem is to use a grinder to slightly widen or open the crevice, then deposit a stringer bead, with the electrode slightly pointing toward the face of the bevel. This technique is veiy important for avoiding deep crevice altogether, See Fig 8-35 С above.

The term stringer bead has different meanings in different situations. For example, it may be used with a bead on plate test, when a stringer bead is deposited on the plate as straight as possible. Or, when hard - facing certain steel, the alloying element that is used in the core wire or the electrode coating should enter the weld and remain as hard parti­cles, with limited dilution to the base metal. The hard particles become densely clustered, offering the effects of a hard surface for the purpose for which it was intended. By applying this metal using a stringer bead—with a heat value slightly above the brazing temperature—the welding is a straight line deposit, with no indication of a free puddle washing up at the edges from side to side. However depositing the stringer bead in pipe welding, the welder must see a definite indication of the puddle washing up to the sides of the groove, and a gradual tran - sition along the edges of the weld, as shown in Fig. 8-36D. Using the

stringer bead, welders need to use a slight oscillation when traveling downhill in order to achieve a homogeneous blending at the edges, and prevent peaks and valleys in situations when a few stringers are deposited side by side in such cases, the welding procedure can be adjusted to provide a higher heat input to the joint or preheat the joint area to a safe temperature.

Welders who are properly trained will be able to complement the pro­cedure, Therefore, they must be aware that the many adjustments they make instantaneously control many variables. Failure of a pipe weld is not always imminent, but success depends on the welder’s ability to make adjustments at the right time.

Pipe welding crews move quickly, and have very little room for errors. But consideration must be given to the added activities that sur­round welding of higher strength piping, in accordance with the API - 1104 Code. Procedure must also conform to the involvement of pre­heating and interpass temperature. Good quality welds are not the only requirement; preheating and interpass temperature are equally impor­tant to achieving the required toughness.

The high-strength, low-alioy pipe for gas and all pipelines requires preheating before welding is started. Preheating must be exercised uni­formly where heat is applied by two heating burners, one on either side, and operated manually around the circumference, allowing the outer and inner walls to be brought up to the required temperature evenly in order to avoid stress.