Page 406 - Pipelines and Risers

Use of High Strength Steel 373

19.3.2 Field Welding Project Experience
Onshore capabilities for mechanized and manual welding have been demonstrated by the
projects listed in Table 19.4, specific details are given in Chaudhari et al. (1995), Graf et al.
(1993).

Manual Welding
The quality requirements of the Mega1 11 and Ruhrgas lines required development of a
welding procedure to overcome concerns over cold cracking of the high strength weld metal
during conventional vertical-down welding with cellulosic electrode. The technique adopted
used conventional cellulosic electrodes for the root and hot passes and basic electrodes for the
fill and cap passes. The root was welded with an under-matched consumable, whilst over-
matched consumables were used for the fill. All welding was downhill.

Pass Consumable
Trpe I AWS Designation I Diameter(mm)
Root Pass cellulosic I E6010 4
Hot pass C e 11 u 1 os i c E9010-G 5
Filler passes Basic E10018-G 4.4.5
Cap passes Basic E10018-G 4

It should be noted that downhill welding is the norm for pipelines, at least outside of Japan,
because it is fastest overall. Downhill is conventionally used with cellulosic electrodes which
have a finite moisture content and are therefore not ‘low hydrogen’ but can be used on
conventional linepipe steels when other suitable precautions are taken to prevent hydrogen
cracking. Apart from pipelines, downhill welding is regarded as a poor practice for high
quality welding and so it appears that the Japanese uphill practice is more cautious.

High strength steels and weld metals are more sensitive to hydrogen cracking. They cannot be
reliably welded with cellulosic electrodes and so ‘low hydrogen’ consumables are required
such as basic electrodes which are normally used in the uphill practice as per Japanese
practice. It appears that cellulosic electrodes were used vertical down on the Ruhrgas line but
only after 2 weeks special training of welders.

This approach allowed conventional welding of the first two passes without loss of
productivity or risk of cold cracking. Chaudhari et al. (1995) states that the use of basic
electrodes caused only a small loss of productivity for the subsequent passes. This is based on
an overall welding cycle time of 5 - 6 hours which includes 3.3 hours for moving equipment
between joints, setting up, etc. If only the welding time is considered Chaudhari et al. (1995)
shows the time to complete a joint was 103 minutes using cellulosic electrodes (for all passes)
compared with 137 minutes using basic, low hydrogen electrodes. At 33%, the increased
welding time is significant and a consequence of requiring the improved mechanical