Cellulosic electrodes are often used for welding pipes in the field because they provide hydrogen control. Austenitic stainless steel electrodes are generally shorter than mild steel electrodes because their electrical conductivity is less than steel. The electrodes for welding low alloy steels should be one size larger than general purpose electrodes. Preheating applies to both assembly and tack welding. Preheating increases cooling and shrinkage stress by slowing the cooling rate after welding. Preheating and interpass heating are used primarily to reduce hydrogen content and slow the cooling rate through heating between weld passes.