Page 22 - SSAB Welding Handbook Edition 2

©2009-2019 by SSAB Group of companies (SSAB). All rights reserved. Only digital PDF file. No distribution. No printing allowed!
No part of this handbook may be reproduced in any form or by any means without permission in writing from SSAB.
4.0 Hydrogen cracks Welding handbook

Welding environment issues There is a natural driving force to equalize these
concentration differences of hydrogen heat. Heat in
Contaminates present in the weld area can often form of preheating accelerates this process.
contain hydrogen. Consequently, it is important to
keep the joint clean prior to and during welding. The rate at which hydrogen diffuses from the weld
Substances like water, oil and grease should be metal in a solid state and from the HAZ rises with
removed from the joint before welding. Also, make increased temperatures.
sure that the welding equipment is working properly so
that it does not add additional hydrogen to the joint. An important function of preheating is to slow down
Welding in a humate climate can also cause hydrogen the cooling time significantly between 400ºC and
pick-up. At these situations, a preventive measure is 200ºC. This effect is exemplified in the following two
mentioned in chapter 4.5.
cases presented in fig. 4.3. The welding conditions,
including the type of joint being welded, are the same
in both cases, with the exception that preheating is
Hydrogen presence in the steel and its only performed in case 2.
primer

Steels themselves contain hydrogen to some extent.
The Hardox and Strenx grades are manufactured in a
manner that results in very low levels of hydrogen in 1600
1400
the plates. ©SSAB Case 1: Preheat
1200
temperature: +20°C
When the shop primer is left on the joint, it Temperature [°C] 1000 Case 2: Preheat
800
contributes to a slightly increased fraction of 600 temperature +100°C
hydrogen in this section joint. However, the hydrogen 400
from the primer is at such a low level that it does not 200 0
influence the recommendations from SSAB for the 0 200 400 600
prevention of hydrogen cracks. Time [s]

Case 1 Case 2
4.5 Preheat temperatures during Type of joint Single-V butt joint Single-V butt joint
welding of the Hardox and Strenx Pt* 5 mm 5 mm
grades Q 0,8 kJ/mm 0,8 kJ/mm
Welding process MAG MAG
Preheating is necessary in some situations to remove t 8/5 16 s 23 s
hydrogen from the joint and minimize the risk for Preheat temperature 20°C 100°C
hydrogen cracks.
*Plate thicknesses throughout the joint.
The hydrogen content is, as mentioned before, higher Fig. 4.3: The thermal cycles in the joint due to welding with and
in the weld metal than in the parent metal. Preheating without preheating. The location in the HAZ is situated closest to the
weld metal.
facilitates a more rapid migration of the diffusible
hydrogen from the weld metal, via the HAZ, to the
unaffected parent metal as well as the air surrounding
the joint. The direction of the hydrogen diffusion is
determined by the differences of hydrogen
concentration in the joint compared to that in the
unaffected parent metal and the surrounding air.

22 This handbook contains general suggestions and information without any expressed or implied warranty of any kind. SSAB hereby expressly disclaims
all liability of any kind, including any damages, in connection with the use of the information and for their suitability for individual applications.
It is the responsibility of the user of this brochure to adapt the recommendations contained therein to the requirements of individual applications.