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S690 structural steel

High strength, quenched and tempered fine-grain structural steel


With minimum yield strength of 690 N/mm2, this grade is intended for structural applications where weight savings is important and excellent welding properties remain. The major advantages ultimately can be found in the cost savings of the construction compared to S355 application.

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These physical properties makes S690 very appropriate for applications such as:

  • Crane construction: booms for mobile cranes
  • Components for offshore structures
  • Pressure vessels: fixed and transportable storage tanks, vessels
  • Mining equipment
  • Load-handling equipment and masts

Niron Staal Amsterdam has gained the required experience over the last years in building constructions and tools for offshore applications and crane components, using S690 grade steel. The experience goes as far as the metallurgical knowledge of the material in the heat effected zone of the welding seams. This knowledge has been gained in close cooperation with two of the Dutch major specialized companies in non-destructive testing and metallurgical laboratories.


For the proper welding of HSS grades such as S690, Niron Staal Amsterdam has invested in a facility which secures optimal welding conditions. It is important to guarantee the pre-welding temperature and the temperature during welding of the material at all times. Therefore drafts of cold air in the factory shall be avoided and the working space shall be a closed area. The condition of the surroundings can be controlled in this way and this will minimize welding costs and failure costs.


Design codes and Notified Bodies

Niron Staal is working according national and international standards (EN, AWS, ASME) and client specific requirements. Niron Staal is certified for ISO 9000:2008 and additionally works under the supervision of notified bodies (NOBO) such as:

  • Lloyd's Register
  • TUV
  • ABS
  • DNV
  • BV
  • Germanische Lloyd

PQR, WPS and welding documentation

Niron Staal has recognized the requirements in the market. The increasing demand of proper documentation is crucial for the production of these high standard steel structures. The documentation is delivered in close cooperation with the customer, classification society and test laboratory.

Test reports include full analyses of sharpy tests according ISO and ASTM, bend test, macro examination, and hardness survey.


Two Welding Engineers

In fabrication the welding and cold deformation of HSS can lead to weld defects and material deterioration resulting in reduced safety of the structure.

Besides our fully certified team of welders, Niron Staal provides the knowledge and support of two welding engineers, which are part of the Niron Staal welding team. Their expertise is used for the proper work preparation, welding procedures, monitoring and coaching of the welders.

It is of utmost importance for our welders to have the competence and discipline to meet the required procedures which have been developed for the specific work. Our foreman welders and welding engineers are well known with the specific material properties and they are well aware of the consequences of not following the procedures of for instance pre-heating. The discipline also involves the feed-back of eventual problems during welding which need to be resolved.

Welding properties, pre-heating and post weld heat treatment (PWHT)

S690 can be welded using all common manual and automatic welding processes.

The weldability is good.

Niron Staal always makes sure that moisture and other sources of hydrogen, such as grease, oil and other impurities, have been removed from the surface of the groove before welding.

The welding grooves can be bevelled either by machining or thermal cutting. Niron Staal is able to perform both methods in house. Obviously machining gives the best and most accurate geometry of the groove. Some of our customers prefer machining despite the price tag.

The need for preheating is determined mainly by the chemical composition of the steel and filler materials. Additionally, the combined plate thickness, heat input and hydrogen content of the welding consumables have to be taken into account.

A steep temperature differential occurs between the localized heat source and the cool base material being welded. This temperature difference causes differential thermal expansion and contraction and high stresses around the welded area. Reducing the temperature differential by preheating the base material will minimize problems associated with distortion and excessive residual stress. If preheating is not carried out, a large differential in temperature can occur between the weld area and the parent material. This can cause rapid cooling, leading to the formation of martensite and probable cracking when welding some materials with high hardenability.

Post weld heat treatment is mainly used to reduce the residual stresses after welding and other workshop fabrication. PWHT is not recommended for quenched and tempered high strength steels.

Storage of welding consumables

To eliminate the risk of cold cracking, the hydrogen content of the filler material must be kept as low as possible. The welding consumables must be protected against moisture during transport, storage and use, to avoid hydrogen absorption. Preferably they must be kept in a conditioned storage before use.

Niron Staal has invested in a conditioned storage in order to comply with the best standards.


Despite their high degree of strength, HSS steels such as S690 are easy to machine. However, some basic rules have to be observed when machining these high strength steels. Vibrations should be avoided. It is therefore advisable to work on a machine that is as rigid as possible, and to keep the gap between the workpiece and the machine(support) to a minimum. Sufficient cooling should be ensured. HSS steels can be machined using tools made of high-speed steel (HSS, TiN, TiCN) and tools with indexable inserts.


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