The Importance of Pre-Weld Heating

Pre-Weld Heating
Pre-heating and metal prep before welding a large section of pipe.
The process of pre-heating steel prior to welding is important to understand. In general, there are two primary reasons to heat treat prior to welding.

First, it increases the temperature of the target material, resulting in a controlled (slower) cooling rate of the target material, as well as that of the weld. Thicker areas of steel, typically 1/2 inch or greater, and high-strength low-alloy steels (HSLA) are prone to the formation of weakened crystalline microstructures if the weld cools too quickly. These weakened crystalline microstructures are called martensite.  Martensite is a steel crystalline structure critical to the steel's hardness and strength; too much martensite leaves steel brittle; too little leaves it soft.

When welding, martensite can form in the newly deposited weld metal, the base target material, or
the HAZ (heat-affected zone). Applying the proper amount of pre-heat prior to welding will assist in preventing the formation of martensite. Pre-heat temperatures and soak times are dependent on the target materials type, thickness, grade, and carbon equivalency. There is ample temperature and time pre-heat information available on the Internet and from industry associations, and one should refer to this information prior to welding.

Pre-Weld Heating
Ceramic mat heaters used to pre-heat pipe spool piece.
Second, preheating also results in the elimination of condensation (moisture) prior to the welding procedure. The presences of moisture is problematic because the water will change phase (from liquid to gas) during welding. This phase change can releases trace amounts of hydrogen, and lingering hydrogen can be absorbed into the weld. When hydrogen molecules are trapped in the newly welded metal, they affect the metals grain boundaries and impose a risk of higher weld failure. As a result, removing moisture before welding is strongly recommended.

Uniformly preheating the target material prior to welding, and then insulating the target area after welding, provides an adequate cooling rate allowing hydrogen to diffuse out of the weld joint, preventing hydrogen cracking.

For more information about the equipment and processes required for weld pre-heating, contact Hotfoil-EHS, a world leading manufacturer of heat treatment equipment. They can be reached by calling 609-588-0900 or visit their web site at https://hotfoilehs.com.

US Power Grids, Oil and Gas Industries, and Risk of Hacking


A report released in June, from the security firm Dragos, describes a worrisome development by a hacker group named, “Xenotime” and at least two dangerous oil and gas intrusions and ongoing reconnaissance on United States power grids.

Multiple ICS (Industrial Control Sectors) sectors now face the XENOTIME threat; this means individual verticals – such as oil and gas, manufacturing, or electric – cannot ignore threats to other ICS entities because they are not specifically targeted.

The Dragos researchers have termed this threat proliferation as the world’s most dangerous cyberthreat since an event in 2017 where Xenotime had caused a serious operational outage at a crucial site in the Middle East. 

The fact that concerns cybersecurity experts the most is that this hacking attack was a malware that chose to target the facility safety processes (SIS – safety instrumentation system).

For example, when temperatures in a reactor increase to an unsafe level, an SIS will automatically start a cooling process or immediately close a valve to prevent a safety accident. The SIS safety stems are both hardware and software that combine to protect facilities from life threatening accidents.

At this point, no one is sure who is behind Xenotime. Russia has been connected to one of the critical infrastructure attacks in the Ukraine.  That attack was viewed to be the first hacker related power grid outage.

This is a “Cause for Concern” post that was published by Dragos on June 14, 2019

“While none of the electric utility targeting events has resulted in a known, successful intrusion into victim organizations to date, the persistent attempts, and expansion in scope is cause for definite concern. XENOTIME has successfully compromised several oil and gas environments which demonstrates its ability to do so in other verticals. Specifically, XENOTIME remains one of only four threats (along with ELECTRUM, Sandworm, and the entities responsible for Stuxnet) to execute a deliberate disruptive or destructive attack.

XENOTIME is the only known entity to specifically target safety instrumented systems (SIS) for disruptive or destructive purposes. Electric utility environments are significantly different from oil and gas operations in several aspects, but electric operations still have safety and protection equipment that could be targeted with similar tradecraft. XENOTIME expressing consistent, direct interest in electric utility operations is a cause for deep concern given this adversary’s willingness to compromise process safety – and thus integrity – to fulfill its mission.

XENOTIME’s expansion to another industry vertical is emblematic of an increasingly hostile industrial threat landscape. Most observed XENOTIME activity focuses on initial information gathering and access operations necessary for follow-on ICS intrusion operations. As seen in long-running state-sponsored intrusions into US, UK, and other electric infrastructure, entities are increasingly interested in the fundamentals of ICS operations and displaying all the hallmarks associated with information and access acquisition necessary to conduct future attacks. While Dragos sees no evidence at this time indicating that XENOTIME (or any other activity group, such as ELECTRUM or ALLANITE) is capable of executing a prolonged disruptive or destructive event on electric utility operations, observed activity strongly signals adversary interest in meeting the prerequisites for doing so.”

Differences Between Arc Welding Processes

Arc welding processes are based on fusion. Fusion requires closeness and cleanliness at the atomic level, both of which can be achieved by shielding the molten puddle with gas or slag. There are several types of arc welding processes as follows:

Shielded Metal Arc Welding (SMAW)

An electric arc is produced between the end of a coated metal electrode and the steel components to be welded (Figure 1). The electrode is a filler metal covered with a coating. The electrode’s coating has two purposes:
  1. It forms a gas shield to prevent impurities in the atmosphere from getting into the weld, and 
  2. It contains a flux that purifies the molten metal.
SMAW is almost exclusively a manual arc welding process. Because of its versatility and simplicity, it is particularly dominant in the maintenance and repair industry. The most common quality problems associated with SMAW include weld spatter, porosity, poor fusion, shallow penetration and cracking.
Figure 1: Shielded Metal Arc Welding (SMAW) 



Gas Metal Arc Welding (GMAW)

Gas Metal Arc Welding (GMAW) is fast and economical. As shown in Figure 2, a continuous wire is fed into the welding gun. The wire melts and combines with the base metal to form the weld. The molten weld metal is protected from the atmosphere by a gas shield that is fed through a conduit to the tip of the welding gun. The process may be semi- automatic or automated. It cannot be used in a windy environment as the loss of the shielding gas from air flow will produce porosity in the weld.
Figure 2: Gas Metal Arc Welding (GMAW)


Flux Cored Arc Welding (FCAW)

Flux Cored Arc Welding (FCAW) is similar to the GMAW process and is usually performed by semi/full automatic methods. The difference is that the filler wire has a center core that contains flux (see Figure 3). With this process it is possible to weld with or without a shielding gas, which makes it useful for exposed conditions where a shielding gas may be affected by the wind.
Figure 2: Flux Cored Arc Welding (FCAW)


Submerged Arc Welding (SAW)

Submerged Arc Welding (SAW) is usually performed by semi/full automatic or handheld methods. As shown in Figure 4, it uses a continuously fed filler metal electrode. The weld pool is protected from the surrounding atmosphere by a blanket of granular flux fed at the welding gun. It results in a deeper weld penetration than the other processes. However, only flat or horizontal positions may be used.
Figure 4: Submerged Arc Welding (SAW)



Process Selection

Selection of the welding process is typically left to the contractor. The characteristics of the various processes are:
  • SAW: long, big, semi/full automatic or handheld methods.
  • FCAW: semi/full automatic methods.
  • SMAW: small, miscellaneous, repair, tack welds and handheld method.
  • GMAW: semi/full automatic methods in shop.
https://hotfoilehs.com  |  609.588.0900 

Reprinted from the Michigan Department of Transportation Field Manual for Structural Welding.

Welding Terminology

    Welding Terminology
  • Arc Welding – A welding process that produces a coalescence of metals by heating them with an electric arc.
  • Arc Welding Electrode – A part of the welding system that conducts current and ends at the arc.
  • Back Gouging – The removal of weld and base metal from the other side of a partially welded joint. The objective is to assure complete penetration upon subsequent welding from that side.
  • Backing – A piece of material placed at the root of a weld joint for the purpose of supporting molten weld metal.
  • Base Metal – The metal to be welded.
  • Bevel – An angled edge preparation.
  • Butt Joint – A joint between two members lying in the same plane.
  • Complete Fusion – Fusion over the entire fusion faces and between all adjoining weld beads.
  • Complete Joint Penetration – A groove weld condition in which weld metal extends through the joint thickness.
  • Defect – A discontinuity or discontinuities that, by nature or accumulated effect (for example, total crack length or amount of porosity), renders a part or product unable to meet minimum applicable acceptance standards or specifications.
  • Depth of Fusion – The distance that fusion extends into the base metal or previous bead from the surface melted during welding.
  • Facing Surface – The surfaces of materials in contact with each other and joined or about to be joined together.
  • Filler Material – The material to be added in making a welded, brazed, or soldered joint.
  • Fillet Weld – A weld of approximately triangular cross section that joins two surfaces approximately at right angles to each other in a lap joint, T-joint, or corner joint.
  • Flat Welding Position – A welding position where the weld axis is approximately horizontal and the weld face lies in an approximately horizontal plane.
  • Flux – Material used to prevent, dissolve, or facilitate removal of oxides and other undesirable surface substances.
  • Flux Cored Arc Welding (FCAW) – An arc welding process that produces coalescence of metals by means of a tubular electrode. Shielding gas may or may not be used.
  • Fusion – The melting together of filler metal and base metal, or of base metal only, to produce a weld.
  • Gas Metal Arc Welding (GMAW) – An arc welding process where the arc is between a continuous filler metal electrode and the weld pool. Shielding from an externally supplied gas source is required.
  • Gas Tungsten Arc Welding (GTAW) – An arc welding process where the arc is between a tungsten electrode (non-consumable) and the weld pool. The process is used with an externally supplied shielding gas.
  • Groove Weld – A weld made in a groove between two members.
  • Heat-Affected Zone (HAZ) – That section of the base metal, generally adjacent to the weld zone, whose mechanical properties or microstructure have been altered by the heat of welding.
  • Hot Crack – A crack formed at temperatures near the completion of weld solidification.
  • Incomplete Fusion – A weld discontinuity where fusion did not occur between weld metal and the joint or adjoining weld beads.
  • Incomplete Joint Penetration – A condition in a groove weld where weld metal does not extend through the joint thickness.
  • Interpass Temperature – In a multi-pass weld, the temperature of the weld area between passes.
  • Joint – The junction of the edges of members that are to be joined or have been joined.
  • Lap Joint – A joint type in which the non-butting ends of one or more workpieces overlap approximately parallel to one another.
  • Leg of Fillet Weld – The distance from the root of the joint to the toe of the fillet weld.
  • Metal Cored Arc Welding – An arc welding process with a tubular electrode where the hollow electrode contains alloying materials.
  • Metal Cored Electrode – A composite tubular electrode consisting of a metal sheath and a core of various powdered materials, producing no more than slag islands on the face of the weld bead. External shielding is required.
  • Peening – The mechanical working of metals using impact blows.
  • Plug Weld – A circular weld made through a hole in one member of a lap or T-joint.
  • Porosity – A hole-like discontinuity formed by gas entrapment during solidification.
  • Post Weld Heat Treatment (PWHT) – Any heat treatment subsequent to welding.
  • Preheating – The application of heat to the base metal immediately before welding, brazing, soldering, thermal spraying, or cutting.
  • Preheat Temperature – The temperature of the base metal immediately before welding is started.
  • Procedure Qualification Record (PQR) – The demonstration that the use of prescribed joining processes, materials and techniques will result in a joint exhibiting specified soundness and mechanical properties.
  • Reinforcement – Weld metal, at the face or root, in excess of the metal necessary to fill the joint.
  • Root Opening – A separation at the joint root between the work pieces. Root Crack – A crack at the root of a weld.
  • Self-Shielded Flux Cored Arc Welding (FCAW-S) – A flux-cored arc welding process variation in which shielding gas is obtained exclusively from the flux within the electrode.
  • Shielded Metal Arc Welding (SMAW) – A process that welds by heat from an electric arc between a flux-covered metal electrode and the work. Shielding comes from the decomposition of the electrode covering.
  • Shielding Gas – Protective gas used to prevent atmospheric contamination.
  • Submerged Arc Welding (SAW) – A process that welds with the heat produced by an electric arc between a bare metal electrode and the work. A blanket of granular fusible flux shields the arc.
  • Tack Weld – A temporary weld used to hold parts in place while more extensive, final welds are made.
  • Tensile Strength – The maximum stress a material subjected to a stretching load can withstand without tearing.
  • Weld Bead – The metal deposited in the joint by the process and filler wire used.
  • Welding Leads – The work piece lead and electrode lead of an arc welding circuit.
  • Weld Metal – The portion of a fusion weld that has been completely melted during welding.
  • Weld Pass – A single progression of welding along a joint. The result of a pass is a weld bead or layer.
  • Weld Pool – The localized volume of molten metal in a weld prior to its solidification as weld metal.
  • Weld Puddle – A non-standard term for weld pool.
  • Welding Sequence – The order in which weld beads are deposited in a weldment.

Reprinted from the Michigan Department of Transportation Field Manual for Structural Welding.