Please contact your local Postle Representative or Technical Center for any information on proper weld parameters.
Managing the heat of the welding process is absolutely critical during the hardbanding procedure. Proper pre-heating and slow cooling will assist the weld metal and the base material (tool joint, tubing upset, or other downhole tool) through their metallurgical transition during the high heat and subsequent cooling process.
Pre-Heating
Pre-heating helps prevent cracks from occurring in the heat affected zone (HAZ), which is the zone directly below and adjacent to the weld bead. The HAZ is created as a result of the arc welding process and consists of the base metal, not the hardbanding alloy. This area cools most rapidly while undergoing important changes in its metallurgical structure and properties that may lead to cracking. The hardness of the HAZ is particularly important because if it is too hard, a crack in the hardbanding could potentially penetrate into the base metal and perhaps lead to failure of the connection. Typically, a hardness of 40 Rc is the maximum recommended in the HAZ region. In order to manage the hardness of the
HAZ, the pre-heat temperature should be adjusted in order to achieve an interpass temperature of approximately 800°F (430°C). The pre-heat must be a “soak heat” (see side column), meaning the heat has penetrated through the entire wall thickness. The interpass temperature is the temperature adjacent to the weld immediately after welding is concluded.
Pre-heating also minimizes shrinking stresses and enhances diffusion of hydrogen from the steel. Improper diffusion of hydrogen can lead to hydrogen embrittlement which can cause cracks.
Slow Cooling
It is imperative that the hardbanded tubular is immediately covered regardless of the temperature or weather conditions. We recommend keeping the hardbands covered to slow cool at an average rate of 50°/hour.
5 Key Points of Proper
Heat Management.
1) The proper pre-heat
temperature for drill pipe is
based upon the diameter of
the connection. Hardbanding
manufacturers
publish charts of pre-heat
temps. versus diameter.
2) Pre-heat temperatures
should reach a soak heat.
The soak heat temperature
is defined as no more than a
50° drop measured at the
surface of the heated area
over a period of 4 minutes
after the heat source is
removed.
3) Slow cooling can be
achieved by using cooling
cans, Hardbanding
Solutions Insulator Bags, or
other forms of insulation
material.
4) Inclement weather should
be avoided. Unless
preparations, welding and
cleanup take place in a
covered area, no welding
should be performed in rain,
freezing rain, snow, sleet, or
any weather that could
affect proper pre-heating or
slow cooling measures.
5) Controlling the HAZ
hardness values is critical to
the performance of the pipe,
tube, or downhole tool.
