T22 Type IV Cracking & Post Weld Treatment
T22 Type IV Cracking & Post Weld Treatment
(OP)
For T22 material, according to ASME Section I Table PW-39, it is not necessary to post weld heat treat provided a minimum pre-heat of 300 F is used along with a few other requirements.
My concern is if the lack of post weld heat treatment in this case will adversely affect the resistance to Type IV cracking. In other words, will the failure rate be higher or the same if the joint is not post weld heat treated.
Tubing is used in a HRSG. We are trying to avoid post heat treatment if at all possible. ASME says it is OK but we want to make sure we dont have problems down the road.
Can anyone help?
thanks,
Alex
My concern is if the lack of post weld heat treatment in this case will adversely affect the resistance to Type IV cracking. In other words, will the failure rate be higher or the same if the joint is not post weld heat treated.
Tubing is used in a HRSG. We are trying to avoid post heat treatment if at all possible. ASME says it is OK but we want to make sure we dont have problems down the road.
Can anyone help?
thanks,
Alex





RE: T22 Type IV Cracking & Post Weld Treatment
RE: T22 Type IV Cracking & Post Weld Treatment
The European Creep Collaborative Committee (ECCC) has done extensive work into identifying a threshold bending stress that results in Type IV creep damage. It is my opinion that the reason for the increased susceptibility and reports of problems with the advanced ferritic materials, like Grade 91, is that designers take advantage of the higher allowable stresses to reduce wall thickness but don’t go beyond this to evaluate in service thermal/mechanical bending stresses.
Unfortunately, thinner wall components can also be subjected to much higher thermal/mechanical bending stresses at structural attachments (hangers) and at nozzle penetrations. The thinner wall components must be evaluated in terms external flexibility during design. The work horse alloys like T11 and T22 have been used successfully for many, many years in boiler construction partly because these alloys are more forgiving (as mentioned in the previous post) and have much lower allowable stress values, which means thicker wall components.
RE: T22 Type IV Cracking & Post Weld Treatment
make sure you meet these requirements, especially if you are near the headers. additionally, i suggest any preheat be done by controlled means and not temp sticks/torch.
RE: T22 Type IV Cracking & Post Weld Treatment
Also thanks eyec for the suggestion near the headers
Alex