Stress relieved on stainless steel tube

[roniprabowo]

Dear fellow,
I have SA-213 TP304L U tube with boiler feed water service. I have indicated that these tubes shall be stress relieved with holding temp: 1050-1100 C, holding time : 10 - 20 second and rapid cooling.
My questions are :
1. Is there any difference between water and compressed air cooling media in stress relieved result ?
2. Where can I find the requirement for holding time ? Is it in the ASME II or ASTM ?
3. Is there any mandatory test after stress relieved ?

Looking forward for your information.

 

[metengr]

Working in the Power industry and having purchased HP and LP feedwater heaters with 3XXL ss tubing,the following are answers to your questions;

1. Typically, u-bends are made in the feedwater heater fab shop and are solution annealed in a fixture that has a portable heating element. Air cooling is used and is adequate.

2. The dwell time for heating U-bends is based on uniform wall temperature of the tubing. Since the tubing is relatively thin and most feedwater heater shops have been performing this operation for many years, dwell time for heating is a well established practice.

3. For our feedwater heater contracts we have required several U -bends on each job to undergo laboratory (destructive) testing to assure adequate solution anneal of u-bends (microhardness testing and microstructure evaluation) and to assure there are no defects in the extrados or intrados of the tube bend.