PWHT below 595 deg C

[WE17]

Dear ALL
I have some case regarding PWHT. I do pwht for vessel with procedure according to ASME IIIV ucs 56. we have 4 Thermocouple put in the vessel. Unfortunately 1 Thermocouple touch 590 deg C. Since we know minimum Temperatur allow by the code ucs 56 is 595 deg C. Fortunately there is note in Table ucs 56 note 1. says alternative PWHT ucs 56.1. Thickness of my vessel 2" Soaking time on my procedure 2 hour 2minute. but actual in production i make 2 hour 36 minutes. My question :
1. It is acceptable according the code ucs 56.1 reduce the temperature 590 deg C for PWHT ? if yes How to calculate ?since my soaking time only 2 hour 36 minutes?
2. is the interpretation correct :
a. since my soaking time 2 hours and 36 minutes so according to ucs 56.1 minimum holding 2 hours so i can reduce 28 deg C ?595 to 567 maksimum ? so 590 still acceptable?

Thankyou

Please advise
WE 17

 

[weldstan]

Table UCS-56.1 permits reduction of the minimum specified PWHT temperature with the increased hold times listed therein.

 

[metengr]

If you used four thermocouples, what were the temperatures of the other three? Were all four at 590 deg C?

 

[metengr]

WE17;
What you have is a nonconformance in PWHT. If you need to disposition the reduced PWHT temperature, the use of Table UCS-56.1 is permitted. However, the hold times and PWHT temperatures are developed from a parametric equation, like the Larson Miller parameter. So, you need to use this equation, and with the stated holding times and PWHT temperatures you can determine the LM parameter and then solve for the actual holding time at 590 deg C.

 

[Fizza453]

Dear Metengr,

If calculated time at 590 is less than that required by Table UCS-56.1, may this lower time be used instead of that required by Table UCS-56.1?
In other words, may the use of Larson Miller parameters be used in lieu of Table UCS-56.1 when PWHT is carried out at lower temperatures than 595C for P-No. 1 materials?


Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[metengr]

Yes.

 

[Fizza453]

Dear Metengr,

Is it not so that Table UCS-56.1 sets the minimum requirements of holding time @ temperature? and these requirements cannot be overruled?
Or Larson Millar equations are considered "as safe as those have been provided by the Code, otherwise" and per U-2(g), these equations can be used? Thank you for your really informative and helpful comments.

Nasir
Welding Engineer
DESCON ENGINEERING LIMITED
PAKISTAN

 

[metengr]

Fizza453;
The data in UCS-56.1 is provided for hold times based on 50 deg F PWHT temperature reductions. If you want to determine a hold time based on a temperature reduction less than 50 deg F increment (say 25 deg F), you cannot interpolate, instead I mentioned you need to use the LMP equation. You most certainly can hold for the 50 deg F PWHT reduction for PWHT reductions less than this.

 

[WE17]

Dear Metengr,weldstan & Fizza 453:
Good mourning,
we use 4 thermocouple ,thermocouple 1.(605 deg C), 2.(607 deg C),3 (603 deg C) and 4. (590 deg C), what is my concern here is maybe because of the position of thermocouple 4 not in good position(all the distance following code within 15ft(4.6meter). we are using Gas Fire Furnace and position of thermocouple 4 put in Head closed with the saddle and far away from the fire.
So according to my interpretation above uncoorect :
2. is the interpretation correct :
a. since my soaking time 2 hours and 36 minutes so according to ucs 56.1 minimum holding 2 hours so i can reduce 28 deg C ?595 to 567 maksimum ? so 590 still acceptable?

Metengr I am still new and not familiar with Larson Miller Parameter ?
Would you like to show how to find the value?
Thankyou for advice

WE 17

 

[metengr]

WE17;
So you have a nonconformance and need to disposition it. Since the fourth TC was below 595 deg C, while the remaining three were above 595 deg C, you can try using the LMP equation below and see if your extended holding time helped;

LMP = T(20 + log t)
T= temperature in degrees K
t= holding time (hours)

You plug in a known PWHT, T and holding time from Table UCS-56.1. Solve for LMP. Using this same LMP, plug in your lower PWHT, T and solve for holding time.