API 510 Preparatory ClassAPI 510 Preparatory Class

Lesson 6Lesson 6Postweld Heat TreatmentPostweld Heat Treatment

The Post Weld Heat Treatment mandatory requirements for and, time at temperature are based on the base metals thickness. The Code defines thickness at a welded joint in a very specific way. As follows:

UW-40 Definition of Nominal Thickness for Butt Welds

Page 150 Section VIII

(f) The term nominal thickness as used in Tables UCS-56, UCS-56.1, UHA-32 and UHT-56, is the thickness of the welded joint as defined below. For pressure vessels or parts of pressure vessels being postweld heat treated in a furnace charge, it is the greatest weld thickness in any vessel or vessel part which has not previously been postweld heat treated..

UW-40 Definition of Nominal Thickness for Butt Welds

(1) When the welded joint connects parts of the same thickness, using a full penetration butt weld, the nominal thickness is the total depthof the weld exclusive of any permitted weld reinforcement.

UW-40 Definition of Nominal Thickness for Butt Welds

Depth of weld

(5) When a welded joint connects parts of unequal thicknesses, the nominal thickness shall be the following:

(a) the thinner of two adjacent butt-welded parts including head to shell connections;……

UW-40 Definition of Nominal Thickness for Butt Welds

UCS-56 Requirements for Post Weld Heat Treatment Page 179 Section VIII

PWHT is performed to specific rules based on the thickness of the weld to be heat treated. We will now examine those rules.

UCS-56 Requirements for Post-Weld Heat Treatment

(a) Before applying the detailed requirements and exemptions in these paragraphs, satisfactory weld procedure qualifications of the procedures to be used shall be performed in accordance with all the essential variables of Section IX including conditions of postweld heat treatment or lack of postweld heat treatment.

Question: What must always be present prior to welding?Answer: A Section IX qualified welding procedure.

UCS-56 Requirements for Post-Weld Heat Treatment

(d) The operation of postweld heat treatment shall be carried out by one of the procedures given in UW- 40 in accordance with the following requirements.

(1)The temperature of the furnace shall not exceed 800°F (427°C) at the time the vessel or part is placed in it.

UCS-56 Requirements for Post-Weld Heat Treatment

(2) Above 800°F (427°C), the rate of heating shall be not more than 400°F/hr (222°C/ hr) divided by the maximum metal thickness of the shell or head plate in inches, but in no case more than 400°F/hr (222°C/hr). …….

400°F / 2 inches so no more than 200°F/hr

Class QuizUCS 56

1. In the example below what is the shortest amount of time allowed to raise the weldment to a PWHT of 1100 °F if the furnace is at 800°F when the part is inserted?

Answer:___________________________________

Solution

1. In the example below what is the shortest amount of time allowed to raise the weldment to a PWHT of 1100 °F if the furnace is at 800°F when the part is inserted?

1100 - 800°F = 300°F/200°F = 1-1/2 Hours

UCS-56 Requirements for Post-Weld Heat Treatment

Turn to Page 180 of Section VIII as we will now examine the requirements for PWHT using the tabular form of UCS-56 for P-Number 1 base metal.

This is just one Table, there are many more based on the material’s P-Number. The others follow the same format and once we have learned to use this one the others will be much easier to understand. You are responsible for all of the tables on this examination however most questions come from the P-Number 1 Table!

The tables cannot be interpreted with out reading the notes that are beneath them. Let’s have a look.

UCS-56 Requirements for Post-Weld Heat Treatment

We can gather the following from the Table for P-Number 1 materials that;

• The normal holding temperature is 1100 oF for P-No. 1.

• The minimum time at holding temperature is based on the thickness of the part.

• Note 1 references alternative PWHT holding temperatures

• Note 2 determines the thickness at which PWHT is mandatory.

Table UCS-56 P-Number 1

There are three cases of thickness listed in the table P-1.

• Up to 2 inches (51 mm) the PWHT is held for 1 hour per inch (25 mm) of thickness with 15 minutes minimum in all cases. The 15 minute minimum applies to cases where;

1. The vessel is in lethal service and requires PWHT in all thicknesses.

2. The vessel is being heat treated voluntarily to prevent a service induced problem such as cracking i.e. Amine service.

UCS-56 Requirements for Post-Weld Heat Treatment

Note (2) Postweld heat treatment is mandatory under the following conditions:

(a) for welded joints over 1-1/2 in. (38 mm) nominal thickness; ( So 1- 9/16” (40 mm) and greater would require PWHT)

(b) for welded joints over 1-1/4 in. (32 mm) nominal thickness through 1-1/2 in. (38 mm) nominal thickness unless preheat is applied at a minimum temperature of 200°F (93°C) during welding;

Based on the various thicknesses up to 2 inches we have the following graphical representation of these rules.

UCS-56 PWHT Thicknesses Up to 2 in.

The Code sets the minimum thickness of a vessel at 1/16” (1.6 mm) in paragraph UG-16, one exception is for an Unfired Steam Boiler which has a 1/4” (6 mm) minimum.

1/16" to ¼” 15 min.

½” 30 min.

¾” 45 min.

1” - 1 hour.

> 1-¼” 1:15 min. No Preheat1-½” 1:30 min. No Preheat

1-¾” 1:45 min.

2” 2 hours.

Exceeds 1-¼” up to 1-½” if no preheat

applied.

1/16" to ¼” Lethal or Service reason

> 1-½” Thickness

Reason For PWHT 1/16 to 2 inches

UCS-56 PWHT Thicknesses Over 2”

The second thickness range:

• Over 2 in. (51 mm) to 5 in. (127 mm) the PWHT is held for a flat 2 hours for the first 2 inches (51 mm) of thickness with an additional 15 minutes per inch over 2 inches. Let’s look at a graphic of this thickness range.

First 2 in. (51 mm) 2 hours

OVER 2 in. to 5 in.(51 mm to 127 mm)

Additional 1 in. (25 mm) 15 min. - Total 2:15 min.

3 in (75 mm)

UCS-56 PWHT Thicknesses Over 5 in.

The third thickness range:

• Over 5 in. (127 mm) the PWHT is held for a flat 2 hours for the first 2 inches (51 mm) of thickness with an additional 15 minutes per inch over 2 inches. For P-Number 1 there is no change from the previous example. This third range does changes for some of the other P-Numbers. Look at the P-Number 4 Table for example;

Class QuizUCS-56 PWHT

1. What is the minimum PWHT time and the minimum holding temperature for a P-Number 5A material that is 3” (inches) thick (75 mm)?

2. What is the PWHT normal holding temperature and time for a P-Number 3 material that is 3” (76 mm) thick?

3. What is the required time at the minimum holding temperature for a P-Number 1 Gr.1 weld that has a nominal governing thickness of 1-1/4” ? The vessel will not be in a lethal service.

Solution

1. 3 hours at 1250 oF (677 oC).

2. 1100 oF (593oC) 2 hours -15 minutes?

3. There is no mandatory heat treatment in this thickness, it must exceed 1-1/4”

UCS-56.1 Alternative Post-Weld Heat Treatment

Requirements for Carbon and Low Alloy Steels Page 187

By Note 1 of Table UCS 56 for P-Number 1 materials, it is possible to PWHT at a temperature lower than that given in Table UCS-56. It involves heat treating for a longer periods of time, based on the amount of reduction in temperature below the stated minimum in Table UCS-56.

The following Table UCS-56.1 outlines these rules.

Table UCS-56.1 Alternative Post-Weld Heat Treatment

Before going any further it must be cautioned that you cannot use this alternate unless you have been referred to it by a note in one of the material tables. In our example we are using Note 1 referenced by P-Number 1.

From the table we find that there are three columns.

• The left column lists the decrease in temperature below that given on the appropriate table in UCS-56 based on material.

• The center lists the Minimum Holding Time at a decreased temperature and;

•The third lists references to notes below the table.

Table UCS-56.1 Alternative Post-Weld Heat Treatment

Reading Note 1 found below the chart and referenced up in the Minimum Holding Time column we see;

(1) Minimum holding time for 1 in. (25 mm) thickness or less. Add 15 minutes per inch(25 mm) fro thickness greater tan 1 in. (25 mm).

Reading Note 2 listed in the Notes column;

(2) These lower postweld heat treatment temperatures permitted only for P-No. 1 Gr. 1 and 2 materials.

As regards Note 2, there is a P-No. 1 Group 3 material. So be cautious on the exam this could be a trick question.

Note 1 is best addressed using a graphic as follows;

UCS-56.1 Alternative PWHT

We will first examine a 50oF (28oC) drop from 1100 to1050oF. Below is the holding time from our previous 3” coupon based on 1100oF. How long would we be required to hold it at 1050oF?

First 1 in. (25 mm) 2 hours

Lower PWHT at 1050 F

Additional 1 in. (25 mm) add 15 min. Total 2:30

3 in (75 mm)Additional 1 in. (25 mm) add

15 min.

UCS-56.1 Alternative PWHT

Which leads to this total time, up from 2:15 min. to 2:30 min.

Now how about 100oF reduction to 1000oF?

First 1 in. (25 mm) 4 hours

Lowered PWHT at 1000 F

Additional 1 in. (25 mm) add 15 min. - Total 4:30 min.

3 in (75 mm)Additional 1 in. (25 mm)

add 15 min.

Class QuizUCS-56.1

What is the total PWHT time at 950oF for a 5 inch thick P-No 1 Group 2 material?

Lowered PWHT at 950 F

5 in (125 mm)

Solution

What is the total PWHT time at 950oF for a 5 inch thick P-No 1 Group 2 material?

First 1 in. (25 mm) 10 hours

Lowered PWHT at 950 F

Additional 1 in. (25 mm) add 15 min. - Total 11 hours.

5 in (125 mm)

Additional 1 in. (25 mm) add 15 min.

Additional 1 in. (25 mm) add 15 min.

Additional 1 in. (25 mm) add 15 min.

The End… I Know You're

Glad