Lesson 06 UW40 UW56.1 New2

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API 510 Preparatory Class

Lesson 6

Postweld Heat Treatment

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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 avery specific way. As follows:

UW-40Definition of Nominal Thickness for

Butt Welds

Page 150Section VIII

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(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 thegreatest weld thicknessin any

vessel or vessel part which has not previously been

postweld heat treated..


Butt Welds

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(1) When the welded joint connects parts of thesame

thickness, using a full penetration butt weld, the nominal

thickness is the total depth of the weld exclusive of any

permitted weld reinforcement.


Butt Welds

Depth of

weld

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(5) When a welded joint connects parts of unequal

thicknesses, the nominal thickness shall be the following:

(a) the thinner of two adjacent butt-weldedparts including

head to shell connections;

UW-40 Definition of Nominal Thickness for

Butt Welds

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UCS-56 Requirements for Post Weld Heat

Treatment Page 179Section VIII

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

rules.

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UCS-56 Requirements for Post-Weld Heat

Treatment

(a) Before applying the detailed requirements andexemptions in these paragraphs, satisfactory weld

procedure qualifications of the proceduresto be used shall

be performed in accordance with all the essential variablesof Section IX includingconditions ofpostweld heat

treatment or lack of postweld heat treatment.

Question: What must always be present prior to welding?

Answer: A Section IX qualified welding procedure.

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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 800F(427C) at the time the vessel or part is placed in it.

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Treatment

(2)Above 800F(427C), the rate of heating shall be not more

than400F/hr (222C/ hr)divided by the maximum metal

thicknessof the shell or head plate in inches, but in no

case more than 400F/hr (222C/hr). .

400F/ 2 inchesso no more than200F/hr

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Class Quiz

UCS 56

1. In the example below what is the shortest amount of time

allowed to raise the weldment to a PWHT of 1100F if the

furnace is at800Fwhen the part is inserted?

Answer:___________________________________

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Solution

1. In the example below what is the shortest amount of time

allowed to raise the weldment to a PWHT of 1100F if the

furnace is at800Fwhen the part is inserted?

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

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Treatment

Turn to Page 180of 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

materials 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 comefrom the P-Number 1 Table!

The tables cannot be interpreted with out reading the notes

that are beneath them. Lets have a look.

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Treatment

We can gather the following from the Table for P-Number

1 materials that;

The normal holding temperature is 1100 oFfor P-No. 1.

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

Note 1 references alternative PWHT holding

temperatures

Note 2 determines the thickness at which PWHT ismandatory.

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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 lethalservice 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.

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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

200F (93C)during welding;

Based on the various thicknesses up to 2 inches we have

the following graphical representation of these rules.

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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 anUnfired Steam Boiler which has a 1/4 (6 mm) minimum.

1/16" to 15 min. 30 min.

45 min.

1 - 1 hour.

> 1- 1:15 min. No Preheat

1- 1:30 min. No Preheat

1- 1:45 min.

2 2 hours.

Exceeds 1- up to

1- if no preheat

applied.

1/16" to Lethal

or Service reason

> 1- Thickness

Reason For PWHT 1/16 to 2 inches

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UCS-56 PWHT Thicknesses Over 2

The second thickness range:

Over 2 in. (51 mm) to 5 in. (127 mm) the PWHT is heldfor a flat 2 hours for the first 2 inches (51 mm) of

thickness with an additional 15 minutes per inch over 2

inches. Lets 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)

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UCS-56 PWHT Thicknesses Over 5 in.

The third thickness range:

Over 5 in. (127 mm) the PWHT is held for a flat 2 hoursfor 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;

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Class Quiz

UCS-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 timefor 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 nominalgoverning thickness of 1-1/4 ? The vessel will not be in a

lethal service.

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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, itmust exceed 1-1/4

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UCS-56.1

Alternative Post-Weld Heat Treatment

Requirements for Carbon and Low AlloySteels 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.

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Table UCS-56.1


Before going any further it must be cautioned that you

cannot usethis 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.

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Table UCS-56.1


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 1in. (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;

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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?


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.

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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?


Lowered PWHT at 1000 F


15 min. - Total 4:30 min.

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

add 15 min.

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Class Quiz

UCS-56.1

What is the total PWHT time at 950oF for a 5 inch thick P-No

1 Group 2 material?


5 in (125 mm)

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Solution

What is the total PWHT time at 950oF for a 5 inch thick P-No

1 Group 2 material?




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.

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The End I Know

You're Glad

Lesson 06 UW40 UW56.1 New2

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