WELDING PROCEDURE SPECIFICATION ESSENTIALS & NON-ESSENTIAL VARIABLES (API 1104)

Essential variables:

A change in essential variable is considered to affect the mechanical properties (other than toughness) of the welded joint. Hence the WPS must be requalified, if the essential variable is changed.

1.?????? Base Materials: A change in base material “nominal SMYS” greater than that of the base material. An increase in carbon equivalent material.

2.?????? Pipeline Operating Conditions: The addition or deletion of deliberate cooling methods or change in cooling rate.

3.?????? Wall Thickness: A change in nominal wall thickness or plus/minus 25% of the nominal thickness when hardness/toughness varies.

4.?????? Weld Deposition Sequence: A change from a deposition sequence i.e. change in bead space beyond the limits

5.?????? Welding Process: A change in welding process for any given pass or passing group (i.e. fill passes or cap passes). A change between manual or semiautomatic application.

6.?????? Joint Design: A change from fillet weld to groove weld but not vice versa. A major change in joint type i.e. change from longitudinal groove seam weld to a branch groove weld.

7.?????? Filler Metal: A change in filler metal grouping (sequence of deposition) / classification when base material SMYS is less than (greater than equal to) the nominal SMYS of Grade X65 having same hardness/toughness.

8.?????? Shielding Gas: A change in shielding gas flow rate (greater than 20% below nominal flow rate)/ classification (in accordance to AWS A5.32)/deletion or change in nominal composition of backing gas (when used).

9.?????? Electrical Characteristics: A change in current/polarity type (DCSP/DCEN, DCRP/DCEP, AC)/waveform controlled process/ heat input (exceeding plus/minus 20% of recorded valve).

10.?? Weld Heat Input: A change in specified heat input range.

11.?? Time between Passes: A increase in maximum time between completion of root bead or the start of second bead and increase in time between completion of the first layer and start of second layer for a temper bead sequence.

12.?? Direction of Welding: A change in direction of welding from vertical down to vertical up, or vice versa.

13.?? Preheat Temperature: Any decrease in minimum base material preheat temperature below the base material Preheat temperature/ when preheat is not applied, the minimum temperature specified shall not less than lesser of 60 degree F or actual base material temperature.

14.?? Inter pass Temperature: An increase in base material inter pass temperature to greater than 100 degree F above minimum-recorded base material inter pass temperature when hardness/toughness varies.

15.?? Post Weld Heat Treatment (PWHT): The change in/addition/deletion of PWHT.

16.??? Post Heat Maintenance to Promote Hydrogen Diffusion: The elimination of post heating for purpose of promoting hydrogen diffusion. A reduction in the specified time or temperature range.

Non-essential variables:

Nonessential variables are those in which a change can be made without requalification of the existing WPS, since it is not considered to affect the mechanical properties of the joint. Though a change in the nonessential variable doesn’t require requalification of the WPS but still it should be properly addressed in the welding procedure specification (WPS).

1.?????? Welding Process: Changes within the same process (e.g., SMAW to SMAW with different electrodes).

2.?????? Base Material: Slight variations in base material composition within the same group.

3.?????? Electrode Size: Changing the diameter of the welding electrode within certain limits.

4.?????? Travel Speed: Adjustments in welding speed that do not affect the overall weld quality.

5.?????? Welding Technique: Modifications in the welding technique (e.g., weave patterns) as long as the fundamental approach remains the same.

6.?????? Material: For in-service fillet welds, SMYS is not an essential variable.

7.?????? Wall Thickness: For in-service welds other than weld deposition repair, wall thickness is non-essential variable. A change in nominal wall thickness plus/minus 25% of the nominal thickness having same hardness/toughness.

8.?????? Filler Metal: A change in filler metal classification for same hardness/ toughness. A change in sequence of deposition of filler metal classification when multiple filler metal classifications are used for a single weld having same hardness/ toughness.

9.?????? Inter pass Temperature: An increase in base material inter pass temperature to greater than 100 degree F above minimum-recorded base material inter pass temperature.

10.?? Joint Design: Minor changes in bevel angle or the land of the welding groove.