IF condition in trigger in SQL Server - sql-server-2012

Question

I converting this Oracle trigger to SQL Server. In Oracle there are using if condition for updating a table. I was wondering is it necessary to use if statement in SQL Server. I'm thinking to use in where clause. Please let me know if that's correct?
Thanks
CREATE OR REPLACE TRIGGER "DB1"."TG_PG_CODES"
BEFORE UPDATE OF "str_number", "op_status"
ON "DB1"."Header_T"
REFERENCING OLD AS oldrow NEW AS newrow
FOR EACH ROW
BEGIN
IF :newrow.op_status = 'X'
THEN
UPDATE DB1.pg_pollutant
SET op_status = 'X',
str_comp_status = '98',
str_mod_person = '3327'
WHERE str_number = :newrow.str_number;
END IF;
IF :newrow.op_status <> 'X'
AND SUBSTR (:oldrow.str_pgcodes, 1, 1) = '1'
AND SUBSTR (:newrow.str_pgcodes, 1, 1) = '0'
THEN
UPDATE DB1.pg_pollutant
SET op_status = 'X',
str_comp_status = '98'
WHERE str_number = :newrow.str_number
AND str_pollutant_key = :newrow.str_number || '0';
END IF;
END;
=============================================
In sql server
CREATE TRIGGER [dbo].[TG_TG_PG_CODES] ON [dbo].[Header_T]
AFTER UPDATE
AS
IF(UPDATE(str_number)
OR UPDATE(op_status))
BEGIN
IF(
(
SELECT op_status
FROM inserted
) = 'X')
BEGIN
UPDATE a
SET
a.op_status = 'X',
a.str_comp_status = '98',
a.str_mod_person = '3327'
FROM DB1.pg_pollutant a
INNER JOIN inserted AS i ON a.str_number = i.str_number;
END;
UPDATE a
SET
a.op_status = 'X',
a.str_comp_status = '98'
FROM DB1.pg_pollutant a
INNER JOIN inserted AS i ON a.[str_number] = i.[str_number]
AND a.str_pollutant_key = i.[str_number]+'0'
INNER JOIN Deleted AS d ON a.[str_number] = d.[str_number]
WHERE i.stroperationalstatus <> 'X'
AND SUBSTRING(d.str_pgcodes, 1, 1) = '1'
AND SUBSTRING(i.str_pgcodes, 1, 1) = '0'; /* I used this condition in where clause */
END;